 |
Description  |
|
|
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a control apparatus for an electronic
musical instrument for generating a musical tone based on an input
waveform signal.
2. Description of the Related Art
More specifically, the present invention relates to an electronic stringed
instrument such as an electronic guitar, a guitar synthesizer, or the
like, or other synthesizer type electronic musical instruments and, more
particularly, to a control apparatus for an electronic musical instrument
which changes the timbre of an output musical tone in accordance with a
music performing manner.
Recently, various electronic musical instruments are known wherein a pitch
(fundamental frequency) is extracted from an acoustic wave generated
according to a human voice or the performance of a conventional musical
instrument, and a sound source device comprising an electronic circuit is
controlled to artificially produce an acoustic sound such as a musical
note.
The following publications disclose such a technique:
(a) U.S. Pat. No. 4,117,757 (issued on Oct. 3, 1978), inventor: Akamatsu.
This patent discloses an electronic circuit for forming a waveform signal
in which "1" and "0" sequentially are inverted at positive and negative
peak points of and input waveform signal. This waveform signal is
converted to a rectangular wave signal, and its frequency corresponds to a
pitch of the input waveform signal.
(b) U.S. Pat. No. 4,606,255 (issued on Aug. 19, 1986), inventor: Hayashi et
al.
This patent discloses a guitar synthesizer. A pitch is extracted for each
string to obtain a corresponding voltage signal, and a musical tone signal
is generated by voltage control.
(c) U.S. Pat. No. 4,644,748 (issued on Jan. 6, 1987), inventor: Takashima
et al.
This patent discloses a technique for converting an acoustic signal input
through a microphone into a digital signal, and extracting a pitch by
digital processing.
(d) U.S. Pat. No. 4,688,464 (issued on Aug. 25, 1987), inventor: Gibson et
al.
This patent discloses a technique for extracting a pitch in accordance with
time intervals crossing three threshold levels, i.e., high, middle, and
low threshold levels of an input waveform signal.
(e) Japanese Patent Publication No. 57-37074 (published on Aug. 7, 1982),
applicant: Roland Kabushiki Kaisha.
(f) Japanese Patent Publication No. 57-58672 (published on Dec. 10, 1982),
applicant: Roland Kabushiki Kaisha.
The contents of these two patents correspond to the above-mentioned patent
(a), U.S. Pat. No. 4,117,757, and disclose techniques for generating a
rectangular wave having a frequency corresponding to a pitch of an input
waveform signal.
(g) Japanese Patent Disclosure (Kokai) No. 55-55398 (disclosed on Apr. 23,
1980), applicant: Toshiba Corp.
This patent application discloses a technique for generating a rectangular
wave having a frequency corresponding to a pitch of an input waveform
signal as in the patent (a), U.S. Pat. No. 4,117,757.
(h) Japanese Patent Disclosure (Kokai) No. 55-87196 (disclosed on July 1,
1980), applicant: Nippon Gakki Seizo Kabushiki Kaisha.
This prior-art invention discloses a technique for generating a fundamental
wave pulse having a period corresponding to a pitch in accordance with an
output from a pickup of a guitar, counting the pulse by an interval
counter to obtain period data, and converting the period data into digital
frequency data.
(i) Japanese Patent Disclosure (Kokai) No. 55-15949 (disclosed on Dec. 11,
1980), applicant: Nippon Gakki Seizo Kabushiki Kaisha.
This prior-art invention discloses a technique wherein when an extracted
pitch is not varied, a musical tone is generated. When two adjacent
periods substantially coincide with each other, a coincidence signal is
generated, and tone generation is started in accordance with the
coincidence signal.
(j) Japanese Utility Model Disclosure (Kokai) No. 55-152597 (disclosed on
Nov. 4, 1980), applicant: Nippon Gakki Seizo Kabushiki Kaisha.
This prior-art device discloses a technique wherein a vibration of a string
is extracted by an optical pickup, and the vibration of the string is
excited by a picked-up signal to obtain a vibration sustain effect.
(k) Japanese Utility Model Disclosure (Kokai) No. 55-162132 (disclosed on
Nov. 20, 1980), applicant: Keio Gikken Kougyo Kabushiki Kaisha.
