Overdubbing apparatus for electronic musical instrument

A tone generation control unit has four waveform read/write channels for selectively reading or writing data in a waveform memory. A plurality of waveform signals stored in the waveform memory are converted into analog signals to be subjected to timbre and tone volume control through voltage-controlled filters and voltage-controlled amplifiers before being fed to a mixing adder. An output signal of the mixing adder is converted into a digital signal which is stored in the waveform memory again through processing of the tone generation control unit.

BACKGROUND OF THE INVENTION 
This invention relates to an electronic musical instrument, in which 
external acoustic signals are recorded in a digital form and sounded at 
desired pitches, and more particularly, to an overdubbing apparatus for 
such an electronic musical instrument, which is capable of superimposing 
and recording a plurality of previously stored acoustic signals as another 
tone signal. 
Heretofore, it has been in practice to store externally applied acoustic 
signals of musical sounds of musical instruments such as piano, violin, 
etc. or voices of birds in a memory in a digital form through a proper 
modulation system, e.g., PCM (pulse coded modulation) and read out the 
stored signals from the memory as tone signals of a keyboard musical 
instrument. 
Copending U.S. patent applications Ser. Nos. 760,290 and 760,291 both filed 
July 29, 1985 and assigned to the same assignee as this application 
disclose a musical instrument of such a type as described above. The '290 
application issued as U.S. Pat. No. 4,681,008 on July 21, 1987, and the 
'291 application issued as U.S. Pat. No. 4,667,556 on May 26, 1987. 
This type of keyboard musical instrument or apparatus, which is called 
sampling machine, because of a sampling function, may be designed to have 
an overdubbing function, i.e., a function of superimposing a plurality of 
previously recorded acoustic signals to produce a separate tone signal. 
None of such apparatuses with overdubbing function, however, has yet been 
put into practice. 
SUMMARY OF THE INVENTION 
An object of the invention is to provide an electronic musical instrument 
having an overdubbing function. 
Another object of the invention is to provide an overdubbing apparatus for 
an electronic musical instrument, which is simple in construction and 
operation and provides pleasant musical performance. 
According to the invention, there is provided an electronic musical 
instrument, in which a waveform signal is recorded in the form of a 
digital signal in a waveform memory and the digital signal recorded in the 
waveform memory is converted into a tone signal having a designated pitch, 
and which comprises control means including a plurality of waveform 
read/write channels, processing means for reading out a plurality of 
digital signals from the waveform memory through at least two of the 
waveform read/write channels of the control means and subjecting the 
read-out digital signals to a predetermined processing, synthesizing means 
for combining a plurality of waveform signals obtained through the 
processing means, and means for supplying the mixed waveform signal 
obtained from the synthesizing means to the control means and storing 
digital signal in the waveform memory through a predetermined one of the 
waveform read/write channels.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Now, the invention will be described in conjunction with an embodiment 
thereof illustrated in the drawings. FIG. 1 shows the circuit construction 
of the embodiment. An input signal IN which is supplied through a 
microphone or the like, is amplified by an input amplifier 1 and then fed 
to an analog adder 2. An output signal of analog adder 2 is fed through a 
filter 3 to a sample/hold (S/H) circuit 5 to be sampled at a proper 
sampling frequency. An output signal of S/H circuit 5 is fed to an 
analog-to-digital (A/D) converter 6. A/D converter 6 converts the input 
analog signal into a corresponding digital signal which is fed to a tone 
generation control unit 8. 
Tone generation control unit 8 has, for example, four waveform read/write 
channels. These waveform read/write channels can independently access 
waveform memory 7 to write or read waveform signals. Tone generation 
control unit 8 may be configured as disclosed in the above-mentioned 
copending application Ser. No. 760,291 (now U.S. Pat. No. 4,667,556). For 
a better understanding of this invention, it will be described later in 
detail with reference to FIG. 3. 
