U.S. patent number 3,878,750 [Application Number 05/418,031] was granted by the patent office on 1975-04-22 for programmable music synthesizer.
Invention is credited to Charles A. Kapps.
United States Patent |
3,878,750 |
Kapps |
April 22, 1975 |
Programmable music synthesizer
Abstract
A programmable music synthesizer which is completely electronic
having no movable parts except for manually operated switches and
controls wherein each note of a sequence of notes is digitally
encoded in terms of a scaler value of the note, its time duration
and relative octave range; the digitally encoded information being
entered into an electronic memory via a keyboard comprising the
manually operated switches and controls; the controls being further
effective during the playback portion of the operation at which
time the digitally encoded information is automatically withdrawn
in accordance with the order in which the notes have been stored, a
portion of the decoded information being used to selectively
actuate a variable frequency generator the output of which appears
as a predetermined sequence of musical notes each of which persists
for a time duration in accordance with another portion of the
prestored information.
Inventors: |
Kapps; Charles A.
(Philadelphia, PA) |
Family
ID: |
23656389 |
Appl.
No.: |
05/418,031 |
Filed: |
November 21, 1973 |
Current U.S.
Class: |
84/609; 84/649;
984/341; 984/388 |
Current CPC
Class: |
G10H
7/00 (20130101); G10H 1/26 (20130101) |
Current International
Class: |
G10H
7/00 (20060101); G10H 1/26 (20060101); G10h
001/00 (); G10h 005/00 () |
Field of
Search: |
;84/1.01,1.03,1.02,1.28 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Wilkinson; Richard B.
Assistant Examiner: Witkowski; Stanley J.
Attorney, Agent or Firm: Synnestvedt & Lechner
Claims
What is claimed is:
1. A music synthesizer comprising means to generate a digital
representation corresponding to each one of a sequence of musical
notes, said last named means further comprising first means to
define the frequency of each note and second means to define the
time duration thereof, electronic means for separately storing each
of said digital representations comprising said sequence of musical
notes, and means for sequentially recovering each of said digital
representations comprising said sequence of musical notes from said
electronic storage means, and means for generating from said
digital representations audio signals corresponding to said
sequence of musical notes.
2. A music synthesizer operative to generate audio signals in the
form of a sequence of musical notes from prestored digital
representations thereof, each of said prestored digital
representations comprising a first plurality of bit positions
defining the frequency of a note and a second plurality of bit
positions defining the time duration thereof, electronic storage
means, said prestored digital representations being stored in said
electronic storage means, and means operatively connected to said
electronic storage means for sequentially recovering said prestored
digital representations from said electronic storage means and for
generating from said digital representations audio signals in the
form of said sequence of musical notes.
3. A programmable music synthesizer operable in a first mode to
store a selected sequence of signals comprising preselected notes
of a musical score and in a second mode to playback said stored
signals comprising said selected sequence of signals to thereby
recreate said musical score therefrom, comprising means for
generating a coded representation for each of said preselected
notes, said coded representation comprising a plurality of
digitally encoded bits a first plurality of which define the
frequency of a note and a second plurality of which define the time
relationship of said note with respect to other of said preselected
notes, means operatively connected to said first named means for
storing said coded representations of said preselected notes, and
means connected to the output of said means for storing said coded
representations for recovering said coded representations of said
preselected notes and for generating audio signals therefrom in
said selected sequence and bearing said predetermined time
relationship with respect to said other of said preselected
notes.
4. A programmable music synthesizer operative to store a digital
representation comprising a sequence of musical notes and wherein
said digital representation comprises a plurality of digitally
encoded bits a first plurality of which defines the frequency of a
note and a second plurality of which defines the time duration
thereof, said synthesizer comprising a keyboard adapted to enable
an operator to sequentially select a series of notes, digital
encoding means operatively connected to said keyboard for
generating a digital representation of each of said notes as said
notes are selected, electronic storage means operatively connected
to said digital encoding means for sequentially storing the digital
representation corresponding to each of said series of notes in the
order in which said notes are selected by an operator of said
programmable music synthesizer, said last named means including
means to automatically scan the successive memory locations of said
electronic storage means at a rate determined by said second
plurality of digitally encoded bits comprising said digital
representation of each note, and means operatively connected to
said last named means for generating audio signals from said first
plurality of digitally encoded bits comprising said digital
representation of each note.