This prior-art device discloses a technique wherein a detector detects a
next zero-cross point of positive and negative peak points of an input
waveform signal, and a flip-flop is set/reset in response to each point
detection to generate a frequency signal corresponding to a pitch.
(l) Japanese Patent Publication No. 61-51793 (published on Nov. 10, 1986),
applicant: Nippon Gakki Seizo Kabushiki Kaisha.
This patent is a publication of the invention (h) above, and has the same
gist as the content of the invention (i) above. That is, digital frequency
data is generated upon detection of a substantial coincidence between two
adjacent periods.
(m) Japanese Utility Model Publication No. 62-20871 (published on May 27,
1987), applicant: Fuji Roland Kabushiki Kaisha.
This is a Japanese publication corresponding to the invention (b), U.S.
Pat. No. 4,606,255.
(n) Japanese Patent Disclosure (Kokai) No. 61-26090 (disclosed on Feb. 5,
1986), applicant: Seikou Denshi Kougyo Kabushiki Kaisha.
This prior-art invention discloses a technique for detecting a pitch from
an input waveform signal, sequentially writing the detected pitch in a
memory, and obtaining accurate pitch data later by executing an arithmetic
operation.
(o) Japanese Patent Disclosure (Kokai) No. 62-163099 (disclosed on July 18,
1987), applicant: Fuji Gen Gakki Seizo Kabushiki Kaisha.
This prior-art invention relates to a guitar controller for a guitar
synthesizer, wherein frequency changing methods are switched in accordance
with monophonic or polyphonic tones generated. More specifically, when a
monophonic tone is generated, a picked-up vibration period is continuously
reflected to determine the frequency of the musical sound to be generated.
When a polyphonic tone is generated, the vibration period is reflected at
chromatic scale steps to determine the same.
Furthermore, the following U.S. patent applications disclose an electronic
stringed instrument and the associated electronic equipment are related to
the present invention assigned: to the present assignee.
(p) U.S. Ser. No. 112,780 (filed on Oct. 22, 1987), inventor: Uchiyama et
al.
This prior-art invention discloses a technique for measuring a time period
between positive and negative peak points or between zero-cross points
associated with these peak points to extract a pitch of an input waveform
signal based on the measured time period, and a technique for performing
various control operations in accordance with the obtained pitch.
(q) U.S. Ser. No. 184,099 (filed on Apr. 20, 1988), inventor: Iba et al.
In this prior-art invention, a musical tone parameter such as a timbre is
designated by a fret operation and a picking operation of a string. In
order to detect an operated fret, a pitch extraction technique, or a fret
switch detection technique is used.
(r) U.S. Ser. No. 256,398 (filed on Oct. 7, 1988), inventor: Iba et al.
This prior-art invention discloses a technique for performing musical tone
generation control in units of strings, changing characteristics of an
output musical tone in accordance with the picking strength of a string,
or controlling an effector or pan (sound localization).
(s) U.S. Ser. No. 252,914 (filed on Oct. 3, 1988), inventor: Uchiyama
In this prior-art invention, a pitch extraction circuit comprises a digital
circuit in place of a conventional analog circuit, and integration of the
electronic circuit can be facilitated.
(t) U.S. Ser. No. 256,400 (filed on Oct. 11, 1988), inventor: Matsumoto
This prior-art invention discloses an electronic apparatus for extracting a
pitch from an input waveform signal and generating a musical tone having
the corresponding tone pitch, and discloses a technique for changing a
tone pitch of an output tone along with a change of the input waveform
signal in pitch without accompanying an unnecessary variation in interval.
(u) U.S. Ser. No. 282,510 (filed on Dec. 9, 1988), inventor: Obata
In this prior-art invention, even if a pitch is unstably extracted at the
beginning of tone generation, a musical tone having a stable pitch can be
generated from the beginning. Start of musical tone generation is
chromatically instructed on the basis of a pitch extracted by a pitch
extraction system.
(v) U.S. Ser. No. 290,981 (filed on Dec. 28, 1988), inventor: Murata et al.
In this prior-art invention, strings are completely electronically tuned.
Before a performance, a reference pitch is determined by plucking at a
specific fret, and a tone pitch of a musical tone to be generated is
determined on the basis of period data obtained by plucking at a
designated fret using the reference pitch.
