U.S. patent number 3,740,450 [Application Number 05/204,853] was granted by the patent office on 1973-06-19 for apparatus and method for simulating chiff in a sampled amplitude electronic organ.
This patent grant is currently assigned to North American Rockwell Corporation. Invention is credited to Ralph Deutsch.
United States Patent |
3,740,450 |
Deutsch |
June 19, 1973 |
APPARATUS AND METHOD FOR SIMULATING CHIFF IN A SAMPLED AMPLITUDE
ELECTRONIC ORGAN
Abstract
A sampled amplitude electronic organ embodies first and second
memories storing groups of amplitude samples that, respectively,
delineate energy levels of the wave shape of a musical tone, and
energy levels of the wave shape having the dominant energy of a
third harmonic or its equivalent of the musical tone. The groups of
amplitude samples are read out at rates determined according to
actuation of a number of keyboard switches so that the repetition
rate of the group as read from the memory is the chosen frequency
of the musical tone to be produced by operation of an actuated
keyboard switch. The two groups of amplitude samples are added for
about the first seven cycles of read out to thereby introduce a
transient chiffing wave to the initial portion of the primary tone
to be generated.
Inventors: |
Deutsch; Ralph (Sherman Oaks,
CA) |
Assignee: |
North American Rockwell
Corporation (El Segundo, CA)
|
Family
ID: |
22759720 |
Appl.
No.: |
05/204,853 |
Filed: |
December 6, 1971 |
Current U.S.
Class: |
84/632; 84/DIG.5;
984/328; 84/603; 84/605; 984/322; 984/392 |
Current CPC
Class: |
G10H
7/04 (20130101); G10H 1/14 (20130101); G10H
1/057 (20130101); Y10S 84/05 (20130101) |
Current International
Class: |
G10H
7/02 (20060101); G10H 1/06 (20060101); G10H
1/057 (20060101); G10H 1/14 (20060101); G10H
7/04 (20060101); G10h 001/02 () |
Field of
Search: |
;84/1.01,1.03,1.24,1.22,1.23,1.25,DIG.5 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Wilkinson; Richard B.
Assistant Examiner: Witkowski; Stanley J.
Claims
I claim:
1. The method of simulating chiff in an amplitude sample musical
tone generation system comprising the steps of
generating repetitive groups of primary amplitude sample
representations collectively delineating the wave shape of a
musical tone, said groups being generated at a group repetition
rate that determines frequency of the musical tone,
generating repetitive groups of chiff amplitude sample
representations collectively delineating the wave shape having a
dominant harmonic of the fundamental of the tone to be
generated,
combining said groups of chiff amplitude sample representations
with said groups of primary amplitude sample representations only
during an initial transient period of the generation of said groups
of primary amplitude sample representations, and
producing an electrical signal representing said primary amplitude
sample representations as modified by transient combination with
said chiff amplitude sample representations.
2. The method of claim 1 wherein said step of adding is initiated
substantially simultaneously with initiation of generation of said
groups of amplitude sample representations.
3. The method of claim 1 wherein said step of combining said chiff
and primary amplitude sample representations is caused to terminate
at the end of an interval that varies in accordance with the
frequency of the tone to be generated.
4. The method of claim 1 wherein said step of combining said chiff
and primary amplitude sample representations comprises the steps of
storing said chiff amplitude sample representations, reading said
chiff amplitude sample representations from storage, and inhibiting
said reading of chiff amplitude sample representations when the
combining of said primary and chiff amplitude signal
representations is to be terminated.
5. The method of claim 1 wherein said step of combining chiff and
primary amplitude sample representations comprises the steps of
counting groups of said primary amplitude sample representations
and inhibiting said combining when a predetermined number of said
groups of primary representations has been counted.
6. An electrical musical instrument comprising
a first memory for storing a first group of amplitude sample
representations delineating energy levels of a complex wave
form,
a second memory storing a second group of amplitude sample
representations delineating energy levels of a wave shape having a
dominant harmonic of said complex wave form,
memory addressing means including a sample point address register
for simultaneously and repetitively addressing both said first and
second memories to cyclically read out therefrom both said first
and second groups of amplitude sample representations at said
repetitive address rate,
means for selectively inhibiting read out of said second
memory,
a cycle counter connected to count cycles of said sample point
address register,
means for initiating counting of said cycle counter,
means responsive to attainment of a preselected count by said cycle
counter for actuating said inhibit means to inhibit read out from
said second memory,
means for adding first and second groups of amplitude sample
representations read out of said first and second memories, and
means responsive to said adding means for producing a combined
output signal including an initial third harmonic transient
thereon.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to methods and apparatus for
enhancing tonal qualities of an electronic organ and more
particularly concerns the simulation of chiff in an electronic
organ embodying sampled amplitude signal generation.
