U.S. patent number 3,610,801 [Application Number 05/011,683] was granted by the patent office on 1971-10-05 for digital music synthesizer.
This patent grant is currently assigned to Triadex Incorporated. Invention is credited to Edward Fredkin, Marvin L. Minsky.
United States Patent |
3,610,801 |
Fredkin , et al. |
October 5, 1971 |
DIGITAL MUSIC SYNTHESIZER
Abstract
In the apparatus disclosed herein, a note generator is
controlled by a long term, quasi-periodic function which is in turn
generated by applying digital feedback in preselected combinations
around a digital register. The register comprises means for holding
a plurality of bits of digital information in a given order, e.g. a
shift register or counter, the held information being changeable
according to a predetermined pattern in response to input signals
applied thereto. Digital feedback is provided by applying to the
register at least one input signal which is obtained according to a
preselectable or adjustable code from bits of information obtained
from various points in the register itself. The apparatus thus, in
effect, composes music as distinguished from merely synthesizing
sound.
Inventors: |
Fredkin; Edward (Brookline,
MA), Minsky; Marvin L. (Brookline, MA) |
Assignee: |
Triadex Incorporated
(Brookline, MA)
|
Family
ID: |
21751527 |
Appl.
No.: |
05/011,683 |
Filed: |
February 16, 1970 |
Current U.S.
Class: |
84/602; 84/648;
984/341; 984/388 |
Current CPC
Class: |
G10H
7/00 (20130101); G10H 1/0025 (20130101); G10H
2210/111 (20130101) |
Current International
Class: |
G10H
1/00 (20060101); G10H 7/00 (20060101); G10f
001/00 (); G10h 005/00 () |
Field of
Search: |
;84/1.01,1.03,1.22,1.26 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
"Build the Psych-Tone," Popular Electronics, Feb. 1971, pp.
25-35..
|
Primary Examiner: Duggan; D. F.
Assistant Examiner: Witkowski; Stanley J.
Claims
We claim:
1. Apparatus for making music, said apparatus comprising:
tone generating means operating to provide a variety of musical
notes in response to respective predetermined combinations of
control signals applied thereto;
a register which comprises means for holding a plurality of bits of
digital information in a given order, said held information being
changeable according to a predetermined pattern in response to
input signals applied to said register;
means for reading digital information held in said register at a
plurality of selected points in said register;
means for applying to said register at least a first input signal
which is obtained according to a preselectable code from bits of
information obtained from said plurality of points;
means for applying to said register a second input signal which
varies according to a predetermined periodic function thereby to
cause the information held in said register to periodically change
in a predeterminable sequence; and
means for applying to said tone generating means control signals
which vary as respective preselectable logical functions of the
information held in said register thereby to cause said tone
generating means to produce a sequence of notes, the pattern of
which is a function of the changing information held in said
register.
2. Apparatus as set forth in claim 1 wherein said register is a
shift register.
3. Apparatus as set forth in claim 2 wherein said means for
applying said one input signal includes a plurality of selector
switches, each of which selects a signal from one of a
predetermined plurality of stages of said shift register and logic
gate means for combining the selected signals according to a
predetermined binary logic function thereby to generate said first
input signal.
4. Apparatus as set forth in claim 3 wherein said logic gate means
comprises an EXCLUSIVE OR gate.
5. Apparatus as set forth in claim 3 wherein said means for
applying a second input signal comprises an oscillator connected to
said shift register to cause information held in said register to
be shifted at a repetition rate which is related to the frequency
of operation of said oscillator.
6. Apparatus as set forth in claim 1 wherein said register
comprises a multistage counter and means for selectively providing
digital feedback to selectively vary the pattern of states
generated by said counter.
7. Apparatus as set forth in claim 6 wherein said means for
applying a second input signal comprises an oscillator connected to
said counter for causing said counter to be incremented through
successive states at a rate which is related to the frequency of
operation of said oscillator.
8. Apparatus as set forth in claim 1 wherein said tone generating
means comprises means for selectively generating a plurality of
note signals representing respective musical notes and gate means
for passing a selected one of said note signals in response to said
control signals.
