Tone signal generation device for changing the tone color of a stored tone waveshape in an electronic musical instrument

A first waveshape memory stores a full waveshape of a tone from the start to the end of sounding of the tone or a portion thereof in plural periods. A second waveshape memory stores waveshape data of a modification waveshape for the full waveshape or the portion thereof. A tone waveshape signal read out from the first waveshape memory and a modification waveshape signal read out from the second waveshape memory are both multiplied with respective coefficients whereby these waveshape signals are weighted. These weighted waveshape signals are added together to provide a mixed tone signal. By controlling the coefficients, the tone color imparted on the mixed signal is variously determined. The coefficients for the tone color control are provided in accordance with key scaling, key touch or operation states of control knobs. Thus, tone signals having a variety of tone color changes can be realized without the necessity of many wave memories.

BACKGROUND OF THE INVENTION 
This invention relates to a tone signal generation device of a waveshape 
memory reading type and, more particularly, to a tone signal generation 
device capable of generating a high-quality tone signal by accessing a 
waveshape memory storing a full or partial waveshape in plural periods 
from the start of sounding of a tone to the end thereof. 
Known in the art is a tone signal generation device capable of generating a 
high-quality tone simulating closely a tone of an acoustic musical 
instrument by storing a full or partial waveshape in plural periods from 
the start of sounding of a tone to the end thereof in a waveshape memory 
and accessing this waveshape memory (e.g., U.S. Pat. No. 4,383,462). 
Since this prior art tone generation device reads out a full waveshape or a 
partial waveshape stored in the waveshape memory and provides the read out 
waveshape directly as a tone signal, a tone color change of a generated 
tone tends to lack in variation and therefore leaves something to be 
improved musically. If, in order to improve this defect, the tone 
generation device is provided with a key scaling control in which a tone 
color is changed in accordance with a tone pitch or a tone range of a tone 
to be generated, a touch response control in which the tone color is 
changed in accordance with an operating manner of a playing key such as a 
depression speed and a depression strength, and an operator control in 
which the tone colors are changed in accordance with an operation manner 
of various control knobs, a plurality of waveshape memories must be 
provided and one of them must be selected for reading for effecting these 
controls with a resulting complicated construction of the device and 
requirement for a tremendous memory capacity of the waveshape memories. 
The present invention, therefore, aims to solve the problem in the tone 
signal generation device generating a high-quality tone signal that the 
attempt for introducing a tone color change control such as the key 
scaling control is inevitably accompanied by a complicated construction of 
the device and the problem that the waveshape memory requires a tremendous 
amount of memory capacity. 
It is an object of the invention to provide a tone signal generation device 
capable of imparting the tone color change such as the key scaling with a 
simple construction using a waveshape memory of a relatively small 
capacity. 
SUMMARY OF THE INVENTION 
The tone signal generation device according to the invention comprises 
basic tone signal generation means including a first waveshape memory 
storing high-quality waveshape data of plural periods and modification 
waveshape generation means including a second waveshape storing waveshape 
data of a modification waveshape for a full or partial waveshape of plural 
periods from the start of sounding of a tone to the end thereof. Waveshape 
data is read out from each of the two memories in accordance with the tone 
pitch of a tone to be generated and, in accordance with the waveshape 
data, a basic tone signal and a modification waveshape signal are 
generated by the respective generation means. These basic tone signals and 
modification waveshape signals are individually weighted by separate 
weighting coefficients corresponding to tone color change parameters. By 
combining the weighted two signals electrically or acoustically, a tone 
signal having a desired tone color change is formed. 
The first waveshape memory prestores a full waveshape or a partial 
waveshape in plural periods (these plural periods may be either continuous 
or intermittent) from the start of sounding of a tone to the end thereof 
and the basic tone signal which is generated on the basis of this 
waveshape data exhibits its proper, high-quality tone color 
characteristics. On the other hand, the second waveshape memory stores 
waveshape data of a modification waveshape for the waveshape stored in the 
first waveshape memory and, by combining the modification waveshape signal 
generated on the basis of the modification waveshape data with the basic 
tone signal at a suitable ratio determined by their corresponding 
weighting coefficients, a tone in which the proper tone color 
characteristics of the basic tone signal are modified in accordance with 
the modification waveshape signal is finally obtained. 
