Electronic musical instrument of waveform memory readout type

Keys of a keyboard are divided into a plurality of tone ranges and a plurality of musical tone waveforms regarding specific ones of the divided tone ranges are stored in a waveform memory device. A number of the plurality of musical tone waveforms is smaller than the number of the divided tone ranges. An address signal generator is provided which generates an address signal having a repetition period corresponding to a tone pitch of a depressed key and supplies the address signal to the waveform memory device, and an arithmetic operating circuit is provided which selects ones from among the plurality of musical tone waveforms and mixes the selected ones of a mixing ratio, thereby forming a new musical tone waveform. The selected ones and the mixing ratio are predetermined corresponding to each of the tone ranges. Different tone colors of a number which is more than the number of the waveforms are realized for the respective tone ranges just like in a natural musical instrument.

BACKGROUND OF THE INVENTION 
This invention relates to an electronic musical instrument, and more 
particularly to an improvement of an electronic musical instrument of the 
waveform memory device readout type. 
An electronic musical instrument of the waveform memory readout type has 
been known wherein a musical waveform prestored in a waveform memory 
device is read out according to an address signal corresponding to the 
tone pitch of a depressed key to produce a musical tone. 
With the electronic musical instrument of the waveform memory readout type, 
once the waveform to be stored in the waveform memory device is 
determined, the tone color of the produced musical tone is the same for 
all tone ranges so that the tone color of the musical tone is respective 
tone ranges does not change as in a natural musical instrument in which 
harmonics are abundant in a low tone range while the harmonics are less in 
a high tone range. 
To obviate this difficulty it has been proposed to provide an electronic 
musical instrument in which a keyboard is divided into a plurality of tone 
ranges and waveform memory devices are provided for respective tone ranges 
so as to produce musical tone waveforms having different waveforms in 
respective tone ranges, as described in U.S. Pat. No. 4,213,366. 
In this electronic musical instrument, however, it is necessary to provide 
waveform memory devices of the same number as the number of the divided 
tone ranges with the result that the size of the electronic musical 
instrument becomes large and its manufacturing cost increases. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of this invention to provide an improved 
electronic musical instrument having a simple construction but capable of 
producing musical tones of different tone colors in respective tone ranges 
just like a natural musical instrument. 
The present invention provide an electronic musical instrument having a 
keyboard including a plurality of keys which are divided into a plurality 
of tone ranges. A plurality of waveform memory devices of a number smaller 
than the number of the divided tone ranges are provided the waveform 
corresponding to memory devices storing musical tone waveforms specific 
ones of the divided tone ranges. An address signal generator is provided 
which, in response to a signal representing a tone pitch of a depressed 
key, forms an address signal having a repetition period corresponding to 
the tone pitch. The signal generator applies the address signal to the 
waveform memory and arithmetic operating means which selects two musical 
tone waveforms corresponding to a tone range of a depressed key among 
musical tone waveforms read out from the waveform memory devices by the 
address signal and interpolates in order to form a musical tone waveform 
corresponding to the tone range of the depressed key by utilizing the two 
musical tone waveforms selected according to the tone range of the 
depressed key.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The electronic musical instrument shown in FIG. 1 has a total of 49 keys, 
not shown, ranging from a note C2 to C6. In this example, the tone ranges 
are divided into 17 ranges each including three keys as shown in the 
following Table I (provided that a tone range for note C6 includes only 
one key). Among these 17 tone ranges, a tone range to which keys of note 
C4 through D4 belong is termed a reference tone range, a tone range to 
which a key of the note C6 belongs is termed a high tone range, and a tone 
range to which keys of notes C2 through D2 belong is termed a low tone 
range. According to this invention, a reference tone range waveform memory 
device, a high tone range waveform memory device and a low tone range 
waveform memory device are provided only for these three tone ranges, the 
memory devices prestoring musical tone waveforms regarding the tone 
ranges. Furthermore, the musical tone waveforms for the other tone ranges 
are produced by interpolating the musical tone waveforms read out from the 
three waveform memory devices in accordance with a specific tone range to 
which a depressed key belongs. In Table I, a signal S and constants 
K.sub.1 and K.sub.2 are used for interpolation. 
