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Claims  |
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What is claimed is:
1. An electronic musical instrument capable of generating a musical tone
having a pitch corresponding to an extracted pitch data from a compressed
input waveform signal, comprising:
conversion means for converting an input waveform signal into a compressed
waveform signal, said conversion means including means for log-converting
said input waveform signal and generating as an out put said compressed
waveform signal, such that the amplification factor of the log-conversion
increases as the level of said input waveform signal is decreased;
A/D converting means coupled to the output of said conversion means for
converting the compressed waveform signal to a digital compressed waveform
signal, said A/D converting means including means for performing an analog
to digital conversion on the compression waveform signal and generating as
an output said digital compressed waveform signal;
pitch extracting means coupled to said A/D converting means for extracting
a pitch of the input wave signal, said pitch extracting means including
means for executing a predetermined digital processing operation on said
digital compressed waveform signal; and
note-on/off control means coupled to said A/D converting means for
controlling note-on/off states of a musical tone to be produced in
accordance with a level of said digital compressed waveform signal.
2. The electronic musical instrument of claim 1, wherein said note-on/off
control means includes means for designating note-on when the level of the
digital compressed waveform signal becomes greater than a predetermined
level.
3. The electronic musical instrument of claim 1, wherein said note-on/off
control means includes means for designating note-off when the level of
the digital compressed waveform signal becomes lower than a predetermined
level.
4. The electronic musical instrument of claim 1, further comprising tone
volume control means for controlling a tone volume of the musical tone in
accordance with a level of the digital compressed waveform signal.
5. The electronic musical instrument of claim 1, wherein said conversion
means converts said input waveform signal into an analog compressed
waveform signal.
6. An electronic apparatus for an electronic musical instrument for
controlling a musical sound to be generated in accordance with a
compressed input waveform signal, comprising:
compression conversion means for converting an input waveform signal into a
compressed input waveform signal, said compression conversion means
including means for performing a predetermined compression conversion on
the input waveform signal and generating as an output of said compressed
input waveform signal, such that the amplification factor of the
predetermined compressed increases as the level of said input waveform
signal is decreased;
A/D converting means coupled to the output of said compression conversion
means for converting the compressed input waveform signal to a digital
compressed waveform signal, said A/D converting means including means for
performing an analog to digital conversion on the compressed input
waveform signal and generating as an output of said digital compressed
waveform signal; and
note-on/off control means coupled to said A/D converting means for
controlling note-on/off states of a musical sound to be generated in
accordance with a level of the digital compressed waveform signal.
7. The electronic apparatus of claim 6, wherein said compression conversion
means includes means for executing a logconversion of the input waveform
signal to obtain the compressed input waveform signal.
8. The electronic apparatus of claim 6, wherein said note-on/off control
means includes means for controlling a note-on operation of the musical
sound when the level of the digital compressed waveform signal becomes
greater than a predetermined level, and for controlling a note-off
operation of the musical sound when the level of the digital compressed
waveform signal becomes lower than the predetermined level.
9. The electronic apparatus of claim 6, further comprising tone volume
control means for controlling a tone volume of the musical sound based on
the level of the digital compressed waveform signal.
10. The electronic apparatus of claim 6, wherein said compression
conversion means converts said input waveform signal into an analog
compressed input waveform signal.
11. An electronic apparatus capable of controlling a musical tone to be
generated in accordance with a compressed input waveform signal,
comprising:
compression conversion means for converting a peak level signal of an input
waveform signal into a compressed peak level signal, said compression
conversion means including means for performing a predetermined
compression conversion on the input waveform signal and generating as an
output said compressed peak level signal, such that the amplification
factor of the predetermined compression conversion increases as the level
of said input waveform signal is decreased;
A/D converting means coupled to the output of said compression conversion
means for converting the compressed peak level signal to a digital
compressed peak level signal, said A/D converting means including means
for performing an analog to digital conversion on the compressed peak
level signal and generating as an output said digital compressed peak
level signal; and
note-on/off control means coupled to said A/D converting means for
controlling note-on/off states of a musical tone to be generated in
accordance with a level of the digital compressed peak level signal.