5. A programmable music synthesizer comprising a keyboard
comprising a plurality of selectively actuatable keys, each of said
keys selectively representing the pitch and time duration of a
particular musical note, a multi-location electronic storage means,
means for sequentially scanning said multi-location electronic
storage means, means operatively connecting said keyboard and said
multi-location electronic storage means, control means operatively
connected to said scanning means and to said multi-location
electronic storage means for sequentially storing digital
information defining the pitch and time duration of musical notes
selected from said keyboard, said control means further operative
to initiate the scanning of the digital information stored in said
plural storage locations of said multi-location electronic storage
means, said control means further comprising means for directing a
first plurality of bits of said digital information comprising a
first portion of the informational contents of a particular one of
said multi-storage locations of said electronic storage means to a
time decoder to determine the time duration of a particular note
and for directing a second plurality of bits of said digital
information comprising a second portion of the information stored
at said particular one of said plural storage locations of said
electronic storage means to a tone decoder for determining the
frequency of said note.
6. An apparatus particularly operative for composing musical scores
comprising a keyboard each key of said keyboard operative to
generate a signal representing a particular note on a musical
scale, said keys being further used to define the time duration of
a particular note relative to other notes and the octave in which
the selected note is to be played, storage means operatively
connected to said keyboard and operative to store a coded
representation of each note selected via said keyboard including
information defining the value of said note on said musical scale
together with the octave and the time duration of said note,
addressing means operatively connected to said storage means and
operative to sequentially scan the plural storage locations of said
storage means, and means for stepping said addressing means, said
last named means further comprising manually actuated means for
stepping said addressing means thereby sequencing said storage
means through said plural storage locations at a rate which
facilitates entry of the coded representation of a note selected
via said keyboard and a second means for automatically stepping
said addressing means at a rate determined by that portion of a
signal entered via said keyboard defining the time duration of a
note relative to said other notes.
Description
SUMMARY OF THE INVENTION
The present invention relates to a programmable music synthesizer
and more particularly to a completely electronic implementation
thereof having no moving parts except for manually operated
switches and controls. An electronic memory is provided for storing
digital information defining a sequence of notes including the
value of each note relative to a standard musical scale, and also
the octave and the time duration of each note. The digital
information is entered into the electronic memory during the
programming portion of an operative cycle. The stored information
is recovered from memory during the playback portion of an
operative cycle. The scale and octave portions of the stored
information are used to generate an audio signal of desired
frequency. The audio signal persists for a predetermined time in
accordance with the time duration portion of the information stored
with each note.
Prior art attempts to synthesize music are readily distinguishable
from the present invention and as such may be generalized by
classification into two categories: the first of which includes
non-programmable music synthesizers an example of which is
disclosed in the patent to Fredkin et al, U.S. Pat. No. 3,610,801;
and secondly, devices comprising crude analogs of mechanical player
pianos, which upon inspection will be found to be lacking, among
other things, any ability to control the relative time relationship
of the notes generated. Examples of the latter devices include the
subject of the patent to D'Agata, U.S. Pat. No. 3,520,983 and a
device called a "Psych-Tone" described in the Popular Electronics'
Electronic Experimenter Handbook, 1973 Edition.
A programmable music synthesizer constructed in accordance with the
principles of the present invention is readily adaptable for a wide
variety of uses. Since a principal feature of the device is its
reprogrammable nature this, coupled with the fact that the unit is
totally self-contained, makes it particularly valuable as an aid in
composing music. The compact nature of the preferred embodiment of
the present invention facilitates its use in this latter
capacity.