TABLE I 
______________________________________ 
Tone range 
Signals S Constant K.sub.1 
Constant K.sub.2 
______________________________________ 
C6 1 1 0 
A5 to B5 1 7/8 1/8 
F.music-sharp.5 to G.music-sharp.5 
1 6/8 2/8 
D.music-sharp.5 to F5 
1 5/8 3/8 
C5 to D5 1 4/8 4/8 
A4 to B4 1 3/8 5/8 
F.music-sharp.4 to G.music-sharp.4 
1 2/8 6/8 
D.music-sharp.4 to F4 
1 1/8 7/8 
C4 to D4 1/0 0 1 
A3 to B3 0 1/8 7/8 
F.music-sharp.3 to G.music-sharp.3 
0 2/8 6/8 
D.music-sharp.3 to F3 
0 3/8 5/8 
C3 to D3 0 4/8 4/8 
A2 to B2 0 5/8 3/8 
F.music-sharp.2 to G.music-sharp.2 
0 6/8 2/8 
D.music-sharp.2 to F2 
0 7/8 1/8 
C2 to D2 0 1 0 
______________________________________ 
As shown in FIG. 1 there is provided a key switch circuit 1 which includes 
a plurality of key switches corresponding to respective keys of the 
keyboard, such that when a key is depressed, a key switch corresponding 
thereto operates to generate and output key codes KC, as shown in the 
following Tables IIa and IIb based on an output signal produced by the key 
switch. Each key code is a seven bit signal consisting of block codes BC 
(B3, B2 and B1) representing an octave tone range of the key and note 
codes NC (N4, N3, N2 and N1). The key switch circuit 1 also produces a 
key-on signal KON representing that a key has been depressed. 
TABLE IIa 
______________________________________ 
Block code BC 
Octave B3 B2 B1 
______________________________________ 
C2 to B2 O 0 1 
C3 to B3 0 1 0 
C4 to B4 0 1 1 
C5 to B5 1 0 0 
C6 1 0 1 
______________________________________ 
TABLE IIb 
______________________________________ 
Note code NC 
Note N4 N3 N2 N1 
______________________________________ 
C 0 0 0 0 
C.music-sharp. 
0 0 0 1 
D 0 0 1 0 
D.music-sharp. 
0 1 0 0 
E 0 1 0 1 
F 0 1 1 0 
F.music-sharp. 
1 0 0 0 
G 1 0 0 1 
G.music-sharp. 
1 0 1 0 
A 1 1 0 0 
A.music-sharp. 
1 1 0 1 
B 1 1 1 1 
______________________________________ 
There is also provided an address signal generator 2 which, in response to 
a key code KC outputted from the key switch circuit 1, generates and 
outputs an address signal ADR having a repetition period corresponding to 
the note of the depressed key. The address signal generator 2 is 
constructed such that it reads out frequency information F corresponding 
to the note of the depressed key from the memory device, and that is 
repeatedly accumulates the frequency information F at a predetermined 
speed to output the accumulated value qF (q=1, 2, . . . ) as the address 
signal. 
There is also provided a reference tone range waveform memory device 3 
storing a musical tone waveform corresponding to tone range to which the 
keys of notes C4 through D4 belong, a high tone range waveform memory 
device 4 storing a musical tone waveform regarding a tone range to which 
the key of note C6 belongs, and a low tone range waveform memory device 5 
storing a musical tone waveform corresponding to a tone range to which 
keys of the notes C2 through D2 belong. When supplied with an address 
signal outputted from the address signal generator 2, these waveform 
memory devices 3, 4 and 5 produce stored waveform signals W.sub.m, W.sub.H 
and W.sub.L respectively. In this embodiment, in the high tone range 
memory device 4 is stored a musical tone waveform containing less number 
of harmonic components, whereas in the low tone range waveform memory 
device 5 is stored a musical tone waveform containing a large number of 
harmonic components. 
A code converter 6 is provided which receives five bit signals B3, B2, B1, 
N4 and N3 among a seven bit key code KC for judging a tone range to which 
the depressed key belongs, the signal S and the constant K.sub.1 and 
K.sub.2 shown in Table I. There is further provided a selector 7 which 
selects the high tone range waveform memory device 4 and outputs the 
musical tone waveform W.sub.H when the signal S outputted from the code 
converter 6 is "1" whereas selects the low tone range waveform memory 
device 5 and outputs the musical tone waveform W.sub.L when the signal S 
is "0"; a multiplier 8 which multiplies the output waveform W.sub.S and 
the constant K.sub.1 ; a multiplier 9 which multiplies the musical tone 
waveform W.sub.m outputted from the reference tone range waveform memory 
device 3 with the constant K.sub.2 ; an adder 10 which adds the output 
waveform (W.sub.S).times.(K.sub.1) of the multiplier 8 to the output 
waveform (W.sub.m).times.(K.sub.2) of the multiplier 9; an envelope signal 
generator 11 which starts its operation in synchronism with the building 
up of the key-on signal KON outputted from the key switch circuit for 
producing an envelope signal EV imparting an amplitude envelope to a 
musical tone waveform to be produced; a multiplier 12 for multiplying the 
output waveform 
.SIGMA.W[=(W.sub.m).times.(K.sub.2)+(W.sub.S).times.(K.sub.1)] outputted 
from the adder 10 with the envelope signal EV; and a sound system 13 which 
converts the output waveform signal (EV).times.(.SIGMA.W) of the 
multiplier 12 into a musical tone signal. 