9. Apparatus as set forth in claim 8 further including a plurality
of selector switches each of which selects a signal from one of a
plurality of predetermined stages of said register, said selected
signals being applied to said gate means as said control
signals.
10. Apparatus as set forth in claim 1 wherein said tone generating
means comprises gate means operable to selectively change a note
being generated and also comprises a plurality of selector switches
each of which selects a signal from one of a plurality of
predetermined stages in said register, said selected signals being
applied to control said gate means.
11. Apparatus as set forth in claim 1 wherein said tone generating
means comprises:
a digital accumulator;
means for generating a plurality of digital signals, one for each
note to be generated, representing respective preselected binary
numbers, the values of said binary numbers being in proportion to
the note frequencies;
means for selecting one of said digital signals and applying the
selected signal to said accumulator;
means for driving said digital accumulator to repetitively and
periodically add the binary number represented by said selected
digital signal to the sum number held in said accumulator; and
means for generating an output signal which represents a selected
carry bit in said sum number, whereby the base frequency of said
output signal is proportional to the number represented by the
selected digital signal and thus also to the note frequency
determined by said control signals.
12. Apparatus as set forth in claim 1 wherein said tone generating
means comprises an oscillator and a multistage frequency dividing
counter driven by said oscillator, said counter having a plurality
of digital feedback paths, each of said paths having gate means for
selectively rendering the respective path inoperative thereby to
change the output frequency of the counter by a predetermined
factor, said control signals being applied to said gate means to
vary the note being generated as a function of the information held
in said register.
13. Apparatus for generating a plurality of tone signals having a
predetermined scalar frequency relationship, said apparatus
comprising:
means for generating a plurality of digital signals, one for each
tone signal, representing respective preselected binary numbers,
the values of said binary numbers being related in the same scalar
manner as said tone signal frequencies;
a digital accumulator;
means for selecting one of said digital signals and applying the
selected signal to said accumulator;
means for driving said digital accumulator to repetitively and
periodically add the binary number represented by said selected
digital signal to the sum number held in said accumulator; and
means for generating an output signal which represents a selected
carry bit in said sum number, whereby the base frequency of said
output signal is proportional to the number represented by the
selected digital signal and thus also to a respective tone
frequency.
14. Apparatus as set forth in claim 13 wherein said accumulator
operates in a serial mode and said digital signals are generated in
a corresponding serial format.
15. Apparatus as set forth in claim 14 wherein said means for
driving said accumulator comprises an oscillator providing a clock
signal at a preselected frequency and wherein said clock signal is
applied also to said digital signal generating means for timing
said serial format, whereby the pitch of said tone signals can be
adjusted by varying the frequency of said oscillator while the
relationship between the various tone frequencies is
maintained.
16. Apparatus for making music, said apparatus comprising:
a shift register for holding a plurality of bits of digital
information in a given order;
means for shifting data held in said register at a preselectable
repetition rate;
means for reading digital information held in said register at a
plurality of selected points in said register;
a first pair of selector switches each of which selects one signal
from a predetermined plurality of stages of said shift
register;
logic gate means for combining the signals selected by said first
pair of switches and applying to said shift register an input
signal which is a predetermined logical function of the signals
selected by said first pair of switches;
means for generating a plurality of digital note signals
representing respective preselected binary numbers, there being one
digital signal for each of a plurality of notes to be generated,
the values of said binary numbers being in proportion to respective
predetermined musical note frequencies;
a digital accumulator;
selection gate means for selecting one of said digital note signals
in accordance with a plurality of control signals applied to said
selection gate means, the selected digital note signal being
applied to said accumulator;
a second pair of selector switches each of which selects one signal
from a plurality of stages of said shift register, the signals
selected by said second pair of switches being applied to said gate
means as said control signals;
means for driving said digital accumulator to repetitively and
periodically add the binary number represented by said selected
digital note signal to the sum number held in said accumulator;
and
means for generating an output signal which represents a selected
carry bit in said sum number,
whereby the base frequency of said output signal at any given time
is proportional to the number represented by the respective
selected digital note signal and thus also to the respective note
frequency and whereby the frequency of said output signal changes
in a pattern determined by the setting of said selector
switches.
17. Apparatus as set forth in claim 16 including means for counting
selected events in the pattern of notes generated and for
periodically modifying one of said control signals after a
predetermined count thereby to provide a grace note.