12. The electronic apparatus of claim 11, wherein said compression
conversion means converts said peak level signal of the input waveform
signal into an analog compressed peak level signal.
13. An electronic apparatus capable of controlling a musical tone to be
generated in accordance with a compressed input waveform signal,
comprising:
compression conversion means for converting a peak level signal of an input
waveform signal into a compressed peak level signal, said compression
conversion means including means for performing a predetermined
compression conversion on the input waveform signal and generating as an
output said compressed peak level signal, such that the amplification
factor of the predetermined compression conversion increases as the level
of said input waveform signal is decreased; and
tone control means coupled to the output of said compression conversion
means for controlling a musical tone to be generated in accordance with
the compressed peak level signal.
14. The electronic apparatus of claim 13, wherein said compression
conversion means includes means for executing a logconversation of the
peak signal to obtain the compressed peak level signal.
15. The electronic apparatus of claim 13, wherein said tone control means
includes means for controlling a note-on/off operation of the musical tone
based on the compressed peak level signal.
16. The electronic apparatus of claim 13, wherein said tone control means
includes means for controlling a tone volume of the musical tone according
to the compressed peak level signal.
17. The electronic apparatus of claim 13, wherein said compression
conversion means converts said peak level signal of the input waveform
signal into an analog compression peak level signal.
18. An electronic apparatus capable of controlling a musical tone to be
generated in accordance with an input waveform signal, comprising:
compression conversion means for converting a level of an input waveform
signal into a compressed level signal, said compression conversion means
including means for performing a predetermined compression conversion on
the input waveform signal and generating as an output said compressed
level signal, such that the amplification factor of the predetermined
compression conversion increases as the level of said input waveform
signal is decreased; and
sound control means coupled to the output of said compression conversion
means for controlling a musical sound to be generated in accordance with
said compressed level signal.
19. The electronic apparatus of claim 18, wherein said compression
conversion means includes means for executing a logconversion of the level
of the input waveform signal to obtain the compressed level signal.
20. The electronic apparatus of claim 18, wherein said sound control means
includes means for controlling a note-on/off operation of the musical
sound in accordance with said compressed level signal.
21. The electronic apparatus of claim 18, wherein said sound control means
includes means for controlling a note-on/off operation of the musical
sound when said compressed level signal becomes greater than a
predetermined level, and for controlling a note-off operation of the
musical sound when said compressed level signal becomes lower than the
predetermined level.
22. The electronic apparatus of claim 18, wherein said sound control means
includes means for controlling a tone volume of the musical tone according
to said compressed level signal.
23. An electronic string musical instrument capable of generating a musical
tone having a pitch corresponding to an extracted pitch data from an input
waveform signal generated by plucking a string, comprising:
log-conversion means for log-converting a peak level signal of the input
waveform signal into a log-converted peak level signal, and including
means for performing a predetermined log conversion on said input waveform
signal, such that the amplification factor of the log-conversion increases
as the level of said input waveform signal is decreased;
A/D converting means coupled to said log-conversion means for converting
the log-converted peak level signal to a digital log-converted peak level
signal, said A/D converting means including means for performing an analog
to digital conversion on the log-converted peak level signal; and
tone control means coupled to said A/D converting means for controlling the
musical tone to be generated in accordance with the digital log-converted
peak level signal.
24. The electronic apparatus of claim 23, wherein said tone control means
includes means for controlling a note-on/off operation of the musical tone
in accordance with the digital log-converted peak level signal.
25. The electronic apparatus of claim 23, wherein said tone control means
includes means for controlling a note-on operation of the musical tone
when the digital log-converted peak level signal becomes greater than a
predetermined level, and for controlling a note-off operation of the
musical tone when the digital log-converted peak level signal becomes
lower than the predetermined level.
26. The electronic apparatus of claim 23, wherein said tone control means
includes means for controlling a tone volume of the musical tone according
to the digital log-converted peak level signal.