Where a key of the note C4, for example, is depressed, the key switch 
circuit 1 produces a key code KC as shown in the following Table III. 
TABLE III 
______________________________________ 
Key code KC 
B3 B2 B1 N4 N3 N2 N1 
______________________________________ 
0 1 1 0 0 0 0 
______________________________________ 
Then, in accordance with this key code KC, the address signal generator 2 
forms an address signal ADR having a repetition period corresponding to 
the note C4 and applies this address signal ADR in parallel to the 
reference tone range waveform memory device 3, the high tone range 
waveform memory device 4 and the low tone range waveform memory device 5. 
Then, these three waveform memory devices 3, 4 and 5 produce musical tone 
waveforms W.sub.m, W.sub.H and W.sub.L respectively prestored therein in 
response to the address signal ADR. In this case, the frequencies of the 
musical tone waveforms W.sub.m, W.sub.H and W.sub.L correspond to the 
repetition period of the address signal ADR, in other words, to the note 
C4. 
Only the bit signals B3, B2, B1, N4 and N3 of the key code KC are inputted 
to the code converter 6, whereby it produces a signal S having the value 
"1" (or "0"), a constant K.sub.1 =0 and a constant K.sub.2 =1. 
Then the selector 7 selects a musical tone waveform W.sub.H (or W.sub.L) 
corresponding to the high tone range (or the low tone range) and supplies 
the selected waveform W.sub.H (or W.sub.L) to the multiplier 8. In this 
case, however, as the multiplier 8 is supplied with the constant K.sub.1 
=0, the amplitude value of the output waveform (W.sub.S).times.(K.sub.1) 
of the multiplier 8 has the value "0". 
On the other hand, since the multiplier 9 is inputted with the constant 
K.sub.2 =1, it produces a musical tone waveform (W.sub.m).times.(K.sub.2) 
having an amplitude value expressed by an equation 
EQU (W.sub.m).times.(K.sub.2)=(W.sub.m).times.1 
This musical tone waveform (W.sub.m).times.(K.sub.2) is applied to one 
input of the adder 10, whereas the musical tone waveform 
(W.sub.S).times.(K.sub.1) is applied to the other input of the adder 10. 
Consequently, the adder 10 produces a musical tone waveform W.sub.m 
corresponding to the reference tone range as a synthesized musical tone 
waveform .SIGMA.W. This synthesized musical tone waveform .SIGMA.W is 
inputted to the multiplier 12 to be multiplied with the envelope signal 
EV, thus setting an amplitude value of the envelope signal. Consequently, 
the sound system 13 produces a musical tone corresponding to the note C4. 
As above described, where a depressed key belongs to the reference tone 
range of the notes C4 through D4, a musical tone would be produced based 
only upon the output musical tone waveform W.sub.m of the waveform memory 
device 3 in which has been previously stored a musical tone waveform 
corresponding to the reference tone range. 
Suppose now that a key of the note C6 is depressed, the key switch circuit 
1 would produce a key code KC as shown in the following Table IV. 
TABLE IV 
______________________________________ 
Key code KC 
B3 B2 B1 N4 N3 N2 N1 
______________________________________ 
1 0 1 0 0 0 0 
______________________________________ 
Then the address signal generator 2 supplies an address signal ADR in 
parallel to the three waveform memory devices 3, 4 and 5. The address 
signal ADR has a repetition frequency corresponding to the note C6. For 
this reason, the three waveform memory devices 3, 4 and 5, respectively, 
produce musical tone waveforms W.sub.m, W.sub.H and W.sub.L corresponding 
to the note C6. 
