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JP2000316199

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DESCRIPTION JP2000316199
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
howling preventing apparatus capable of effectively preventing howling even when a room to be
used is narrow.
[0002]
2. Description of the Related Art In a system in which a microphone and a speaker are used at
the same time, it is necessary to incorporate a howling prevention device for preventing the
generation of sounding from the sound generation from the speaker as it gets around the
microphone.
[0003]
Here, the configuration of the known howling prevention device 1 is shown in FIG.
In this figure, 10 is a signal generating circuit which generates white noise which is uniform in
frequency. 11はスピーカ、12はマイクである。 Reference numerals 131 to 13 n denote BPFs
(band pass filters), respectively, and their center frequencies are set to be different from each
other. Reference numerals 141 to 14n denote peak-and-hold circuits, which output peak values
of signals obtained by rectifying the corresponding BPF outputs. A selector 15 sequentially
switches the outputs of the peak and hold circuits 141 to 14 n and supplies the same to the A / D
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1
converter 16. The CPU 17 controls the switching of the selector 15 and measures the peak value
converted into a digital signal by the A / D converter 16.
[0004]
In the howling device, white noise that is uniform in frequency is produced from the speaker 11
and collected by the microphone 12. At this time, some of the speakers 11 to the microphone 12
may be directly propagated, and some may be reflected on a wall of a room to be used for
indirect propagation. The CPU 17 sequentially switches the selectors 15, measures the peak
output from the BPFs 131 to 13n, and detects the BPF whose output is high. Then, howling is
suppressed by inserting an equalizer circuit that lowers the gain of the BPF frequency band in
series with the microphone input.
[0005]
By the way, the number of bands in which equalization is performed in the above-described
conventional howling preventing device is about 5 to 9, mainly from the relationship of hardware
restricted by the installation space and the like. In this case, if the frequency at which the
howling occurs does not match any of the center frequencies of the BPFs 131 to 13 n, the
problem that the howling can not be sufficiently prevented occurs.
[0006]
As described above, the propagation from the speaker 11 to the microphone 12 may be direct or
indirect. In particular, when the room to be used is narrow, the rate of indirect propagation can
not be ignored, and multiple reflections and interference occur. As a result, the frequency
characteristic of the room to be used tends to be complicated to have multiple peaks. is there. In
such a case, even with the above-described conventional apparatus, howling can not be
sufficiently prevented because the improvement can be made in only one band. Recently, as socalled karaoke is explosively popular, there are many opportunities to use speakers and
microphones even in small rooms. Including this, the demand for preventing howling in a room
having complex frequency characteristics is extremely high.
[0007]
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2
Therefore, the present applicant has proposed a howling preventing apparatus which solved the
above-mentioned problem and has received a patent (No. 2773656). This howling prevention
device includes a noise generator that generates white noise, a speaker that generates white
noise, first to nth equalizers that give arbitrary frequency characteristics to the output of a
microphone, and a band that can change the center frequency. It has a pass filter. In such a
configuration, first, the first to nth equalizers are set to the through state, and while the center
frequency of the band pass filter is moved, the loop gain of one round including the speaker to
the microphone is measured. The frequency to be detected is detected. The first equalizer is then
coarsely adjusted to suppress this maximum level of frequency. Thereafter, the frequency at
which the loop gain reaches the maximum level is measured again in the setting state where the
peak characteristic is suppressed, and the frequency characteristic of the first equalizer is finely
adjusted. That is, by measuring the frequency characteristic twice, first, the frequency
characteristic of the first equalizer is determined. Thereafter, coarse adjustment and fine
adjustment are performed on the second equalizer, and thereafter, similar operations are
sequentially performed on the n-th equalizer. This makes it possible to prevent howling even
when the frequency characteristic of the room to be used has a plurality of peaks.
[0008]
By the way, in the above-described howling preventing apparatus, it is necessary to measure the
loop gain 2 n times in order to set the frequency characteristics for the first to n-th equalizers
respectively. Therefore, there is a problem that it takes a long time to set desired frequency
characteristics in the first to nth equalizers. In addition, since white noise is to be produced from
the speaker during measurement of the frequency characteristics, the user of the howling
prevention device is uncomfortable.