18. Apparatus as set forth in claim 16 including means for counting
selected events in the pattern of notes generated and for
periodically, in response to the count, changing the repetition
rate at which data is shifted in said register thereby to provide a
change in tempo.
19. Apparatus as set forth in claim 16 including means for counting
selected events in the pattern of notes generated and for
periodically, in response to the count, changing the sample bit of
the sum number in the accumulator thereby to change the pitch of
the note sequence being generated by one octave.
Description
BACKGROUND OF THE INVENTION
This invention relates to apparatus for making music and more
particularly to such apparatus employing digital logic
elements.
In recent years substantial efforts have been directed toward
developing apparatus and/or methods for generating or composing
music synthetically, that is, with a human operator imposing only
minimal constraints on the form of the composition and with the
details of note sequence and rhythm being provided automatically,
Typically, these efforts have involved the use of a relatively
large, general purpose computer, i.e. one utilizing a stored
program. To this end, considerable effort has been expended in
analyzing various types of music and in attempting to determine the
requisites for pleasing music. These requisites have then been
incorporated into the music composing program in keeping with
various statistical methods and approaches. In one such prior art
method of generating music, various elaborate constraints are
imposed upon the output of a program which is itself designed to
generate a sequence of numbers having a very high degree of
randomness.
In accordance with one of its aspects, the present invention
utilizes an understanding or appreciation that a very high degree
of randomness is not necessary but rather it is preferable to
generate logical sequences of notes or musical sounds having a very
long period of repetition. As will be apparent hereinafter, this
understanding facilitates the construction of relatively simple
apparatus which nonetheless automatically generates relatively
pleasing music.
Among the several objects of the present invention may be noted the
provision of apparatus for automatically generating pleasing
sequences of musical notes or sounds; the provision of such
apparatus which is capable of generating a wide variety of such
sequences or compositions with the exercise of only minimal control
by a human operator; the provision of such apparatus which is easy
to operate; the provision of such apparatus which is compact and
requires little power; the provision of such apparatus which is
reliable and which is relatively simple and inexpensive. Other
objects and features will be in part apparent and in part pointed
out hereinafter.
SUMMARY OF THE INVENTION
Briefly, apparatus constructed in accordance with the present
invention is adapted to make or compose music, that is, to generate
pleasing sequences of musical notes or sounds. The apparatus
employs tone generating means operative to provide a variety of
musical notes in response to predetermined combinations of control
signals applied thereto. A register is provided which includes
means for holding a plurality of bits of digital information in a
given order, the held information being changeable according to a
predetermined pattern in response to input signals applied to the
register. Associated with the register are means for reading the
held digital information at a plurality of selected points in the
register. At least one of the input signals applied to the register
is obtained according to a preselectable or adjustable code from
bits of information read out of the register. Another input signal
applied to the register varies according to a predetermined
periodic function. The tone generating means is then operated in
response to control signals which vary as respective preselectable
logic functions of the information held in the register.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of music making apparatus constructed in
a accordance with the present invention employing digital
electronic circuitry;
FIG. 2 is a block diagram of a counting circuit useful with various
modifications of the apparatus of FIG. 1, e.g. those illustrated in
FIGS. 3-5, to provide added varieties of musical form;
FIG. 3 is a block diagram of an alternative form of sequence
generating circuitry which may be employed with the apparatus
illustrated in FIG. 1 to provide grace notes;
FIG. 4 is a block diagram of an alternate rhythm generating circuit
which may be employed with the apparatus illustrated in Fig. 1;
FIG. 5 is a block diagram of an alternate note selection circuit
which may be employed with the apparatus illustrated in FIG. 1 to
prove octave shifts in tone; and
FIG. 6 is a block diagram of another embodiment of the invention,
also employing digital circuitry.