Since the depressed key is in a tone range of the note C6, the code 
converter 6 produces a signal S having a value "1" and constants K.sub.1 
=1 and K.sub.2 =0. As a consequence, the selector 7 selects a musical tone 
waveform W.sub.H corresponding to the hight tone range and supplies the 
selected musical tone waveform W.sub.H to the multiplier 8. Since the 
multiplier 8 is supplied with the constant K.sub.1 =1, it produces a 
musical tone waveform (W.sub.S).times.(K.sub.1) having an amplitude value 
expressed by an equation 
EQU (W.sub.S).times.(K.sub.1)=(W.sub.S).times.1 
On the other hand, since the constant K.sub.2 is equal to "0", the 
multiplier 9 produces an output waveform (W.sub.m).times.(K.sub.2) having 
an amplitude value of "0". Consequently, as a synthesized musical tone 
waveform .SIGMA.W, the adder 10 produces a musical tone waveform 
containing only the musical tone waveform W.sub.H corresponding to the 
high tone range. Accordingly, where the depressed key belongs to the high 
tone range of the note C6, the musical tone would be produced only by the 
musical tone waveform W.sub.H outputted from the high tone waveform memory 
device 4 corresponding to the high tone range. 
The operations are also performed where the depressed key belongs to the 
low tone range including the notes C2 through D2. More particularly, where 
the depressed key belongs to the low tone range, since the signal S has 
the value "0" (see Table I), the selector 7 selects and outputs a musical 
tone waveform W.sub.L corresponding to the low tone range. At this time, 
constants K.sub.1 =1 and K.sub.2 =0. Accordingly, the amplitude value of 
the waveform (W.sub.S).times.(K.sub.1) of the multiplier 8 becomes 
(W.sub.L).times.1, while the amplitude value of the waveform 
(W.sub.m).times.(K.sub.2) outputted from the multiplier 9 becomes "0". 
Consequently, the synthesized musical tone waveform .SIGMA.W outputted 
from the adder 10 contains only the musical tone waveform W.sub.L 
corresponding to the low tone range. 
Suppose now that a key of the note F3, for example, is depressed. Then the 
address signal generator 2 supplies to the three waveform memory devices 
3, 4 and 5 an address signal ADR having a repetition period corresponding 
to the note F3 so as to cause them to produce musical tone waveforms 
W.sub.m, W.sub.H and W.sub.L having frequencies corresponding to the note 
F3. However, since the depressed key belongs to a tone range to which keys 
of the notes D.sup..music-sharp. 3 through F3 belong, the code converter 6 
produces a signal S having the value "0", a constant K.sub.1 =3/8, and a 
constant K.sub.2 =1/8, as can be clearly noted from Table I. For this 
reason, the selector 7 selects a musical tone waveform W.sub.L 
corresponding to the low tone range and supplies it to the multiplier 8. 
Then, this multiplier outputs a musical tone waveform 
(W.sub.S).times.(K.sub.1) having an amplitude value expressed by an 
equation 
EQU (W.sub.S).times.(K.sub.1)=W.sub.L .times.(3/8) 
because the constant K.sub.1 is equal to 3/8. 
On the other hand, since the constant K.sub.2 =5/8, the multiplier 9 
produces a musical tone waveform W.sub.m K.sub.2 having an amplitude value 
expressed by an equation 
EQU (W.sub.m).times.(K.sub.2)=W.sub.m .times.(5/8) 
These two musical tone waveforms (W.sub.S).times.(K.sub.1) and 
(W.sub.m).times.(K.sub.2) are added together or synthesized by the adder 
10. Thus, the adder 10 produces a synthesized musical tone waveform W 
whose amplitude value is expressed by an equation 
EQU .SIGMA.W=[(W.sub.L).times.(3/8)]+[(W.sub.m).times.(5/8)] 
More particularly, where the depressed key belongs to a note range of from 
D.sup..music-sharp. 3 to F3, in other words, when the depressed key 
belongs to an intermediate tone range between the reference tone range (C4 
through D4) and the low tone range (C2 through D2), the adder 10 produces 
two musical tone waveforms (W.sub.S).times.(K.sub.1) and 
(W.sub.m).times.(K.sub.2) such that the amplitudes of the musical tone 
waveforms W.sub.m and W.sub.L outputted from the reference tone range 
waveform memory device 3 and the low tone range waveform memory device 5, 
respectively, are controlled by complementary constants K.sub.1 and 
K.sub.2 corresponding to the notes of the depressed keys. Accordingly, the 
musical tone waveform finally outputted would contain the musical tone 
waveform W.sub.m corresponding to the reference tone range, and the 
musical tone waveform W.sub.L corresponding to the low tone range at a 
ratio of 5:3, thereby producing a musical tone having a tone color similar 
to that of a natural musical instrument. This is also true for other tone 
ranges. 
