U.S. patent number 3,610,799 [Application Number 04/872,597] was granted by the patent office on 1971-10-05 for multiplexing system for selection of notes and voices in an electronic musical instrument.
This patent grant is currently assigned to North American Rockwell Corporation. Invention is credited to George A. Watson.
United States Patent |
3,610,799 |
Watson |
October 5, 1971 |
**Please see images for:
( Certificate of Correction ) ** |
MULTIPLEXING SYSTEM FOR SELECTION OF NOTES AND VOICES IN AN
ELECTRONIC MUSICAL INSTRUMENT
Abstract
In an electric organ, the actuation of keys in accordance with
corresponding, audible tones to be reproduced effects the gating of
pulses into time slots of a time division multiplex signal, the
time slots of the multiplex signal being structured in accordance
with a desired assignment sequence to correspond to the keys and to
be representative thereof for identifying each note capable of
being generated by the organ. A set of note, or tone, generators
with availability assignment control means for capturing a pulse in
the multiplex signal are each rendered responsive to a given
captured pulse for generating the tone represented by that pulse. A
second multiplex system having time slot pulse assignments
additionally provides for generation of a time division multiplex
signal for control of voices and other characteristics to be
imparted to the reproduced tones.
Inventors: |
Watson; George A. (Tustin,
CA) |
Assignee: |
North American Rockwell
Corporation (N/A)
|
Family
ID: |
27582831 |
Appl.
No.: |
04/872,597 |
Filed: |
October 30, 1969 |
Current U.S.
Class: |
84/617; 84/622;
84/635; 984/332; 984/392; 84/627; 84/655; 984/323; 984/338 |
Current CPC
Class: |
G10H
1/0575 (20130101); G10H 1/182 (20130101); G10H
7/04 (20130101); G06F 1/02 (20130101); G06F
1/0328 (20130101); G10H 1/20 (20130101) |
Current International
Class: |
G10H
1/20 (20060101); G10H 1/057 (20060101); G10H
1/18 (20060101); G06F 1/02 (20060101); G10H
7/04 (20060101); G06F 1/03 (20060101); G10H
7/02 (20060101); G10h 001/00 () |
Field of
Search: |
;84/1.01,1.03,1.18,1.22,1.24,1.28 ;340/171 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Hirshfield; Milton O.
Assistant Examiner: Witkowski; Stanley J.
Claims
What is claimed is:
1. In an electronic musical instrument having keys selectively
actuable to cause the production of sounds corresponding to
respective notes of the musical scale, the combination
comprising:
means for repetitively and sequentially scanning said keys to
detect the actuation of any one or more thereof,
means responsive to actuation of one or more of said keys as
detected by said scanning means to generate a digital signal
containing assignments of the notes associated with the respective
actuated keys, and
means responsive to the assignments of notes in said digital signal
for selectively producing the sounds corresponding to said assigned
notes.
2. In the electronic musical instrument of claim 1, said
combination further including:
means coupled to said digital signal generating means for
selectively keying percussive rhythm accompaniment in accordance
with said note assignments.
3. An electronic musical instrument, comprising:
a plurality of switches selectively operable to develop signals for
calling forth respectively associated notes as audible sounds from
said instrument, and
means responsive to operation of switches among said plurality of
switches for processing the respectively developed signals in a
digital multiplexed waveform to select the corresponding sounds to
be produced from said instrument.
4. An electronic musical instrument according to claim 3 further
including:
means responsive to said digital multiplexed waveform for keying
percussion sound accompaniment from said developed signals.
5. An electronic organ for simulating the sounds produced by a pipe
organ, said electronic organ comprising:
a plurality of switches,
means responsive to said actuation and deactuation of said switches
for encoding information representative thereof in a digital format
of control data indicative of order and combination of actuation
and deactuation of said switches,
means responsive to said digital format for entering the control
data produced in that format into selected time intervals of a
time-division multiplexed signal, and means responsive to the
control data of said time-division multiplexed signal and
representative of the selective actuation and deactuation of said
switches for developing signals from which to generate the pipe
organ sounds desired to be reproduced by the electronic organ.
6. The electronic organ according to claim 5 wherein said switches
comprise keys on each keyboard of said organ, and wherein said
signal developing means includes tone generating means for
producing signals representative of the notes of the musical scale
for each octave encompassed by the keyboards of said electronic
organ.
7. The electronic organ according to claim 6 wherein there are
provided plural said keyboards and wherein said means responsive to
actuation and deactuation of switches includes:
means for cyclically scanning said plural keyboards in a sequence
of scanning intervals respectively corresponding to each said
keyboard of said organ, and
means responsive to selective actuation and deactuation of the keys
to derive pulses representative of such selective actuation and
deactuation on parallel paths representative of the keys of an
octave for each of the plural octaves of each keyboard in
successive, and during respective successive portions of the
respectively corresponding scanning interval, as said digital
format of control data.
8. The electronic organ according to claim 7 wherein:
said scanning means sequentially scans the notes over an octave of
the musical scale cyclically and repetitively, and
said means responsive to said digital format is responsive to said
sequential note scanning of said scanning means and to said derived
pulses occurring on said parallel paths for conversion of the
parallel format of pulses to a serial format constituting said
time-division multiplexed signal containing said control data.
9. The electronic organ according to claim 5 wherein:
said switches comprise stops for selecting desired organ
voices,
said signal developing means includes a memory containing digital
voice information corresponding to a plurality of desired voices
available to be produced, and
said means responsive to the control data selectively accesses said
memory in response to actuation of one or more of the stops in the
corresponding locations thereof to supply the respective digital
voice information contained in the accessed locations for
developing the sounds to be reproduced.
10. The electronic organ according to claim 9 wherein said stops
are arranged in groups corresponding to groups of said voices, and
said means responsive to actuation and deactuation of switches
includes:
means for cyclically and sequentially scanning said groups of stops
corresponding to said groups of organ voices, and
said means responsive to selective actuation and deactuation of
said stops produces said pulses representative of such selective
actuation nd deactuation in a multiplexed signal, as said digital
format of control data.
11. The electronic organ according to claim 10 wherein said means
responsive to the control data of the multiplexed signal for
developing signals includes:
further, plural memory means containing digital information
relating to corresponding, specific organ voices in said groups,
and
voice computing means responsive to pulses appearing in said
multiplexed signal for selection of digital voice information from
said further plural memories and for combining said selected
digital information for storage in the first-named memory.
12. A digital electronic musical instrument having switches
selectively operable to bring forth respective notes of the musical
scale, comprising:
means assigning each of said switches to bring forth respective
notes of the musical scale to a distinct and different time slot in
a sequence of cyclically repeated time slots, and
means responsive to selective operation of a switch to provide a
signal representative of such operation of said switch in the
respective assigned time slot for that switch in each cycle of
repetition of said sequence of time slots during which said switch
is operated.
13. The instrument according to claim 12 further including:
controllable tone generating means, and
means synchronized with said cyclically repeating sequence of time
slots to which said switches are assigned and responsive to a
signal appearing in any time slot as provided by said means
responsive to selective operation of a switch, for controlling said
tone generating means to produce a tone corresponding to the
frequency of the respective note to be brought forth by said
operated switch.
14. The instrument according to claim 12 further including:
means for generating tones corresponding in frequency to notes of
the musical scale, and
means synchronized with said time slot assigning means for
recognizing the note associated with a signal in a time slot of
said cyclically repeating sequence of time slots as furnished by
said switch operation-responsive means, each time the last-named
signal repeats, and for constraining said means for generating
tones to produce a tone corresponding in frequency to the
recognized note.
15. In an electronic musical instrument in which information
representative of the actuation of selected switches to bring forth
respectively associated notes of the musical scale is furnished in
the form of a time-division multiplexed signal containing a
cyclically repeating sequence of time slots associated respectively
with switches, and in which a pulse in a time slot is indicative of
the actuation of the switch associated with that time slot,
means for generating tones corresponding in frequency to notes of
the musical scale, and
means responsive to said multiplexed signal and synchronized with
the time slots in said multiplexed signal for recognizing the note
associated with a time slot containing a pulse and for directing
said tone generating means to produce a tone corresponding in
frequency to the recognized note throughout the time interval over
which the pulse in the last-named time slot is repeated.
16. In an electronic organ simulating true pipe organ sounds and
having a plurality of keys selectively operable to call forth notes
of the musical scale, the combination comprising:
a plurality of tone generators substantially smaller in number than
the number of notes which an instrument is capable of
generating,
means for generating a time-division multiplex waveform
constituting a cyclically repeating sequence of time slots,
means for assigning each note to a corresponding time slot and
responsive to operation of a respective key to provide a signal in
said corresponding time slot, and
means for determining the availability of said tone generators and
responsive to the note assignment signals in said time-division
multiplex waveform for assigning to the operated keys, as indicated
by pulses appearing in their respective time slots, tone generators
capable of producing tones corresponding to the respective notes
associated with the operated keys.
17. The combination according to claim 16 wherein each of said tone
generators is operable to produce a tone corresponding in frequency
to the frequency of each note in every octave of sounds encompassed
by said electronic organ.
18. In an electronic organ having a memory unit for storing digital
representations of organ voices to be selectively produced by
actuation of corresponding tab switches associated with the
keyboards of the organ in generation of sounds thereby, and wherein
the voices are arranged in groups of plural voices, the combination
comprising:
means for producing a multiplex waveform having a plurality of time
slots,
means for scanning the organ voices of each of the groups of organ
voices in a succession of time intervals corresponding to the
groups,
means for responding to an actuated tab switch in a given group
during an interval over which that group is scanned by said
scanning means to supply a signal in a respective time slot of the
multiplexed waveform, and
means responsive to signals in said multiplexed waveform
representative of selection of desired voices for retrieving said
digital representations of the respective desired voices as stored
in said memory unit for subsequent audible reproduction of sounds
by the organ in accordance with the selected voices.
19. An electronic musical instrument comprising:
means for generating sounds corresponding to notes of the musical
scale,
means for keying said instrument to call forth desired ones of said
notes, and
means responsive to said keying means for producing and providing
to said generating means keying signals in a time-shared signal
format in which the positions of the keying signals are indicative
of the notes for which corresponding sounds are to be generated by
said generating means.
20. The electronic musical instrument of claim 19 wherein said
keying signal-providing means includes:
means for repetitively scanning said keying means in accordance
with said time-shared format and including a plurality of time
slots to which respective notes are assigned, and
means for introducing into the time slots of said format the
signals indicative of the keyed notes.
21. The electronic musical instrument of claim 19 wherein said
generating means comprises:
means for storing amplitude samples of a waveform corresponding to
the sound desired to be produced by said instrument and
means for accessing said storing means in response to a signal in
said time-shared format and at a rate corresponding to the time
slot position of that signal to reproduce the sound at the
frequency of the keyed note.
22. The electronic musical instrument of claim 19 further
including:
gating means responsive to said keying of said instrument for
producing a transient percussion control signal in response to the
initial occurrence of a signal in a given time slot of said format
corresponding to selected ones of said keyed notes, and
percussion means responsive to said transient percussion control
signal for bringing on percussive sounds in synchronism
therewith.
23. The electronic musical instrument of claim 19 further
including:
gating means responsive to said keying signal-providing means for
producing a steady state percussion control signal in response to
each repetition of a signal in a given time slot of said format
corresponding to a keyed note, and
means responsive to each said steady state percussion control
signal for introducing percussive sounds in rhythm therewith.
24. The electronic musical instrument of claim 19 further
including:
means for storing a plurality of different musical voices in which
said sounds may be produced, and
means associated with said keying means for selecting desired ones
of said musical voices in which the sounds selected by actuation of
said keying means are to be produced.
25. The electronic musical instrument of claim 24 further
including:
a registration memory,
means responsive to said voice selection means for deriving
selected musical voices from said storing means and storing thereof
in said registration memory, and
means for deriving said musical voices from said working memory for
generating sounds in the selected voices in response to the keying
signals of said time-shared signal format.
26. The electronic musical instrument of claim 25 wherein:
said keying means comprises a plurality of keyboards with at least
predetermined ones of said voices available for selection by
corresponding ones of said voice selection means associated with
said keying means of each keyboard, and said registration memory
comprises a plurality of storage locations each available for
storing therein a desired voicing arrangement for a sound to be
produced, and
said means for deriving said musical voices from said storing means
is operative to combine two or more voices for storage as a voicing
arrangement in one of said storage locations of said registration
memory to be accessed in response to a keying signal of a given
keyboard in producing sounds of the desired, selected voices.