2. Description of Prior Art
The term "chiff" as used in todays organ design refers to a
well-known phenomenon in wind-driven organ pipes. A common defect
of flue or labial organ pipes is that when they are first blown,
they tend to sound at a higher harmonic than the fundamental pitch
they produce after the initial transient. Shortly after the initial
transient, the pitch quickly drops to the normal steady state
frequency and tone. This phenomenon of the dominant higher harmonic
that occurs during the initial transient has been called by many
names, including the name "chiff". In fact, certain pipes have been
given the name "spitz flote" because of the analogy to a "spit type
tone during the initial transient.
Chiffed tones were long considered to be undesirable and a defect
in the organ pipes. During the last century organ voicers have
developed several techniques which eliminate or greatly reduce
chiffing. These techniques usually involve introduction of
mechanical knicks along the organ pipes languid (languet). However,
as subjective evaluation of music and tonal qualities evolves,
todays pipe organs and electronic organs have undergone a
retrogressed form of innovation. Changing musical preferences favor
the building of new organs which have certain of the tonal
advantages and also the defects of the Baroque period. Following
this reversion to older musical tonal characteristics, organs are
now deliberately voiced to have at least several ranks of pipes
that chiff. In particular the 8 foot voice is desirably chiffed in
present day organs.
In several electronic organs that are commercially available, chiff
is simulated by introducing a short grace note during the attack
time of a tone that is to be chiffed. The grace note is most
commonly selected as the nearest equal tempered note to the third
harmonic of the fundamental tone being keyed. It has been judged
that such third harmonic provides an optimum simulation of a chiff
organ pipe. However in such an arrangement the chiffing note is
mechanically coupled with the primary note being played, or at best
electronically coupled for a time predetermined according to
conventional delay circuits. In such an arrangement, the duration
of the chiffing transient will have little or no relation to the
frequency of the note being played. Further, prior systems are not
applicable to sampled amplitude organs.
Accordingly it is an object of the present invention to provide a
method and apparatus for simulating chiff in a sampled amplitude
musical tone generation system.
SUMMARY OF THE INVENTION
In carrying out principles of the present invention in accordance
with a preferred embodiment thereof, groups of representations of
primary and chiff amplitude samples collectively delineating the
wave shape of a musical tone and a wave shape having a
predetermined relation to the first wave shape are generated at
group repetition rates that determine frequency of the primary
musical tone to be played. The groups of chiff amplitude sample
representations are combined with the groups of primary amplitude
sample representations during an initial transient period. A
further feature of the invention is control of the duration of the
initial transient period in accordance with a number of cycles of
the primary group repetition rate.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1a represents a wave form of a musical note having an
amplitude envelope showing an initial attack and a final decay,
FIG. 1b illustrates a chiffing wave form,
FIG. 1c illustrates the desired combination of the normal wave form
and the chiffing wave form,
FIG. 2 is a block diagram of a sampled amplitude musical tone
generation system embodying chiffing simulation of the present
invention.
DETAILED DESCRIPTION
As illustrated in FIG. 1, a normal wave form of a musical tone
takes the general shape shown in this figure. Amplitude of the tone
builds up from its time of its initiation, t.sub.0, during the
attack which terminates at a time t.sub.1. During the major portion
of the tone, from time t.sub.1 until time t.sub.2 the amplitude
envelope remains substantially constant. At time t.sub.2 a decay
period is initiated which terminates with termination of the note
at time t.sub.3.
A desirable chiffing wave form is shown in FIG. 1b, which
illustrates a tone having its dominant energy content at the third
harmonic of the tone of FIG. 1a. This chiffing wave form also
builds up in its amplitude envelope during the attack time, from
t.sub.0 to a point just preceding the end of the attack time
t.sub.1. At a point at the end of the attack time, or slightly
before, amplitude of the chiffing wave form rapidly falls to
zero.
Combining the wave shapes of FIG. 1a and FIG. 1b yields the wave
shape shown in FIG. 1c. This is the desired chiff wave form, having
a dominant third harmonic during the attack interval t.sub.0
through t.sub.1. At about time t.sub.1 the chiffing wave form
rapidly falls to zero and the primary wave form continues as in the
normal wave form.