According to the present invention, therefore, proper tone color 
characteristics of a high-quality basic tone signal are subtly variably 
controlled in response to tone color change parameters such as key 
scaling, key touch and operated state of a control knob. The degree of the 
tone color change is determined by the weighting coefficients. If, for 
example, the weighting coefficient of the basic tone signal is large and 
the one of the modification waveshape signal is small, the tone color 
change from the proper tone color characteristics of a finally obtained 
tone is small and vice versa. Since it is not an object of the invention 
to change the proper tone color characteristics themselves, tone signals 
having proper tone color characteristics corresponding to individual tone 
color kinds (e.g., piano, flute etc.) which can be selected by a tone 
color selection switch can be selectively generated by storing waveshape 
data for the respective tone colors individually in the first waveshape 
memory. In the second waveshape memory also, waveshape data for these tone 
colors may preferably be stored individually. 
The modification waveshape generation means preferably includes tone color 
changing means for changing a modification waveshape having been read out 
or to be read out from the second waveshape memory in response to the tone 
color change parameters. By the provision of such means, the tone color 
change can be controlled in an even more complicated manner. 
According to the present invention, in generating a high-quality tone 
signal in response to waveshape data read out from a waveshape memory 
storing waveshape data of plural periods, storing of waveshape data 
individually for each tone color change parameter is unnecessary so that 
there is no problem of requirement for a waveshape memory of a large 
capacity and the construction of the device can therefore be simplified. 
Preferred embodiments of the invention will now be described in conjunction 
with the accompanying drawings.

DESCRIPTION OF PREFERRED EMBODIMENTS 
FIG. 2 is a block diagram showing the entire construction of an electronic 
musical instrument to which this invention has been applied and an example 
of an internal construction of a tone generator 10 shown there is 
illustrated in FIG. 1. The feature of the invention is illustrated mainly 
in FIG. 1. 
Referring first to FIG. 2, the entire construction of the electronic 
musical instrument incorporating this example will be described. 
The electronic musical instrument has a plurality of time division tone 
generation channels and is capable of generating simultaneously tones 
corresponding to plural depressed keys by assigning the depressed keys on 
a keyboard to available ones among these time division tone generation 
channels. In FIG. 2, a keyboard 1 has keys for designating tone pitches of 
tones to be generated. A key assigner 2 detects depressed key or keys on 
the keyboard 1, assigns key codes KC corresponding to the depressed keys 
to available ones of the time division tone generation channels 
(hereinafter referred to simply as "tone generation channels") and outputs 
these key codes KC at timings synchronized with the assigned channels on a 
time shared basis. Simultaneously with the assignment of the key codes KC 
corresponding to the depressed keys, the key assigner 2 produces a key-on 
signal KON which keeps logic "1" during a period until the depressed keys 
are released in synchronism with the assigned channels and, when key code 
KC for a newly depressed key has been assigned to any of the tone 
generation channels, produces a key-on pulse KONP (a "1" signal) with a 
short pulse width at a timing synchronized with the channel to which the 
newly depressed key has been assigned. 
A note clock generator 3 produces, responsive to the key code KC produced 
by the key assigner 2, a note clock signal NCK of a frequency 
corresponding to the depressed key with respect to each of the tone 
generation channels on a time shared basis. A gate 4 selectively delivers 
the note clock signal NCK. An address counter 5 counts the note clock 
signals NCK applied through the gate 4 with respect to each of the tone 
generation channels to form address signals AD of a waveshape memory in a 
tone generator 10 to be described later. This address counter 5 has count 
channels corresponding to the tone generation channels and counts, in 
corresponding count channels, the note clock signals NCK applied from the 
note clock generator 3 via gate 4 at timings corresponding to the 
respective tone generation channels, delivering out counts in the 
respective count channels as the address signals AD of the waveshape 
memory on a time shared basis. 
In the respective count channels, preceding counts are reset by the key-on 
pulse KONP produced by the key assigner 2 when a newly depressed key has 
been assigned to the corresponding tone generation channels and a new 
counting operation is started from this reset value. 