Corresponding reference characters indicate corresponding parts
throughout the several views of the drawings.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the FIG. 1 apparatus, the note or tone generating
portion of the circuit includes a 16 bit shift register 11 which is
operated as a serial accumulator in conjunction with a single bit
adder 15 for determining or controlling the frequency of the note
being generated. While serial operation has been shown by way of
illustration, it should be understood that parallel operation can
also be used. An adjustable oscillator 13 generates a square-wave
clock signal which is applied to the shift input terminal of
register 11, through a line 14, for periodically shifting data held
in the register. The signal generated by oscillator 13 is at a
relatively high frequency, i.e. at a multiple of the highest tone
frequency which is to be generated, and is designated the fast
clock signal FC.
Data spilled over from the last stage of register 11 as a result of
shifting is applied to the adder 15 through line 9 as one of its
input signals and the output signal from the adder is applied to
the input terminal of the register 11. Register 11 and adder 15
thus form a 16-bit serial accumulator as will be understood by
those skilled in the art. In other words, a binary number
circulating through the register 11, can be cumulatively increased
by applying an appropriate binary signal to the other input
terminal of adder 15 in appropriate serial format. The circulating
binary number is conveniently designated the sum or accumulated
total. As will be apparent hereinafter, the period required to
circulate the 16-bit sum number through the register 11, i.e. a
period equal to 16 times the period of oscillator 13, forms a basic
timing interval of the entire apparatus.
The fast clock signal from oscillator 13 is also applied, through a
lead 16, to a four-bit counter 17. Output signals from each stage
of counter 17 are applied to a decoding matrix 19 which provides,
at sixteen respective output terminals, pulse signals (I.phi.-T15)
which occur during respective successive states of the counter 17.
Counter 17 and decoder 19 thus in one sense provide a function or
operation similar to that of a ring counter and the various timing
pulses T.phi.-T15 serve to identify particular bit positions within
the binary "word" being circulated within the serial accumulator
which includes register 11. Not all of these signals are used,
however, as will be apparent hereinafter.
Selected ones of the timing pulses, i.e. T5-T10, are applied to an
encoding matrix 41. Matrix 41 combines the timing pulses T5 and T10
in various combinations so as to provide on each of eight output
leads a serial binary signal which represents a number defining the
frequency of a corresponding musical note or tone with the desired
degree of accuracy. The various leads correspond to the musical
notes C, D, E, F, G, A, B and C' and are identified accordingly.
Matrix 41 thus functions as a serial note generator. The serial
format in which the note frequency numbers are encoded is chosen to
correspond with the format used in the serial accumulator which
includes adder 15 and shift register 11. One of the eight note
signals is selected by a conventional selection gating circuit 50
in response to a three-bit binary selection signal applied thereto
through leads 51-53. The selected note signal is then applied to
the remaining input of adder 15 through a lead 54.
From the foregoing, it will be apparent to those skilled in the art
that a number representing the frequency of a selected musical note
is repetitively added to the sum being circulated through register
11. As the numbers being added occupy only bit positions
corresponding to the timing pulses T5--T10, it can be seen that the
more significant bit positions hold only data which represents the
accumulation of carry signals from the repetitive addition. Given
the fact that the repetitive addition proceeds on a regular basis
or frequency under the control of oscillator 13, it can be shown
that each of the more significant bit positions in the circulating
sum is itself a signal having a frequency which is substantially
proportional to the selected note frequency, i.e. as designated by
the signals formed by matrix 41. There is some short-term error or
jitter but the long-term proportionality is substantially
exact.
In the embodiment illustrated, the sum number circulating around
register 11 is sampled during the T2 pulse interval by means of a
sampling gate 55, the T2 pulse from decoder 19 being applied to
gate 55 through a lead 56 for this purpose. The sampled signal is
applied to a flip-flop 57 to obtain a symmetrical square-wave
signal which represents the state of the selected bit in the
circulating sum. This square-wave signal is then amplified, as
indicated at 59, and applied to a loudspeaker 61. Loudspeaker 61
will thus produce a tone or musical sound having a basic frequency
component which is proportional to the selected note frequency as
defined by the matrix 41. This note is also proportional in
frequency to the frequency of oscillator 13. Thus, by varying or
adjusting of the output frequency of oscillator 13 the pitch of the
notes being generated may be scaled upwards or downwards as
desired. The ratio in frequency between one selected note and the
next will, however, remain unchanged since this proportionality is
determined by the frequency numbers which are defined by the
encoding matrix 41.