27. The electronic apparatus of claim 23, wherein said log-conversion means
converts said peak level signal of the input waveform signal into an
analog log-converted peak level signal. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus for extracting pitch data
from an input waveform signal and an electronic system of a type for
generating a musical tone having a pitch corresponding to extracted pitch
data and, more particularly, to an electronic stringed instrument such as
an electronic guitar or a guitar synthesizer, wherein the reproduced
note-on time is prolonged by compression of an input waveform signal prior
to an analog-to-digital conversion of the input waveform signal.
2. Description of the Related Art
In recent years, various types of electronic systems have been developed to
extract pitch (fundamental frequency) data from a waveform signal
generated in accordance with human varies and/or tones of acoustic musical
instruments and to control a sound source constituted by an electronic
circuit so as to artificially obtain an acoustic effect such as a musical
tone.
The following prior arts disclose the above technique:
U.S. Pat. No. 4,117,757 (issued on Oct. 3, 1978), inventor: Akamatsu,
U.S. Pat. No. 4,606,255 (issued on Aug. 19, 1986), inventors: Hayashi et
al.,
U.S. Pat. No. 4,633,748 (issued on Jan. 6, 1987), inventors: Takashima et
al.,
U.S. Pat. No. 4,688,464 (issued on Aug. 25, 1987), inventors: Gibson et
al.,
Japanese Patent Publication No. 57-37074 (published on Aug. 7, 1982),
applicant Roland Kabushiki Kaisha,
Japanese Patent Publication No. 57-58672 (published on Dec. 10, 1982),
applicant Roland Kabushiki Kaisha,
Japanese Patent Disclosure (Kokai) No. 55-55398 (disclosed on Apr. 23,
1980), applicant: TOSHIBA CORP.,
Japanese Patent Disclosure (Kokai) No. 55-87196 (disclosed on July 1,
1980), applicant: Nippon Gakki Co., Ltd.,
Japanese Patent Disclosure (Kokai) No. 55-159495 (disclosed on Dec. 11,
1980), applicant: Nippon Gakki Co., Ltd.,
Japanese Utility Model Disclosure (Kokai) No. 55-152597 (disclosed on Nov.
4, 1980), applicant: Nippon Gakki Co., Ltd.,
Japanese Utility Model Disclosure (Kokai) No. 55-162132 (disclosed on Nov.
20, 1980), applicant: Keio Giken Kogyo Kabushiki Kaisha,
Japanese Patent Publication No. 61-51793 (published on Nov. 10, 1986),
applicant: Nippon Gakki Co., Ltd., and
Japanese Utility Model Publication No. 62-20871 (published on May 27,
1987), applicant: Fuji Roland Kabushiki Kaisha.
A U.S. patent application disclosing a system relating to the present
invention was filed by Uchiyama et al. as U.S. Ser. No. 112,780 on Oct.
22, 1987.
In these prior arts, in order to extract pitch data from an input waveform
signal, a time interval between two positive peaks, between negative
peaks, or between zero-crossings immediately after these peaks of the
input waveform signal is measured. A circuit for detecting a peak is
generally exemplified by an analog circuit including capacitors and
resistors. It is often difficult to perform good peak detection of the
input waveform signal of the musical instrument due to variations in
circuit components, durability, and deteriorations over time. The peak
detector comprises an analog system which requires a large number of
circuit components, resulting in high cost. It is also inconvenient to
realize easy element mounting. In particular, in an electronic musical
instrument incorporating a sound source circuit, a mounting space must be
minimized. In a conventional circuit arrangement, it is impossible or is
very difficult to obtain a mounting space. When condition parameters are
to be changed for pitch extraction, special circuits must be prepared
every time the parameters are changed. Therefore, it is very difficult to
change such parameters.
Further, in the known art, reliable detection of actual note-on and
note-off play conditions of the instrument can not always be obtained.
Also, a tone desired by a player to be sustained may be attenuated by the
prior apparatus at a timing that is not intended by the player.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an apparatus for
extracting a pitch data from an input waveform signal or an input
apparatus for an electronic system for generating a musical tone
corresponding to the pitch data, wherein a circuit arrangement is simple
and inexpensive, and peak detection can be performed with high precision,
and condition parameters can be easily changed regardless of variations in
circuit components and deteriorations over time.