Other uses of the subject invention include: the teaching of music,
as an electronic music box, and as a musical door bell.
According to the present invention, the device for composing,
recording and playing back a sequence of musical notes comprises a
keyboard the respective keys of which represent the notes capable
of being generated including the octave, the time duration of each
note and the control signals for stepping the apparatus through its
various modes of operation. The keyboard is operatively connected
to a memory portion having a plurality of storage locations each of
which is adapted to store digital information defining a note in
terms of its value on a scale of notes as well as the time duration
and octave range of the note. An address register is connected to
the memory portion to permit the storage locations of the memory to
be sequentially scanned thus initially facilitating the storage of
digital information pertaining to a new sequence of notes; and
subsequently thereto, during the playback portion of an operative
cycle, enabling the automatic and sequential scanning of the plural
memory locations at a rate determined by the time durational
information stored therein. For purposes of determining the time
duration of each note, a time decoder is connected to the output of
the memory, an output signal being generated therefrom in
accordance with the time duration portion of the information stored
at that particular memory location. The output of the time decoder
is in turn used to step the address register such that upon the
occurrence of each output signal the address register is stepped;
this in turn initiates the referencing of the next storage location
in memory. Also connected to the output of the memory is a tone
decoder which is operative from the time a particular memory
location is first referenced until such time as the time decoder
generates an output signal to initiate referencing of the next
successive memory location. The tone decoder generates an audio
signal having a frequency determined by the balance of information
contained at the memory storage location being referenced including
the information defining the relative value of the note on the
musical scale and its octave.
Although the preferred embodiment of the present invention has a
limited memory capacity of some sixteen 8 -bit words, with each
word generating a corresponding note, it is possible to increase
the memory capacity without altering the operating principles of
the present invention thereby enabling an entire musical score or a
plurality thereof to be selectively played-back after having been
programmed therein. Similarly, the preferred embodiment of the
present invention is disclosed as embodying a single tone decoder.
It should be immediately apparent to those having ordinary skill in
the art that additional tone decoders may be conveniently added so
as to program the device to simultaneously reproduce a plurality of
notes. By extending the design principles to include a plurality of
time decoders the notes will be available for play-back in a time
overlap manner. These and other features should become more readily
apparent from the following specific description.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagrammatic representation showing the principal
operating portions of a programmable music synthesizer constructed
in accordance with the principles of the present invention.
FIG. 2 is a detailed representation of the time decoder of FIG.
1.
FIG. 3 is a detailed representation of the tone decoder of FIG.
1.
DETAILED DESCRIPTION OF THE INVENTION
Turning now to FIG. 1, therein is illustrated a diagrammatic
representation of the preferred embodiment of the subject
programmable music synthesizer, the heart of which comprises a
memory 10. In the prefered embodiment, memory 10 comprises sixteen
8-bit words selectively addressable on a half word basis. The first
three bits of each word, corresponding to bits B.sub.1, B.sub.2,
and B.sub.3, define the time duration of a note i.e. how long the
note or rest is to persist. These 3 bits facilitate eight possible
time lengths; from a 16th note to a whole note. The means for
selecting and determining the time length of a note are discussed
in further detail below in connection with the explanation of FIG.
2.
The balance of the bits comprising the 8 bit word are used to
define the octave; the relative value of a note within an octave;
and, a possible rest or stop condition. In the preferred embodiment
bit B.sub.4 defines one of two octave ranges available; while bits
B.sub.5, B.sub.6, B.sub.7, and B.sub.8 are used to define the
relative value of a note within an octave as well as the stop and
rest conditions.
Memory 10 is perhaps most conveniently implemented using
semiconductor memory chips which may be mounted on a "mother-board"
thus facilitating the ready substitution of the memory portion of
the apparatus. Such semiconductor memory chips are commercially
available, an example of which is presently being marketed by
Fairchild Semiconductor Manufacturing Co. under part number 93403.