According to the prior art techniques described above, an intensity of an
input waveform signal is detected at its leading edge, and a musical tone
is generated while changing a tone volume and timbre of an output tone
from a sound source.
Since the tone volume and timbre of a musical tone are changed using one
parameter, that is, a signal intensity of the input waveform signal, if
the input waveform signal is changed and a tone volume of a musical tone
is increased, a timbre sounds hard. That is, these variables are always
changed to have a correlation therebetween.
However, when an acoustic guitar or the like is actually plucked to
directly produce a tone, even if a picking strength of a string is made
constant to keep a constant one volume, a hard timbre is obtained upon
picking near a bridge (fixing portion of strings) and a soft timbre is
obtained upon picking near a fret (finger board).
Therefore, in the conventional electronic musical instrument wherein a tone
volume and a timbre are changed by only a signal intensity, the tone
volume and the timbre color cannot be independently controlled by shifting
a string picking position. Thus, an abundant performance effect cannot be
obtained.
SUMMARY OF THE INVENTION
The present invention has been made in consideration of the above
situation, and has as its object to provide an electronic musical
instrument which can independently control parameters such as tone volume,
timbre, and the like of a musical tone according to an input waveform
signal when a musical tone is generated.
According to the present invention, there is provided a control apparatus
for an electronic musical instrument, comprising intensity detection means
for detecting a signal intensity data at a leading edge of an input
waveform signal, intensity change degree detection means for detecting a
signal intensity change degree data at the leading edge of the input
waveform signal, and musical tone generation control means for performing
control such that at least two characteristics of a musical tone are
changed in accordance with the signal intensity data and the signal
intensity change degree.
More specifically, the electronic musical instrument is realized as an
electronic stringed instrument (electronic guitar) for detecting a
vibration of a metal string by a pickup and controlling a musical tone on
the basis of the detected vibration although not limited to this.
The intensity detection means outputs a leading strength of an input
waveform signal as a signal intensity data. In contrast to this, the
intensity change degree detection means outputs a degree of change in
intensity of an input waveform signal at its leading edge as a signal
intensity change degree data.
As one arrangement of the intensity detection means, an average value of a
maximum peak value, obtained in advance, of an input waveform signal at
its leading edge and the next peak value having the same sign as the
maximum peak value is calculated, and is output as a signal intensity
parameter.
As one arrangement of the intensity change degree detection means, a ratio
of the maximum peak value to the next peak value having the same sign a
the maximum peak value is calculated, and is output as a signal intensity
change degree parameter.
Therefore, if an intensity and a change degree of the intensity at the
leading edge of the input waveform signal are independently changed in
accordance with a performance method, the musical tone generation control
means independently changes at least two characteristics of a musical
tone, e.g., a tone volume and a timbre in accordance with the signal
intensity and the signal intensity change degree, thus obtaining an
abundant performance effect.
In particular, in an electronic stringed instrument, when a string picking
position is shifted, only a signal intensity change degree can be changed
while the signal intensity remains the same at the leading edge of the
input waveform signal. Thus, only a timbre of a musical tone can be
changed without changing its tone volume, and a great performance effect
can be provided.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other objects and features of the present invention will be
apparent from the description of the preferred embodiment taken in
conjunction with the accompanying drawings, in which:
FIG. 1 is a block diagram showing the overall arrangement of an embodiment
of the electronic musical instrument according to the present invention;
FIG. 2 is a block diagram of a pitch extraction digital circuit;
FIG. 3 is an operation flow chart of an interruption processing routine;
FIG. 4 is an operation flow chart of a main routine;
FIG. 5 is an operation flow chart of STEP 0;
FIG. 6 is an operation flow chart of STEP 1;
FIG. 7 is an operation flow chart of STEP 2,
FIG. 8 is an operation flow chart of STEP 3;
FIG. 9 is an operation flow chart of STEP 4 or 5;
FIG. 10 is a chart for explaining a schematic operation of this embodiment;
FIGS. 11A and 11B are waveform charts for explaining an operation for
determining a tone volume and a timbre of this embodiment;
FIG. 12 is a chart for explaining a basic operation of this embodiment;
FIGS. 13A and 13B are charts for explaining repetition processing in STEP
1;
FIGS. 14A, 14B, and 14C are charts for explaining repetition processing in
STEP 2;
FIG. 15 is a chart for explaining noise removal processing in STEP 3;
FIG. 16 is a chart for explaining relative-off processing in STEP 4;
FIG. 17 is a chart for explaining a processing operation when a detected
pitch is inappropriate in STEP 4;
FIG. 18 is a chart for explaining repetition processing in a route 1; and
FIG. 19 is a chart for explaining repetition processing in a route 2.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
An embodiment of the present invention will now be described in detail.
