Electronic musical instrument

An electronic musical instrument is provided with a first programmable counter for generating a reference clock signal corresponding to a musical frequency and a plurality of cascade-connected programmable counters which are each triggered by the preceding programmable counter. A multi-level signal which assumes one of a plurality of levels for each period specified by one of the cascade-connected programmable counters is output as a primary waveform. The electronic musical instrument is capable of setting various variations of the primary waveform abundantly containing harmonics and is satisfactory in the tone quality and in the degree of freedom in setting tones, and hence is of high musicality.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an electronic musical instrument which 
creates a musical tone through use of a tone filter for a primary waveform 
signal abundantly containing harmonics. 
2. Description of the Prior Art 
Conventionally, a musical tone generating system for electronic musical 
instrument, represented by an electronic organ, a synthesizer and so 
forth, is roughly divided into an analog and a digital tone generating 
system. The digital tone generating system permits the synthesization of 
musical waveform elements by digital operations and has possibilities of 
creating timbre over a wide range. But the digital tone generating system 
has the defects of an enormous circuit arrangement and limitations on the 
sound synthesis owing to restrictions on the amount of operation and the 
operation time, and have been employed only in some high grade models. The 
analog tone generating system is comprised of a primary waveform generator 
which generates a primary waveform signal corresponding to a musical 
frequency and abundantly containing harmonic components, a filter circuit 
for controlling the harmonic components of the primary waveform signal in 
accordance with timbre desired to create and an envelope circuit for 
providing a desired envelope. These circuit elements are well-known VCO 
(Voltage-Controlled Oscillator), VCF (Voltage-Controlled Filter) and VCA 
(Voltage-Controlled Amplifier) which use voltage as a common control 
parameter, and have undergone various improvements. Also in connection 
with the analog tone generating system, many problems have been pointed 
out. For instance, the tone generating circuit has not markedly been 
improved as compared with other circuit elements of the musical 
instruments. Conventional tone generating circuits are mostly liable to 
produce what is called a "characteristic tone" which has a specific 
harmonic structure, and the "character" cannot be removed however 
intensively the tone is subjected to filtering by a tone filter. The 
reason for this is that since frequencies handled by the tone generating 
circuit are note frequencies which vary with the playing status, is is 
very difficult to form a predetermined primary waveform signal at any of 
the frequencies, which has been effected mostly by a duty ratio changing 
method through use of an even-order frequency divider. It has also been 
proposed to set the duty ratio or generate a pulse train by the employment 
of a shift register, ring counter, Johnson counter or the like. But these 
prior art methods are within the scope of an integral multiple of a basic 
clock signal, and are unable to completely eliminate the "character". Even 
if a circuit for producing a certain primary waveform signal should be 
implemented through utilization of complex and elaborate techniques, it 
would encounter the problems that in the case of creating a plurality of 
tones, no variations cannot be produced and that if many tones are 
produced, their tonal quality will be degraded. 
SUMMARY OF THE INVENTION 
It is therefore a primary object of the present invention to provide an 
electronic musical instrument which is free from the above said defects of 
the prior art. 
Briefly, stated, the electronic musical instrument of the present invention 
is provided with a first programmable counter which produces a reference 
clock signal corresponding to a musical frequency and a plurality of 
cascade-connected programmable counters which are respectively triggered 
by the preceding-stage programmable counter one after another. A 
multilevel signal is created as a primary waveform which assumes one of 
plural kinds of levels for each period specified by one of the 
cascade-connected programmable counters. The electronic musical instrument 
of the present invention permits setting of many variations of the primary 
waveform which abundantly contains complex harmonics, and hence satisfies 
the requirements of tonal quality and the freedom in setting tones and is 
rich in musicality.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In FIG. 1 reference numeral 1 indicates a keyboard, 2 a CPU for controlling 
the entire system, 3 a primary waveform generator according to the present 
invention, 4 an envelope circuit, 5 a timbre circuit and 6 a sound system. 