[0009]
The present invention has been made in view of the above-described circumstances, and an
object thereof is to provide a howling prevention device capable of significantly reducing the
time until setting a desired frequency characteristic.
[0010]
SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, in the invention
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according to claim 1, a sound pickup means for picking up the generated sound, and the sound
picked up by the sound pickup means A howling prevention device for preventing howling when
using sound generation means for amplifying and generating sound, the first to n-th equalizers
for giving an arbitrary frequency characteristic to the output of the sound collection means are
connected in multiple stages Equalizing means and a predetermined signal are supplied to the
sound generation means to produce sound, while measuring a signal collected by the sound
collection means to measure frequency characteristics from the sound generation means to the
sound collection means Based on frequency characteristic measurement means, and
measurement results of the frequency characteristic measurement means and respective
frequency characteristics of the assumed first to n-th equalizers, the total from the sound
generation means to the equalizer means The detecting means detects the frequency at which the
gain of the total frequency characteristic is maximum based on the simulating means for
simulating the frequency characteristic by calculation, the simulation result of the simulating
means, and the detecting means And setting means for sequentially setting the frequency
characteristics of the first to n-th equalizers based on the frequency.
In the second aspect of the invention, the setting means is detected by the detection means based
on a simulation result on the assumption that each frequency characteristic of the first to n-th
equalizers is flat. The frequency characteristic of the first equalizer is set so as to suppress the
vicinity of the determined frequency, and then the vicinity of the frequency detected by the
detection means is suppressed based on the simulation result reflecting the setting state. The
frequency characteristic of the second equalizer is set as described above, and this operation is
repeated thereafter to set the frequency characteristic to the nth equalizer.
[0011]
In the invention according to claim 3, the frequency characteristic measuring means is a band
pass filter with variable center frequency, and at least one low pass filter having a cutoff
frequency having a predetermined relationship with the center frequency. And measuring the
signal through a cascade connection.
[0012]
In the invention according to claim 4, the setting means detects an average level in a
predetermined frequency range, and the frequency level at which the loop gain is maximized
becomes the average level. Attenuation amounts of the first to nth equalizers are respectively set.
[0013]
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Further, in the invention according to claim 5, the setting means has storage means for storing in
advance a relationship between the Q value and the attenuation amount as a table, and reads out
the Q value with respect to the attenuation amount. The frequency characteristic at the time of
suppression is set to each of the first to nth equalizers.
[0014]
According to the sixth aspect of the present invention, there is provided an adjustment means for
adjusting the sound generation level by the sound generation means, and an amplification means
for amplifying the signal collected by the sound collection means in a variable gain manner. In
setting, the setting means sets the adjustment means so that the sound generation level becomes
small, while setting the gain in the amplification means large.
[0015]
According to the first aspect of the present invention, a loop of loop gains including the sound
generating means to the sound collecting means is measured.
Then, the total frequency characteristic is simulated based on the measured frequency
characteristic and the frequency characteristics of the first to n-th equalizers assumed.
Then, based on the simulation result, the frequency characteristics of each equalizer are set so
that the peak of the total frequency characteristics is flat.
Therefore, the measurement of the frequency measurement is performed only once, and the
frequency characteristics of each equalizer are determined by simulation thereafter, so that the
processing time can be significantly shortened.
[0016]
According to the invention described in claim 2, first, the first equalizer is set to suppress the
frequency of the maximum level, and then the frequency at which the loop gain is at the
maximum level in the suppressed setting state Is simulated.
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Then, the second equalizer is set so as to suppress the frequency that is at the maximum level at
this point. A similar operation is set up to the n-th equalizer, which makes it possible to prevent
howling even when there are a plurality of peaks in the frequency characteristic. Also, in this
case, the measurement of the frequency measurement is performed only once, and the frequency
characteristics of each equalizer are determined by simulation thereafter, so that the processing
time can be significantly shortened.
[0017]
According to the invention as set forth in claim 3, by measuring the signal through the cascade
connection of the band pass filter and the low pass filter of at least one or more stages, the cutoff
characteristic at the output of these filters becomes better on the high frequency side . Therefore,
it is possible to more accurately measure the loop gain at low frequency.