In the following description, items are classified in the order of
underlined captions enclosed in symbols {11}, (11), and <11>.
{Arrangement of Electronic Musical Instrument of the Present Invention}
This embodiment is realized as an electronic guitar, wherein six metal
strings are kept taut on a body, and a desired string is picked while
pressing a fret (finger board) arranged below the metal strings so as to
make a performance. Note that its outer appearance will be omitted.
FIG. 1 is a block diagram showing the overall arrangement of this
embodiment.
Pitch extraction analog circuit 1 is connected with the six strings (not
shown). Hexa-pickups convert vibrations of the corresponding strings into
electrical signals. These signals pass through low-pass filters (not
shown) to remove a harmonic component thereof, thereby obtaining 6
waveform signals Wi (i=1 to 6). Furthermore, circuit 1 generates a
zero-cross pulse signal Zi (i=1 to 6) which goes to H (High) or L (Low)
level every time the sign of the amplitude of each waveform signal Wi is
changed to positive or negative. These 6 waveform signals Wi are converted
to a digital output (time-divisional waveform signal) D1 through
corresponding A/D converters (not shown) or the like. These 6 zero-cross
signals Zi are converted to a time-divisional serial zero cross signal
ZCR. These digital signals are then output.
A pitch extraction digital circuit 2 comprises a peak detector 201, a time
constant conversion controller 202, a peak value fetching circuit 203, and
a zero-cross time fetching circuit 204. These circuits shown in FIG. 2
time-divisionally process data for the six strings on the basis of the
time-divisional serial zero-cross signal ZCR and the digital output D1
corresponding to data of the six strings. In the following description,
processing for one string will be described for the sake of easy
understanding, and the serial zero-cross signal ZCR and the digital output
D1 will be described as signals for one string. However, time-divisional
processing for the six strings is performed unless otherwise specified.
In FIG. 2, the peak detector 201 detects maximum and minimum peak points of
the digital output D1 on the basis of the serial zero-cross signal ZCR and
the digital output D1. Although not shown, the detector 201 includes a
peak hold circuit for holding an absolute value of a previous peak value
while subtracting (attenuating) it. The peak detector 201 detects the
timing of a peak value by using a peak hold signal output from the peak
hold circuit after the preceding detection of the peak value as a
threshold value. That is, the peak detector 201 detects the timing when
the absolute value of the digital output D1 exceeds the threshold value
after the next serial zero-cross signal ZCR is generated. Note that timing
detection of the peak value is executed for positive and negative signs of
the digital output D1. At the detection timing of the peak value, the
detector 201 outputs a maximum peak value detection signal MAX in the case
of the positive sign, and outputs a minimum peak value detection signal
MIN in the case of the negative sign. Note that these signals are
time-divisional signals for the six strings, as a matter of course.
The time constant conversion controller 202 is a circuit for changing an
attenuation factor of the peak hold circuit in the peak detector 201, and
is operated in accordance with the maximum and minimum peak detection
signals MAX and MIN under the control of a main control processor (to be
referred to as an MCP hereinafter) 3 shown in FIG. 1. This operation will
be described later.
The peak value fetching circuit 203 demultiplexes the digital output D1
time-divisionally sent from the peak extraction analog circuits 1 into
peak values corresponding to the strings, and holds their peak values in
accordance with the peak value detection signals MAX and MIN from the peak
detector 201. The circuit 203 sequentially outputs to the MCP 3 through a
bus BUS the maximum or minimum peak value for a string accessed by the MCP
3 (FIG. 1) through an address decoder 4 (FIG. 1). The peak value fetching
circuit 203 can output an instantaneous value of a vibration of each
string in addition to the peak values.