The CPU 2 detects play or performance information of the keyboard 1 and 
performs required processing, for instance, for generator assignment, 
setting of timbre, setting of a musical frequency, setting of various 
parameters and so forth. The primary waveform generator 3 generates a 
desired primary waveform signal in accordance with various parameters from 
the CPU 2. The primary waveform signal is converted by the envelope 
circuit 4 and the timbre circuit 5 to a musical signal, which is further 
converted by the sound system 6 including an effect circuit, an amplifier 
and a speaker to an acoustic signal. 
FIG. 2 illustrates in block form a specific circuit arrangement of a 
primary waveform generating and envelope producing part according to the 
present invention which is implemented by the primary waveform generator 3 
and the envelope circuit 4 in FIG. 1. Reference numeral 10 indicates a 
CPU, 11 a first programmable counter, 12 a second programmable counter, 13 
a third programmable counter, 14 an envelope generator, 15 a first analog 
switch, 16 a second analog switch, 17 a third analog switch and 18 a 
mixing amplifier. Now a description will be given of the first, second and 
third programmable counters 11, 12 and 13 which are individually 
controlled by the CPU 10. The programmable counters 11 to 13 are each 
capable of frequency dividing an input clock signal at a desired rate in 
accordance with programmable frequency dividing data which is supplied 
from the CPU 10, and they can easily be implemented using, for example, 
Intel's "8253" type CPU peripheral LSI. In many cases programmable 
counters of such CPU peripheral LSIs have, in addition to an ordinary 
frequency dividing mode, variations of operation modes such as, for 
example, a one-shot operation mode, a control trigger signal input mode 
and so forth. The example in FIG. 2 also selectively utilizes such 
operation modes. The first programmable counter 11 is activated in a mode 
in which it normally performs a programmable frequency division to produce 
an output signal of a 50% duty ratio. The second programmable counter 12 
is activated in a "programmable one-shot operation" mode in which it is 
triggered ON by the positive-going edge of the output signal of the first 
programmable counter 11 and enters and remains in its OFF state after 
counting a preset length of time. The third programmable counter 13 is 
also activated in a "programmable one-shot operation" mode in which it is 
triggered ON by the negative-going edge of the output signal of the second 
programmable counter 12 and enters and remains in its OFF state after 
counting a preset length of time. Such operations of the programmable 
counters can be set simply by applying an output signal 23 of the first 
programmable counter 11 to a gate signal input of the second programmable 
counter 12 and by applying an output signal 24 of the second programmable 
counter 12 to a gate signal input of the third programmable counter 13 
after inverting the signal 24, as required. Further, it is necessary only 
that commands for setting the operation modes of the respective 
programmable counters be provided thereto by control signals 20, 21 and 
22. 
FIG. 3 illustrates in detail an example of the arrangement, of the envelope 
circuit 14 used in the example depicted in FIG. 2. The envelope circuit 14 
does not use an ordinary single envelope signal but handles two kinds of 
envelope signals, i.e. a positive envelope signal 26 and a negative 
envelope signal 27. On account of this, the envelope circuit 14 comprises 
an inverting amplifier 33 and a non-inverting amplifier 32 other than an 
envelope generator 31 which is controlled by the CPU 30, as shown in FIG. 
3. In the above arrangement, since the envelope generator 31 needs only to 
create an ordinary single envelope signal, a conventional envelope 
generating system is employed therefor. It is, for example, as an analog 
system, a system which effects charging and discharging through use of a 
time constant circuit, as in a music synthesizer, and, as a digital 
system, a system which reads out an envelope memory and D-A converts the 
output signal and, as a combination of the analog and digital systems, a 
system in which charging and discharging by pulses of a fixed current are 
controlled in terms of the number of pulses. An output signal 40 of the 
envelope generator 31 is provided to the inverting and non-inverting 
amplifiers 33 and 32 which are both formed by operational amplifiers or 
the like, and by which are produced positive and negative envelope signals 
41 and 42. The magnitudes of the absolute values of the two envelope 
signals 41 and 42 can be freely set by suitably selecting the resistance 
values of resistors R1, R2, R3 and R4 which are connected to the 
operational amplifiers, respectively. 