Tone generation control unit 8 operates under control of CPU 9 comprised of 
a microcomputer or the like. Tone generation control unit 8 reads out from 
wavefrom memory 7 digital signals corresponding to at most four tones on a 
time-division basis via the four waveform read/write channels, and feeds 
the read out digital signals on a time-division basis to a 
digital-to-analog (D/A) converter 10. Analog signals of D/A converter 10 
are fed to S/H circuits 11a to 11d. 
S/H circuits 11a to 11d sample corresponding analog signals during 
respective periods under control of timing signals t1 to t4 generated from 
a timing generator 20. 
S/H circuits 11a to 11d feed their respective hold voltage signals to 
voltage controlled filters (VCFs) 12a to 12d, respectively. VCFs 12a to 
12d filter input signals according to respective voltage signals FCV1 to 
FCV4. 
VCFs 12a to 12d feed filtered analog waveform signals to voltage controlled 
amplifiers (VCAs) 13a to 13d. 
VCAs 13a to 13d have their gain controlled independently according to 
control voltage signals ACV1 to ACV4 applied thereto to determine the 
output level or envelope of the waveform signals. 
The output signals of VCAs 13a to 13d are fed as respective channel output 
signals OUT1 to OUT4 to be suitably amplified and sounded. The output 
signals of VCAs 13a to 13d are also mixed in an analog adder 14, an output 
signal of which may be output as mixed output OUT MIX. 
The output signal of VCF 12d corresponding to the fourth channel and the 
output signal of analog adder 14 are fed to an analog switch 15, which is 
switched under control of CPU 9. 
Analog switch 15 thus selects one of the output signal of VCF 12d and 
output signal of analog adder 14 to be applied to VCA 16. VCA 16 amplifies 
the input signal according to a control voltage signal ACV0 for feedback 
to analog adder 2. 
Thus, an external signal supplied to input amplifier 1 and a waveform 
signal read out from waveform memory 7 can be mixed in analog adder 2 and 
then stored again in waveform memory 7. 
Reference numeral 4 in FIG. 1 designates a keyboard having play keys 
corresponding to respective musical notes and various control switches and 
a liquid crystal display panel or the like for displaying various states 
of a musical instrument. The keyboard and display are coupled to CPU 9 for 
data transmission. 
FIG. 2 shows the construction of an essential part of keyboard/display 4. 
Tone switches 41 to 44 are provided to designate four different tone 
numbers. Display elements 41a to 44a consisting of LEDs are provided to 
display tone numbers designated by tone switches 41 to 44. 
Reference numeral 45 in FIG. 2 designates a record switch. Display element 
45a is lit in response to the operation of record switch 45. Reference 
numeral 46 designates an overdubbing switch for designating an overdubbing 
mode. Display element 46a is lit in response to the operation of 
overdubbing switch 46. Reference numeral 47 designates a trigger switch 
for providing a trigger signal. Display element 47a is lit in response to 
the operation of trigger switch 47. A procedure of operation of switches 
45 to 47 will be described later. 
Keyboad/display 4 also has a display 48 consisting of a liquid crystal dot 
matrix display panel as noted above. Display 48 displays the state of 
various switches and operation mode in characters. In FIG. 2, an example 
of display representing a certain state is shown, and the meaning of the 
display will be described later. 
CPU 9 in FIG. 1 is programmed to feed digital signals to D/A converters 17 
for providing voltage signals which serve as control signals FCV1 to FCV4, 
ACV1 to ACV4 and ACV0 noted above (these signals being generally referred 
to as control signal CV). 
D/A converter group 17 may consist of a plurality of D/A converters 
corresponding in number to the number of control signals CV. 
Alternatively, a single D/A converter may be used on a time division basis 
to obtain the control signals CV. 
The circuit construction of tone generation control unit 8 will now be 
described with reference to FIG. 3. 
A digital signal representing a waveform from A/D converter 6 is fed 
through gate 81 to waveform memory 7 and also fed through gate 82 to D/A 
converter 10. A gate 81 is controlled by a read/write signal R/W which is 
fed from an internal control circuit 80 of tone generation control unit 8 
in response to a control command from CPU 9. Gate 81 is enabled or open 
when a waveform signal is written into waveform memory 7. Gate 81 is 
disabled or closed when a waveform signal is read out from waveform memory 
7. Actually, gate 81 is controlled by a signal R/W which is obtained by 
inverting the read/write signal R/W. 