Each chip contains 16 four bit words, thus two such chips are
necessary to implement the memory in the preferred embodiment.
The design of the subject music synthesizer is such that the memory
10 may be readily enlarged. Thus, increasing the number of words in
the memory 10 results directly in the increase of the number of
notes which may be played back provided addressing means are
available to address all word locations in memory. Likewise,
increasing the number of bits in each word results in a
corresponding increase in the amount and type of information
available to define each note.
Alternative modes of implementation of the memory 10 include the
use of static and dynamic shift registers. Another alternative
concerns the use of read only memory techniques, these being
particularly useful as a means for cutting the unit price of a
music synthesizer to be used as a door bell or for some other
application wherein there is no need to continuously update, or
change, the sequence of notes. The use of a read only memory
nevertheless facilitates periodic reprogramming in the sense that a
different memory board may be readily substituted for the one
currently in the unit. There is also the possibility of using a
"reprogrammable" read only memory, such as that marketed by the
Intel Corporation under number 1702A.
Addressing of the memory 10 is accomplished by means of an address
register 12 which in the preferred embodiment of the present
invention comprises a conventional four stage binary counter the
output of which is capable of addressing any of the sixteen storage
locations of memory 10. As will be noted from the explanation which
follows, an output from the highest order stage of the address
register 12 appears as a carry (C), the signal normally occurs
after the highest order location in memory 10 has been scanned. The
carry signal serves to toggle a flip flop 14; this condition
signals the completion of either the programming or playback
portion of an operative cycle of the music synthesizer.
The count stored in the address register 12 is advanced manually by
means comprising an advance button 16, or alternatively is advanced
automatically by the output of a time decoder 13. The advance
button 16 is used to advance the address register 12 during the
programming portion of an operative cycle during which time
information is being stored in memory 10. Alternatively address
register 12 is automatically stepped by the output of the time
decoder 13 during the playback portion of an operation.
The sequencing of the address register 12 by means of the advance
button 16 enables the memory 10 to be selectively addressed for
arbitrary periods of time during which digitally encoded
information may be stored in both half-words of the memory address
currently being referenced by the address register. Storage on a
half word basis is effected by the selective actuation of RIGHT
WRITE and LEFT WRITE control keys, as is discussed in detail below.
Stepping of the address register 12 by means of the output of the
time decoder 13 occurs at a rate determined by the informational
content of the memory address location currently being referenced
by the address register 12. A detailed explanation of the time
decoder 13 both from the standpoint of construction and operation
is given below in conjunction with the explanation of FIG. 2.
A clock 15 is shown in FIG. 1 as being operatively connected to the
time decoder 13. The clock 15 functions to supply the time decoder
with a continuous stream of periodic pulses which are employed in
the time decoder to generate synchronized output signals including
the signal used to step the address register 12. The clock 15
utilized in the preferred embodiment of the present invention
comprises a variable frequency oscillator of conventional design
having a controlled output which may be varied over the range of 2
to 10 Hz. Although the clock 15 may be operated at a variety of
frequencies, the output thereof is generally left unchanged during
the playback of any particular sequence of notes. The facility to
vary the base frequency of the signal generated by clock 15 affords
an independent degree of control over the rate at which a sequence
of notes may be played back from the music synthesizer.
It should be noted that the signals generated by the advance button
16 and the time decoder 13 are selectively gated into the address
register 12 by means of NAND gate 30 and AND gate 42 with the
output of the advance button being inhibited during the playback
mode while output signals from the time decoder are inhibited
during the reprogramming mode.
Information is entered into the memory 10 from a keyboard 21 via a
binary encoder 22. The keyboard 21 comprises 16 selectively
actuated microswitches representing the 16 notes capable of being
played by the subject device over a two octave range. The
information comprising the note selection is encoded in a
conventional manner by means of the binary encoder 22 into a four
bit code which in turn is stored as a half word in memory 10.