The positive and negative envelope signals 26 and 27, obtained by such 
circuit arrangement as shown in FIG. 3, are provided as switch input 
signals to the first, second and third analog switches 15, 16 and 17. 
Supplied as control signals to the first to third analog switches 15 to 17 
are the output signals of the first to third programmable counters 11 to 
12, respectively. These input control signals are shown in FIG. 4. The 
first programmable counter 11 operates in the mode in which it performs, 
in its steady state, the programmable frequency division to yield an 
output signal of a 50% duty ratio, as mentioned previously, and it 
responds to the control signal 20 from the CPU 10 to produce such an 
output signal as shown in FIG. 4A which has a period corresponding to the 
musical frequency to be generated. This output signal is applied as the 
input control signal 23 to the first analog switch 15. The second 
programmable counter 12 performs such a "programmable one-shot operation" 
that it is triggered ON by the positive-going edge of the output signal 23 
of the first programmable counter 11 and enters and remains in the OFF 
state after counting a length of time set by the control signal 21 from 
the CPU 10, thereby producing such an output signal as depicted in FIG. 
4B, which is provided as the input control signal 24 to the second analog 
switch 16. The third programmable counter 13 performs such a "programmable 
one-shot operation" that it is triggered ON by the negative-going edge of 
the output signal 24 of the second programmable counter 12 and enters and 
remains in the OFF state after counting a length of time set by the 
control signal 22 from the CPU 10, thereby yielding such an output signal 
as shown in FIG. 4C, which is provided as the input control signal 25 to 
the third analog switch 17. FIG. 4D shows a signal which takes a fixed 
positive level during the ON state of the output signal 24 of the second 
programmable counter 12 and assumes a fixed negative level during the ON 
state of the output signal 25 of the third programmable counter 13. This 
is the basic idea of the primary waveform generating system according to 
the present invention. Since the output signal 23 of the first 
programmable counter 11 is a mere reference signal for the second and 
third programmable counters 12 and 13 to conduct the "programmable 
one-shot operation" with a period corresponding to the musical frequency, 
the first analog 15 can be dispensed with basically. 
FIG. 5 is a signal diagram for explaining the operation of the circuit 
arrangement shown in FIG. 2. The circuit arrangement of FIG. 2 carries 
out, by itself, not only the generation of a primary waveform but also an 
envelope modulation, and hence offers a low cost electronic musical 
instrument with a very simple structure. Since its principles of operation 
are difficult to understand as compared with the envelope modulation by an 
ordinary VCA (Voltage-Controlled Amplifier), however, the first analog 
switch 15 which is controlled by the output signal 23 of the first 
programmable counter 11 will be described in detail, by way of example. As 
the positive output signal 26 of the envelope generator 14 in FIG. 2, an 
envelope signal such, for example, as shown in FIG. 5A, is provided. This 
envelope signal is formed using, as parameters, such four states as 
indicated by A (Attack), D (Decay), S (Sustain) and R (Release) in FIG. 
5A. These parameters are set, by the CPU 10, as an attack time 50, a decay 
time 51, a sustain level 52 and a release time 53. Let is be assumed here 
that the negative output signal 27 of the envelope generator 14 is 
provided as a signal which is equal in absolute value to but opposite in 
polarity from the positive output signal 26. These positive and negative 
envelope signals 26 and 27 are applied as switch input signals 
corresponding to make and break terminals of the first analog switch 15, 
and either one of them is selected under control of the output signal 23 
of the first programmable counter 11. In consequence, the positive and 
negative envelope signals are alternately output from the first analog 
switch 15 with a period corresponding to the musical frequency, and are 
supplied to the mixing amplifier 18. This is shown in FIG. 5B, from which 
it will be seen that the positive, and negative signals are switched by a 
pitch signal. 