Gate 82 is supplied with a gate signal GATE which is provided from a gate 
signal generator 83 responsive to a control signal from control circuit 
80. Gate 82 is enabled only when a digital signal supplied through gate 81 
is output or a digital signal read out from waveform memory 7 is output. 
Reference numeral 84 in FIG. 3 designates an address shift register having 
four stages (corresponding to the four channels) each consisting of a 
predetermined number of bits. The shift operation of address register 84 
is performed by master clock .phi..sub.s to be described later which is 
provided from a timing generator 20. Address register 84 operates on a 
time division basis as a 4-channel address register. Data in its last 
stage is fed as address data to waveform memory 7. When read/write signal 
R/W is low, a waveform signal fed through gate 81 is written into a memory 
location designated by the address data. When read/write signal R/W is 
high, a digital signal is read out from the memory location. Data of 
address register 84 is fed to gate 85, gate signal generator 83 and 
control circuit 80. The address signal is fed through gate 85 to adder 86, 
which performs an addition or subtraction operation for address updating. 
The output of adder 86 is fed back to address register 84. Initial address 
CA is fed from control circuit 80 through gate 87 to adder 86. 
More specifically, a load signal LD is fed directly to gate 85, while it is 
fed through inverter 88 to gate 87. When load signal LD is low, initial 
address CA from control circuit 80 is fed through gate 87 to adder 86. 
When the load signal is high, on the other hand, gate 85 is enabled, and 
the data in the last stage of address register 84 is fed to adder 86. 
Clock signal CK is fed from clock generator 89 to adder 86. When a digital 
signal is read out from waveform memory 7 at a tone pitch frequency, a 
clock signal is fed to adder 86 at a rate corresponding to pitch data from 
control circuit 80. When digital data is written into waveform memory 7, a 
clock signal is generated at a rate of the sampling frequency to effect 
address updating. 
The operation of the embodiment will now described. FIGS. 4A to 4F are 
timing charts of the time division processing of the individual channels 
of tone generation control unit 8 and timing signals t1 to t4 fed to S/H 
circuits 11a to 11d. As noted above, in this embodiment the four waveform 
read/write channels are realized by a time division arrangement as 
depicted in FIG. 4A, and either read operation or write operation is 
selectively designated independently for each waveform read/write channel. 
In an example shown in FIG. 4 (B), in case of channel 1 (ch1) a waveform 
signal obtained through filter 3, S/H circuit 5 and A/D converter 6 is 
written in waveform memory 7, while in cases of the other channels 2 to 4 
(ch2 to ch4) digital waveform signals are read out from predetermined 
areas of waveform memory 7. 
Timing signals t1 to t4 shown in FIG. 4 (C) through (F) go high during 
periods corresponding to the respective channels (ch1 to ch4). During the 
respective channel times analog waveform signals provided from D/A 
converter 10 are sampled and held in S/H circuits 11a to 11d. 
FIG. 5 shows divided areas of waveform memory 7. For example, N different 
waveform signals having variable length can be stored. Each waveform 
read/write channel of tone generation control unit 8 can independently 
designate a read/write memory area. For example, in the cases of channels 
2 to 4, tone data 1 to 3 shown in FIG. 5 are read out to be fed through 
VCFs 12b to 12d, VCAs 13b to 13d, analog adder 14, switch 15 and VC16 to 
analog adder 2 and then mixed with an external sound signal, if necessary. 
The output signal of adder 2 is stored in waveform memory 7 as tone data N 
in accordance with processing of channel 1. It is to be noted that it is 
possible to effect overdubbing. 
Further, it is possible that CPU 9 switches analog switch 15 to apply a 
waveform signal read out from waveform memory 7, in accordance with the 
processing of channel 4, through S/H circuit 11d, VCF 12d and VCA 16 to 
analog adder 2 for mixing with an external sound signal before being 
written in a predetermined area of waveform memory 7 in the manner as 
described above. 