Another object of the invention is to provide apparatus wherein a
compression of an input waveform signal is performed to obtain a wide
dynamic range and a high-efficiency control of the tone generation
process.
A further object of the invention is to enable a reproduced time period
between detection of a note-on and a note-off condition to be prolonged,
so as to coincide more closely with the actual or intended play of an
instrument when using a constant note-off threshold value.
Another object of the present invention is to prevent a tone generated by a
player from being attenuated at a timing that was not intended by him or
her.
According to the invention, electronic apparatus capable of controlling a
musical sound to be generated in accordance with an input waveform signal,
includes compression conversion means for converting a level of the input
waveform signal into a compressed level signal by performing a
predetermined compression conversion, and sound control means coupled to
the compression conversion means for controlling the musical sound in
accordance with the compressed level signal.
According to another aspect of the invention, electronic apparatus for an
electronic musical instrument for controlling a musical sound to be
generated in accordance with an input waveform signal from the instrument,
includes compression conversion means for converting the input waveform
signal into a compressed input waveform signal by a predetermined
compression conversion, A/D converting means coupled to the compression
conversion means for converting the compressed input waveform signal to a
digital compressed waveform signal by analog-to-digital conversion, and
note-on/off control means coupled to the A/D converting means for
controlling note-on/off states of the sound to be generated in accordance
with a level of the digital compressed waveform signal
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other objects, features, and advantages of the present
invention will be apparent from a preferred embodiment in conjunction with
the accompanying drawings, in which:
FIG. 1 is a diagram showing an overall arrangement of an embodiment of the
present invention;
FIGS. 2A and 2B are diagrams showing a detailed arrangement of a pitch
extraction analog circuit in FIG. 1;
FIG. 3 is a timing chart for explaining the operation of the pitch
extraction analog circuit;
FIG. 4 is a diagram showing a detailed arrangement of a log converter in
FIG. 2B;
FIG. 5 is a graph for explaining characteristics of a log converter in FIG.
4;
FIG. 6 is a timing chart for explaining the operation of the pitch
extraction analog circuit shown in FIGS. 2A and 2B;
FIGS. 7(a) and 7(b) are graphs for explaining the function of the log
converter shown in FIG. 4;
FIG. 8 is a block diagram of a pitch extraction digital circuit shown in
FIG. 1;
FIGS. 9(a) and 9(b) are a diagram and a waveform chart, respectively, of a
peak detector shown in FIG. 8;
FIG. 10 is a diagram showing a detailed arrangement of the peak detector;
FIG. 11 is a timing chart showing the operation of the circuit in FIG. 10;
FIG. 12 is a diagram showing a detailed arrangement of a time constant
conversion control circuit in FIG. 8;
FIG. 13 is a diagram showing a detailed arrangement of a zero-crossing time
receiving circuit in FIG. 8;
FIG. 14 is a diagram showing a detailed arrangement of a peak value
receiving circuit in FIG. 8;
FIG. 15 is a timing chart for explaining the operation of the circuit shown
in FIG. 10;
FIG. 16 is a timing chart for explaining the operation of the time constant
conversion control circuit in FIG. 12;
FIG. 17 is a timing chart for explaining the operation of the circuit shown
in FIG. 13; and
FIGS. 18(a) and 18(b) are timing charts for explaining an operation of the
embodiment in response to an input waveform signal.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
A preferred embodiment of the present invention will be described in detail
with reference to the accompanying drawings. The present invention is
applied to an electronic guitar but can also be applied to electronic
musical instruments of other types or other electronic systems
FIG. 1 is a block diagram showing an overall circuit arrangement. Pitch
extraction analog circuit PA to be described in detail later is arranged
for each of six strings which are kept taut on an electronic guitar body
(not shown). Circuit PA includes a hexa pickup for converting string
vibrations into electrical signals and a converting means such as
analog-to-digital converter A/D (to be described in detail later) for
outputting zero-crossing signals Zi and waveform signals Wi (i=1 to 6) on
the basis of outputs from the pickup and converting these signals into
time-divisional serial zero-crossing signal ZCR and digital output
(time-divisional waveform signal) D1.