27. An electronic musical instrument comprising:
means for generating sounds to be produced by said instruments, a
plurality of switch means for selected desired sounds, and
means responsive to the operation of said switch means for
introducing signals indicative of the selected sounds corresponding
to the operated switch means into a serial digital format, and
means responsive to the serial digital format of signals for
recognizing the selected sounds thereby indicated for activating
said generating means to produce said selected sounds as an audible
output of said instrument.
28. The electronic musical instrument defined by claim 27 wherein
said generating means includes:
means storing a plurality of amplitude samples of at least one
cycle of a complex waveform conforming to the waveshapes of said
sounds, and
means responsive to signals in said serial digital format for
retrieving samples of said waveform from said storing means at a
rate consonant with the frequency of the sound indicated by the
respective signal.
29. The electronic musical instrument defined by claim 31 wherein
said sound generating means further comprises:
means affording a plurality of possible voices in which the
selected notes may be produced, and
said plurality of switch means comprises a plurality of stops for
selecting said voices.
30. The electronic musical instrument defined by claim 29 wherein
said signal introducing means comprises:
means for cyclically and repetitively generating a succession of
time slots in a serial digital format, each said time slot being
associated respectively with a particular one of said voices,
and
said means responsive to operation of one of said voice selection
switch means produces a digital signal in the time slot associated
with the voice selected by that switch means, to bring forth the
desired sounds of the selected voices from said sound generating
means.
31. The electronic musical instrument defined by claim 30 wherein
said sound generating means includes:
means for storing digital data representing a plurality of
individual voices,
means for accepting and storing an accumulation of digital data
representing a composite of said individual voices for notes
produced as an audible output of said instrument, and MEANS FOR
ACCEPTING AND STORING AN ACCUMULATION OF DIGITAL DATA REPRESENTING
A COMPOSITE OF SAID INDIVIDUAL VOICES FOR NOTES PRODUCED AS AN
AUDIBLE OUTPUT OF SAID INSTRUMENT, AND
means responsive to signals in said serial digital format for
deriving the digital data from said individual voice storing means
according to the selected voices indicated by said signals and for
accumulating the derived individual voice digital data and
supplying said data accumulations to said data accepting and
storing means.
32. The electronic musical instrument defined by claim 27 wherein
said instrument includes a keyboard of plural keys for actuating
corresponding ones of said switches to produce said sounds as
corresponding notes of the musical scale and there is further
provided:
means selectively operable for enabling the production of
percussive sounds in conjunction with actuation of the keys of the
keyboard for producing corresponding notes,
gating means enabled by said enabling means for responding to a
signal in said serial digital format corresponding to actuation of
a key on said keyboard of said instrument for producing a steady
state percussive control signal in response to each repetition of
that signal for successive ones of the serial digital formats of
signals, and
means responsive to the succession of steady state percussive
control signals for producing percussive sounds in rhythm with the
note called for by said key actuation.
33. The electronic musical instrument defined by claim 27 wherein
said instrument includes a keyboard of plural keys for actuating
corresponding ones of said switches to produce said sounds as
corresponding notes of the musical scale and there is further
provided:
means selectively operable for enabling the production of
percussive sounds in conjunction with actuation of the keys of the
keyboard for producing corresponding notes,
gating means enabled by said enabling means for responding to a
signal in said serial digital format corresponding to actuation of
a key on said keyboard for producing a single transient percussion
control signal for the initial one only of a succession of said
signals in successive ones of the serial digital formats of
signals, and
percussive sound producing means activated in response to said
single transient percussion control signal and thus only to the
initial actuation of a key.
34. An electronic musical instrument having switches operable to
generate notes of the musical scale, comprising:
main counting means for generating a cyclically repeating multiplex
signal having a plurality of time slots at least as great in number
as the number of switches, and wherein each switch is assigned to a
corresponding time slot,
means for scanning said switches to produce a pulse in the
corresponding time slot for each actuated switch,
a plurality of tone generating means each selectively operable to
produce all notes of the musical scale encompassed by the
organ,
assignment control means responsive to the pulses of said multiplex
signal for individually assigning said tone generating means to
generate the corresponding notes as selected by operation of said
switches and for determining the availability of further said tone
generating means for further assignments in response to successive
note selections,
a further counting means associated with each said tone generating
means and synchronized in its counting rate with said main counting
means,
means for normally synchronizing the count of said further counting
means with the count of said main counting means, and said
synchronizing means being responsive to assignment of said
associated tone generating means by said assignment control means
to reset and initiate counting by said associated counting means
simultaneously with the time slot of the pulse to which the
generator is assigned, and
means for comparing the count of each said further counting means
with said main counting means to identify the time slot position of
the assigned pulse and thus the corresponding note to be
produced.
35. An electronic musical instrument as recited in claim 34 further
comprising:
means responsive to the reset count of said associated counter and
the time slot position of the multiplex signal to determine the
continued presence of the assigned pulse therein in successive
cyclical multiplex waveforms for maintaining the generator
assignment during continued operation of the switch and to
recognize release of the switch upon the absence of that pulse.
36. An electronic musical instrument as recited in claim 34 wherein
said assignment control means includes:
means associated with each tone generator and set by said
assignment control means for storing an indication of the assigned
state thereof,
means for resetting said associated counter upon reset of said main
counter to establish synchronization of the counting cycle
therewith, and
said synchronizing means is disabled from resetting said associated
counter by said assigned stage storing means when the latter is
set.
37. An electronic musical instrument as recited in claim 34 having
a plurality of keyboards of plural keys actuable to operate
corresponding ones of said switches, further comprising:
means associated with each said keyboard for selecting percussion
sounds to be generated in response to actuation of keys
thereof,
gating means respectively associated with each said keyboard and
selectively enabled in response to said scanning means during
scanning of the keyboard, and
each said gating means is rendered conductive, when thus enabled,
by a signal corresponding to actuation of a key of that keyboard to
produce an output percussion control signal.
38. An electronic musical instrument as recited in claim 37 wherein
there is further provided:
means responsive to the assignment of each said tone generator to
supply said signal to said gating means for producing a transient
percussion control signal upon the initial key actuation.
39. An electronic musical instrument as recited in claim 37 wherein
said gating means receive and are rendered conductive upon receipt
of pulses in said multiplex signal, and wherein there is further
provided means for storing a steady state indication of the key
actuation in response to successive pulses of a given time slot in
successive cycles of the multiplex signal to produce a steady state
percussion control signal for the duration of actuation of each
corresponding key.
40. An electronic musical instrument as recited in claim 34 having
a plurality of keyboards of plural keys actuable to operate
corresponding ones of said switches, further comprising:
means for storing a plurality of individual voices in which the
notes may be produced,
stop tab means individually associated with said keyboards for
selecting corresponding, desired voices in which the notes of each
said keyboard are to be reproduced,
plural registration means corresponding to said keyboards for
registering the selected ones of said voices derived from said
voice storing means to afford an operating memory of selected
voices,
said tone generating means accessing said operating memory for
deriving the notes to be produced in the desired voices,
means for scanning said stop tabs to produce a time-division
multiplex signal having time slot positions corresponding to said
stop tabs and producing a pulse in each time slot for which the
corresponding stop tab is actuated,
means operating in a repeating cycle and synchronized with said
scanning means to enable entry of voices into said plural
registration memory means individually and in succession, and
further means synchronized with said enabling means and said
scanning means to derive from said voice memory, individually and
in succession, the voices identified by the pulses of said stop tab
multiplexing signal for registration in the registration memories
respectively corresponding to the keyboards for the actuated stop
tabs.
41. An electronic musical instrument as recited in claim 40 wherein
said further synchronized means comprises:
means for combining plural voices read from said voice memories in
accordance with plural pulses in said stop tab multiplexing signal
corresponding to plural stop tab actuations for a given keyboard,
for storing a composite voice of the selected, plural voices in
said registration memory.
42. An electronic musical instrument as recited in claim 40 wherein
the plural voices are arranged in groups of plural voices and the
groups are normally assigned to corresponding ones of the
registration memories, and there are further provided:
coupling means for modifying the synchronization of said scanning
means relative to said enabling means for permitting stop tab
selection of moices and entry of those voices thus selected into a
registration memory to which they are not normally assigned.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention resides broadly in the field of electronic musical
instruments, and is particularly adaptable for use in electronic
organs as a digital selection system for calling forth desired
tones and voices from those available to be produced by the organ.
The term "organ" is used throughout the specification and claims in
a generic sense (as well as in a specific sense) to include any
electronic musical instrument having a keyboard such as an
electronic organ, electric pianos and accordions, and the
principles of the present invention are, in fact, applicable to any
musical instrument in which musical sounds are generated in
response to the actuation of key switches regardless of whether
those switches are actuated directly, i.e., by the musician's
fingers, or indirectly, e.g., by the plucking of strings. The term
"key" is also used in a generic sense, to include depressible
levers, actuable on-off switches, touch- or proximity-responsive
(e.g., capacitance- or inductance-operated) devices, closable
apertures (e.g., a hole in a "keyboard" of holes which when covered
by a musician's finger closes or opens a fluidic circuit to produce
a tonal response), and so forth.
2. Description of the Prior Art
The function of an electronic organ is to faithfully reproduce, or
to simulate by electronic means, the sounds or tones developed by a
true pipe organ in response to playing of the organ by the organist
in the selection of notes, and voices and other characteristics of
those notes. Generally, true pipe organs are unavailable to the
public due to the substantial expense and size thereof and thus
electronic organs have been developed as a substitute which is more
readily available to the public. Electronic organs which have been
available heretofore have either been inadequate in their capacity
and operating characteristics for simulating pipe organ sounds,
and/or have been themselves excessively complex and expensive while
presenting substantial maintenance problems.
One significant problem in the design and construction of prior art
electronic organs resides in the amount of wiring required in order
that the playing of each particular note in each octave available
in the electronic organ effects an appropriate audible response
from the organ. A simple electronic organ may have a pair of
hand-operated keyboards, conventionally termed manuals, and a set
of pedals, referred to as a pedal board or keyboard, or division.
More complex organs may have as many as five manuals and two pedal
keyboards. Moreover, it is not unusual for each manual to have keys
encompassing four or more octaves, while each pedal keyboard may
range from one octave to two or more octaves. Although two or more
manuals may be adapted to permit play of the same note, the note
produced by each has its own distinctive or characteristic sound.
In addition to the large number of keys and pedals available to be
selected during playing of the organ, a typical electronic organ
has several stops or tabs associated with each keyboard, including
the manuals and the pedal boards, to permit selection of specific
organ voices (particularly tone quality and timbre, or color).
Heretofore, the selectively actuated connections required between
each key and the circuitry capable of generating the appropriate
tone has been provided by a mass of cabling and electrical
connecting points within the organ. Interestingly, it is not
unusual for organ dealers to point with pride to the large number
of conductors in the organ as a factor to impress the prospective
customer. In truth, however, each conductor, and particularly its
terminal connections, constitutes a potential source of failure,
and the vast number of conductors and connections often represents
a servicing nightmare. The more complex the organ, of course, the
more complex and unwieldly is the assemblage of cabling and
electrical connecting points. Accordingly, it is highly desirable
to reduce, or minimize the number of wires and electrical
connecting joints while still retaining the capability of proper
response to each key selection.
When a key on any keyboard is depressed, it should call forth an
audiofrequency tone corresponding to the appropriate note of the
musical scale. The tone must be controlled as to its waveshape to
produce the desired characteristics, or quality thereof and
amplified and fed to an electroacoustic transducer (e.g., a
loudspeaker) to develop the audio output. The subsystem of the
organ for performing these functions is typically called a tone, or
note, generator which may include, or have associated therewith,
additional control circuits for controlling the note
characteristics and for providing related functions. Since 12
musically related frequencies are required for each octave, a
sufficient number of tone generators and associated circuitry must
be available to produce the respective signals having the specific
frequencies for every note in every octave to be covered by the
organ. A variety of conventional methods have been employed to
achieve this objective, the particular method utilized depending in
part on the type of tone generator utilized. Although virtually all
organs in which sounds related to notes of the musical scale are
synthesized by electrical devices, in whole or in part, are
customarily referred to as electronic organs, the tone generators
may not be entirely electronic in nature. Any one of three
principal forms of tone generator may frequently be found in the
modern organ, viz, electronic, electromechanical, or
mechanicoacoustical generators. The particular form of tone
generator used is immaterial to the applicability of the present
invention, as will be better understood from further consideration
of this specification, although a specific form is preferred. Since
electronic tone generators are achieving greater popularity than
the other generator forms, primarily because of lower cost, absence
of moving parts, and greater variety of species, the electronic
tone generator will be discussed as representative, and will
indicate another aspect of the problem to which the present
invention is directed.