[0018]
According to the invention of claim 4, since equalization is performed by matching the peak level
of the loop gain to the average level of the predetermined frequency range, not only howling is
prevented but also the frequency characteristic is made flatter. It is possible to
[0019]
According to the fifth aspect of the present invention, since the Q values of the frequency
characteristics set in the first to n-th equalizers are set according to the attenuation amount, not
only howling is prevented but also It is possible to make the frequency characteristic at that time
flatter.
[0020]
According to the sixth aspect of the present invention, when a predetermined signal is sounded
by the sounding means, the sounding level is suppressed to a low level.
Therefore, the measurer does not feel uncomfortable.
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[0021]
BEST MODE FOR CARRYING OUT THE INVENTION <1.
Configuration of the Embodiment> An embodiment of the present invention will be described
below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of the
howling prevention device 2 of this embodiment.
[0022]
In this figure, 21 is a signal generation circuit for generating white noise as a digital signal, 22 is
a selector, 23 is a D / A converter, 24 is a volume for adjusting the output level, 25 is an
amplifier, and 26 is a speaker. Then, this sound generation is collected by the microphone 27. 28
is an amplifier, 29 is an A / D converter, and 30 is a gain variable amplifier. 311 to 31 n are
parametric equalizers (PEQs) connected in cascade with each other, and the gain and frequency
characteristics for the input signal are controlled by the CPU 40, respectively.
[0023]
Reference numeral 32 denotes a BPF, and 331 to 33k denote low pass filters (LPF). These filters
are connected to each other in cascade, and the cutoff frequencies fC of the LPFs 331 to 33 k are
set to be, for example, twice the center frequency f0 of the BPF 32. As a result, while the BPF 32
band characteristic is not affected by the LPFs 331 to 33k, the high-frequency side slope of the
BPF 32 output is rapidly attenuated by blocking over multiple stages of the LPFs 331 to 33k. The
center frequency fO of the BPF 32 and the cut-off frequencies fC of the LPFs 331 to 33 k are
continuously changed under the control of the CPU 40 while maintaining the above relationship.
[0024]
A peak program meter (PPM) 32 detects the peak level of the LPF 33k located at the final stage,
and supplies the detection result to the CPU 40. Thereby, the CPU 40 can obtain the loop gain
corresponding to the frequency f0 at that time based on the output level of the signal generation
circuit 21, the setting of the volume 24, the gain of the gain variable amplifier 30, and the output
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of the PPM 32.
[0025]
<2. Operation of the Embodiment> Next, the operation of this embodiment will be described
with reference to FIG.
[0026]
(Measurement of Frequency Characteristic) First, the CPU 40 measures the overall frequency
characteristic including the transfer characteristic from the speaker 26 to the microphone 27
(step S1). First, the CPU 40 sets each of the PEQs 311 to 31n in the through state, that is, the
state in which the input signal is output as it is, and switches the selector 22 to the A side to
cause the speaker 26 to emit white noise. Thereby, the microphone 27 inputs the sound to which
the propagation characteristic with the speaker 24 is given, and outputs the signal.
[0027]
The CPU 40 measures the output signal of the microphone 27 via the BPF 32 and the LPFs 331
to 33k, and obtains the loop gain for the center frequency initially set in the BPF 32 at that time.
At this time, the CPU 40 sets the gains of the volume 24 and the variable gain amplifier 30 as
follows so that the change in white noise is sufficiently included in the output signal of the
microphone 27. That is, at the time of measurement, the CPU 40 sets the gain of the volume 24
small, while setting the gain of the variable gain amplifier 30 large.
[0028]
As a result, in the room at the time of measurement, the level of the measurement signal can be
suppressed to a low level, so that the user is less likely to feel uncomfortable. In addition, since a
signal with a large level is not suddenly input to a small allowable speaker such as a tweeter at
the time of measurement, it is possible to prevent such a speaker from being broken.