Now, processing made mainly by CPU 9 in the overdubbing mode will be 
described in detail with reference to the flow chart of FIG. 6. 
The overdubbing mode is designated by overdubbing switch 46 in 
keyboard/display 4. In step S1, CPU 9 checks as to whether a keyboard 
operation or switch operation is done in keyboard/display 4 to determine a 
waveform signal to be read out from waveform memory 7 and a note pitch 
thereof. 
In this embodiment, the pitch of a tone to be generated is designated by a 
corresponding performance key on the keyboard. The waveform signal stored 
in waveform memory 7 is read out at a high readout rate when a high tone 
pitch note is designated while it is read out at a low read out rate when 
a low tone pitch note is designated. In other words, pitch data applied to 
clock generator 89 corresponds to the designated note. 
In step S1, when it is detected that there is a key input, a decision "Yes" 
is yielded, and the routine goes to step S2. In step S2, CPU 9 stores the 
number of tone data to be read out from waveform memory 7 as designated by 
keyboard/display 4. CPU 9 also stores a note designated by key operation. 
Further, CPU 9 stores data for determining a corresponding tone volume. 
The tone volume are set by operating numeral keys and up/down keys 
provided on keyboard/display 4. The routine then goes to step S3. 
For example, tone switch 42 is operated to designate tone 2, and thus 
display element 42a flickers. Then, the key corresponding to note C3# is 
operated on the keyboard and the tone volume is set to a level of "56" by 
the tone volume setter. 
In step S3, the tone number is indicated by display element 42a and the 
note of C3# and the tone volume level of "56" are visually displayed on 
display unit 48. FIG. 2 shows such a state as described above on the 
display panel 48. 
The routine then goes to step S4 for checking as to whether trigger switch 
47 is on. If trigger switch 47 is not on, the routine goes back to step 
S1. In case where tone switch 43 designating tone 3 is operated, the key 
of note C4# is operated on the keyboard, and the tone volume is set to 
level "50", a similar display is obtained through steps S2 and S3. 
At this time, if a different note is designated on the keyboard while 
designating the same tone number, this state is indicated by display 
elements 41a to 44a and display unit 48. 
Finally, the stored digital signals and externally supplied signals, if 
any, are combined to designate a tone number to be set. If tone switch 44 
is operated while operating record switch 45, then, in the above example, 
the sound of tone 2 is reproduced at the pitch of note C3# and tone volume 
of level "56", and the waveform signals of tones 2 and 3 are synthesized 
to be recorded as tone 4 in waveform memory 7. At the time of operation of 
record switch 45 display elements 42a and 43a are turned on and display 
element 44a is caused to flicker, thus indicating the tone number of the 
tone being reproduced and the tone number of the tone being recorded. 
Step S4 is also executed if the check of step S1 yields "No". In step S4, a 
check is done as to whether a trigger signal for starting actual recording 
is supplied from keyboard/display 4. If no trigger signal has been 
provided yet, the routine goes back to step S1. Subsequently, steps S1 and 
S4 or steps S1 through S4 are repeatedly executed in a standby state. 
When a plurality of keys are operated on the keyboard, up to three 
different notes can be allotted to channels 2 to 4. When different tone 
numbers are designated in the individual channels, waveform signals of 
different timbres are reproduced with the designated notes. When the same 
tone number is designated in the individual channels, a waveform signal of 
the same timbre is reproduced with different designated pitches. The 
reproduced signals are overdubbed with different tone volumes. 
If it is detected in step S4 that there is a trigger input from trigger 
switch 47, the routine goes to step S5. Alternatively, it may be arranged 
such that when the input signal IN exceeds a predetermined level, a 
trigger input is given to CPU 9, causing the routine to go to step S5 
automatically. 
In step S5, CPU 9 feeds the saved tone number and note data to tone 
generation control unit 8 and designates the area and note of waveform 
data to be read out from waveform memory 7 in the individual waveform 
read/write channels. 