Storage of a code representation of a selected note in memory 10 is
accomplished by depressing a RIGHT WRITE key 19. Similarly a LEFT
WRITE key 18 is provided to store an indication of the octave range
and the time duration of a note; one bit of the left half word
being used to determine the octave while the other three bits are
used to determine how long a note, or rest, is to be.
On the output side of the memory 10 is an output register 23 which
serves to buffer information from the memory to the time decoder 13
and to a tone decoder 24. The tone decoder comprises a variable
modulo counter which cycles at a varying rate depending upon the
value of a preset count entered therein. The variable modulo
counter is driven by a constant frequency clocking signal from a
clock 26. As will be explained below in conjunction with the
explanation of FIG. 3, the clock 26 is capable of generating an
output signal over a range of from 100 to 500 kHz; however, during
a particular operative cycle clock 26 operates at a predetermined
frequency, which in the preferred embodiment is normally set to
260.6 kHz in order to obtain an output of middle C for the lowest
note. Varying this frequency allows the range of the device to be
transferred up or down. The stable output signal of the clock 26 is
divided into desired frequency components by the tone decoder 24
which functions to generate a signal having a frequency
corresponding to the tone, or note, to be reproduced. The manner of
construction and mode of operation of the tone decoder 24 should
become more readily apparent from the detailed discussion thereof
given below in conjunction with the explanation of FIG. 3. For now
it should suffice to say that the output of the tone decoder 24
corresponds in frequency to a particular musical note; the output
signal being fed to a power amplifier 25 and from thence to a
speaker 27.
Consideration is now given to the execution of an operative cycle
of the programmable music synthesizer of FIG. 1 commencing with the
programming portion thereof. For this purpose a switch 20 when set
to PROGRAMMING MODE removes the ground or zero voltage which in
turn results in the partial conditioning of NAND gates 30, 32, and
34. These latter gates afford protection against the accidental
"dumping" of memory during the playback mode of operation.
Also at this time a start button 17 is depressed which "sets"
flip-flop 14 thus activating the synthesizer. Just prior to the
setting of flip-flop 14, i.e. when the flip-flop 14 is reset, the
audio output of the tone decoder 24 is muted, the address register
12 is reset, the memory 10 is disenabled, and the output of the
time decoder 13 is inhibited. Thus, at such time as flip-flop 14
becomes set the address register 12 will register a count of 0. The
Start signal conditions the corresponding memory location to accept
information from the keyboard 21 via the binary encoder 22. The
first information to be entered into the keyboard 21 comprises the
relative value of a note which, in accordance with the
representation of Table 1, is associated with a particular one of
the 16 keys comprising the keyboard 21.
TABLE 1
__________________________________________________________________________
CONTROLS KEY 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 RIGHT/ PITCH C
C Sharp D D Sharp E F F Sharp G G Sharp A A Sharp B Rest Stop WRITE
LEFT/ TIME/ 1/16 1/8 3/16 1/4 3/8 1/2 3/4 1 1/16 1/8 3/16 1/4 3/8
1/2 3/4 1 WRITE OCTAVE
__________________________________________________________________________
LOWER OCTAVE UPPER OCTAVE
The note being selected is entered into memory by simultaneously
depressing the appropriate key on the keyboard 21 and the RIGHT
WRITE key 19. This automatically transfers a signal on the output
line corresponding to the selected key on the keyboard 21, which
output signal is converted in the binary encoder 22 into a four bit
binary representation which appears as bits B.sub.5, B.sub.6,
B.sub.7, and B.sub.8 at memory 10 where it is stored as the right
half of word 0.
The next step is to enter "time" and "octave" information,
corresponding to the note just selected, into the left half of
memory word 0. This is done by simultaneously depressing the LEFT
WRITE control key and one of the 16 keys of the keyboard 21
representing the desired time and octave selected in accordance
with the provisions of Table 1. A corresponding four bit
representation will be entered into bit locations B.sub.1, B.sub.2,
B.sub.3, and B.sub.4 of memory location 0.