Pitch extraction digital circuit PD will be described later. Digital
circuit PD includes peak detector PEDT, time constant conversion control
circuit TCC, peak value receiving circuit PVS, and zero-crossing time
receiving circuit ZTS, as shown in FIG. 8. Digital circuit PD detects the
positive or negative peak value on the basis of zero-crossing signals Zi,
serial zero-crossing signal ZCR, and digital output D1, all of which are
output from pitch extraction analog circuit PA, generates MAXI and MINI
(I=1 to 6) and outputs interrupt signal INT at a zero-crossing to
microcomputer MCP. In addition, pitch extraction digital circuit PD
outputs time information and peak value information at the zero-crossing,
and an instantaneous value of the input waveform signal to microcomputer
MCP through bus BUS. Peak detector PEDT includes a circuit for subtracting
previous peak values and holding a subtracted value.
Microcomputer MCP includes memories (e.g., a ROM and a RAM) and timer T and
controls signals supplied to musical tone generator SOB. Generator SOB
comprises sound source SS, digital-to-analog converter D/A, amplifier AMP,
and loudspeaker SP and generates a musical tone having a pitch designated
by a pitch designation signal for changing a frequency and controlled by
the signals of note-on (tone generation) and note-off (muting) which are
supplied from microcomputer MCP. Interface MIDI (Musical Instrument
Digital Interface) is arranged between the input side of sound source SS
and the microcomputer MCP. In response to address read signal AR, address
decoder DCD outputs string number read signal RDI, time read signal RDj
(j=1 to 6), and MAX and MIN peak read signals RDAI (I=1 to 12) to pitch
extraction digital circuit PD.
FIGS. 2A and 2B are circuit diagrams showing a detailed arrangement of
pitch extraction analog circuit PA in FIG. 1. Input waveform signals
corresponding to the respective strings and output from the hexa pickup
are supplied to input terminals 11 to 16 of low-pass filters (LPFs) 21 to
26, respectively. These signals are amplified, and their high-frequency
components are removed, so that the fundamental waveforms are extracted.
Since a frequency of an output tone of each string falls within a
predetermined two-octave range, these LPFs have different cutoff
frequencies in units of strings.
Outputs from low-pass filters 21 to 26, are supplied as waveform outputs W1
to W6. The outputs from the low-pass filters 21 to 26 are also input to
zero-crossing comparators 31 to 36, respectively, and are compared with a
reference signal, thereby generating zero-crossing signals Z1 to Z6.
Zero-crossing signals Z1 to Z6 are input to an input section of
zero-crossing parallel-to-serial converter 4 comprising AND gates a1 to a6
and OR gate .phi.1. More specifically, signals Z1 to Z6 are respectively
input to AND gates al to a6 which are sequentially enabled in response to
pulses .phi.1 to .phi.6 (to be described later), so that signals Z1 to Z6
are converted into serial zero-crossing signal ZCR. In this case,
converter 4 outputs serial zero-crossing signal ZCR of logic "1" if values
of signals Z1 to Z6 are positive. However, converter 4 outputs serial
zero-crossing signal ZCR of logic "0" if the values of signals Z1 to Z6
are negative.
Waveform outputs W1 to W6 from low-pass filters 21 to 26 are input to the
input section of analog parallelserial converter 5, i.e., analog gates g1
to g6. Analog gates g1 to g6 are sequentially enabled in response to
pulses .phi.1 to .phi.6, so that outputs W1 to W6 are converted into an
analog serial signal. In this case, gates g1 to g6 are enabled when pulses
.phi.1 to .phi.6 are set at high level. However, analog gates g1 to g6 are
disabled when pulses .phi.1 to .phi.6 are set at low level. An output from
converter 5 is input to inverting amplifier (OPl) 6 connected to resistors
r1 and r2. The positive and negative waveforms are converted into positive
waveforms. More specifically, serial zero-crossing signal ZCR from
converter 4 is directly input to analog gate g7 and to the gate terminal
of analog gate g8 through inverter il. An output from inverting amplifier
6 is input to the input terminal of analog gate g8. Therefore, the output
from analog gate g8 always has a positive value. Analog gate g7 is enabled
in response to serial zero-crossing signal ZCR of logic " 1", and outputs
from analog gates g1 to g6 are gated to the output terminal. Therefore,
the output signals always have positive values.