The portion of the FIG. 1 apparatus which determines the sequence
in which notes are played includes a shift register 65 of suitable
length, e.g., 32 bits. A second adjustable oscillator 69 provides a
second timing signal, designated the slow clock signal, which is
applied to the shift control terminal of register 65. Data held in
register 65 is thus periodically shifted. Signals taken from
various selected stages of shift register 65 are applied to the
selection terminals of each of four separate single-pole,
ten-position switches SW1-SW4. These signals are designated X1-X10.
The first two switches SW1 and SW2 control the application of
digital feedback around the shift register 65, the signals selected
by these switches being combined in an EXCLUSIVE OR gate 67 with
the output signal from gate 67, or its complement, being applied as
the input signal to the shift register. Thus, as the existing data
held in the shift register 65 is periodically shifted under the
control of oscillator 69, the new data being introduced into the
register depends upon or is a logical function of bits of
information obtained from the register itself at selected points.
As will be apparent to those skilled in the art, register 65 will
therefore operate to generate a relatively complicated binary
sequence which may have a very long period of repetition, depending
upon the settings of the switches SW1 and SW2. The complexity and
length of the pattern produced can be increased if desired by
increasing the number of components which are combined, e.g., by
adding additional switches to switches SW1 and Sw2, and by varying
the combination arrangement, e.g., by using other and more
complicated logic functions in place of the EXCLUSIVE OR. If
desired, means may also be provided for preloading the register so
as to define the starting point in the sequence or function and to
permit sequences to be duplicated.
The signals selected by the other two switches SW3 and SW4 are
applied, through leads 52 and 53, as two of the tree signals which
control the note-selecting gate circuit 50. The other control
signal, applied through lead 51, is obtained from a fixed one of
the points in shift register 65. It can thus be seen that the note
being played at any given moment will be determined as a
preselectable logical function of the information held in register
65, the particular function being dependent upon the setting of the
switches S3 and S4. As the data held in register 65 is periodically
shifted under the control of oscillator 69, the note being played
will change in a sequence which depends both upon the setting of
the switches S3 and S4 and the particular pattern or sequence of
binary signals being generated by the shift register 65 in response
to the particular settings of switches S1 and S2. The frequency
with which the note being played is changed will, of course, depend
upon the frequency of operation of oscillator 69. In other words,
oscillator 69 determines the basic tempo. Thus, the tempo may be
adjusted, without affecting the pitch of the notes being played, by
varying the frequency of operation of oscillator 69. While the
frequency of operation of oscillator 69 determines basic tempo, it
should be understood that the note being played will not
necessarily change pitch once for each cycle of the oscillator.
Although the binary pattern or sequence produced by the register 65
will typically continue for a relatively long interval without
repeating, various intervals may frequently occur in which there is
no change in the particular bits used for note selection. In fact,
this is preferably the case for pleasing music. Thus, though there
is a possibility of a note change for each cycle of oscillator 69,
the actual notes being played may persist for several of the basic
beats determined by the oscillator. In other words, oscillator 69
determines the basic tempo but individual notes may last for
different intervals. Thus, changing the settings of the switches
SW1-SW4 will alter not only the sequence in which different notes
are played but also the rhythm or patterns of note duration. As
noted previously, though the sequences or patterns generated by the
shift register are typically quite long, they are basically
repetitive or periodic in nature and it has been found that, with
only minor constraints on the selections made by the switches
SW1-SW4, quite pleasing music is generated by the apparatus
illustrated.
The musical themes or compositions generated by the apparatus of
FIG. 1 can be further varied by including in the apparatus one or
more of the modifier circuits illustrated in FIGS. 3-5, each of
these modifier circuits being adapted for operation in association
with a respective counting or control circuit such as that
illustrated in FIG. 2. Referring now to Fig. 2, the slow clock
signal SC and selected ones of the signals provided by the various
stages of shift register 65 are provided to fixed positions or
poles of a selector switch SW5. One of the switch positions is left
unconnected to permit the respective modification circuit to be
rendered inoperative.