Some organs include a separate electronic tone generator
(oscillator) for each note on the keyboard, to achieve the desired
tone range. This approach may require several hundred oscillators
in a single organ, but it has some advantages. For example, each
generator need be activated into oscillation only when its
associated key on the keyboard is depressed; greater flexibility is
available in timbre, than with other methods. No special scheduling
or selection technique is required to permit access to a tone
generator upon actuation of a key on a keyboard. However, a more
common approach to providing the desired tone range, because much
less circuitry is required, and because the techniques is less
expensive than the one-key one-generator approach, is the use of
only 12 basic tone generators, each corresponding to a respective
one of the 12 musically related notes in an octave, as required. If
the master oscillators develop frequencies corresponding to notes
of the highest octave of the organ, their respective output
frequencies are successively divided by associated series of
divide-by-two circuits to obtain the corresponding notes in the
lower octaves. Similarly, where the master oscillators develop the
frequencies associated with the lowest octave of the organ,
respective sets of multiply-by-two circuits are used to obtain the
corresponding notes in the higher octave.
Still another approach involves the sharing of a set of generators,
much smaller in number than the total number of notes to be
available for play, each generator capable of developing any one of
the frequencies in a sequence of two or more adjacent frequencies
in accordance with appropriate selection of frequency determining
elements of the oscillator of the generator by actuation of a key.
This arrangement is quite popular in small electronic organs. Thus,
for example, while a small instrument may have well over 100 keys,
only a dozen or so tone generators may be available; hence, only
the latter number of tones can be developed in any given instant.
Since it is unlikely that more than 10 tones will be selected
simultaneously, the problem that arises is not the small number of
tones that can be concurrently generated, but the manner in which
actuation of a key gains access to a tone generator. In the other
cases, of one-key one-generator, and a master oscillators with
associated dividers and multipliers, the wiring problem is further
aggravated.
Generally speaking, then, the problem to which the present
invention is addressed is twofold. First, there is the mass of
conductors that have been required to provide electrical
connections between the keys of each keyboard (manuals and pedal
boards) and the tone generators. Second, there is the required
mapping of the subset of depressed keys, from the overall set of
keys of the organ, into the available tone generators so that a
tone generator is virtually instantaneously assigned to a key when
that key is depressed.
It is the principal object of the present invention to provide a
note selection system for an electronic organ which enables a
substantial reduction of the number of electrical conductors and
connections required between the keyboards and the electronic
circuitry of the organ, relative to that required in electronic
organs of the prior art.
It is another object of the invention to provide a note selection
system commensurate with the immediately preceding object, by which
actuated keys are assigned to tone generators in the organ by a
simple and efficient priority technique, in comparison with the
wiring modes that have been required in electronic organs of the
prior art.
Similar problems to those discussed above for the keyboards and
tone generators, exist with respect to the stops or tabs associated
with the various keyboards to permit selection of desired organ
voices, or special effects, e.g., to enable choice of instrument
sounds and footage to be simulated during play of the organ.
Accordingly, it is a further object of the invention to provide a
stop tab information selection system for reducing the number of
wires between the tabs and the electronic circuitry that effects
the desired controls, and for assigning the stop tab information to
the available control circuitry.
SUMMARY OF THE INVENTION
Briefly, according to one aspect of the present invention, every
key of every keyboard of the organ is scanned in cyclic sequence,
and the actuation of a key or keys on any keyboard is entered as
information in a parallel digital format indicative of the order
and combination of keys that have been actuated and deactuated. The
parallel format is continuously converted to a serial format
comprising pulses in appropriate time slots, preassigned to
corresponding keys, of a time division multiplexed signal to
provide information regarding key actuation. The multiplexed signal
is supplied to the tone generating section of the organ for
bringing forth the tones corresponding to those keys that have been
actuated, in the order and combination of actuation.
In addition to overcoming those problems that have been mentioned
earlier, this aspect of the present invention serves to overcome
the difficulties encountered as a result of faulty or dirty
contacts on any key switch that would otherwise lead to
intermittent electrical contact and discontinuity of tone in the
conventional electronic organ. By using a time division multiplex
signal, the problem of intermittent contact is overcome since the
presence of a pulse in a particular time slot is sufficient to
represent the actuation of the corresponding specific key actuation
(note selection). This pulse is repeatedly recognized, as the keys
of the organ are scanned in cyclic sequence, by the system for
producing the desired audio tone.
Further advantages of the invention include the capability of using
very simple switches of the single-pole single-throw (SPST) type as
the key switches, compared to that amount of space needed by the
usual multiplicity of wires in prior art organs, and the use of
logic circuitry that need occupy only a small volume of space in
the organ, and which logic circuitry may also be time shared by
other sections of the organ, as required.
According to a further aspect of the present invention, the
actuation of stop tab switches for selecting desired organ voices
and footage or pitch lengths is also accomplished on the basis of a
scanning of the stop switches and related components in a cyclic
sequence. Information relating to the specific stop switches that
have been actuated is furnished in a parallel format based on organ
voices, to a voicing computer for accepting the incoming voice
control data and for accessing a related memory to compute the
desired composite voicing information for entry into a serial
digital format in a time division multiplexed waveform.
This stop tab multiplexing aspect of the invention shares the same
advantages as the keyboard multiplexing system.
Again, each of these features and aspects of the invention is
applicable to substantially any key or switch operated electronic
musical instrument, although the advantages of the invention are
realized to a greater extent as the size or capacity of the
instrument, and its capability of tone generation, increases. For
example, the invention may be utilized to provide multiplexed
signals in an electric accordion or an electric guitar, for
example, by scanning the keyboard or the set of strings,
respectively, of such instruments although only a single octave or
perhaps less than one octave is available. In such cases,
miniaturized, reliable logic circuitry can be employed which
provides certain benefits over prior art circuit arrangements in
nonmultiplexed instruments, but the extent of these benefits is
less than in an electronic organ having several keyboards.
BRIEF DESCRIPTION OF THE DRAWINGS
In describing the present invention, reference will be made to the
accompanying Figures of drawings in which:
FIG. 1 is a simplified block diagram of a system for producing a
time division multiplexed signal containing a recycling sequence of
time slots each associated with a particular key of the organ and
in which each time slot containing a pulse is indicative of the
actuation of the associated key;
FIG. 2 is a circuit diagram of an exemplary decoder for use in the
system of FIG. 1;
FIG. 3 is a more detailed circuit diagram of the switching array
and encoder used in the system of FIG. 1;
FIG. 3A is a circuit diagram of an alternative encoder to that
shown in FIG. 3, for use in the system of FIG. 1;
FIG. 4 is a circuit diagram of the input-output bus connecting
means at each intersection of the switching array of FIG. 3;
FIG. 5 is illustrative of a multiplex waveform developed by the
system of FIG. 1 in response to actuation of selected keys;
FIG. 6 is a simplified block diagram of generator assignment and
tone generating apparatus for processing the multiplexed signal
produced by the system of FIG. 1 to develop the desired tones as an
audible output of the organ;
FIGS. 7A and 7B together constitute a circuit diagram of one
embodiment of the tone generator assignment logic for the system of
FIG. 6;
FIG. 8 is a block diagram of a tone generator suitable for
synthesizing the frequency of every note capable of being played in
the organ, for use with the assignment logic of FIGS. 7A and 7B in
the system of FIG. 6;
FIG. 9 is illustrative of a complex waveshape of the type produced
by a pipe organ, and of the sample points at which amplitude values
are taken, for simulation at selected note frequencies;
FIG. 10 is a block diagram of an attack and decay control unit for
use in the instrument;
FIG. 11 is a block diagram of a percussive control or keying system
to provide appropriate percussion sound accompaniment in the
instrument; and
FIGS. 12 through 18 are block diagrams of an overall stop rail
multiplexing system and subsystems thereof, according to the
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIG. 1, the keyboard multiplexing system or note
selection system includes a keyboard counter 1 which is implemented
to provide a specified count for each key of each keyboard
(including manuals and pedal divisions) of the organ. If, for
example, the electronic organ in which the multiplexing system is
used has four keyboards, such as three manuals and a pedal board,
each encompassing up to eight octaves, then keyboard counter 1
should have the capability of generating 4.times.8.times.12=384
separate counts (digital words). It is essential that the counter
be capable of developing a count representative of every key on
every keyboard of the organ; however, it may be desirable to
provide a counter that can produce a count greater than the number
of available keys in order to have available certain redundant
counts not associated with any keys. Such redundancy is readily
provided by simply utilizing a counter of greater capacity than the
minimum required count.
In any event, it is preferred that keyboard counter 1 be divided
into three separate sections (or separate counters) designated 2, 3
and 4. The first section (designated 2) is constructed and arranged
to count modulo 12 so as to designate each of the 12 keys
associated with the 12 notes in any octave. The second section
(designated 3) is adapted to count modulo 8, to specify each of the
eight octaves encompassed by any of the four keyboards. The last
section (designated 4) is designed to count modulo 4 to specify
each keyboard of the organ. Therefore, the overall keyboard counter
is arranged to count modulo 384, in that at the conclusion of every
384 counts, the entire set of keyboards has been covered (scanned)
and the count repeats itself. To that end, each counter section may
be composed of a separate conventional ring counter, the three
counters being connected in the typical cascaded configuration
(see, e.g., Ledley, Digital Computer and Control Engineering,
McGraw Hill, 1960, pp. 488 et seq.) such that when section 2
reaches its maximum count it advances the count of counter section
3 by one, and will automatically initiate a repetition of its own
count. Similarly, attainment of its maximum count by counter
section 3 is accompanied by advancement of the count of section 4
by one, and is immediately followed by a repetition of the modulo 8
count.
Advancement of the lowest counter section 2, i.e., the section of
least significant count, is accomplished by application of clock
pulses thereto from a master clock source 5. Clock source 5 is
designed to deliver clock pulses at a sufficiently rapid repetition
rate (frequency) to ensure resolution of depression (actuation) and
release (deactuation) of any key on any keyboard, i.e., to supply a
pulse at the instant of either of these events. Scanning of all
keyboards of the organ at a rate of 200 or more times a second is
deemed quite adequate to obtain this desirable resolution. For the
exemplary keyboard arrangement and keyboard counter set forth
above, this is equivalent to a minimum of 200.times.384=76,800
counts per second. Accordingly, a master clock delivering clock
pulses at a rate of 100 kc./s. is quite suitable.
A total of four lines emanate from counter section 4, one line
connected to each ring counter stage, to permit sensing of the
specific keyboard which is presently being scanned. Similarly,
eight lines are connected to the eight ring counter stages,
respectively, of octave counter section 3 to detect the octave
presently being scanned. Thus, a total of 12 lines extend from
sections 3 and 4 of keyboard counter 1, and these 12 lines can
carry signals indicative of 32 (8.times.4) possible states of the
keyboard counter. The specific one of the 32 states, representative
of a particular octave on a particular keyboard, which is presently
being scanned is determined by use of a decoder circuit 7. In its
simplest form, decoder 7 may be composed of 32 AND gates designated
8-1, 8-2, 8-3, ..., 8-32 (FIG. 2), each with two input terminals
and an output terminal. The 32 gates are arranged in four groups of
eight each, with every gate of a particular group having one of its
two input terminals (ports) connected to one of the four lines of
keyboard counter section 4. Distinct and different ones of the
eight lines from counter section 3 are connected to the other input
terminal of respective ones of the eight AND gates of that group. A
corresponding situation exists for each group of AND gates, with
the only difference being that each group is associated with a
different output line of counter section 4. Using this arrangement,
the decoder logic designates every octave of keys in the organ by a
respective driver pulse when a count corresponding to that octave
is presently contained in the counter.