Outputs from analog gates g7 and g8 are input to log converter 7. The
waveform data is log-converted by log converter 7 into compressed data.
Necessary memory bits are eliminated. An output from log converter 7 is
converted into digital output D1 by analog-to-digital converter (to be
referred to as an A/D converter hereinafter) 8 in accordance with a
logical state of A/D conversion clock signal ADCK.
FIG. 3 is a timing chart for explaining the operation of pitch extraction
analog circuit PA in FIG. 2. Sequential pulses .phi.1 to .phi.6 are output
from timing generator TG (FIG. 8) (to be described later) and are
generated in order upon every interval corresponding to two periods of A/D
conversion clock signal ADCK. Serial zero-crossing signal ZCR generated in
response to pulses .phi.1 to .phi.6 represents a zero-crossing of each
string. Digital output D1 represents peak values (the polarity is inverted
to obtain a positive value) of each string Digital output D1 is delayed by
a conversion time of A/D converter 8 from sequential pulses .phi.1 to
.phi.6. This delay time can be corrected in a manner to be described
later. Referring to FIG. 3, reference symbols Q5 and M05 denote timing
signals output from pitch extraction digital circuit PD shown in FIG. 8,
and functions of these signals will be described later.
FIG. 4 is a circuit diagram showing a detailed arrangement of log converter
7 in pitch extraction analog circuit PA shown in FIGS. 2A and 2B. Log
converter 7 comprises a four-polygonal approximation log converter but is
not limited thereto.
Log converter 7 comprises inverting amplifiers OP3 and OP4, transistors T1,
T2, and T3, and resistors R0, R0, R1, R2, R3, R4, R, R, R/2, and R/4.
Resistances of resistors R2 to R4 are determined to obtain voltage VOUT
below:
R2=(1/2)VDD-0.6v
R3=(3/4)VDD-0.6v
R4=(7/8)VDD-0.6v
With this arrangement,
(1) If condition VOUT<(1/2)VDD is established, transistors T1 to T3 are
kept off. In this case, gain A can be calculated to be 4 according to the
following equation:
A=VOUT/VIN=R/(R/4)=4
(2) If condition (1/2)VDD<VOUT<(3/4)VDD is established, transistors T2 and
T3 are kept off. However, since the emitter voltage vs. base voltage of
transistor T1 exceeds -0.6v, transistor T1 is turned on. Most of the
emitter current flows in the collector. For this reason, a feedback
resistance of second inverting amplifier OP4 is given as R/2. Gain A is
reduced into 1/2 that of case (1), i.e., 2 as follows:
A=[1/(1/R+1/R)]/(R/4)=2
(3) If condition (3/4)VDD<VOUT<(7/8)VDD is established, transistors T1 and
T2 are turned on while transistor T3 is kept off. In this case, gain A can
be calculated to be 1 according to the following equation:
A=[1/(1/R+1/R+2/R)]/(R/4)=1
(4) If condition (7/8)VDD<VOUT is established, transistors T1 to T3 are
turned on. Gain A can be calculated to be 0.5 according to the following
equation:
A=[1/(1/R+1/R+2/R+4/R)]/(R/4)=0.5
FIG. 5 is a graph of characteristics showing the relationship between input
voltage VIN and output voltage VOUT in log converter 7 arranged as shown
in FIG. 4.
FIG. 6 is a timing chart showing sequential pulse .phi.1, waveform output
W1, input voltage VIN of log converter 7, output voltage VOUT, and serial
zero-crossing signal ZCR in the arrangement of FIGS. 2A and 2B when the
first string is picked. As is apparent from FIG. 6, data is log-compressed
by log converter 7 to reduce the number of bits.