An end address detection circuit 6 detects whether or not the address 
signal AD for each tone generation channel produced by the address counter 
5 has reached a last address value in the waveshape memory. When the 
address signal AD has reached the last address in the waveshape memory, 
the circuit 6 supplies an inhibit signal to the gate 4 at a time division 
timing of this address signal AD to cease the counting operation in the 
count channel in the address counter 5 in which the count has reached the 
last address value. 
A tone color selection circuit 9 selects a desired tone color such as piano 
and violin and produces, upon selection, tone color selection information 
TC representing the selected tone color. 
The tone generator 10 comprises a waveshape memory storing waveshape 
information about the entire waveshape from the start of generation of a 
tone to the end thereof with respect to each tone color which can be 
selected by the tone color selection circuit 9 and generates tone signals 
G corresponding to the tone pitches of the depressed keys by reading out 
waveshape information stored in this waveshape memory by the address 
signals AD provided by the address counter 5. As described above, the tone 
generator 10 has tone generation channels corresponding to the number of 
tones which can be simultaneously produced. These tone generation channels 
are constructed by using the circuit including the waveshape memory on a 
time shared basis. 
A touch detection circuit 11 detects the depression speed (touch speed) or 
depression strength (touch strength) with respect to a key depressed on 
the keyboard 1 and produces touch information TS representing such 
depression speed or strength. A touch data generation circuit 12 
generates, responsive to the touch information TS provided by the touch 
detection circuit 11 and the tone color selection information TC provided 
by the tone color selection circuit 9, touch data TD of characteristics 
suited to the selected tone color in accordance with the touch information 
TS. In the present embodiment, touch data TD.sub.1 -TD.sub.4 of four 
channels are produced. 
An envelope signal generation circuit 13 generates an envelope signal ENV 
for changing in a timewise fashion the tone color and amplitude of the 
tone signal G formed in each tone generation channel from the rise to the 
fall thereof, starting its operation in response to the key-on signal KON 
produced by the key assigner 2. The envelope signal ENV produced in this 
circuit has a different waveshape depending upon the selected tone color 
represented by the tone color selection information TC and is delivered 
out as envelope signals ENV.sub.1 -ENV.sub.4 of four channels for each 
selected tone color. 
A key scaling control circuit 14 generates, responsive to the key code KC 
produced by the key assigner 2 and the tone color selection information TC 
produced by the tone color selection circuit 9, key scaling information KS 
for controlling the tone color and amplitude of the tone signal G 
generated in each tone generation channel in accordance with the tone 
range and the selected tone color of the depressed key. In the same manner 
as in the above described circuits 12 and 13, the key scaling control 
circuit 14 produces key scaling information KS.sub.1 -KS.sub.4 of four 
channels. 
A control knob circuit 15 has control knobs for controlling tone colors, 
tone volume and other musical tone elements for controlling brightness of 
the tone and produces control knob information OPD corresponding to 
operated states of these control knobs. This circuit likewise produces 
control knob information OPD.sub.1 -OPD.sub.4 of four channels. 
A digital-to-analog converter 16 converts the digital tone signals G for 
the respective tone generation channels formed in the tone generator 10 to 
analog tone signals to sound them as musical tones from a sound system 17. 
The touch data generation circuit 12, the envelope signal generation 
circuit 13 and the key scaling control circuit 14 respectively produce, at 
time division timings corresponding to the respective tone generation 
channels, touch data TD.sub.1 -TD.sub.4, key scaling information KS.sub.1 
-KS.sub.4 and envelope signals ENV.sub.1 -ENV.sub.4 respectively of four 
channels for controlling the tone color and amplitude of the tone signal G 
with respect to each of the tone generation channels. Examples of the 
touch data TD.sub.1 -TD.sub.4 generated by the touch data generation 
circuit 12, the envelope signal ENV.sub.1 -ENV.sub.4 produced by the 
envelope signal generation circuit 13 and the key scaling information 
KS.sub.1 -KS.sub.4 produced by the key scaling control circuit 14 are 
shown respectively in FIGS. 3a, 3b and 3c. In these examples, data output 
characteristics of the circuits 12 to 14 differ depending upon the tone 
color represented by the tone color selection information TC. 