The output pulses deriving from the AND gates (or drivers) of
decoder circuit 7 are supplied on respective ones of 32 bus bars
(or simply, buses), generally designated by reference numeral 10,
to a keyboard switching array 11. From the preceding description,
then it will be clear that array 11 has one input bus 10 for every
octave of keys in the organ (including every octave on every
keyboard), and that a drive pulse will appear on each input bus
approximately 200 times per second, the exemplary rate of scan of
the keyboards, as noted above, for obtaining adequate resolution of
operation of the keys. Switching array 11 also has 12 output buses,
generally designated by reference number 12, each to be associated
with a respective one of the 12 notes (and hence, the 12 keys) in
any given octave.
Array 11 is basically a diode switching matrix, in which spaced
input buses 10 and spaced output buses 12 are orthogonally arranged
so that an intersection or crossing occurs between each input bus
and each output bus (see FIG. 3), for a total of 384 intersections,
one for each count of the keyboard counter 1. As is typical in this
type of matrix, the crossed lines or buses are not directly
interconnected. Instead, a "jump" diode, such as that designated by
reference number 13 in FIG. 4, is connected between the input bus
10 and the output bus 12 at each intersection, the diode poled for
forward conduction (anode-to-cathode) in the direction from an
input bus 10 to an output bus 12. Wired in series circuit or series
connection with each diode 13 is a respective switch 14 which is
normally open circuited and is associated with a distinct
respective one of the keys of the organ, such that depression of
the associated key produces closure (close circuiting) of the
switch 14 whereas release of the associated key results in return
of the switch to its open state. Alternatively, each of switches 14
may itself constitute a respective key of the various keyboards of
the organ.
While switch 14 is shown schematically as being of mechanical
single-pole, single-throw (SPST) structure, it will be understood
that any form of switch, electronic, electromechanical,
electromagnetic, and so forth, may be utilized, the exact nature of
the switch depending primarily upon the nature of the energization
produced upon operation of the associated key. Switch 14, then, is
adapted to respond to the particular form of energization or
actuation produced upon operation of a key on any keyboard (or, as
observed above, may itself constitute the key), to complete the
circuit connecting associated diode 13 between a respective input
bus 10 and a respective output bus 12 at the intersection of those
buses, when the key is depressed, and to open the circuit
connecting the diode between respective input and output buses at
that intersection when the key is released. Positive pulses
occurring at the rate of approximately 200 per second, for example,
according to the timing established by master clock 5, are
transferred from input bus 10 to output bus 12 via the respective
diode 13 and closed switch 14 when the associated key is depressed.
While a switch alone (i.e., without the series connected diode)
would serve the basic purpose of transferring a signal between the
input and output lines of array 11, the diode provides a greater
degree of isolation from sources of possible interference (noise)
and acts to prevent feedback from output to input lines.
In FIG. 3, the output buses 12 from switching array 11 are
connected to an encoder circuit 15 to which are also connected the
12 output lines, generally designated by reference number 16, from
keyboard counter section 2. To produce an orderly arrangement in
which each key of the organ is assigned a distinct and different
time slot in a time-division multiplex waveform, the switches 14
associated with the respective keys are conveniently arranged in a
specific sequence in the switching array 11. Assume, for example,
that a specific output bus 17 of the switching array is to be
associated with note A of any octave, a second output bus 18 is to
be associated with note B of any octave, and so forth. Then
switches 14 in the row corresponding to output bus 17 in array or
matrix 11 are associated with the keys corresponding to the note A
in each octave of keys in the organ. The column position of each
switch 14 in matrix 11 corresponds to a specific octave of keys in
the organ, and hence, to a specific octave encompassed by a
specific keyboard of the organ. Each of the output buses 12,
including 17, 18, and so forth, is connected to one of the two
input ports or terminals of a respective AND gate of the 12 AND
gates 20-1, 20-2, 20-3, ..., 20-12, of encoder circuit 15. An
output lead 16 of counter section 2 associated with the ring
counter stage designating the count for a particular note (key) in
a given octave is connected to the remaining port of an encoder
circuit AND gate having as its other input a pulse on the output
bus 12 associated with that same note. A similar arrangement is
provided for each of the remaining 11 output lines 16 of counter
section 2 with respect to the AND gates 20 and the output buses 12.
Thus, for example, if output bus 17 (associated with the row of
switches 14 in matrix 11 for note A) is connected to one input
terminal of AND gate 20-1, then output line 22 from the stage of
counter 2 designating the count associated with note A is connected
to the remaining input terminal of gate 20-1. The output terminal
of each of AND gates 20 is connected to a respective input terminal
of OR gate 23, the output of the OR gate constituting the output
signal of the encoder circuit. By virtue of its structure, encoder
circuit 15 is effective to convert the parallel output of array 11
to a serial output signal in accordance with the scanning of output
buses 12 as provided by the advancing and repeating count sensed in
the form of pulses (at a rate of about 200 per second) appearing on
output lines 16. The end result of this circuitry is the production
of a time-division multiplex (TDM) signal on a single conductor 25
emanating from encoder 15.
As an alternative to the specific logic construction shown for
encoder 15 in FIG. 3, the encoder may have the circuit
configuration exemplified by FIG. 3A. Referring to the latter
Figure, the encoder includes a shift register 80 having 12 cascaded
stages designated SR1, SR2, SR3, ..., SR12, each connected to a
respective output bus 12 of switching matrix 11 to receive a
respective output pulse appearing thereon. The shift register
stages are loaded in parallel with the data read from switching
array 11 on output buses 12, in response to each of the pulses
appearing (i.e., each time a pulse appears) on one of the 12 output
leads 16 of note counter 2. That one output of the note counter
which is to supply the load command for all 12 stages of shift
register 80 is selected to permit the maximum amount of settling
time to elapse between each advance of octave counter 3 and
keyboard counter 4 and the loading of the shift register. In other
words, it is extremely desirable that the data to be entered into
the shift register from the switching array be stabilized to the
greatest possible extent, and this is achieved by allowing the
counters whose scanning develops this data, to settle at least
immediately prior to loading. Thus, the first note counter stage,
or one of the early stages, is selected to provide "load" pulses to
shift register 80.
"Shift" pulses are supplied to the shift register by master clock
5, which also supplies note counter 2, to shift the contents of
each shift register stage to the next succeeding stage except
during those bit times when the shift pulse is preempted by a load
pulse from the note counter. Accordingly, shift register 80 is
parallel loaded, and the data contents of the register are then
shifted out of the register in serial format on encoder output line
25 until a one-bit pause occurs when another set of data is
parallel loaded into the shift register, followed again by serial
readout on line 25. This serial pulse train constitutes the
time-division multiplexed output signal of encoder 15 just as in
the embodiment of FIG. 3, except that with the FIG. 3A
configuration, decoder 7 (and the counters 3 and 4 supplying pulses
thereto) undergo a greater amount of settling time.
It will be observed that this operation constitutes
parallel-to-serial conversion of the information on output buses 12
to a time-division multiplexed waveform on the output line 25 of
encoder 15.
In the TDM signal, each key has a designated time slot in the 384
time slots constituting one complete scan of every keyboard of the
organ. In the specific example of the time base provided by master
clock 5, the TDM waveform (shown by way of example in FIG. 5) is
initiated about 200 times per second. The development of this
waveform itself constitutes a principal feature of the present
invention in that the waveform contains all of the note selection
information, in serial digital form on a single output line, that
had heretofore required the complex wiring arrangements previously
discussed. This waveform development will be more clearly
understood from an example of the operation of the circuitry thus
far discussed. It should be observed first, however, that all of
the counter and logic circuitry described up to this point can be
accommodated within a very small volume of space by fabrication in
integrated circuit form using conventional microelectronic
manufacturing techniques.
When the main power switch for the electronic organ is turned on,
all components are energized to an operational state, the master
clock delivering pulses to keyboard counter 1 at the aforementioned
rate. Upon depression of a key on any keyboard of the organ,
including the manuals and pedal divisions, a respective switch 14
associated in series connection with a diode 13 at the intersection
between the appropriate input bus 10 and output bus 12 of the
switching array 11 is closed, thereby connecting the two buses to
supply pulses appearing on a given bus 10 from decoder 7, to the
appropriately connected output bus 12 for application to encoder
15. If, for example, the key that was depressed in associated with
note C in the second octave, C.sub.2 appears in the appropriate
time slot of the multiplexed signal emanating from encoder 15 and
will repetitively appear in that time slot in each scan of the
keyboards of the organ as long as that key is depressed. That is to
say, a pulse appears on output line 10 of decoder 7 associated with
the second octave in the manual being played, in accordance with
the scan provided by master clock 5, as the counter stage
associated with that octave is energized in keyboard counter octave
section 3 and the counter stage associated with that manual is
energized in section 4 of the keyboard counter. The connection
between the appropriate input bus 10 and output bus 12 of switching
array 11 for the particular octave and keyboard under consideration
is effected by the depression and continued operation of the key
associated with the switch 14 for that intersection in the array.
Since, as previously stated, each switch is associated with a
particular note (key) and is positioned in a specific row of the
switching array, a signal level is thereby supplied to the
appropriate output bus 12 of the switching array arranged to be
associated with that note. Each time the specified note, here the
note C, is scanned in the sequence of count in the note section 2
of the keyboard counter, a second input is provided to the AND gate
20 receiving the signal level on output bus 12, and a pulse is
delivered to OR gate 23. By virtue of this operation, the pulse
which appears at the output of OR gate 23 always appears in the
identical specified time slot in the multiplexed signal for a
specific note associated with a particular key on a particular
keyboard of the organ.
If more than one key is depressed, regardless of whether one or
more keyboards is involved, operation corresponding to that
described above for a single depressed key is effected for every
operated key. Thus, for example, assume that the key associated
with note C.sub.2 is played on one manual, the note B.sub.4 is
played on a second manual, and the notes D.sub.5, E.sub.5, and
G.sub.5 are played on a third manual, the associated keys being
depressed substantially simultaneously to produce desired
simultaneous reproduction of all notes as the audio output of the
organ. Under these conditions, the associated switches 14 in the
switching array 11 are closed to provide through connections
between the respective input buses 10 and output buses 12 for the
specific octaves and manuals involved. As the appropriate AND gates
20 in encoder 15 are supplied with gating signals from the
sequentially energized counter stages of note section 2, during the
scanning operation provided by that keyboard counter section, pulse
levels appearing on output buses 12 for which switches 14 have been
closed are gated in the appropriate time slots of the multiplex
signal on the output lead 25 from OR gate 23 of encoder 15, for the
specific notes involved.
An example of the multiplex signal waveform thus generated is shown
in FIG. 5. While the pulses appearing in the time slots associated
with the specific notes mentioned above are in a serial format or
sequential order, their appearance is repetitive during the
interval in which the respective keys are actuated. Hence, the
effect is to produce a simultaneous reproduction of the notes as an
audio output of the organ, as will be explained in more detail in
connection with the description of operation of the tone generation
section.
Referring now to FIG. 6, the multiplexed signal arriving from
encoder 15 is supplied to generator assignment logic network 26
which functions to assign a tone generator 28 to a depressed key
(and hence, to generate a particular note) when the associated
pulse first appears in its respective time slot in the multiplexed
signal supplied to the assignment logic. If only 12 tone generators
28 are available in the particular organ under consideration, for
example, the assignments are to be effected in sequence (order of
availability), and once particular pulses have been directed to all
of the available generators (i.e., all available tone generators
have been "captured" by respective note assignments), the organ is
in a state of saturation. Thereafter, no further assignments can be
made until one or more of the tone generators is released. The
availability of 12 (or more) tone generators, however, renders it
extremely unlikely that the organ would ever reach a state of
saturation since it is quite improbable that more than 12 keys
would be depressed in any given instant of time during performance
of a musical selection. The output waveforms from the captured tone
generators at the proper frequencies for the notes being played,
are supplied as outputs to appropriate waveshaping and
amplification networks and thence to the acoustical output speakers
of the organ. If the tone generators 28 supply a digital
representation of the desired waveform, as is the case in one
embodiment to be described, then the digital format is supplied to
an appropriate digital-to-analog converter, which in turn supplies
an output to the waveshaping network.