The zero-cross time fetching circuit 204 latches an output from a time-base
counter 2041 common to the strings at a zero-cross timing of each string,
strictly, at a zero-cross point immediately after a passage timing of the
maximum and minimum peak determined by the maximum and minimum peak value
detection signals MAX and MIN output from the peak detector 201 in
accordance with the serial zero-cross signal ZCR from the pitch extraction
analog circuits 1 (FIG. 1). When this latch operation is performed, the
zero-cross time fetching circuit 204 outputs an interruption signal INT to
the MCP 3 shown in FIG. 1. Thus, the circuit 204 sequentially outputs a
number of string of which vibration has been past through a zero-cross
point, the latched zero-cross time and positive/negative data
corresponding to the string (to be described later) to the MCP 3 through
the bus BUS in accordance with a control signal (to be described later)
output from the MCP 3 through the address decoder 4 (FIG. 1).
A timing generator 205 shown in FIG. 2 outputs timing signals for
processing operations of the circuits shown in FIGS. 1 and 2.
Referring again to FIG. 1, the MCP 3 has memories, e.g., a ROM 301 and a
RAM 302, and also has a timer 303. The ROM 301 comprises a nonvolatile
memory for storing various musical tone control programs (to be described
later), and the RAM 302 comprises a programmable memory used as a work
area for various variables and data during a control operation. The timer
303 is used for note-off (muting) processing (to be described later).
A musical tone generating unit 5 comprises a musical tone generator 501, an
A/D converter 502, an amplifier 503, and a loudspeaker 504, and produces a
musical tone corresponding to musical tone control data from the MCP 3.
Note that an interface (Musical Instrument Digital Interface) MIDI is
arranged at the input side of the musical tone generator 501, and is
connected to the MCP 3 through a special-purpose bus MIDI-BUS for
transmitting musical tone control data. When the musical tone generating
unit 5 is arranged in the guitar body, another internal interface can be
arranged between the unit 5 and the MCP 3.
The address decoder 4 shown in FIG. 1 supplies a string number read signal
RDNUM and then a time read signal RDTlMi (i=1 to 6) to the zero-cross time
fetching circuit 204 in accordance with an address read signal AR
generated by the MCP 3 (FIG. 1) after the interruption signal INT is
generated by the zero-cross time fetching circuit 204 (FIG. 2). Similarly,
the decoder 4 outputs a waveform read signal RDAj (j=1 to 18) to the peak
value fetching circuit 203 (FIG. 2). These operations will be described
later in detail.
{General Operation of This Embodiment}
The operation of the embodiment with the above arrangement will now be
described.
A general operation of this embodiment will be described first.
A waveform D1 in FIG. 10 represents the digital output D1 for one string
output from the pitch extraction analog circuit 1 shown in FIG. 1 in an
analog manner. This output waveform signal is a digital signal, which is
obtained from an electrical signal detected by the corresponding pickup
when one of the six strings of the guitar (not shown) is plucked The
waveform signal has pitch periods indicated by T.sub.0 to T.sub.5 in FIG.
10 in accordance with a position where the string is pressed on a fret
(finger board) (not shown).
In this embodiment, the pitch periods T.sub.0 to T.sub.5 are extracted in
real time, so that the MCP 3 generates corresponding tone pitch data and
causes the musical tone generator 501 shown in FIG. 1 to generate a
musical tone having the tone pitch. Therefore, when a player changes a
tension of the string using a tremolo arm (not shown), the pitch period of
the digital output D1 is changed accordingly, and tone pitch data is also
changed accordingly. As a result, an abundant expression can be added to a
musical tone.
In this embodiment, peak values a.sub.0 to a.sub.3 or b.sub.0 to b.sub.3 of
the digital output D1 shown in FIG. 10 are detected, and a tone volume and
a timbre of a musical tone can be controlled based on the peak values
a.sub.0 and a.sub.1 at the leading edge (upon plucking of a string).
More specifically, the MCP 3 shown in FIG. 1 calculates an average value of
the peak values a.sub.0 and a.sub.1, and transfers the average value as
tone volume data to the musical tone generator 501. Thus, a musical tone
having a tone volume corresponding to a string plucking strength can be
generated.