As shown in FIG. 1, the tone generator 10 comprises basic tone signal 
generation means 18 including a first waveshape memory 20 and modification 
waveshape generation means 19 including a second waveshape memory 21. In 
the present embodiment, it is assumed that the first waveshape memory 20 
stores waveshape data concerning a full waveshape from the start of 
sounding of a tone to the end thereof in a pulse-code modulation (PCM) 
system, storing one set of waveshape data individually for each of tone 
colors which can be selected by a tone color selection circuit 9. The 
second waveshape memory 21 stores modification waveshape for a full 
waveshape of a tone from the start of sounding of the tone to the end 
thereof (i.e., a full waveshape to be added for modification from the 
start of sounding of the tone to the end thereof) similarly in the PCM 
system individually for each of the tone colors. The modification 
waveshape herein means not a waveshape which can realize proper tone color 
characteristics themselves which can be selected by tone color selection 
information TC (such as the waveshape stored in the first waveshape 
memory) but a waveshape which is suitable for imparting a tone color 
change to a waveshape having such proper tone color characteristics. 
The tone color selection information TC is applied to the respective 
waveshape memories 20 and 21 to designate a set of waveshape data to be 
read out from these memories 20 and 21 in accordance with a selected tone 
color. In the respective waveshape memories 20 and 21, the set of 
waveshape data designated by the tone color selection information TC is 
sequentially read out at each sample point in response to an address 
signal applied to the address input. The address signal AD provided by an 
address counter 5 (FIG. 2) is applied directly to the address input of the 
first waveshape memory 20 and to the address input of the second waveshape 
memory 21 through an adder 22. 
The modification waveshape generation means 19 includes, as tone color 
changing means for changing the modification waveshape to be read out from 
the second waveshape memory 21 in response to a tone color change 
parameter, the adder 22 and a multiplier 23. For feeding back the output 
signal of the waveshape memory 21 at a rate corresponding to the tone 
color change parameter, the multiplier 23 is provided for receiving the 
output signal of the waveshape memory 21, multiplying it by a coefficient 
E.sub.3 and applying the result of multiplication to the adder 22. The 
adder 22 modulates the address signal AD by the memory output signal fed 
back through the multiplier 23 and supplies the modulated address signal 
to the address input of the waveshape memory 21. Thus, the address signal 
for accessing the second waveshape memory 21 is modulated by the read out 
output signal of the waveshape memory 21 itself whereby an effect 
equivalent to the frequency modulation is obtained. By this modulation, 
the modification waveshape formed on the basis of the waveshape data read 
out from the waveshape memory 21 becomes different from the modification 
waveshape which is originally stored in the memory 21 and a tone color 
change caused by changing the modification waveshape itself is realized. 
The degree of the change in the modification waveshape is determined by 
the modulation factor and this modulation factor is controlled by the 
coefficient E.sub.3 which sets the amount of the feedback. The modulation 
of the address signal AD of such feedback type becomes a complicated 
modulation since a further modulation by a modulated signal (i.e., the 
read out output signal of the waveshape memory 21) is performed. When the 
modulation factor is zero (i.e., the coefficient E.sub.3 is zero), 
waveshape data which realizes the modification waveshape stored in the 
waveshape memory 21 is read out and, as the modulation factor is increased 
(i.e., the coefficient E.sub.3 is increased), waveshape data which 
realizes modification waveshape containing more abundant harmonic 
components is read out. 
The waveshape data read out from the first waveshape memory 20 is provided 
from the basic tone signal generation means 18 as a basic tone signal Mw 
and applied to a multiplier 24 for weighting. The waveshape data read out 
from the second waveshape memory 21 is provided from the modification 
waveshape generation means 19 as a modification waveshape signal Cw and 
applied to a multiplier 25 for weighting. Weighting coefficients E.sub.1 
and E.sub.2 generated individually by coefficient generation circuits 26 
and 27 are applied to the multipliers 24 and 25 and the input signals Mw 
and Cw are weighted by these coefficients E.sub.1 and E.sub.2 (i.e., the 
amplitudes are controlled). 