It will be noted that in addition to the twelve notes entered into
the right half of a memory word it is possible to enter a "rest"
signal or a "stop code". As will become apparent from the
explanation of the synthesizer in its playback mode, the occurrence
of a rest signal results in the muting of the output of the tone
decoder 24 for a period of up to 1 full note. The occurrence of a
stop code indicates that there are no further notes in the
particular tune being played.
After both the right and left half words have been entered into
memory location 0 the Advance button 16 is depressed thus
permitting a pulse to appear at the output of AND gate 30 which in
turn steps the address register 12 by one count thus referencing
memory location 1. Information defining the second note in the tune
is now ready to be entered into the right half word of memory
location 1 by means of the appropriate key on the keyboard 21. This
operation is effected in the manner outlined above with respect to
the entry of similar information into the right half word of memory
location 0. In similar manner the left half word of memory location
1 receives information defining the time and octave range of the
corresponding note. Thereafter the Advance button 16 is again
depressed causing the address register 12 to reference memory
location 2. This process is repeated until information has been
stored in all sixteen locations of memory 10. Alternatively, a stop
code may be entered as desired.
This completes the explanation of the programming portion of the
operation; however, it should be noted that after the sixteenth
note has been stored, in memory location 15, and the advance key is
thereafter depressed the resultant input to the address register 12
causes the address register to recycle generating a carry signal
which is returned to the flip-flop 14 causing it to be reset. When
the control flip-flop 14 is reset it mutes the audio output, it
resets the memory address counter to 0, it disenables the memory,
and inhibits the time decoder. Nothing else happens.
Attention is now directed to the operation of the programmable
music synthesizer in its playback mode. This mode of operation is
initiated by positioning switch 20 to PLAY MODE. Subsequently,
depressing the Start key 17 sets the flip-flop 14 and partially
conditions NAND gate 40 and AND gate 42. The tone decoder 24 will
generate an output signal to the speaker 27 corresponding in
frequency to the note registered in the 0 word location of memory
10, this latter information being buffered through the output
register 23 of memory 10 and into the tone decoder 24 as
information bits B.sub.4, B.sub.5, B.sub.6, B.sub.7, and B.sub.8 .
The corresponding time duration information is buffered into the
time decoder 13 as bits B.sub.1, B.sub.2, and B.sub.3. These latter
bits are decoded in the time decoder which generates a timed output
signal in consequence thereof which output signal completes the
conditioning of AND gate 42 thus stepping the address register 12
to memory location 1. In addition to stepping the address register
the output of the time decoder temporarily mutes the output of the
tone decoder 24 so that there is a slight pause between notes. This
latter feature permits the same note to be played successively such
that they appear as distinct notes rather than as one long note.
Succeeding notes are played in the same manner with play continuing
until flip-flop 14 is reset by a carry from the address counter 12
or alternatively by an output from AND gate 38 and NAND gate 40
signalling the detection of a stop code.
Referring now to FIG. 2 therein is disclosed a detailed
representation of the time decoder 13 of FIG. 1. As indicated
above, the time decoder serves to step the address register 12
during the playback mode of operation. The separation between
successive stepping signals to the address register 12 determines
the time duration of a note generated in tone decoder 24. The
information determining the separation between successive stepping
pulses is derived from the time duration portion of the digital
information stored in memory 10, i.e. the informational contents of
bit locations B.sub.1, B.sub.2, and B.sub.3. This latter
information is used to selectively gate a particular one of a
stream of pulses being generated by the clock 15 onto the output
line of the time decoder 13. In this respect clocking signals from
clock 15 are used to toggle a four-stage counter 28 capable of
generating, in timed sequence, a binary coded representation of
from 0 through 15; these latter signals are partially decoded in
logic 29 forming a corresponding number of independent signals,
each of which occurs during respective successive states of counter
28. In the preferred embodiment, only 8 of the 16 signals generated
by the decoding logic 29 are required since notes of only eight
different time durations are provided for. The outputs of the
decoder 29 condition a conventional selection gating circuit 31
such that an output signal is generated therefrom upon coincidence
with the digitally encoded information stored in memory 10 as bits
B.sub.1, B.sub.2, and B.sub.3.