The signal selected by switch SW5 is applied to a 3-bit down
counter 71 which, as is explained hereinafter, controls the
frequency of appearance of the respective theme modification. Down
counter 71 is of the type which can be preset to a preselected
value, e.g. a value determined by a 3-bit binary-coded switch as
indicated at 73, upon application of a control signal to a SET
input to the counter. Counter 71 is also operative to provide a
DONE signal when the counter has counted back to zero from the
selected preset value. The DONE signal and the slow clock signal SC
are combined in a NAND gate 75 to provide a signal which controls
the presetting of the counter. As will be understood by those
skilled in the art, this feedback connection causes the down
counter 71 to be preset to the preselected value on the nest beat
following that in which the DONE signal is initiated. Thus, after
the selected event has occurred the preset number of times, a DONE
signal is produced for a period of one beat. As noted previously,
one circuit such as that illustrated in FIG. 2 is used with each of
the modifier circuits and thus if all three modifier circuits are
employed, three FIG. 2 circuits will be used with the apparatus of
FIG. 1. The DONE signals from the FIG. 2 circuits are applied as
the GRACE, TEMPO or OCTAVE Control signals indicated in FIGS. 3-5
respectively.
The modification illustrated in FIG. 3 effectively operates to
provide a grace note at intervals or after sequences of events
determined by the operation of the respective FIG. 2 counting
circuit. The GRACE signal provided by the respective FIG. 2 circuit
is combined in an EXCLUSIVE OR gate 77 with the signal obtained
from the note sequence selector switch SW4 (Fig. 1), this being the
signal which determines the least significant bit in the 3-bit note
selection code. The output signal from the gate is then applied to
the note selection circuit 50 in place of that selector switch
signal.
Since the operation of the exclusive OR gate 77 is to, in effect,
complement the signal from switch SW4 whenever the GRACE signal is
present, the note selection circuit 50, in effect, selects a note
musically adjacent to that which would ordinarily be selected.
Since the GRACE signal complements after an interval corresponding
to one period of the slow clock oscillator 69, the "adjacent" note
lasts for just one beat and the overall effect is that of providing
a grace note.
In the modification illustrated in FIG. 4, the output signal from
the slow clock oscillator 69 is applied to a divide-by-two counter
or flip-flop 79 so as to obtain a half-frequency signal. The TEMPO
signal from the respective Fig. 2 counting circuit is applied to
trigger a flip-flop 81 which in turn controls a selection gate
circuit 83. The selection gate circuit 83 permits either the direct
or the half-frequency signal obtained from the oscillator 69 to be
applied to the shift input terminal of register 65. Thus, whenever
the respective Fig. 2 counting circuit generates a TEMPO signal,
the flip-flop 81 is reversed in state so that the effective tempo
or beat frequency is either doubled or halved depending upon the
previous state of the flip-flop. In this way, the tempo of the
music generated can be varied by a factor of two upon sequence of
events predetermined by the operation of the respective FIG. 2
counting unit.
The modification illustrated in FIG. 5 operates to selectively
change, by one octave, the overall musical pitch of the note
sequence being generated. As will be understood by those skilled in
the art, the effective frequency of the carry signal which is
sampled from the sum number circulating through the serial
accumulator can be effectively halved by selecting a bit in the sum
number which is one place more significant than the original. Since
the accumulator in the FIG. 1 embodiment operates in a serial mode,
the bit selected can be varied by varying the sample timing. In the
FIG. 5 modification, a selection gate circuit 85 is controlled by a
flip-flop 87 so as to pass either the T2 timing pulse of the T3
timing pulse to the sampling gate 55. Flip-flop 87 is, in turn,
controlled by the OCTAVE signal provided by the respective FIG. 2
counting unit. Accordingly, whenever the counting circuit generates
an OCTAVE signal pulse, the state of the flip-flop 87 is reversed
and the resulting change in sample timing causes the pitch of the
note sequence being generated to change by one octave. The change
will be up or down depending upon the previous state of the
flip-flop 87.
Since the various theme modifications can be caused to occur
frequently or infrequently as desired, e.g. by selecting low or
high preset counts and by varying the type of input signal which
increments the counter, it can be seen that considerable additional
variation in the composition being generated is made possible by
the variations illustrated in FIGS. 2-5.