Coefficient generation circuits 26 and 27 are provided for generating 
weighting coefficients E.sub.1 and E.sub.2 in response to various tone 
color change parameters. Among the touch data TD.sub.1 -TD.sub.4, envelope 
signals ENV.sub.1 -ENV.sub.4, key scaling information KS.sub.1 -KS.sub.4 
and control knob information OPD.sub.1 -OPD.sub.4 produced by the circuits 
12-15, data TD.sub.1, ENV.sub.1, KS.sub.1 and OPD.sub.1 are applied to the 
circuit 27. To the coefficient generation circuit 28 for generating the 
feedback coefficient E.sub.3 are applied, as the tone color change 
parameters, data TD.sub.3, ENV.sub.3, KS.sub.3 and OPD.sub.3 and, 
responsive thereto, the coefficient E.sub.3 is generated. Further, to a 
coefficient generation circuit 29 to be described later are applied, as 
the amplitude control parameters, data TD.sub.4, ENV.sub.4, KS.sub.4 and 
OPD.sub.4 and, responsive thereto, the amplitude coefficient E.sub.4 is 
generated. These coefficient generation circuits 26-29 are constructed of 
operation circuits such as addition circuits or coefficient memories or a 
combination thereof and generate the coefficients E.sub.1 -E.sub.4 as 
functions of the respective parameters TD.sub.1 -TD.sub.4, ENV.sub.1 
-ENV.sub.4, KS.sub.1 -KS.sub.4 and OPD.sub.1 -OPD.sub.4. The tone color 
selection information TC may be applied to the respective circuits 26-29 
as shown in the dotted line so as to change the contents of the 
coefficients E.sub.1 -E.sub.4 in response to the tone color. 
The basic tone signal Mw and modification waveshape signal Cw which have 
been weighted by the multipliers 24 and 25 are added in an adder 30 and a 
tone signal imparted with a desired tone color change corresponding to the 
tone color change parameters is outputted. The tone signal outputted from 
the adder 30 is applied to a multiplier 31 in which its amplitude (volume) 
is controlled in accordance with the amplitude coefficient E.sub.4. The 
output of this multiplier 31 is provided from the tone generator 10 as the 
tone signal G. 
All these circuits 20-31 constituting the tone generator 10 operates on the 
time shared basis, forming the tone signals G assigned to the respective 
tone generation channels in time division. 
The degree of the tone color change is basically determined by the 
weighting coefficients E.sub.1 and E.sub.2. For example, the larger the 
weighting coefficient E.sub.1 of the basic tone signal Mw and the smaller 
the weighting coefficient E.sub.2 of the modification waveshape signal, 
the smaller is the tone color change from the proper tone color 
characteristics in the finally obtained tone signal G, and vice versa. In 
addition to this, the degree of the tone color change is controlled by the 
coefficient E.sub.3 for the tone color change control in the modification 
waveshape generation means 19. 
If, for example, the key scaling information KS.sub.1 -KS.sub.4 are 
generated with characteristics as shown in FIG. 3c and the coefficients 
E.sub.1 -E.sub.4 are also generated with characteristics corresponding 
thereto, in a weighting control by the coefficients E.sub.1 and E.sub.2 
corresponding to data KS.sub.1 and KS.sub.2, the ratio of the basic tone 
signal Mw decreases and that of the modification waveshape signal Cw 
increases as the tone pitch of the tone to be generated rises so that the 
tone color change increases. In the feedback control by the coefficient 
E.sub.3 corresponding to the data KS.sub.3, the amount of feedback 
increases and the modulation factor thereby increases as the tone pitch 
rises so that harmonic components of the modification waveshape signal 
increase. In the level control by the coefficient E.sub.4 corresponding to 
the data KS.sub.4, key scaling which matches hearing in such a manner that 
the level decreases as the tone pitch rises is realized. 
If the touch data TD.sub.1 -TD.sub.4 are generated with characteristics as 
shown in FIG. 3a and the coefficients E.sub.1 -E.sub.4 are also generated 
with characteristics corresponding thereto, the weighting control by the 
weighting coefficients E.sub.1 and E.sub.2 corresponding to the data 
TD.sub.1 and TD.sub.2 is made in such a manner that the ratio of the basic 
tone signal Mw decreases and that of the modification waveshape signal Cw 
increases as the key touch becomes stronger so that the tone color change 
increases. In the control by the coefficient E.sub.4 corresponding to the 
data TD.sub.4, harmonic components of the modification waveshape signal 
increase as the key touch becomes stronger. Further, in the level control 
by the coefficient E.sub.4 corresponding to the data TD.sub.4, the level 
increases as the key touch becomes stronger. 