As described above, this embodiment enables production of musical tone 
waveforms having different waveforms in a total of seventeen tone ranges 
with only three waveform memory devices and an arithmetic operation unit 
that interpolates by utilizing the outputs of these waveform memory 
devices based on the notes of the depressed keys, thus producing a musical 
tone having different tone colors in respective tone ranges in a manner 
similar to a natural musical instrument. 
FIG. 2 shows a modified embodiment of the present invention which is 
similar to the embodiment shown in FIG. 1 except as described below. 
In the modified embodiments, the musical tone waveform W.sub.m the note 
range C4 through D4 and to be stored in the reference tone corresponding 
to range memory device 3 is the same as in the embodiment shown in FIG. 1. 
The musical tone waveforms W.sub.H ' and W.sub.L ' in the modified 
embodiment a note range covering notes C6, C2 to D2 and to be respectively 
corresponding to stored in the high tone range waveform memory device 4 
and the low tone range waveform memory device 5 are different from those 
in the first embodiment and are expressed by the following equations. 
EQU W.sub.H '=(W.sub.H -W.sub.m).times.(1/8) 
EQU W.sub.L '=(W.sub.L -W.sub.m).times.(1/8) 
Consequently, the code converter 6 is constructed to produce a signal S and 
a constant K.sub.1 as shown in the following Table V. 
The circuit construction is modified as shown in FIG. 2 such that the 
output W.sub.m of the reference tone range waveform memory device 3 is 
directly applied to the adder 10. 
TABLE V 
______________________________________ 
Tone range Signal S Constant K 
______________________________________ 
C6 1 8 
A5 to B5 1 7 
F.music-sharp.5 to G.music-sharp.5 
1 6 
D.music-sharp.5 to F5 
1 5 
C5 to D5 1 4 
A4 to B4 1 3 
F.music-sharp.4 to G.music-sharp.4 
1 2 
D.music-sharp.4 to F4 
1 1 
C4 to D4 1/0 0 
A3 to B3 0 1 
F.music-sharp.3 to G.music-sharp.3 
0 2 
D.music-sharp.3 to F3 
0 3 
C3 to D3 0 4 
A2 to B2 0 5 
F.music-sharp.2 to G.music-sharp.2 
0 6 
D.music-sharp.2 to F2 
0 7 
C2 to D2 0 8 
______________________________________ 
Thus, with this modification, when a key of the note C6 is depressed, the 
adder 10 produces a musical tone waveform .SIGMA.W expressed by an 
equation 
EQU .SIGMA.W=W.sub.m +(W.sub.S ').times.(K.sub.1)=W.sub.m +8.times.(W.sub.H 
-W.sub.m)/8=W.sub.H. 
When a key belonging to a tone range C2 through D2 is depressed the output 
musical tone waveform .SIGMA.W of the adder 10 is expressed by the 
following equation. 
EQU .SIGMA.W=W.sub.m +(W.sub.S ').times.(K.sub.1)=W.sub.m +8.times.(W.sub.L 
-W.sub.m)/8=W.sub.L. 
When a key belonging to a tone range D.sup..music-sharp. 3 through F3 is 
depressed the musical tone waveform .SIGMA.W outputted from the adder 10 
is expressed by the following equation 
EQU .SIGMA.W=W.sub.m +(W.sub.S ').times.(K.sub.1)=W.sub.m +3.times.(W.sub.L 
-W.sub.m)/8=(5/8).times.(W.sub.m)+(3/8).times.(W.sub.L). 
Thus, in the same manner as in the example shown in FIG. 1, it is possible 
to obtain a musical tone signal having waveforms which differ according to 
the tone range. 
As described above, by storing in the waveform memory devices musical tone 
waveforms corresponding to high and low tone ranges by taking into 
consideration the difference in the amplitude values of these musical tone 
waveforms and of the musical tone waveform corresponding to the reference 
tone range, the capacities of the memory devices can be reduced more or 
less than that of the example shown in FIG. 1. 
In the foregoing examples, the constants K.sub.1 and K.sub.2 that control 
the ratio of interpolation are set to change with three key units. 
However, when they are set to change with a single key unit, a more 
advantageous effect can be obtained. Furthermore, while in the foregoing 
example the tone range of the keyboard was divided with three key units, 
the keyboard can be divided with units including any desired number of 
keys. 
Instead of providing three waveform memory devices, two memory devices can 
be used, one for the high tone range and the other for the low tone range. 
As can be noted from the foregoing description of the present invention, it 
is possible to produce a musical tone having different tone colors for 
tone ranges to which depressed keys belong.