FIGS. 7(a) and 7(b) show string vibration envelopes before and after
conversion in log converter 7. When the string vibration envelope shown in
FIG. 7(a) is input to log converter 7, the envelope shown in FIG. 7(b) can
be obtained. Attention should be paid for a note-on time. When the
waveform shown in FIG. 7(a) is converted by A/D converter 8 to obtain a
note-off region having a value below a given threshold value, the note-on
time is short. However, when a note-off operation is performed with the
threshold value after the log conversion, as shown in FIG. 7(b), the
note-on time can be prolonged. Therefore, tone generation control can cope
with an abrupt attenuation in string vibration in this embodiment.
Log converter 7 is not arranged in pitch extraction digital circuit PD,
i.e., log conversion is not performed in the digital circuit. Log
converter 7 is arranged in pitch extraction analog circuit PA to perform
log conversion in the analog circuit due to the following reason. For
example, assume that A/D converter 8 comprises an 8-bit converter and a
note-off threshold value in FIG. 7(b) is 3. In order to prolong the
note-on time in FIG. 7(a) as in FIG. 7(b), a threshold value must be set
to be 3/4=0.75. This threshold value cannot be set without replacing the
A/D converter. It is possible to perform the above setting if a 10-bit
converter having the number of bits larger than the currently used
converter by 2 bits is used. However, a circuit arrangement becomes
expensive by an increase in cost of the converter.
Due to the compression operation on the input analog waveform as described
above in connection with FIGS. 4 to 7(a) and 7(b), the "relative off"
process is simplified. The relative off processing is that processing
wherein if the level of string vibration, obtained when the player removes
his or her fingers from the strings, i.e., the difference between a
previously-detected peak value and a currently-detected peak value is
greater than a predetermined value (that is, if the currently-detected
value is considerably reduced), an operation corresponding to a note-off
condition is considered to have been performed by the player, and note-off
signal processing is then carrier out. In reality, however, the envelope
of the vibration-waveform rapidly attenuates at the start of string
vibration, and thereafter slowly attenuates as is shown in FIG. 7(a).
Thus, it is necessary to increase the level of the predetermined
difference value (before any conversion, such as a log conversion of the
waveform is performed) at the start of the string vibration, and to
decrease it gradually thereafter. Unless the mentioned predetermined value
is varied, the relativeoff processing will be carried out even in a case
where the generated tone attenuates naturally. To prevent this problem, in
the presently claimed apparatus, the relative-off processing is carried
out after a waveform is subjected to a conversion, such as log conversion,
whereby the envelope of the vibration waveform is changed as shown in FIG.
7(b). This eliminates the need to vary the predetermined value, mentioned
above, in accordance with the natural change of the vibration waveform.
Furthermore, relative-on processing, as is performed in the case of playing
instrument strings in a tremolo-touch manner, is also simplified. If,
during the relative-on processing, the difference between a
previously-detected peak value and a currently-detected peak value is
greater than a predetermined value (i.e., if the currently-detected peak
value is considerably reduced), an operation corresponding to
tone-regeneration is regarded as having been carried out by the player,
with the result that note-on processing will again be performed. In the
case of using the actual waveform, a problem occurs in that the
abovementioned predetermined value must be varied in accordance with the
level change of the waveform. For example, when a peak value is increased,
the predetermined value must also be increased by a corresponding amount.
To eliminate this need, a waveform, after being subjected to a conversion
such as log conversion, is used in the present apparatus with the result
that the relative-on processing can be performed without having to vary
the predetermined value.
Moreover, it is not necessary with the present apparatus to vary the
threshold level in accordance with the level of the peak value, when a
currently detected peak value is compared with previously-detected peak
value for such processing as resonance elimination processing or harmonic
elimination processing.
According to the arrangement of FIGS. 4 to 7(a) and (b), a
rapidly-attenuating input waveform is processed by th | | |