If the envelope signals ENV.sub.1 -ENV.sub.4 are generated with 
characteristics as shown in FIG. 3b and the coefficients E.sub.1 -E.sub.4 
are also generated with characteristics corresponding thereto, the 
respective coefficients E.sub.1, E.sub.2 and E.sub.3 have attack and decay 
characteristics which change timewise as shown in FIG. 3b. Accordingly, 
the ratio of weighting and the amount of feedback are controlled in 
accordance with the rise and fall of the tone and the tone color change 
corresponding thereto is realized. In the figure, the envelope signals 
ENV.sub.1 -ENV.sub.3 are illustrated as having the same shape for the sake 
of convenience. The envelope signals can have their own shapes by 
independently controlling the attack time, attack level, sustain level, 
decay level and decay time. The envelope signal ENV.sub.4 corresponding to 
the amplitude coefficient E.sub.4 maintains a constant level during the 
depression of a key as shown in FIG. 3b because the basic tone signal and 
modification waveshape signal have been imparted with the level envelope 
of at least the attack portion. 
As regards the control knob information OPD.sub.1 -OPD.sub.4, corresponding 
coefficients E.sub.1 -E.sub.4 are generated in the same manner as 
described above and the tone color change control and the level control 
corresponding thereto are performed. 
A more complicated variation in the tone color can be achieved by applying, 
as shown by a dotted line in FIG. 2, the key code KC, touch information 
TS, control knob information OPD.sub.1 -OPD.sub.4 to the envelope signal 
generation circuit 13 and suitably changing the rise time and decay time 
and levels of respective portions of the envelope signals ENV.sub.1 
-ENV.sub.4 in accordance with the tone range, depression speed or strength 
of the depressed key and the operated states of the control knobs in the 
control knob circuit 15. 
Modified examples of the tone signal generation device according to the 
invention will be described with reference to FIGS. 4, 5 and 6. In these 
figures in which illustration of the circuits for generating the various 
coefficients E.sub.1 -E.sub.4 are omitted, it is assumed that these 
coefficients are generated in response to the key scaling information, 
touch data, envelope signals and control knob information. 
The circuitry shown in FIG. 4 includes, as the tone color changing means of 
the modification waveshape generation means 19, a feedback loop including 
a multiplier 23 and an adder 22 for modulating the address signal as in 
the circuitry shown in FIG. 1 and further includes a digital filter 32 in 
this feedback loop. The digital filter 32 may be provided either on the 
input side of the multiplier 23 or on the output side thereof. 
Frequency-amplitude characteristics of this filter 32 are variably 
controlled by a filter control coefficient E.sub.5. By this filter 
controlling, the harmonic components of a signal fed back from the output 
side of the second waveshape memory 21 to the input side thereof are 
controlled whereby further control of the tone color change is effected. 
FIG. 5 shows a modified example in which, as the tone color changing means 
of the modification waveshape generation means 19, a digital filter 33 is 
further provided aside from a feedback type frequency modulation circuit 
consisting of a multiplier 23 and an adder 22 as in the circuitry of FIG. 
1. This filter 33 may alternately be provided on the output side the 
multiplier 25. Frequency-amplitude characteristics of this filter 33 are 
controlled by a filter control coefficient E.sub.6. By this controlling, 
the harmonic components of the modification waveshape signal are 
controlled and the tone color change is further controlled. 
FIG. 6 shows a modified example of the tone signal generation device in 
which, as the tone color changing means of the modification waveshape 
generation means 19, a digital filter 34 is provided on the output side of 
the waveshape memory 21. Frequency-amplitude characteristics of the filter 
34 are controlled by a filter control coefficient E.sub.7. By this 
controlling, the harmonic components of the modification waveshape signal 
read out from the second waveshape memory 21 are controlled and the tone 
color change thereby is controlled. 
The adder 22 for modulating the address signal may be substituted by other 
type of operation circuit such as a subtractor and the multiplier 23 for 
controlling the amount of the feedback may be also substituted by other 
type of operation circuit. 
In the above described embodiments, description has been made on the 
assumption that the first waveshape memory 20 stores a full waveshape from 
rise (start of sounding) to fall (end of sounding) of a tone. 