In effect, the time decoder of FIG. 2 counts the signals generated
by the clock 15 and when a count corresponding to the count stored
in memory 10 is reached, the time decoder generates an output
signal to the address counter 12 resulting in the stepping of the
latter to the next successive memory location.
To this end the time decoder of FIG. 2 is further provided with
gating circuitry including NAND gates 35 and 37 and AND gate 39.
The NAND gate 35 permits the stepping of the counter 28 by clocking
signals from clock 15 only when flip flop 14 is set to the start
state. NAND gate 37 and AND gate 39 function collectively to
transfer an output signal from the time decoder 13 to the address
counter 12 and AND gate 38 of FIG. 1, only during the last half of
a clock cycle during which coincidence is detected in the
multiplexer 31 between the input bits B.sub.1, B.sub.2, and B.sub.3
and the count represented in counter 28. It is on the trailing edge
of the output signal from AND gate 39 that the address register 12
is incremented. The trailing edge of the output signal from AND
gate 39 is made to persist for a sufficient length of time to
ensure stability in AND gate 38 thus avoiding premature or
accidental conditioning of the latter. This may conventionally be
effected by inserting a suitable time delay at the input to AND
gate 38. The counter 28 is reset by the first clock pulse following
the appearance of an enable signal from the output lead of the
multiplexer 31. A flip flop 33 is set by the first clock pulse
after the inhibit signal, generated at the output of AND gate 36 of
FIG. 1, is removed. This prevents the starting of a playback
operation until the beginning of a clock pulse, and insures that
the first note will not have a variable length.
Turning now to FIG. 3, therein are disclosed the details of the
tone generator 24 of FIG. 1. The tone generator functions as a
frequency divider which uses the high frequency output signal from
clock 26 as an input to a frequency dividing network which in turn
selectively generates the desired frequency components
corresponding to the musical notes to be generated. The heart of
the tone generator 24 is the variable modulo counter 44. Counter 44
functions as a preset counter which is loaded with a predetermined
count chosen such that the complement thereof when divided into the
high frequency output of clock 26 results in the cycling of counter
44 at a rate equal to four times the frequency of a note to be
generated. This signal is in turn stepped down to two times the
desired note frequency, i.e. one octave above the desired note, by
permitting the signal to toggle a complementary type flip-flop. A
further reduction to the desired frequency is obtained by using the
output of the aforementioned flip-flop as an input to a second
complementary type flip-flop, the note of desired frequency
appearing at the output thereof.
The synchronous counters 28 and 44 of FIGS. 2 and 3 respectively,
are constructed from integrated circuit four bit synchronous
counters marketed by Fairchild Semiconductor under catalog number
9316. Counter 28 requires one unit and counter 44 requires two.
In the preferred embodiment of the present invention counter 44
comprises an eight stage counter capable of generating an output
signal every 256 input clocking pulses. Thus, if a count of seven
is preset into counter 44, the first clock pulse to be inputted
from clock 26 will step the counter to a count of 8 such that an
output signal will be generated after some 249 clocking pulses. By
dividing 249 into the base frequency of 260.6 kHz and thereafter
dividing the result by 4, there is produced at the output of the
tone decoder 24 a signal having a frequency of approximately 261.6
Hz corresponding to a middle C. Other notes are similarly derived
by entering a predetermined count into counter 44 in accordance
with the following Table of Values.