While the embodiment illustrated in FIG. 1, employs shift registers
both for determining the sequence of notes played and for
synthesizing the frequencies or tones corresponding to these notes,
suitable patterns and note frequencies can also be generated using
multistage counters with selectively controllable digital feedback.
Like a shift register, a multistage counting circuit with provision
for feedback is a form of register comprising means for holding a
plurality of bits of digital information in a given order. Further,
the held information is likewise changeable according to a
predetermined pattern in response to input signals applied to the
register. In other words, a shift register is one particular kind
of register and a multistage counter is another. FIG. 6
illustrates, in a general way, apparatus which employs counting
registers with digital feedback in place of the shift register of
FIG. 1.
As in the previous embodiments, the FIG. 6 arrangement employs a
first oscillator 101 which acts as a slow clock and provides the
basic timing unit for rhythm or note sequencing. A second
oscillator 103 acts as a fast clock and provides a basic timing
unit for frequency synthesis.
Oscillator 103 drives a succession of counting stages 105-109 which
provide a maximum frequency division sufficient to reach the lowest
note to be played. The last counting stage (109) drives a
loudspeaker 111 through an amplifier 113 and a flip-flop 115 which
provides a balanced or symmetrical waveform as described
previously. The counting chain is provided with a plurality of
interlocking digital feedback paths, designated 117-121, each of
which includes a respective gate 123-128 for permitting the path to
be selectively opened or closed. The particular feedback paths are
selected so that the change in the ultimate output frequency
produced by changing the state of each gate has a desired musical
significance. For example, the various gates are preferably
arranged to produce changes in frequency of an octave (2:1). a 5th
(3:1), a (4th 4:3), a 2nd (about 64:57 ) and a 3rd (about 63:50 ).
The particular interconnections necessary to achieve these ratios
with particular, commercially available, integrated circuit logic
systems will be apparent to those skilled in the art. In this
embodiment, it can thus be seen that the various tones or
frequencies are provided by selective frequency division or
counting, rather than by repetitive addition or accumulation of a
number related to the desired frequency as in the FIG. 1
embodiment.
For note sequencing, the slow clock oscillator 101 drives a counter
comprising a plurality of binary stages 141-144. The last stage
(144) provides the clock or shift input to an eight-stage shift
register 145. Spill over from the shift register 145 triggers a
commutating flip-flop 146 and the output signal from the flip-flop
is in turn fed back to the input terminal of the shift register to
provide a feedback mode of operation. If desired, this feedback
function can be further modified by data taken from various stages
in the shift register, as in the embodiment of FIG. 1, so as to
provide further varieties of long-term periodic sequences.
The tone shifting gates 123-128 are controlled as preselectable
logical functions of the various digital signals obtained from the
counting stages 141-144 and from the various stages or points of
the shift register 145. As will be understood, myriad combinations
of these signals can be devised and will generate corresponding
sequences of notes. One particular set of selection switches is
illustrated in the embodiment of FIG. 1 but, as will be understood,
various types of switching and/or logic gating may be employed.
Thus, in FIG. 6 this function of combining various control signals
is designated generally as permutative switching circuitry 160. As
is also understood, this switching can be employed to apply
feedback to the various counting stages 141-144, which feedback
varies as a logical function of the signals present in the counting
stages 141-144 and the bits of information circulating through the
shift register 145. As will be understood by those skilled in the
art, the use of various combinations of feedback signals will cause
the counting stages 141-144 and the shift register 145 to generate
a great variety of periodic sequences, typically having a very long
repetition period. Thus, the note sequences generated by the
synthesis portion of this circuit can also be widely varied as were
the sequences provided by the FIG. 1 embodiment.
While the embodiments described above are electronic in nature and
are adapted for construction using available digital logic modules
or using large scale integration technique, it should be understood
that other embodiments can be constructed using mechanical or
fluidic logic elements. Individual mechanical equivalents for the
various logic elements used in this invention are known in the art
and such elements can be assembled into a system in accordance with
the present invention.
In view of the foregoing, it may be seen that several objects of
the present invention are achieved and other advantageous results
have been attained.
As various changes could be made in the above constructions without
departing from the scope of the invention, it should be understood
that all matter contained in the above description or shown in the
accompanying drawings shall be interpreted as illustrative and not
in a limiting sense.
* * * * *