At any given instant of time, each tone generator 28 may be in only
one of three possible states, although the concurrent states of the
tone generators may differ from one tone generator to the next.
These three states are as follows:
(1) a particular note represented by a specific pulse in the
multiplexed signal has captured (i.e., claimed) the tone
generator;
(2) the tone generator is presently uncaptured (i.e., unclaimed or
available), but will be captured by the next incoming pulse in the
multiplexed signal associated with a note which is not presently a
tone generator captor; and
(3) the tone generator is presently available, and will not be
captured by the next incoming pulse.
It should be apparent from this delineation of possible states that
any number of the tone generators provided (12, in this particular
example) may be in one or the other of the states designated (1)
and (3), above, but that only one of the tone generators can be in
state (2) during a given instant of time. That is, one and only one
generator is the next generator to be claimed. When the specific
tone generator in state (2) is claimed by an incoming pulse, the
next incoming pulse which is not presently claiming a tone
generator is to be assigned to the generator that has now assumed
state (2). For example, if the third tone generator (-3) of 12
generators is captured by an incoming pulse (note representation)
and the fourth generator (-4) was and still is captured by a
previous note selection, then tone generator -4 is unavailable to
the next incoming pulse, and the privilege of capture must pass to
the next tone generator which is not presently in a state of
capture. If all of the tone generators are captured, that is, all
are in state (1) as described above, then the organ is saturated
and no further notes can be played until at least one of the tone
generators is released. As previously observed, however, the
saturation of an organ having 12 (or more) tone generators is
highly unlikely.
Generator assignment system 26 is utilized to implement the logic
leading to the desired assignment of the tone generators 28, and
thus to the three states of operation described above. An exemplary
embodiment of the generator assignment logic is shown in FIGS. 7A
and 7B. Referring to FIG. 7A, a ring counter 30, or a 12-bit
recirculating shift register in which one and only one bit position
is a logical "1" at any one time, is used to introduce a claim
selection, i.e., to initiate the capture, of the next available
tone generator in the set of tone generators 28 provided in the
organ. A shift signal appearing on line 32 advances the "1" bit
from one register or counter stage to the next, i.e., shifts the
"1" to the next bit position. Each bit position is associated with
and corresponds to a particular tone generator, so that the
presence of the logical "1" in a particular bit position indicates
selection of the tone generator to be claimed next, provided that
it is not already claimed.
Each time the logical "1" appears in a stage of shift register 30,
a "claim select" signal appears on the respective output line 34
associated with the stage. This "claim select" signal is supplied
in parallel to one input of a respective one of AND gates 35, on
line 36, and to further logic circuitry (to be described presently
with reference to FIG. 7B), on line 37. The output line of each of
AND gates 35 is connected to a separate and distinct input line of
an OR gate 40 which, in turn, supplies an input to an AND gate 42
whose other input constitutes pulses from the master clock 5.
In operation of the portion of the generator assignment logic shown
in FIG. 7A, assume that shift register stage -2 contains the
logical "1." That stage therefore supplies "claim select 2" signal
to the respectively associated AND gate 35 and, as well, to further
logic circuitry on line 37. If this further logic circuitry
determines that the associated note generator may be claimed, a
"claimed" signal is applied as the second input to the respectively
associated AND gate 35. Since both inputs of that AND gate are now
"true," an output pulse is furnished via OR gate 40 to the
synchronization gate 42. The latter gate produces a "shift" pulse
on line 32 upon simultaneous occurrence of the output pulse from OR
gate 40 and a clock pulse from master clock 5. Accordingly, the
logical "1" is advanced one bit position, from stage -2 to stage -3
of shift register 30, in preparation for the claiming of the next
tone generator.
Suppose, however, that the tone generator 28 corresponding to stage
-3 is already claimed by a previous note pulse in the multiplexed
signal. In that event a "claimed" signal appears as one input to
the associated AND gate 35, and with the "claim select" signal
appearing as the other input to that gate by virtue of stage -3
containing the single logical "1," another shift pulse is
immediately generated on line 32 to advance the logical "1" to
stage -4 of the shift register. Similar advancement of bit position
of the "1" continues until an unclaimed tone generator is selected.
If it should happen that no note is presently being selected on a
keyboard of the organ at the time when an unclaimed tone generator
is selected, the "1" bit remains in the shift register stage
associated with the selected tone generator until such time as a
"claimed" signal is concurrently applied to the respective AND gate
35, i.e., until the selected tone generator is claimed, because
until that time no further shift signals can occur.
Referring now to FIG. 7B, each tone generator also has associated
therewith a respective portion of the generator assignment logic as
shown in that figure. In other words, the circuitry of FIG. 7B,
with minor exceptions to be noted in the ensuing description, is
associated with the i th tone generator (where i=1, 2, 3, ..., 12),
and since each of these portions of the assignment logic is
identical, a single showing and description will suffice for all.
An AND gate 50 has four inputs, one of which is the multiplexed
signal deriving from encoder 15 (this being supplied in parallel to
the AND gates 50 of the remaining identical portions of the
assignment logic for the other tone generators, as well), a second
of which is the "claim select" signal appearing on line 37
associated with the i th stage of shift register 30 (FIG. 7A), a
third of which is a signal, on line 52, indicating that the pulse
in the multiplexed signal has not captured any tone generator as
yet, and a fourth which indicates that the note generator is
unclaimed. Of course, these signals are not present unless the
respective events which produce them are actually occurring, but if
all four signals are simultaneously presented as inputs to AND gate
50, a "set" signal is applied to a claim flip-flop 53 to switch
that flip-flop to the "claimed" state and simultaneously therewith
to supply a "claimed" signal to the AND gate 35 associated with the
i th stage of shift register 30 and to the respectively associated
tone generator 28.
A modulo 384 counter 55 is employed to permit recognition by the
respective portion of the generator assignment logic of the
continued existence in the multiplexed signal of the pulse (time
slot) which resulted in the capture of the associated tone
generator. To that end, counter 55 is synchronized with keyboard
counter 1 (also a modulo 384 counter) by simultaneous application
thereto of clock pulses from master clock 5. The count of each
counter 55 associated with an uncaptured tone generator is
maintained in synchronism with the count of keyboard counter 1 by
application of a reset signal to an AND gate 58 each time the
keyboard counter assumes a zero count, i.e., each time the count of
the keyboard counter repeats. However, that reset signal is
effective to reset counter 55 only if the associated tone generator
is uncaptured. The latter information is provided by the state of
flip-flop 53, i.e., a "not claimed" signal is supplied as a second
input to AND gate 58 whenever flip-flop 53 is in the "unclaimed"
state.
When the flip-flop (and hence, the associated tone generator) is
claimed, however, it is desirable to indicate the time slot
occupied by the pulse which effected the capture, and for that
reason a "reset" signal is applied to counter 55 at any time that
an output signal is derived from AND gate 50. Thus, in the captured
state, the zero count of counter 55 occurs with each repetition of
the "capturing" pulse in the TDM waveform. Such information is
valuable for a variety of reasons; for example, to prevent capture
of an already captured tone generator when the zero count continues
to appear simultaneously with a pulse in the TDM waveform, and to
provide a "key released" indication when the zero count is no
longer accompanied by a pulse in the TDM waveform. Capture
prevention is effected by feeding a signal representative of zero
count from counter 55 to the appropriate input terminal of an OR
gate 60 associated with all of the tone generators and their
respective generator assignment logic. The logical "1" supplied to
OR gate 60 is inverted so that simultaneous identical logical
inputs cannot be presented to AND gate 50. On the other hand, when
the zero count is merely synchronized with the zero count of the
keyboard counter and is not the result of capture of the associated
tone generator it does not interfere with subsequent capture of
that tone generator since it does not occur simultaneously with a
pulse in the TDM signal. A "key release" indication is obtained by
supplying the "zero count" signal to an AND gate 62 to which is
also supplied any signal deriving from an inverter 63 connected to
receive inputs from the TDM signal. If the zero count coincides
with a pulse in the multiplexed signal, the inversion of the latter
pulse prevents an output from AND gate 62, and this is proper
because the coincidence of the zero count and the TDM pulse is
indicative of continuing depression of the key which has captured
the tone generator. Lack of coincidence is indicative that the key
has been released, and results in the "key release" signal.
Scanning of the keyboards is sufficiently rapid that any delay
which might exist between actual key release and initiation of the
"key release" signal is negligible, and in any event is
undetectable by the human senses. Furthermore, the generation of a
false "key release" signal when the tone generator is presently
unclaimed, as a result of the occurrence of a zero count from
counter 55 synchronized with the zero count of the keyboard counter
and the simultaneous absence of a pulse in the TDM signal, can have
no effect on the audio output of the organ since the associated
tone generator is not captured and is therefore not generating any
tone. In any case, the "key release" signal deriving from AND gate
62 is supplied to attack/decay decay logic of the tone generator to
initiate the decay of the generated tone.
The "set claim" signal output of AND gate 50 that occurs with the
simultaneous appearance of the three input signals to that gate is
utilized to provide a "key depressed" indication to the
attack/decay circuitry of the tone generator (and to percussive
controls, if desired), as well as to provide its previously recited
functions of "setting" flip-flop 53 and "resetting" counter 55.
The assignment logic embodiment of FIGS. 7A and 7B may be
associated with only a small number of tone generators (12, in the
example previously given), the exact number being selected in view
of the cost limitations and the likely maximum number of keys that
normally may be actuated simultaneously. In that case, each tone
generator must supply every desired frequency corresponding to
every note in every octave that may be played on the electronic
organ. To that end, a digital tone generator of the exemplary
configuration shown in block diagrammatic form in FIG. 8 is
employed.
Before describing the cooperative structural and functional
relationships between the elements of the tone generator shown in
FIG. 8, it is instructive to consider some of the available
alternatives in the construction and operation of digital tone
generators for ultimately generating a desired audiofrequency for a
note corresponding to an actuated key. When a key is depressed on
any keyboard of the digital electronic organ, a waveform is to be
generated with a periodicity corresponding to the desired note
frequency in the audible range. The waveform is computed in digital
format consisting of a series of numbers (digital words) which
represent the magnitude of the waveform at a series, or sequence,
of uniformly spaced sample points. The digital sample point values
thus generated are subsequently converted to analog form.
The sample points are preferably uniformly spaced because such a
format permits the most direct analysis, and therefore the most
direct synthesis, of the desired waveform. If desired, the uniform
spacing of sample points may be such that there is provided an
integral number of samples per cycle for each note frequency to be
generated. Such a technique requires a sampling rate that varies
directly with the frequency. Alternatively, the samples may be
spaced uniformly in time, in which case the phase angle between
samples points varies with the frequency of the note to be
generated. Although the synthesis of a multiplicity of note
frequencies can be implemented for either technique, using a single
clock frequency, the preferred frequency synthesis technique is
that in which the phase angle between the sample points varies with
frequency, i.e., in which the sampling rate is fixed for all note
frequencies to be generated, and the various generated note
frequencies are produced as a result of the different phase
angles.
FIG. 8 shows, in block diagram form, a specific exemplary structure
of a tone generator for generating the required note frequencies of
the organ from a memory containing amplitude samples of the desired
waveform obtained at uniformly spaced points in time. The sample
points are accessed at a fixed, signal clock frequency for all note
frequencies to be generated and the phase angle between the sample
points thereby varies with the frequency of the note to be
generated. The tone generator includes, as basic components, a
phase angle calculator 100, a phase angle register 101, a sample
point address register 102, a read-only memory 103, an address
decoder 103a, an accumulator 104, a sampling clock 105, and a
comparator 107. As will be apparent hereafter, the phase angle
calculator 100 and the read-only memory 103 may be shared by all of
the tone generators 28. In addition, each tone generator is
addressed or accessed individually and in sequence and thus once in
each cycle of addressing all tone generators. For that reason, the
sampling clock 105 may comprise a clock rate provided by a master
sampling clock, successive clock pulses of which are directed to
the series of tone generators. The sampling clock addressed to a
given tone generator is thus at a rate comprising the pulse
repetition rate of the master sampling clock divided by the number
of tone generators provided in the system. Further, since the same
read-only memory may be addressed by all tone generators, the
accumulator 104 may be a composite structure associated with
appropriate gating circuitry related to each tone generator for
accumulating the information read from the memory 103 in response
to accessing thereof by a given tone generator.