FIG. 6 is a signal diagram for explaining another example of operation of 
the circuit arrangement shown in FIG. 2. This is an example of operation 
by the second and third programmable counters 12 and 13, this is the most 
practical embodiment of the primary waveform generating system according 
to the present invention. In FIG. 6 the signal assumes three kinds of 
values. A first one of them is a signal level in the state in which the 
positive envelope signal 26 is selected by the second analog switch 16 
under control of such an output signal 24 from the second programmable 
counter 12 as shown in FIG. 4B. This corresponds to a portion above the 
zero level in FIG. 6. The second value is a signal level in the state in 
which the negative envelope signal 27 is selected by the third analog 
switch 17 under control of such an output signal 25 from the third 
programmable counter 13 as shown in FIG. 4C. This corresponds to the 
portion below the zero level in FIG. 6. The third value is a signal lever 
in the state in which the output signals of the second and third 
programmable counters 12 and 13 are both inactive and the second and third 
analog switches 16 and 17 both select the zero level. This corresponds to 
the portion at the zero level in FIG. 6. In FIG. 6 the time from the 
instant when the second programmable counter 12 becomes inactive to the 
instant when the third programmable counter 13 becomes active is shown in 
exaggeration in the interests of clarity. Conversely, in the case of 
requiring such a signal waveform as shown in FIG. 6, it is necessary only 
to provide a fourth programmable counter which is triggered at the instant 
when the second programmable counter becomes inactive, stays in its ON 
state for a required period of time set by the programmable one-shot 
operation and supplies its end signal, as a trigger signal, to the third 
programmable counter 13. 
FIG. 7 is a signal diagram for explaining another operation of the primary 
waveform generating system according to the present invention. In the 
above a certain primary waveform is set by an arrangement composed of a 
first programmable counter which generates a reference clock signal 
corresponding to the musical frequency and a plurality of 
cascade-connected programmable counters which are each triggered by the 
preceding stage programmable counter. The primary waveform need not be 
constant in the steady state once it is set, but is controllable by a 
control signal from the CPU in real time. This is also an important 
feature of the primary waveform generating system according to the present 
invention. FIG. 7A shows the output signal of the first programmable 
counter. The first programmable counter is set by the control signal from 
the CPU to operate in such a mode that it performs a programmable 
frequency division in its steady state to create an output signal of a 50% 
duty ratio and a period corresponding to the musical frequency to be 
generated. FIG. 7B shows an example of the output signal in the case where 
a certain primary waveform is set by the arrangement composed of the 
plurality of programmable counters each of which is triggered by the 
preceding programmable counter. This can easily be implemented through use 
of a second programmable counter which determines a period of time for 
which the primary waveform takes a fixed positive level, a third 
programmable counter which determines a period of time for which it takes 
the zero level, and a fourth programmable counter which determines a 
period of time for which it takes a fixed negative level. Now consider the 
state in which these programmable counters are controlled by the CPU in an 
actual electronic musical instrument. Since the musical frequency of a 
musical tone to be created varies with the playing status, the period of 
the output signal of the first programmable counter, shown in FIG. 7A, is 
set first in accordance with the musical frequency. Then programmable 
frequency division data for the second, third and fourth programmable 
counters are individually set as data corresponding to the musical 
frequency of the musical tone to be created. The programmable frequency 
division data needs only to be prepared as data in a ROM provided in the 
CPU system, or as data which is stored in a RAM in the CPU system when the 
power supply is connected to the system. In the latter case, it is 
possible to employ, for example, a method in which only base data is 
stored in a ROM and the other data is individually set in a RAM by an 
operation in terms of software, or a method which transfers data from an 
external auxiliary storage means such as a ROM pack, bubble cassette, 
floppy disc or the like to a RAM. Even if such a primary waveform signal 
as shown in FIG. 7B is thus obtained, the primary waveform generating 
system is insufficient for generating a primary waveform in the electronic 
musical instrument if it merely continues to produce such a primary 
waveform in the steady state. Now consider musical waveforms of natural 
musical instruments. As is marked in musical instruments such as a piano, 
a trumpet, etc., tone usually undergoes changes with time, and tone seldom 
remains unchanged as in a pipe organ. Two methods can be utilized for 
implementing such temporal variations of tone in an electronic musical 