Apparatus for generating the wave forms of FIGS. 1a and 1b and
combining these to provide a chiffed wave form is embodied in the
stored sampled amplitude organ that is illustrated in block form in
FIG. 2. The system illustrated in FIG. 2 is basically the same as
the systems shown in U. S. Pat. No. 3,610,799, for Multiplexing
System for Selection of Notes and Voices In An Electronic Musical
Instrument and U. S. Pat. No. 3,639,913, for Method and Apparatus
for Addressing a Memory at Selectively Controlled Rates, both
issued to George A. Watson, and assigned to North American Rockwell
Corporation, the assignee of the present invention. Although the
invention is described herein as applied to the digital organ
system of the Watson patent, it will be readily appreciated that it
is not limited to systems employing digital representations of
sampled amplitudes. Principles of the invention may also be applied
to instruments and systems that delineate complex wave shapes of
musical tones by means of other types of representations of sampled
amplitudes. Such other representations may include various well
known forms of analog arrangements, such as voltage, current,
electrical charge, and the like.
Briefly the organ that is described in full detail in the Watson
patent and generally illustrated in FIG. 2 hereof, embodies a
multiplexor 24 that provides a series of output signals on a line
25, each of which occurs in a unique specifically allocated time
slot of each multiplexor cycle. As the operator actuates a given
key or pedal or some combination of keys or pedals of the
instrument, the arrangement scans each key and pedal during each
multiplexor cycle and produces a pulse or no pulse at particular
time slot allocated to a given key, depending upon whether such key
or pedal has been actuated. The multiplexed signal on line 25 is
fed to a generator assignment logic circuit 26 which feeds the
pulses representing actuated keys or pedals to a tone generating
circuit including a phase angle number selector 28, a phase angle
register 32, a sample point address register 34, and a gate 30.
Although in an actual system there may be as many as twelve such
tone generating circuits, only one is shown herein and only one is
necessary for an understanding of the practice of the present
invention. Where several of such tone generators are employed, each
may be identical to the others. The function of the generator
assignment logic is to direct a signal from the multiplexor that
represents actuation of a given key to one of the tone generators
that is not already engaged in receiving a signal and producing a
tone therefrom.
The phase angle number selector 28 which may be common to all of a
number of tone generators and shared by these, selects (either from
storage or by repetitive calculation) a number from a set of
distinct and different numbers that vary according to the twelfth
root of two. As is well known, a semi tone, or half tone in the
musical scale of equal temperament is the frequency ratio between
any two tones whose frequency ratio is the twelfth root of two.
Therefore, the several numbers of the set calculated by or stored
in selector 28 identify phase angles or frequencies of the
individual notes of the scale of notes to be played. These phase
angle numbers identify read out rate of stored sampled points of
the complex wave form for the respective note frequencies in the
entire range of frequencies of the musical scale of the particular
instrument. Details of such calculation and/or storage together
with circuitry therefore are set forth in the above-identified U.S.
Pat. 3,639,913.
The tone generator, by means of its sample point address register
34, addresses a memory 40 by means of an address decoder 42. When
generator assignment logic 26 determines that a particular tone
generator is claimed (available for reception of the next note
identified in the multiplexed signal), gate 30 is opened to allow a
number corresponding to a particular note or actuated key that is
to be assigned to this tone generator to be introduced into the
phase angle register 32.
Phase angle register 32 feeds the number stored therein to the
sample point address register 34 and, upon each clock pulse
received from a sampling clock, augments the number stored in the
sample point address register 34 by the number in the phase angle
register. As the sample point address register is augmented, its
count advances and is fed to address decoder 42 which then
addresses the memory 40. Stored in the memory 40 are groups of
representations of amplitude samples that collectively delineate
the wave shape of a musical tone. These groups of representations,
which are eight bit digital words in the exemplary embodiment, are
read out of the memory at a group repetition rate that determines
the frequency of the musical tone. The memory output is fed to
circuitry 29 for further processing and conversion to a musical
tone. This circuitry may accumulate various signals, impose attack
and decay amplitude envelopes, combine various voices, and convert
the resulting electrical signal to an audible tone, all as more
particularly described in the above-identified U.S. Pat.
3,610,799.
Thus it will be seen that the arrangement described to this point,
all of which is further detailed in the above identified Watson
patent, responds to actuation of a selected key on the instrument
keyboard, selects a phase angle number according to the identity of
the actuated key, gates the selected number into the phase angle
register, and then causes the sample point address register to be
repetitively augmented by the number stored in the phase angle
register at a rate determined by a sampling clock. As the sample
point address register is augmented, the number contained therein
is decoded to address the memory 40. The memory thereupon provides
on output lines generally identified at 44, groups of
representations of amplitude samples that collectively delineate
the wave form of a primary note that has been selected by the
particular key actuated.