When a claim flip-flop of the tone generator assignment logic, such
as flip-flop 53 (FIG. 7B), is switched to the claimed state in
accordance with capturing of a pulse in the incoming multiplexed
waveform by a given tone generator 28, the phase angle calculator
100 is instructed to determine the appropriate phase angle for the
frequency of the note to be reproduced as identified by the
captured pulse. A determination of the value of the phase angle
constant, and hence, of the particular note corresponding to the
key that has been actuated, is initiated by supplying both the
count from the main keyboard counter 1 and the count of the modulo
384 counter 55 (e.g., of FIG. 7B) associated with the captured
flip-flop, and which is reset to zero upon that capture, to a count
comparator 107. Comparator 107 subtracts the count of counter 55
from the count of the keyboard counter 1 and supplies a number
representative of the difference, and hence, representative of the
time slot position corresponding to a particular note (i.e., that
note which captured the flip-flop), to phase angle calculator 100.
The difference computed by comparator 107 will always be positive,
or zero, because the computation is elicited from the comparator
only when the associated flip-flop 53 is captured and at that
moment counter 55 is reset to zero, whereas the keyboard counter
probably has some greater count or contains at least count, i.e.,
zero.
On the basis of the difference count supplied by comparator 107,
calculator 100 is informed as to the note for which the phase angle
calculation is to be performed, i.e., the note and thus the
frequency to be produced by the tone generator. The calculator 100
may compute the phase angle as a function of the frequency of the
note to be reproduced and of the number of memory sampling points
of the waveform in storage and thus as approximately equal to the
phase angle of the fundamental between adjacent memory sampling
points for the frequency to be produced. An alternatively
embodiment of the phase angle calculator 100 is a conventional
storage unit with look-up capabilities, or simply a memory from
which the correct phase angle is extracted when the memory is
suitably addressed with the identification of the count of the
captured pulse. Alternatively, a combination of a memory with
look-up capabilities and of a calculator capable of computation for
determination of the phase angles may be employed. The synthesis of
note frequencies in accordance with the digitally stored waveform
sample points may be arbitrarily as accurate as desired and, in
effect, provides a true equally tempered scale of the synthesized
note frequencies wherein the notes within the scale differ by the
power of 2.sup.1/12. The degree of accuracy in a practical system,
however, must be realized within a finite maximum information
content and thus the stored phase angles are quantized and rounded
off.
The phase angle thus developed is supplied to the stored in the
phase angle register 101. Thus, upon capture of a given tone
generator, a command control means such as flip-flop 53 which
establishes the captured state of the tone generator controls of
the operation of the comparator 107 and, in turn, the phase angle
determination function of the phase angle calculator 100 for the
given note frequency to be generated, for supply of that phase
angle to the register 101. Since this operation must precede the
addressing function, a delay may be provided (as by use of a delay
multivibrator 106) to actuate a switch 108 for passage of pulses
from the sampling clock source 105 (which may be an appropriately
gated pulse from a master sampling clock source) to the registers
101 and 102.
If desired, the sample point address register 102 may be cleared
when claim flip-flop 53 reverts to a noncaptured state, so that it
is prepared for entry of information from the phase angle register
101 upon each calculation. However, it is important to note that
during accessing the memory it is the rate at which the value of
register 102 increases and not the absolute value thereof which is
significant in the control of the rate of read out of the memory
103 and thus the cyclic frequency of read out of the memory and,
ultimately, the frequency of the note reproduced by the given tone
generator.
Once each sampling clock time as determined by the sampling clock
source 105, the phase angle value stored in phase angle register
101 is added to the previously stored value of the sample point
address register 102. An address decoder 103a decodes preselected
bit positions of the count established in register 102 to effect
accessing, or addressing, of the memory 103. The transfer from the
register 101 to the register 102 is a nondestructive transfer such
that the phase angle value is maintained in the register 101 as
long as that tone generator is captured by a given pulse.
Thus, once each clock time, the phase angle register value,
comprising a digital binary word, is added to the sample point
address register value and correspondingly, for each such clock
time, the memory location corresponding to the sample point address
then existing in the register 102 is accessed. As a practical
matter, only a relatively small, finite set of amplitudes can be
stored in the memory 103, because of practical limitations on its
capacity, and thus only a finite number of addresses are available.
Furthermore, the registers such as 101 and 102 must be of a finite,
practical length. In particular, the length of the phase angle
register 101 is determined by the accuracy with which the frequency
of the note is to be generated. The frequency actually produced
will be exactly the value of the phase angle in register 101 times
the memory sampling rate. The sample point address register 102, on
the other hand, must be sufficiently long to accept data from the
phase angle register 101. The register 102, however, preferably
includes additional bit positions which are not used, or not used
at all times, for accessing the memory. In this respect, it will be
apparent that one bit position in the register 102 is scaled at one
cycle of the fundamental of the frequency of the note to be
generated. A set of next successive less significant bits may
therefore specify the sample point address in accordance with the
function of the decoder 103a. The more significant bits of the
register 102 may be used to count numbers of cycles of the waveform
for various control functions not here pertinent. In addition, by
selecting appropriate bit positions by means of decoder 103a, the
frequency of the note reproduced may be readily adjusted to
different octaves. That is, a one-bit positional shift constitutes
division or multiplication by two, depending upon direction of
shift. For example, if the most significant bit is numbered 1 and
thus bit positions 2 through 6 comprise the sample point address
bits normally used for an 8-foot voice, then a 16-foot voice can be
obtained by using bits 1 through 5 as the sample point address
source. Correspondingly, a 4-foot voice can be obtained by using
bits 3 through 7 as a sample point address bits.
The read-only memory 103 contains digital amplitude values of a
single cycle of the complex periodic waveform to be reproduced for
all note frequencies. That is to say, the same complex periodic
waveform is to be reproduced for each note played, the only
difference being the frequency at which the complex waveform is
reproduced.
Referring to FIG. 9, illustrating a typical complex waveshape 110
of the type that may be produced by a pipe organ, the wave may be
sampled at a multiplicity of points, shown as vertical lines in the
Figure, to provide the amplitude data for storage in memory 103. If
absolute amplitude data is stored in memory 103, then the data
accessed is the actual amplitude of the output waveform at the
respective sample points (i.e., with respect to a "zero" level at
time axis 111). In the event, the digital amplitude data
successively read from the memory may be applied directly to an
appropriately digital-to-analog conversion system. On the other
hand, if incremental amplitude information (i.e., simply the
difference in amplitude between the present sample and the
immediately preceding sample) is stored in memory 103, then the
data accessed must be added to an accumulator (e.g., 104 in FIG. 8)
to provide the absolute amplitude information at each sample point
prior to digital-to-analog conversion. Each of the sample points of
the memory 103 may comprise a digital word of approximately seven
or eight bits.
The digital words thus read out from the memory 103 are supplied to
the accumulator 104 which provides a digital representation of the
waveform at selected sample points over a cycle of the waveform and
at a frequency corresponding to the note to be reproduced. As above
described, this digital waveform representation may itself be
operated upon for waveshape control, e.g., attack and decay, and
subsequently is supplied to a digital-to-analog converter for
producing an analog signal suitable for driving the acoustical
output means, such as audio speakers, of the organ.
Memory 103 may be a microminiature diode array of the type
disclosed by R. M. Ashby et al. in U.S. Pat. No. 3,377,513, issued
Apr. 9, 1968, and assigned to the same assignee as is the present
invention. The array may, for example contain an amplitude
representation of the desired waveform in the form of an eight bit
binary word at each of 408 or more sample points. Such a capacity
permits the storage of up to 128 amplitude levels in addition to a
polarity (algebraic sign) bit. In any event, the capacity of memory
103 should be sufficient to allow faithful reproduction of note
frequencies.
If whole values of amplitude levels at the sample points of the
waveform are read from memory 103 in the embodiment of FIG. 8, the
same sample point may be addressed several times in succession.
This is the result of the requirement that the memory be accessed
at a fixed rate for every note frequency, a requirement which
implies that for decreasing note frequencies an increasing number
of sample points must be read out during each cycle; and since the
number of sample points is fixed and no sample points can be
skipped regardless of note frequency, this simply means repetition
of the same sample point possibly several times in succession. This
does not undesirably affect the ultimate waveform generated,
however, because there is consistent plural sampling of each point
of the stored waveform.
On the other hand, if incremental values of the waveform have been
stored in memory 103, each increment can be read out only once
during each cycle of the waveform. This is because an accumulation
of incremental values is required, and repetition will produce a
significant error in the accumulation and the ultimate waveform to
be generated, regardless of the note frequency. Since the same
sample point may be read out of memory 103 several times in
succession depending upon the note frequency to be produced, just
as in the whole value sample point case noted above, for
incremental values all but one readout for each sample point must
be inhibited to prevent repetitive application to accumulator 104.
To that end, a gate 103b (shown dotted in FIG. 8) is positioned in
the output line of memory 103 preceding accumulator 104 if
incremental values are utilized. Gate 103b is preferably enabled to
pass the sample value being read from the memory only when the
least significant bit in address register 102 changes. Since such
change occurs upon a "carry" into that position, indicating
advancement to the next memory address, a bit change sensor 102a
may be used to detect the change and to enable gate 103b at each
advancement to a new address. The same sample point may still be
accessed several times in succession, but only one such value will
be "read out" (i.e., will be passed by the gate since it is
disabled at all other times).
The phase angle calculations should be such that the highest note
playable is that note for which a sample point value is read out
each time the memory is addressed. Since the ratio between adjacent
notes on the equally tempered musical scale is an irrational
number, it is preferable that the largest number in the phase angle
register be slightly smaller than the least significant bit in the
address register. If the phase angle number were larger, it would
be necessary to occasionally skip a sample point and this would
lead to inconsistency in the note frequency, whereas if the phase
angle number were equal to the least significant bit in the address
register the note frequency would be slightly higher (i.e., about
one-half of a halftone higher) than the highest note that can be
played. By requiring the phase angle number to be slightly smaller,
the highest note capability of the instrument will not be
exceeded.
The same read-only memory 103 may be shared by all of the tone
generators 28 of the data words (amplitude values of sample points)
read therefrom are gated to respective wave shapers in synchronism
with the addressing of the memory for the respective notes being
played. In other words, simultaneous or concurrent play of two or
more notes requires that these be distinguished as separate sets of
sample points, if a single memory is to be shared for all tone
generators.
In the present embodiment, however, it is assumed that each tone
generator has its own memory (and, incidentally, memories composed
of microminiature diode arrays of the type disclosed in the
aforementioned Ashby et al. patent are readily fabricated with more
than 5,000 diode elements per square inch), which supplies its
digital output to a respectively associated attack and decay
control unit. The binary-valued amplitude samples are applied
directly to the attack and decay circuitry of each sample is a
whole value, or may be applied via an accumulator 104 of each
sample is an incremental value. Alternatively, accumulation of
incremental values may be performed after shaping, if desired.
Referring to FIG. 10, an embodiment of the attack and decay unit
associated with each tone generator includes a multiplier 120 to
which the sample values from memory 103 are applied for
multiplication by an appropriate scale factor to control the
leading and trailing portions of the note waveform envelope. As is
well known, the faithful similation of true pipe organ sounds by an
electronic organ requires that the latter be provided with the
capability to shape each tone envelope to produce other than an
abrupt rise and fall. Without special attack and decay control, the
note waveform produced by an electronic organ normally rises
sharply to full intensity immediately upon depression of the
respective key, and ceases abruptly when that key is released. At
times, this may be a desirable effect to maintain during the play
of a musical selection. In those cases, the attack and decay
controls may be avoided entirely, or the scale factor supplied to
multiplier 120, and with which the amplitude samples are to be
multiplied, may be set at unity. More often, however, attack and/or
decay are desirable for or in conjunction with special effects,
such as percussion, sustain, and so forth.
The multiplying scale factor is varied as a function of time to
correspondingly vary the magnitude of the digital samples, with
which it is multiplied, on a progressive basis to simulate attack
and/or decay. In the embodiment of FIG. 10, the total time duration
and the time constant(s) for the attack or decay are controlled by
a counter 122 which may be selectively supplied with uniformly
timed pulses that are independent of the specific note frequency
under consideration, such as pulses obtained or derived from the
master clock, or with pulses having a repetition rate
representative of or proportional to the note frequency. In this
respect, the counter 122 may be considered as determining the
abscissa of a graph of envelope amplitude versus time and
representative of the attack or decay. The ordinate or amplitude
scale of the graph is represented by the series of scale factors
stored in a read-only memory 125 to be accessed by the counter
itself, or by an address decoder 126 which addresses the memory for
readout of scale factors on the basis of each count (or timed,
separated counts) of counter 122.