instrument. One is to have temporal variations in the characteristic of 
the tone filter circuit, and the other is to directly change the 
parameters with time in the primary waveform generating portion. Since 
conventional primary waveform generating systems are not only low in the 
degree of freedom in selecting the shape of the primary waveform that can 
be generated, but also encounter difficulty in changing the parameters of 
the primary waveform, there has been employed exclusively the system which 
provides temporal characteristic variations in the tone filter circuit 
portion. However, the temporal variations operable by the tone filter 
circuit are also limited, and hence are not satisfactory. According to the 
primary waveform generating system of the present invention, the 
parameters of the primary waveform to be created can arbitrarily be set by 
data signals which are supplied as programmable frequency division data of 
the second, third and fourth programmable counters from the CPU, and the 
parameters can easily be changed in real time by means of hardware 
provided in the CPU system or software of the CPU itself. This is nothing 
but the temporal variation of the primary waveform, i.e. temporal 
variation of tone to be created. Accordingly, the present invention offers 
a tone generating system which allows ease in causing temporal variation 
in tone which has been difficult with the conventional analog type 
electronic musical instruments. Even if such a temporal variation in tone 
for the primary waveform signal shown in FIG. 7B, the abovesaid primary 
waveform generating portion is not satisfactory if it merely continues to 
generate the waveform with such parameter changes alone. Now consider 
musical waveforms of natural musical instruments. As is remarkable in a 
saxophone, a guitar and other similar instruments, tone usually varies 
with the strength of playing operation, that is, touch response in a 
keyboard instrument, and tone seldom remains unchanged regardless of touch 
as in a pipe organ. Such tonal variations with touch response can be 
implemented in electronic musical instruments by two methods, that is, one 
is to have a touch response characteristic in the tone filter circuit 
portion and the other is to directly change the parameters in the primary 
waveform generating portion according to touch response information. Since 
the prior art primary waveform generating system is not only low in the 
degree of freedom in selecting the shape of the primary waveform that can 
be created, but also encounter difficulty in causing changes in the 
parameters of the primary waveform, there has been employed exclusively 
the system in which the tone filter circuit portion is give a touch 
response characteristic. But the touch response that can be obtained with 
the tone filter circuit is also limited, and hence is not always 
satisfactory. According to the primary waveform generating system of the 
present invention, the parameters of the primary waveform that is to be 
produced can freely be set by data signals which are supplied as 
programmable frequency division data of the second, third and fourth 
programmable counters, and these parameters can easily be varied instantly 
by means of hardware in the CPU system or software of the CPU in 
accordance with touch response information. This is no other than a touch 
response change in the shape of the primary waveform, i.e. a tonal 
variation for touch response. Accordingly, the present invention offers a 
tone generating system which permits the touch response variation in the 
tone which has been difficult with the conventional analog type electronic 
musical instruments. As described above, the primary waveform generating 
system of the present invention easily implements the temporal variation 
of the primary waveform corresponding to the temporal variation of tone 
and the touch response variation of the primary waveform corresponding to 
the touch response variation of tone. FIG. 7C shows how this is achieved. 
Since the length of each arrow can freely be controlled, it is possible to 
arbitrarily set a primary waveform abundantly containing harmonics. By 
selecting an integral multiple of the length of this pulse to agree with 
the musical frequency in FIG. 7A, the so-called "characteristic tone" 
having a specific harmonic suppressed, peculiar to wind instruments, is 
produced. Conversely, by slightly deviating the pulse length, it is 
possible to obtain a tone which contains many harmonics as in the case of 
a piano or the like. FIG. 7D shows how the interval between two positive 
and negative pulses is controlled. The length of the arrow can freely be 
controlled. This is a control parameter which is of particular utility 
when employed in creating a piano sound. In the sound producing mechanism 
of a piano, a part of a music wire with high tension is instantaneously 
struck by a hammer, and impulses are reflected at opposite fixed ends of 
the music wire. The music wire can be regarded as vibrating in its steady 
state in such a waveform as shown in FIG. 7D. The control of the interval 
between the two pulses can be used as a relative change in position of the 
striking point of the hammer, i.e. as a variation in the primary waveform 
corresponding to the note range, and it can also be utilized in the tonal 
variations with time. 