In a normal acoustic guitar, even if the plucking strength remains the
same, a hard timbre is obtained when a string is plucked near a bridge,
and a soft timbre is obtained when a string is plucked near a fret. In
this embodiment, when such a string vibration is detected by the pickup,
if the string is plucked near the bridge, a characteristic in which the
peak value a.sub.0 in the first pitch period becomes larger than the next
peak value a.sub.1 is obtained, as shown in FIG. 11A. On the other hand,
when the string is plucked near the fret, the peak values a.sub.0 and
a.sub.1 become substantially the same values, as shown in FIG. 11B.
In this embodiment, the MCP 3 in FIG. 1 calculates a ratio of the peak
values a.sub.0 and a.sub.1, and transfers the ratio to the musical tone
generator 501 as timbre data. Thus, when the value of the timbre data is
large, the musical tone generator 501 controls a harmonic envelope or
harmonic overtones of a musical tone so that a hard timbre is obtained. On
the contrary, when the value is small, the generator 501 controls the
harmonic envelope or overtones to obtain a soft timbre. Thus, a musical
tone having a timbre according to a string picking position can be
generated. In this manner, the characteristic feature of this embodiment
is that the tone volume and timbre can be independently controlled.
Since the above-mentioned operation is achieved by time-divisional
processing for the time-divisional digital output D1 for the six strings
of the guitar, the musical tone generator 501 can simultaneously generate
musical tones for the six strings. These musical tones can be set to have
desired tone volumes and timbres, and various effects can be
electronically added thereto. Therefore, a great performance effect can be
obtained.
{Operation of Pitch Extraction Digital Circuit}
An operation of this embodiment for realizing the above-mentioned operation
will be described in detail below.
(General Operation)
The operation of the pitch extraction digital circuit 2 shown in FIG. 1 or
2 will be described below. The following description will be made for one
string, and the serial zero-cross signal ZCR, the digital output D1, and
the maximum and minimum peak value detection signals MAX and MIN will be
described for one string. However, in practice, time-divisional processing
is performed for the six strings.
The circuit 2 extracts the peak values a.sub.0 to a.sub.3 or b.sub.0 to
b.sub.3, and at the same time, extracts zero-cross times t.sub.1 to
t.sub.7 immediately after the corresponding peak values from the digital
output D1 shown in FIG. 10 for each of the strings. Furthermore, the
circuit 2 extracts data indicating "1" or "0" in accordance with whether
the peak value immediately before the corresponding zero-cross time is
negative or positive, and supplies the extracted data to the MCP 3 shown
in FIG. 1. Based on these data, the MCP 3 extracts the pitch periods
T.sub.0 to T.sub.5 shown in FIG. 10 from intervals of the zero-cross
times, generates various musical tone data described above, and performs
error processing, note-off (muting) processing, relative-on/off
processing, and the like as needed, as will be described later.
(Detailed Operation)
For this purpose, in the peak detector 201 shown in FIG. 2, in response to
the digital output D1 input as shown in FIG. 10, the minimum peak value
detection signal MIN goes to H level at a timing x.sub.0 when the absolute
value of the output D1 exceeds 0 in a portion taking a negative value.
In response to this signal, the peak value fetching circuit 203 shown in
FIG. 2 detects a minimum peak value (negative peak value) b.sub.0
(absolute value) from the separately input digital output D1 at a timing
x.sub.1 immediately after the minimum peak value detection signal MIN goes
to H level, and holds the value in an internal latch (not shown). At the
same time, the circuit 203 sets the minimum peak value detection signal
MIN at L level.
The serial zero-cross signal ZCR shown in FIG. 10 is input from the pitch
extraction analog circuit 1 shown in FIG. 1 to the zero-cross time
fetching circuit 204 shown in FIG. 2. This signal is obtained as follows.
That is, a comparator (not shown) in the pitch extraction analog circuit 1
determines a positive or negative level of the digital output D1, and
outputs an H- or L-level binary digital signal according to the
determination result.
The zero-cross time fetching circuit 204 latches time t.sub.0 (FIG. 10)
counted by the time-base counter 2041 shown in FIG. 2 at an edge timing
when the serial zero-cross signal ZCR changes immediately after the
minimum peak value detection signal MIN output from the peak detector 201
goes to H level at the timing x.sub.0 i.e., the zero-cross timing of the
digital output D1. Note that a positive/negative flag of "1" or "0"
indicating that an immediately preceding peak value is positive or
negative (0 for minimum peak value b.sub.0) is added to the most
significant bit (MSB) of this latch data.