The counter may be of the reversible, up-down (forward-backward)
type in which it is responsive to incoming pulses to count upwardly
when its "up" (here, attack) terminal is activated, and to count
downwardly when its "down" (here, decay) terminal is activated. The
attack mode of the overall control unit is entered when the
associated tone generator is captured by a hitherto unclaimed note
pulse in the multiplexed signal. The capture of a tone generator is
accompanied by a signal indicative of a key having been depressed
(see FIG. 7B), from the assignment logic, and it is this signal
which initiates the attack count of counter 122. In particular, the
first "key depressed" signal (and possibly the only one) that
occurs upon capture of a tone generator 28 is effective to produce
a count in the first stage of ring counter 128, thereby supplying a
trigger signal from that stage to a monostable delay multivibrator
130 which is set to have an ON time (delay time) of sufficient
duration to ensure that the attack is completed despite release of
the key prior to the normal end of the attack interval. It has been
found that a delay time equal to or greater than approximately the
time occupied by seven cycles (e.g., seven periods) of the lowest
frequency note is quite adequate for multivibrator 130 to ensure
this positive attack. During that interval, the "up" control of
counter 122 is activated by the quasi-stable state of multivibrator
130 and the counter continues to count incoming pulses until the
multivibrator spontaneously returns to its stable state, or until
the note envelope reaches the full desired intensity (magnitude),
if earlier. This full intensity value may be preset into the
attack/decay control logic or it may be determined by logic
circuitry responsive to such factors as the force with which the
respective key is struck (i.e., to velocity-responsive or
touch-responsive device outputs). In the embodiment shown in FIG.
10, the former arrangement is utilized in which a maximum desired
count is set into a fixed counter 131 for continuous comparison in
comparator 133 with the present count of up-down counter 122. If
the latter exceeds the former, a "disable" command is applied to
the counter to terminate the attack.
Pulses to be counted by counter 122 may be obtained at a rate which
is a function of note frequency, as by supplying the output of
phase angle calculator 100 to a phase-to-frequency converter 135,
or at a rate based on the master clock rate, whichever is desired.
Selection of either rate is accomplished by appropriately setting a
switch 136 coupled to an associated switch or key on or adjacent to
one of the keyboards.
In operation of the attack/decay control unit of Figure 10, after
switch 136 has been set at the desired position, the pulses to be
counted appear at the input of counter 122 but no count is
initiated until a key is depressed and the associated pulse in the
multiplexed signal from the keyboard results in the capture of a
tone generator 28. The "key depress" signal from the generator
assignment logic initiates a count in ring counter 128, which had
been reset by completion of decay the immediately preceding time
the attack/decay control unit had been used. Preferably, the latter
reset signal is obtained upon switching of the claim flip-flop 53
in the assignment logic 26 to the "not claimed" (delay complete)
state. The up count of counter 122 is thereby enabled and continues
through completion of attach regardless of whether or not the key
remains depressed. If the count pulses are a function of note
frequency, the duration of attack is based upon note frequency as
well; otherwise, the positive attack interval is fixed regardless
of note frequency.
With each count of counter 122 (or less frequently, by use of
suitably timed "enabling" commands), address decoder 126 develops a
related address code for accessing a digital scale factor stored in
the appropriate address of read-only memory unit 125, to be
combined as a product in multiplier 120 with the amplitude samples
being read from tone generator 28 of Figure 8. By presetting memory
125 such that the scale factors stored therein are logarithmically
increasing (up to the equivalent of unity) with addresses decoded
according to progressively increasing count in counter 122 (up to
the maximum desired count, representing full note intensity), a
logarithmic attack is provided in the note being played.
Furthermore, since the initial attack is positive, i.e., continues
to completion regardless of the present condition of the key which
was struck to produce the attack, the logarithmic rise at the
leading edge of the note waveform continues smoothly to full
intensity of the note.
When the key is released, a "key release" signal is applied from
AND gate 62 of assignment logic 26 (FIG. 7B) to a flip-flop 138 to
initiate the decay mode of the attack/decay control unit by
enabling the "decay" (down) count of counter 122. Accordingly,
incoming pulses to the counter are counted downwardly from the
count representative of full intensity, until a zero count is
obtained unless decay is terminated earlier. As in the case of the
attack mode, the count of counter 122 is periodically decoded
(e.g., once each count) by unit 126 for addressing the memory 125,
there supplying logarithmically decreasing scale factors, from
unity to zero, for multiplication with amplitude samples from the
tone generator in multiplier 120. This procedure the desired fall
in note intensity at the trailing portion of the note waveform.
Alternatively to relying on zero count, scaler control logic may be
implemented to signal completion of the decay mode.
If during decay the same note pulse should reappear in the
multiplexed keyboard signal, indicating depression of the
associated key virtually immediately after release thereof, a
second "key depress" signal is applied to ring counter 128 thus
increasing the count therein to the second stage and switching
flip-flop 138 from the decay state to its other state, which
reintroduces the attack mode. Since decay is incomplete in this
particular instance, the count of counter 122 now proceeds upward
from the minimum count which had been of delay MV 130), flip-flop
138 may be switched to its "attack" state upon full completion of
decay, by the "not claimed" signal of flip-flop 53 in the
assignment logic unit which produced capture of the associated tone
generator. Concurrent operation of flip-flop 138 in the "attack"
state and MV 130 in the quasi-stable state will not effect the
above-described operation of the attack/decay control unit.
Upon completion of decay of a note whose representative pulse in
the keyboard multiplexed signal resulted in capture of a tone
generator, a "decay complete" signal is applied to the claim
flip-flop 53 (FIG. 7B) of the respective assignment logic unit to
cause that flip-flop to return to its "not claimed" state, and
thereby to release the tone generator for claiming by another note.
The "decay complete" signal may be supplied by the zero count of
counter 122 or by any conventional detector for sensing the absence
of further output from multiplier 120.
With reference now to FIG. 11, a keying system is provided for use
with percussive tone generators (e.g., noise generators) to
selectively produce sounds simulating those of percussion
instruments. In the past, various types of pipe organs, such as
theater organs, have been implemented with miniature reproductions
of different percussion instruments, such as drums, cymbals, wood
blocks, temple blocks, brush, and so forth, which could be actuated
by the organist according to the desired rhythm accompaniment for
the organ. The natural sounds of the miniature instruments were
amplified to produce a percussion level consistent with the
intensity of tones produced by the organ itself. Because of their
miniaturized form, the percussion instruments were frequently
referred to as "toys," and the beat or rhythm actuating devices by
which the organist "played" those instruments were often called
"toy counters." To some extent the latter name has remained in
usage despite the much more prevalent use today of electronic
organs in which special tone generators keyed by electronic signals
are utilized to produce the desired percussion sounds for rhythm
accompaniment of the organ.
The toy counter logic or percussion control logic of FIG. 11 is
suitable for actuation of either the miniature percussion
instruments or the percussion sound tone generators, depending upon
which of these forms are provided, in conjunction with a keyboard
multiplexing digital electronic organ of the type which has thus
far been described herein. In particular, keying signals may be
developed in the keyboard multiplexing system for use in generating
the desired special percussive effects. Two types of keying
signals, transient and steady state, are provided independently for
each keyboard in the embodiment of FIG. 11.
The transient signal consists of a pulse which occurs upon
depression of a key on any keyboard of the organ, and only upon
depression of a key. To that end, the "set claim" signal (or "key
depressed" signal) that occurs as an output of AND gate 50 in the
tone generator assignment logic (FIG. 7B) upon coincidence of input
signals to that gate, is used to indicate the depression of a key
on one of the organ keyboards. Clearly, since the "set claim"
signal can be produced only when a tone generator 28 is available
(and results in capture of that tone generator), no such signal can
occur if the organ is saturated, i.e., if all tone generators are
in use, regardless of depression of a key. Except in the event of
saturation, which is unlikely, each time a key is depressed a
signal is supplied to an OR gate 150 of the percussion control
logic. In the exemplary organ embodiment thus far described, 12
tone generators are provided and hence 12 "set claim" signals, each
associated with a separate and distinct tone generator assignment
logic unit, can be produced. Accordingly, OR gate 150 has an input
terminal for each "set claim" signal, for a total of 12 input
terminals. Each time a signal appears as an input to the OR gate,
indicating depression of a key, an output signal is supplied by the
OR gate in parallel to four AND gates 152-1, 152-2, 152-3, and
152-4, for the specific example of an organ having four keyboards
(three manuals and a pedal board).
Sequential gating signals are supplied to the four AND gates 152
over the respective intervals in which the associated keyboard is
being scanned by connecting the second input terminal of each AND
gate to a respective output lead of keyboard counter section 4
(FIG. 1). Thus, the transient keying signal that occurs upon
depression of a key is gated on an output line associated with the
keyboard on which that key is located. This signal, in the form of
a pulse, may be used to actuate actual miniature percussion
instruments or to actuate percussion sound generators. The specific
manner in which the keying signals are employed for that purpose
may follow conventional practice, using conventional percussion
systems. Reference is made, by way of example, to U.S. Pat. Nos.
3,309,454 to Cutler et al., 3,358,069 to Hearne, 3,433,880 to
Southard, and 3,439,569 to Dodds et al., as representative of known
techniques for use of keying signals to initiate percussion sounds.
In the case of the transient keying signal, zero count detector 60
and associated components of the tone generator assignment logic
preclude the "key depressed" signal from recurring with each
repetition of the respective pulse in the multiplexed signal during
the interval over which the key remains depressed, as previously
explained in conjunction with the description of FIGS. 7A and
7B.
The other type of keying signal, viz, the steady state signal, is
derived directly from the multiplexed signal appearing as an output
from encoder 15 (FIG. 1). The multiplexed signal is applied in
parallel to four AND gates 156-1, 156-2, 156-3, and 156-4 (again,
for the specific case in which four keyboards are available), and
the pulses associated with keys on each respective keyboard are
gated only during the occurrence of gating signal for that keyboard
as supplied from keyboard counter section 4 to the other input
terminal of each of the AND gates 156. An output from any one of
the AND gates is applied as a set signal to a respective one of
four flip-flops 158-1, 158-2, 158-3, and 158-4. Thus, each
flip-flop 158 is set by the occurrence of a pulse in the
multiplexed signal during the time period provided for the
corresponding keyboard. All of flip-flops 158 are reset
simultaneously upon occurrence of the keyboard counter reset
signal.
Assumption by a flip-flop 158 of its set state results in a signal
applied to a respective one of a set of AND gates 160, and
similarly, the resetting of flip-flops 158 results in signals
representative of that state of the flip-flops to others of the AND
gates 160. Each pair of AND gates 160 associated with a specific
flip-flop 158 is also associated with one of a further set of
flip-flops 161-1, 161-2, 161-3, 161-4, so that upon occurrence of
the keyboard counter reset signal the respective states of
flip-flops 158 are transferred to corresponding ones of flip-flops
161. The effect is that of a sample and hold system, to provide the
desired steady state percussion keying signals from each keyboard,
each such keying signal being taken only from the "set" state
output terminal of the respective flip-flop 161.
As in the case of the transient keying signals, the steady state
keying signals may also be utilized to supply desired percussion
sounds by known techniques.
Each keyboard of the organ usually has associated with it a set of
stops or tabs, alternatively referred to as stop tabs, stop keys,
or stop switches. In a generic sense, the stops as well as the keys
of each keyboard may be referred to as switches. The stops
associated with each keyboard are utilized to select appropriate
pitch length or footage and the desired organ voice, including the
tonal quality, or timbre, and the harmonic content of the sound to
be reproduced by the electronic organ. Stops may be actuated in
various combinations, if desired, and may also be preset or
programmed to permit the organist to reactuate one or more stop
combinations during performance of a particular musical piece, by
means of a so-called "combination action." The terminology "stop
rail" is also used to refer to a set of stop or tab switches by
which the organist may select particular voices prior to and/or
during play of the organ.