In subsequent step S6, CPU 9 supplies D/A converter group 17 with digital 
signals for generating control signals corresponding to the levels set in 
keyboard/display 4. Thus, voltage control signals CV are generated and 
applied to VCFs 12a to 12d, VCAs 13a to 13d and VCA 16. 
Further, CPU 9 feeds a switching signal to analog switch 15 to feed the 
mixed waveform signal from adder 14 to VCA 16. The routine then goes to 
step S7, in which CPU 9 starts actual recording using channel 1. At this 
time, the designated channels among channels 2 to 4 operate to read out 
waveform data of acoustic signals, which have already been determined, 
from waveform memory 7. 
When the input processing is over, an end state is brought about, whereupon 
CPU 9 returns to process a main routine (not shown). 
As has been shown, with the above embodiment tone generation control unit 8 
is provided with four waveform read/write channels for independently 
reading and writing waveform signals, and the same digital signal or 
different digital signals are read out from the waveform memory through at 
least two channels, the read-out digital signal or signals being subjected 
to independent timbre and tone volume control through VCFa 12a to 12d and 
VCAs 13a to 13d, the output signals of which are mixed to be written as a 
new tone signal in waveform memory 7 using a particular channel. Thus, it 
is possible to fulfil the overdubbing function and provide pleasant 
musical effects. 
In addition, waveform data can be read out from waveform memory 7 using at 
most three of the four waveform read/write channels, and this reproduced 
waveform data may be combined, if necessary, with input waveform signal IN 
to produce tone waveform data. Thus, it is possible to provide various 
forms of overdubbing. 
Further, waveform memory 7 can be divided into a plurality of areas, and a 
waveform signal obtained as a result of overdubbing may be written in an 
area different from the area where the original waveform signal is 
recorded. Thus, it is possible to obtain overdubbing without erasing the 
original waveform signal. 
Further, for waveform signals read out from waveform memory 7 through a 
plurality of waveform read/write channels the tone volume level may be set 
independently using VCAs 13a to 13d. 
Further the same waveform data may be read out from the same memory area 
through a plurality of waveform read/write channels at different note 
pitches, and the resultant data may be combined while varying the mixing 
ratio through VCAs 13a to 13d. 
Further, in the above embodiment the tone number, note and tone volume are 
displayed by display elements 41a to 44a and display unit 48, which 
promotes the efficiency of the overdubbing process and improves the 
operability. 
Further, in the above embodiment the timbre and tone volume are controlled 
through VCFs 12a to 12d and VCAs 13a to 13d. However, it is also possible 
to use digital filters or digital multipliers for the control of the 
timbre, tone volume, envelope, etc. Further, other processings may be 
applied to the waveform signal. Further, other systems than PCM may be 
employed as the modulation system for digitalizing the waveform signal. 
Further, in the above embodiment the tone generation control unit 8 is 
provided with a plurality of waveform read/write channels constructed by a 
time division arrangement. However, it is also possible to provide a 
plurality of waveform read/write channels by using separate hardware of 
like circuit construction for each channel. 
Further, only particular channels among a plurality of channels may be made 
exclusive write channels for only writing waveform signal in waveform 
memory 7, while the other channels are made exclusive read channels for 
only reading out waveform signal form waveform memory 7. The "waveform 
read/write channel" according to the invention means a channel which is 
capable of both read and write operations or only either read or write 
operation. 
Further, in the above embodiment the tone number of the tone to be 
overdubbed is indicated by display elements 41a to 44a which are provided 
separately of display unit 48. However, it is possible to display such 
data on a single display unit. 
Furthermore, while in the above embodiment only the tone volume is 
displayed, it is also possible to provide a display concerning a timbre, 
e.g., a filter cut-off frequency, which will be more convenient to the 
performer. 
In summary, according to the invention it is possible to provide an 
overdubbing apparatus for an electronic musical instrument, which is 
convenient to use, has high operability and provides pleasant musical 
effects.