According to principles of the present invention, a chiffing
arrangement is added to the above-identified system of Watson to
produce a resulting wave form such as illustrated in FIG. 1c. To
this end, there is provided a second memory 50 which may comprise a
separate section of the primary memory 40. Memory or memory section
50 has its own address decoder 52 which also decodes the same
address number contained in sample point address register 34.
Therefore, as sample point address register 34 is augmented to
achieve a step by step addressing of the various sample
representations in memory 40, it also achieves a step by step
addressing of the amplitude sample representations in memory 50.
Preferably the amplitude sample representations in memory 50
represent the energy content or amplitudes, at selected points
along the time axis, of a complex wave form having a dominant third
harmonic of the wave form represented by the amplitude samples
stored in memory 40.
For example, where amplitude sample representations stored in
memory 40 represent an eight foot voice, the chiffing wave form is
preferably stored in the form of amplitude sample representations
for an eight foot voice having a dominant third harmonic. However,
it will be readily appreciated that, as an alternative, the
chiffing wave form may be stored as amplitude sample
representations of a sixteen foot voice having its energy
concentrated in its sixth harmonic. For storing representations of
a sixteen foot voice, twice as many memory representations are
located in the memory as in the case of an eight foot voice.
Accordingly for a given rate of addressing the memory, it takes
twice as long to scan the sixteen foot voice whereby a lower
frequency is produced.
As the sample point address register is augmented, primary
representations of amplitude samples are read out of memory 40 and
chiff amplitude sample representations are read out of memory 50.
These amplitude sample representations, which are digital words in
the described embodiment, are combined in an adding network 54
which then feeds the circuitry 29 to impose attack, decay, shaping,
voicing and the like, and convert the selected and combined signals
to an audio tone.
As previously mentioned the chiffing signal to be combined with the
primary signal is only a transient. Accordingly, the chiffing
signal is read from memory 50 only for a short duration of the
initial portion of the read out. In the embodiment illustrated in
the drawings, the read out of the chiffing wave form from memory 50
is controlled by an inhibiting gate 60 that is normally open to
allow read out. The gate closes to block further read out upon
receipt of an inhibit signal from a chiff counter 62. Chiff counter
62 receives a counting pulse input on line 64 from the sample point
address register 34. A counting pulse occurs on line 64 once during
each full cycle of address register 34. A preferred arrangement is
to employ a stage of the address register 34 that is an order of
higher or highest significance so that such stage is uniquely
logical one when the last memory location is being addressed. In
other words, chiff counter 62 will advance one count for each read
out cycle of the memory, and will advance one count for each group
of amplitude sample representations that is read from the
memory.
Initiation of the counting of the chiff counter 62 is enabled by a
key depress signal appearing on line 66 from the generator
assignment logic 26 as more particularly described in the
above-identified Watson patent. The key depress signal indicates
initiation of a note. When the chiff counter 62 attains a
predetermined count, such as the count of seven for example, it
feeds an inhibit signal to close gate 60 and thereby block any
further read out from the chiff memory 50. It will be readily
appreciated that the location of gate 60, as shown in FIG. 2, is
exemplary only. Alternatively this gate may be located at the
output of the memory. Further, the inhibit signal may be otherwise
applied, so as to terminate the combining of chiff and primary
amplitude sample representations at the desired moment. For
example, upon occurrence of the predetermined count of chiff
counter 62, the primary amplitude sample representations on lines
44 may be caused to bypass adder 54 so that chiff amplitude
representations are no longer combined therewith.
Although the chiff counter 62 is shown as a separate counter, in
order to more readily describe its functions, this counter may
simply be comprised of a group of higher order stages of sample
point address register 34.
It will be seen that a significant advantage of the described
system derives from the fact that the transient duration of the
chiffing signal, as effectively combined with the primary signal,
varies according to the frequency of the output or desired primary
signal. In the described arrangement regardless of the frequency of
the tone to be played and regardless of the repetition rate of the
groups of amplitude representations read from the memories, the
chiff counter will inhibit addition of the chiff amplitude signals
after the selected number of initial cycles of the desired wave
form. This timing of the chiff transient is readily selected and
precisely controlled.
The foregoing detailed description is to be clearly understood as
given by way of illustration and example only, the spirit and scope
of this invention being limited solely by the appended claims.
* * * * *