A system for multiplexing information representative of the
selection of particular tab switches in each stop rail and for the
storage of such voicing information to be subsequently accessed by
the organist during performance of the musical selection, is
illustrated by way of example in FIG. 12. Referring to that Figure,
the stop rail multiplexing system includes a stop rail counter 200,
a stop rail decoder 201, a stop rail switching array 202, a stop
rail encoder 203, a set of voice memories 204, a voice memory
selector 205, an address decoder 206, a voicer 207, a set of
registration memories 208, and a set of couplers 209.
The stop rail counter 200 comprises four separate sections as is
indicated with greater clarity in FIG. 13. The most significant
section or portion of the stop rail counter is referred to as the
registration memory (RM) counter 211 and the remaining stop rail
counter portions are of decreasing significance, from the RM
address counter 212 and voice group counter 213, down through the
voice counter 214 which constitutes the least significant portion
of stop rail counter 200. Voice counter portion 214 is a modulo-4
ring counter which is advanced by pulses derived from the master
clock and which sequentially energizes its output leads, designated
V1, V2, V3, V4, in accordance with advancement of its count. All
four output leads of voice counter 214 are connected to encoder 203
and to voice memory selector 205, whereas only the last stage, V4,
is connected to voicer 207, for a purpose to be described
presently.
The next more significant portion of the stop rail counter 200,
namely, the voice group counter 213 is a modulo-10 ring counter,
having 10 stages and associated output leads designated GSF, GGF,
GS1, GS2, GS3, GG1, GG2, GP1, GP2, and GP3, advancing from the
least to the most significant stage of that counter portion. For
the sake of clarity, the first letter of each of these designations
indicates "group," and the next two characters indicate particular
voice groups such as swell flute (SF), great flute (GF), swell (S),
great (G) and pedal (P), although it is to be understood that there
is no intention here to restrict the voicing section to voices of
these particular types. All output leads of voice group counter 213
are connected to decoder 201 and to voice memory selector 205,
whereas the last stage, GP3, alone is connected to voicer 207. The
voice group counter sequences through all of these groups once
during each of its cycles, and advances to the next successive
stage (group) once for each cycle of voice counter 214. In other
words, the voice counter must sequence through all four of its
stages before the count is advanced by one in voice group counter
213.
The next more significant counter section or portion of the stop
rail counter 200 is the RM address counter 212 which, in this
particular embodiment, is a modulo-64 six-bit binary counter
utilized to specify the addresses of the registration memories 208,
the latter constituting the working storage from which digital
waveforms are read under control of the note generators for
generating the audio output. In the present example, five
registration memories are employed, these being designated swell
flute, great flute, swell, great and pedal. In particular, the
registration memories are to be loaded with data from the voice
memories 204 which contain the fixed, stored data representing
individual voices, and thereby to form a composite of individual
voices which are keyed simultaneously and sounded in the same audio
channel. Stop rail counter 200, decoder 201, switching array 202,
and encoder 203 together provide the stop rail tab switch
information to voicer 207 in the form of a multiplexed signal. The
multiplexed signal is used for selecting the appropriate voice data
from voice memories 204 to provide the composite data in
registration memories 208. Specifically, it is the function of
voicer 207 to accumulate the voice data from voice memories 204 to
form the composite data for entry into the registration memories
208. It will be realized from the preceding description that the
registration memories must be updated as necessary to enter the
composite voice data therein, and it is to that end that the
outputs of the RM address counter 212 and of the RM counter 211, a
modulo-5 ring counter, are supplied to registration memories
208.
The registration memories are updated one at a time in sequential
order as determined by RM counter 211, its outputs RSF, RGF, RS,
RG, and RP being sequenced in the order recited with advancement by
one stage upon conclusion of each cycle of the count of RM address
counter 212. It is the function of the RM address counter 212 to
specify the addresses of the registration memories such that each
memory location is updated sequentially in the order of those
addresses. The latter counter advances once for each cycle of the
count of voice group counter 213. The outputs of RM counter 211 are
supplied to the registration memories 208 and to decoder 201,
whereas RM address counter 212 supplies all of its outputs to the
registration memories for specifying the addresses thereof, and as
well supplies the outputs from the first five of its stages to
address decoder 206 and the output of the fifth stage alone to
voicer 207.
The exemplary embodiment of the stop rail multiplex system may be
provided with 40 voices, arranged in 10 groups of four voices each
for the sake of convenience. Each group of voices is associated
with only one of the five registration memories, although more than
one group may be associated with a particular one of those
memories. Except for the coupling information provided by couplers
209, a voice group is loaded only into that registration memory
with which it is associated. The relationship between voice groups,
couplers, and registration memories is illustrated in the following
Table. ##SPC1## The four voices in each group are specified in
sequence by the voice counter 214.
Stop rail decoder 201 is implemented to modify the group counter
213 outputs and the RM counter 211 outputs in accordance with the
coupler switch information from couplers 209, to drive stop rail
array 202. Preferably, a decoder 201 is implemented to produce the
10 logical outputs designated by the logic equations listed
below.
Dsf = gsf (rsf+rgf sgc+rp spc)
dgf = ggf (rgf+rp gpc)
ds1 = gs1 (rs+rg sgc+rp spc)
ds2 = gs2 (rs+rg sgc+rp spc)
ds3 = gs3 (rs+rg sgc+rp spc)
dg1 = gg1 (rg+rp gpc)
dg2 = gg2 (rg+rp gpc)
dp1 = gp1 (rp)
dp2 = gp2 (rp)
dp3 = gp3 (rp)
stop rail array 202 is a matrix of switches constructed in an
analogous manner to the construction of the keyboard array of FIG.
1. In particular the stop rail array is provided with 10 input
buses driven respectively by the decoder outputs, and with four
output buses designated VS1, VS2, VS3, and VS4. At each
intersection of an input bus and an output bus of the stop rail
array there is provided a series connection of a normally open
switch and a diode poled anode-to-cathode in the direction from the
input bus to the output bus, corresponding to that arrangement
shown in FIG. 4 for the keyboard switching array of FIG. 1. In the
stop rail array, however, the switches are controlled by the voice
selection stop tabs.
Encoder 203 is implemented to accept the four parallel outputs VS1
through VS4 of the stop rail array 202 and the four parallel output
lines V1 through V4 of voice counter 214, and to produce therefrom
a multiplexed signal consisting of information in the form of
pulses indicating which of the voice selection stop tabs has been
actuated, to institute the selection of the voice composite data.
To that end, and as shown in FIG. 14, the stop rail encoder 203 may
include four AND gates 220-1, 220-2, 220-3, and 220-4, each of
which has a pair of input terminals and an output terminal, the
latter connected in parallel with outputs of the other AND gates to
supply inputs to an OR gate 222. Each AND gate 220 receives as one
of its inputs the signal appearing on a respective one of the four
output buses VS1, VS2, VS3, VS4 from array 202, and as the other
input a signal appearing on the lead from a respective one of the
four stages of the voice counter 214. Thus, as the voice counter is
sequenced through its four stages, the signals appearing on the
four output buses of array 202 are gated in the same sequence to OR
gate 222, thereby forming a serial digit format as the multiplexed
signal MS containing voice selection data for application to voicer
207.
In an exemplary embodiment, voice memories 204 may comprise a set
of 40 fixed memories, each provided with a select line VSi and a
four-bit address VA1 to VA4. Each of the 40 voice memories consists
of 16, seven-bit words defining a half cycle of the waveform to be
sounded. The arrangement of voice memories is shown in exemplary
form in FIG. 15, the 40 fixed memories being read one at a time in
accordance with the selection performed by the voice memory
selector unit 205 which supplies selection outputs VS1 through VS40
thereto. When a voice memory is read, one seven-bit word is
addressed and the seven bits are read out in parallel. While there
are only 16 words in each voice memory, there are 64 registration
memory addresses, and the address decoder 206 is implemented so
that as the RM address counter 212 advances from 0 to 63, the voice
memory address is advanced from 0 to 15, from 15 to 0, from 0 to
15, and again from 15 to 0. Since each set of 16 seven-bit words
defines a half cycle of the desired waveform, this addressing of
the voice memory is effective to provide complete cycles of that
waveform.
An embodiment of voice memory selector 205 is shown in FIG. 16.
Preferably, it consists of a set of 40 AND gates arranged in groups
of 10 such that each group of AND gates receives respective inputs
from the 10 output lines of voice group counter 213 and each
successive set of four of those AND gates receives its other input
from a respective one of the output lines of voice counter 214 so
that a voice memory selection is performed by a coincidence of the
group counter and the voice counter active outputs. The 40 voice
selection outputs VS1 to VS40 are supplied in the activated
sequence to voice memories 204.
An exemplary embodiment of address decoder 206 is shown in FIG. 17.
Preferably, that decoder comprises a set of four exclusive OR gates
each receiving as one of its inputs an output from a respective one
of the first four stages of the RM address counter 212, and all
receiving, as the other input, the output of the fifth stage of the
RM address counter. Thus, four addresses VA1 to VA4 are supplied in
sequence as voice memory addresses, as either one, but not both, of
the inputs of the respective exclusive OR gate is activated, and
the arrangement is such that the advancement of voice memory
addresses is in the forward and reverse sequence noted above to
produce complete cycles of the waveform.
The voice data consisting of the seven-bit parallel output VD1
through VD7, provided by the selected memories, is supplied as an
output of the voice memories 204 to voicer 207. The voicer
accumulates this voice data in accordance with control exercised by
the multiplexed signal MS from encoder 203. A preferred embodiment
of the voicer is shown in FIG. 18. Voice data read out of the voice
memories as the latter are sequentially addressed, is read into
voicer 204 either (1) directly into a parallel adder 232 if no
signal RA5 is applied to one's complement gate 230 and a pulse
appears in the multiplexed signal MS to enable gate 231; or (2)
complemented as the result of application of signal RA5 from the RM
address counter 212 to gate 230, and then read into the parallel
adder 232 in response to an appropriate concurrent pulse in the
multiplexed signal at gate 231; or (3) entirely inhibited by virtue
of the absence a pulse in the multiplexed signal applied to gate
231, so that a binary zero is read into the parallel adder. Thus,
if bit five of the RM address counter 212 is "true," the data from
the voice memories is complemented. If the multiplexed signal is
"true," indicating that the respective voice was selected by the
tab switches, and by the couplers, then the voice data or its two's
complement is read into adder 232. Otherwise, a zero is read into
the adder.
With reference to the specific logic for the voicer 207 as shown in
FIG. 18, the one's complement gate 230 may consist of seven
exclusive OR gates (not shown), each having two inputs, one a voice
data bit, and the other the bit five of the RM address counter 212.
The output of gate 230 is either the voice data or its bit-by-bit
complement. Enable gate 231 may consist of eight AND gates (not
shown), seven of which have two inputs, one constituting an output
from a respective one of the seven exclusive OR gates in complement
gate 230 and the other constituting the multiplexed signal MS. The
eighth AND gate is supplied with the multiplexed signal as one of
its inputs and bit five (RA5) of the RM address counter. The output
of the eighth AND gate in enable gate 231 is entered into the least
significant bit carry input to parallel adder 232 to perform the
two's complement of the data. Parallel adder 232 receives both the
outputs of enable gate 231 and of a copy register 234. Copy
register 234 in turn receives the contents of parallel adder 232 to
hold the sum of the selected voices as they are accumulated. The
copy register is reset during the selection of the 40th voice by a
reset signal which occurs upon coincidence of the V4 output of
voice counter 214 and the GP3 output of voice group counter 213 as
inputs to an AND gate 235. The accumulated sum appearing in
parallel adder 232 is written into the appropriate registration
memory in accordance with an enable signal produced by coincidence
of the reset signal and a master clock pulse, and in accordance
with the selection provided by the RM counter 211 and the address
provided by RM address counter 212.
Thus, when a particular stop switch is operated, a pulse appears in
the corresponding preassigned time slot of the multiplexed signal
output of encoder 203 as a consequence of a completed circuit
connection having been established between an input bus and an
output bus of switching array 202 allowing a signal from the
scanning counter to pass through that connection. This pulse
produces the previously described operation in voicer 207 to load
the registration memories with the proper voice information in
accordance with address information supplied by RM counter 211 and
RM address counter 212.
* * * * *