FIGS. 8A and 8B are signal diagrams for explaining another operation of the 
primary waveform generating system of the present invention. In this case, 
the primary waveform generating section is comprised of a first 
programmable counter which produces a reference clock signal corresponding 
to the musical frequency, and seven cascade-connected programmable 
counters each of which is triggered by the preceding programmable counter, 
and a multilevel signal is created which takes one of five kinds of levels 
for each period specified by one of the cascade-connected programmable 
counters. The five kinds of levels herein mentioned are a preset positive 
first envelope signal EV1, a positive second envelope signal EV2 the level 
of which is one-half that of the first envelope signal EV1, a negative 
third envelope signal EV3 is obtained by inverting the second envelope 
signal EV2, a negative fourth envelope signal EV4 obtained by inverting 
the first envelope signal EV1 and the zero level. FIG. 8B shows how the 
multilevel signal which assumes one of the five levels for each specified 
period is generated by the seven cascade-connected programmable counters. 
As parameters representing the abovesaid five levels are shown a level 
parameter g representing the preset positive first envelope signal EV1, a 
level parameter h representing the positive second envelope signal EV2, a 
level parameter j representing the negative third envelope signal EV3 and 
a level parameter i representing the negative fourth envelope signal EV4. 
As the time for which these levels are selected are shown a time parameter 
a representing the period which is specified by the second programmable 
counter, a time parameter b representing the period which is specified by 
the third programmable counter, a time parameter c representing the period 
which is specified by the fourth programmable counter, a time parameter d 
representing the period which is specified by the fifth programmable 
counter, a time parameter e representing the period which is specified by 
the sixth programmable counter and a time parameter f representing the 
period which is specified by the seventh programmable counter. With such 
an arrangement, the primary waveform obtainable with combinations of these 
parameters undergoes substantial variations, and it is also possible to 
create the primary waveform by, for instance, giving a specific meaning to 
each of the parameters. That is, a character corresponding to so-called 
"formant" is set first as the basic harmonic structure of the musical tone 
by substantially fixing the periods of the parameters a, b and f. Then the 
period of the parameter d is set very short just like an impulse signal. 
In such a case, the portion corresponding to the period of the parameter d 
forms a so-called "noisy" musical tone element which does not 
substantially affect the basic harmonic structure of the musical tone but 
rather contains a lot of very higher harmonics, and effectively functions 
to create a tone of, for instance, a harpsicord, sitar or similar 
instrument. Furthermore, variations of the periods of the parameters c and 
e in real time are effective for producing a tone of temporal variations, 
such as a piano sound, as compared with variations of the periods of the 
parameters a, b and f. Thus the primary waveform can effectively 
controlled without the necessity of controlling all the parameters at all 
time. 
As described above, the present invention offers a primary waveform 
generating system which creates a primary waveform signal of many 
variations with a simple arrangement and performs an envelope modulating 
operation as well and, further, easily implements temporal variations of 
the primary waveform corresponding to temporal variations of a tone and 
touch response variations of the primary waveform corresponding to touch 
response variations of the tone which are difficult to implement by the 
conventional electronic musical instruments of the analog system. 
Accordingly, the present invention provides, at a relatively low cost, an 
electronic musical instrument of high musicality which satisfactory in the 
tone quality and the degree of freedom of setting the tone, and hence 
greatly contributes to the production of good music. 
It will be apparent that many modifications and variations may be effected 
without departing from the scope of the novel concepts of the present 
invention.