Alternatively, the waveshape memory may store a full waveshape of the rise 
portion and a part of subsequent waveshape of a tone. The same applies to 
the second waveshape memory 21. Instead of storing waveshape data of all 
sample points in a waveshape to be generated, the respective waveshape 
memories may store waveshape data of skipped sample points only and 
waveshape data of intermediate sample points may be calculated by an 
interpolation operation. Waveshape of plural periods to be stored in the 
respective waveshape memories need not necessarily be continuous plural 
periods but may be skipped periods. For example, an arrangement may be 
made such that a tone waveshape from its rising to decaying are divided 
into several frames and representative waveshape data of waveshapes of one 
or two periods for each of these frames are stored and such waveshape data 
is repeatedly read out one waveshape data after another. Further, if 
necessary, in switching of waveshape data, a smoothly changing waveshape 
may be formed by interpolating interval between a preceding waveshape and 
a subsequent waveshape. Further, as disclosed in Japanese Preliminary 
Patent Publication No. 142396/1983, waveshape data of a tone waveshape for 
plural periods only may be stored and this waveshape data may be 
repeatedly read out. By such arrangement, the capacity of a waveshape 
memory can be further reduced. 
The method for coding waveshape data to be stored in the waveshape memory 
is not limited to the above-described PCM system but other suitable 
methods such as the difference PCM (DPCM) method, delta modulation (DM) 
system, adapted PCM (ADPCM) system and adapted delta modulation (ADM) 
system may be used. In that case, in the basic tone signal generation 
means or the modification waveshape generation means, not only waveshape 
memory but also a demodulation circuit for demodulating the output read 
out from the waveshape memory (i.e., obtaining a pulse-code-modulated 
signal) according to the employed coding method is provided. 
In the above embodiments, the coefficient generation circuit is of such a 
construction as to respond to all of the key scaling information, envelope 
signals, touch data operator information and tone color selection 
information. Alternatively, the coefficient generation circuit may respond 
only to a part of such information. The characteristic curves shown in 
FIG. 3 are only exemplary and any other suitable curves may be formed 
depending upon the tone color and other factors. 
In the above embodiments, the address signal for reading out waveshape data 
in the waveshape memory is formed by counting the note clock signal. The 
address signal may instead be formed by accumulating or adding or 
subtracting frequency information corresponding to the tone pitch of a 
depressed key. Depending upon the construction of the waveshape memory, 
the address signal may remain to be the note clock signal instead of being 
converted into a binary code. In the case where the waveshape memory 
stores waveshape data with respect to each tone pitch, the address signal 
may be generated at a changing rate which is common to all tone pitches. 
In the above embodiments, a tone is generated applying the present 
invention to its entire period from the rise to the fall thereof. A tone 
may be generated applying the invention to only a part of period (e.g., 
the attack portion or a connecting portion after the attack portion). 
Memory system or data format of the first and second waveshape memories 
may be the same or different from each other. 
In the above described embodiments, single modification waveshape 
generation means 19 is provided. This means 19 may however be provided in 
plural channels. 
In the above embodiments, the basic tone signal Mw and modification 
waveshape signal Cw are electrically mixed in the adder 30. Alternatively, 
tones corresponding to the waveshape signals Mw and Cw may be sounded from 
separate loud-speakers and mixed acoustically (spatially). 
The present invention is applicable not only to polyphonic electronic 
musical instruments but also to monophonic electronic musical instruments. 
The invention is also applicable not only to generation of tones 
corresponding to scale notes but also to generation of rhythm sounds. 
According to the invention, a musical tone exhibiting a desired tone color 
change can be generated by synthesizing a basic tone signal formed in 
accordance with read out output of the first waveshape memory and a 
modification waveshape signal formed in accordance with a read out output 
of the second waveshape memory upon weighting these signals at a ratio 
corresponding to tone color change parameters. Accordingly, 
notwithstanding the fact that only a single high-quality waveshape is 
stored in the first waveshape memory, similar high-quality waveshapes can 
be realized with various tone colors (i.e., tone color change depending 
upon the key touch or tone pitch of the depressed key or other tone color 
changing factors) on the basis of the single stored waveshape. 
Consequently, such tone color change of high-quality can be achieved with 
a relatively small and inexpensive construction.