The zero-cross time fetching circuit 204 outputs the interruption signal
INT to the MCP 3 shown in FIG. 1 upon completion of the above-mentioned
operation. Thus, when the interruption signal INT is generated, the peak
value fetching circuit 203 shown in FIG. 2 holds the minimum peak value
b.sub.0 (absolute value), and the zero-cross time fetching circuit 204
latches zero-cross time including the positive/negative flag immediately
after the minimum peak value b.sub.0 is generated.
After the interruption signal INT is output, the MCP 3 in FIG. 1 makes
access (to be described later) through the address decoder 4, so that the
zero-cross time including the positive/negative flag and the minimum peak
value b.sub.0 are transferred to the MCP 3 through the bus BUS. Note that
since the above-mentioned processing is achieved by the time-divisional
processing for the six strings, the zero-cross time fetching circuit 204
outputs data indicating an interrupted string number to the MCP 3 before
the respective data are output.
In the peak detector 201 shown in FIG. 2, the internal peak hold circuit
(not shown) holds the minimum peak value b.sub.0 (absolute value) shown in
FIG. 10, and outputs a peak hold signal q.sub.0 shown in FIG. 10. In
response to this signal, the peak detector 201 again sets the minimum peak
value detection signal MIN at H level using the peak hold signal (absolute
value) as a threshold value at a timing x.sub.2 when the absolute value
exceeds the threshold value on the negative side of the digital output D1.
The peak value fetching circuit 203 in FIG. 2 holds the next minimum peak
value b.sub.1 (absolute value) at a timing x.sub.3 immediately after the
minimum peak value detection signal MIN goes to H level in the same manner
as described above. The zero-cross time fetching circuit 204 in FIG. 2
latches zero-cross time t.sub.2 including the positive/negative flag (0 in
this case) immediately after the minimum peak value b.sub.1 is generated.
The held value and the latched time are transferred to the MCP 3 after the
interruption signal INT is generated.
Detection of the maximum peak values a.sub.0 to a.sub.3, and the like,
detection of zero-cross times t.sub.1, t.sub.3, t.sub.5, t.sub.7, and the
like, and output operations of peak hold signals p.sub.0 to p.sub.3, and
the like on the positive side of the digital output D1 are executed in the
same manner as the detection of the minimum peak values b.sub.0 to b.sub.3
(absolute values), and the like, the zero-cross times t.sub.0, t.sub.2,
t.sub.4, t.sub.6, and the like, and output operations of the peak hold
signals q.sub.0 to q.sub.3, and the like on the negative side of the
digital output D1 shown in FIG. 10. Note that in this case, the peak
detector 201 outputs the maximum peak value detection signal MAX, as shown
in FIG. 10. The peak value fetching circuit 203 and the zero-cross time
fetching circuit 204 shown in FIG. 2 latch the maximum peak values a.sub.0
to a.sub.3, and the like, and zero-cross times t.sub.1, t.sub.3, t.sub.5,
t.sub.7, and the like including the positive/negative flag (1 in this case
because of a positive peak) respectively.
With the above-mentioned operations, the zero-cross time fetching circuit
204 shown in FIG. 2 outputs the interruption signal INT to the MCP 3 shown
in FIG. 1 at each of the zero-cross times t.sub.0 to t.sub.7 shown in FIG.
10, and pairs of minimum or maximum peak values (absolute values) and
zero-cross times, such as b.sub.0 and t.sub.0, a.sub.0 and t.sub.1,
b.sub.1 and t.sub.2, a.sub.1 and t.sub.3, . . . , are output to the MCP 3
at the corresponding times based on the interruption signal INT. In the
MCP 3, determination of the minimum peak value (negative peak value) or
maximum peak value (positive peak value) can be performed by the
positive/negative flag added to the MSB of the zero-cross time.
In addition to the above-mentioned operation, the peak value fetching
circuit 203 can arbitrarily output an instantaneous value of the digital
output D1 upon accessing from the MCP 3. This operation will be described
later.
The attenuation factor (time constant) of each of the peak hold signals
p.sub.0 to p.sub.3, q.sub.0 to q.sub.3, and the like shown in FIG. 10
generated by the peak hold circuit in the peak detector 201 in FIG. 2 are
changed by the t | | |