TABLE OF VALUES ______________________________________ VARIABLE
OUTPUT STANDARD FREQ. PRESET MODULO FRE- (EQUAL TEMPERA- COUNT
COUNT QUENCY NOTE MENT SYSTEM
______________________________________ 7 249 261.6 C 261.6 21 235
277.2 C sharp 277.2 34 222 293.4 D 293.7 46 210 310.2 D sharp 311.1
58 198 329.0 E 329.6 69 187 348.4 F 349.2 80 176 370.2 F sharp
370.0 90 166 392.5 G 392.0 99 157 415.0 G sharp 415.3 108 148 440.2
A 440.0 116 140 465.4 A sharp 466.2 124 132 493.6 B 493.9
______________________________________
The predetermined count to be entered into the variable modulo
counter 44 is established by means of a diode matrix 46. The diode
matrix may be of conventional design and it together with the
binary decoder 48 converts the four bits, B.sub.5, B.sub.6,
B.sub.7, and B.sub.8, comprising the right half word of a memory
location into the proper signal representation to establish a
desired precount in the variable modulo counter 44. As indicated,
the outputs from the binary matrix 46 selectively condition inputs
to the variable modulo counter 44 to in turn establish any desired
predetermined count in the corresponding flip-flops of the modulo
counter 44. It should be noted that after the predetermined count
has been entered into the flip-flops comprising modulo counter 44,
the clocking signals from clock 26 step the counter along until an
overflow or carry is generated in the highest order stage. An
output from the highest order stage of the variable modulo counter
44 re-establishes the predetermined count in the flip-flops. The
counter continues to cycle in this manner with every second output
from the highest order stage being used to toggle a flip-flop 49 to
its set state and correspondingly every fourth output of the
highest order flip-flop of variable modulo counter 44 is used to
toggle the flip-flop 50 to its set state.
Logical gating means comprising: a pair of NAND gates 52 and 54,
inverters 56 and 58, and NAND gate 60, are partially conditioned by
the octave information comprising the bit B.sub.4. The manner in
which these logic components cooperatively function with the
outputs of flip-flops 49 and 50 to deliver an output signal of
desired frequency to the audio amplifier 25 of FIG. 1 and in turn
to speaker 27 is explained below.
It will be noted that variable modulo counter 44 cycles at a rate
determined by the complement of the preset count divided into the
base clock frequency of 260.6 kHz. Also, an output signal from the
flip-flop 49 partially conditions NAND gate 52 every second output
pulse from the variable modulo counter 44 while an output signal
from flip-flop 50 partially conditions NAND gate 54 every fourth
output signal of the variable modulo counter 44. The output of the
in-line, inverters 56 and 58 completes the conditioning of NAND
gate 52 or NAND gate 54. Which of the NAND gates 52 and 54 is
conditioned depends upon the state of the input signal
corresponding to bit B.sub.4. Thus, if B.sub.4 is "low" the signal
on the output side of inverter 58 will be "high" thus conditioning
NAND gate 52. Under these same conditions the signal on the output
side of inverter 56 will be "low" and as a consequence NAND gate 54
will not be conditioned. Conversely, if B.sub.4 is "high" the
output side of inverter 58 will be "low" while the output of
inverter 56 will be "high". Thus NAND gate 54 will be conditioned
by NAND gate 52 will not. A "low" signal from AND gate 36
de-conditions NAND gate 60, and prevents sound from being generated
during a REST, between notes, or when flip-flop 14 is reset.
Alternatively, a "high" signal on the Inhibit lead to NAND gate 60,
permits the audio signal being generated by NAND gates 52 and 54 to
appear as an input to the audio amplifier 25 of FIG. 1.
While a preferred embodiment of the present invention has been
disclosed and the operation has been described in terms thereof, it
should be readily apparent that various substitutions may be
readily made without departing from the spirit of the invention. As
an example, the tone generator 24 may conveniently be implemented
by means other than a variable modulo counter. In similar fashion
the keyboard may be altered to vary the sequence of steps involved
in the operation of the subject synthesizer in its PLAYBACK and
PROGRAMMING modes. Accordingly, while the particular form of the
device has been shown and described, it is not intended that the
scope of the invention be limited to the particular form disclosed
in that alternative forms of the device will immediately be evident
to those skilled in the art.
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