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[0029]
Next, the CPU 40 changes the center frequency fO of the BPF 32 and the cutoff frequencies fC of
the LPFs 331 to 33k while maintaining the above relationship to obtain a loop gain for the center
frequency set in the BPF 32. In detail, this embodiment divides the frequency at a total of 61
points every 1/6 octave in the frequency range of 18 to 18, 432 Hz, obtains the loop gains for
these points, and stores the measurement results.
[0030]
(Simulation) Next, when the loop gain at each point is obtained, the CPU 40 sequentially
determines the frequency characteristics of the n parametric equalizers PEQ 311 to PEQ 31 n by
simulation. In this case, the CPU 40 manages the number of times of simulation using an internal
register, and writes data i (= 0) indicating the number of times there (step S2).
[0031]
Next, the CPU 40 simulates the integrated frequency characteristic including the characteristics
of the PEQ 311 to PEQ 31 n. (ステップS2)。 Specifically, the comprehensive frequency
characteristic is determined by adding the frequency characteristic of the PEQ set in step S5 to
the frequency characteristic measured in step S1. However, in the first simulation, no frequency
characteristic is set yet for any of the PEQ 311 to PEQ 31 n, so the frequency characteristic of
the PEQ 311 to PEQ 31 n is treated as flat. On the other hand, in the second simulation, since the
frequency characteristic of the PEQ 311 is set in step S5, the integrated frequency characteristic
is simulated by superposing the frequency characteristic of the PEQ 311 on the measured
frequency characteristic. Furthermore, in the third simulation, the integrated frequency
characteristics are simulated by superimposing the frequency characteristics of the PEQ 311 and
PEQ 312 on the measured frequency characteristics. Thereafter, the overall frequency
characteristic is simulated while reflecting the frequency characteristic of the PEQ already
determined.
[0032]
(Setting of Frequency Characteristic of PEQ) Next, based on the simulation result of step 3, the
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CPU 40 detects the frequency fA where the loop gain is maximum among the comprehensive
frequency characteristics (step S4). Thereafter, the CPU 40 sets the frequency fA to the
frequency characteristic of the PEQ as the center frequency at the time of correcting the
frequency characteristic (step S5). Specifically, for example, a gain is set whose attenuation is the
difference between the average value of the loop gain in the frequency range limited to 100 to
10 kHz and the loop gain at the frequency fA, and the Q value of this attenuation characteristic is
Set to PEQ corresponding to the gain. Here, the correspondence between the Q value and the
gain set in the PEQ is stored in advance as a table, and the Q value corresponding to the set gain
is read and set.
[0033]
Further, the setting of the frequency characteristic and the target PEQ are performed with
reference to the value of the data i stored in the internal register. The CPU 40 sets the frequency
characteristic of the PEQ 311 when i = 0, sets the frequency characteristic of the PEQ 312 when i
= 1, and sequentially sets the frequency characteristics of the PEQ 313 to PEQ 31 n. The CPU 40
stores and manages the frequency characteristic data set in each of the PEQs 313 to 31n. After
that, the CPU 40 increments the value of the data i stored in the internal register by "1" (step S6),
and then determines whether the setting has been completed for all PEQs (step S7). In this
determination, the CPU 40 checks whether the value of the data i is n or more. If it is n or more,
the setting of the PEQ is ended and the selector 22 is switched to the B side. On the other hand, if
the value of the data i is less than n, the process returns to step S3, and the processing from step
S3 to step S7 is repeated.
[0034]
By repeating the simulation of the total frequency characteristic and the setting of the PEQ in this
manner, in the PEQ 311 to PEQ 31 n, each peak of the frequency characteristic that is highly
likely to cause howling can be made flatter. Moreover, when the frequency characteristic is set
for a certain PEQ, in the next simulation, the integrated frequency characteristic is calculated by
reflecting the frequency characteristic set in the PEQ, and the next REQ is calculated based on the
simulation result. Set frequency characteristics. Therefore, when there are a plurality of peaks in
the measured frequency characteristics, the frequency characteristics of the entire apparatus
including the room to be used is compared with the case where the frequency characteristics of
PEQ 311 to PEQ 31 n are calculated corresponding to each peak. Get closer to flatter. Further, by
setting the gain and the Q value in association with each other, it is possible to reduce the
influence of standing waves and the like which may occur in a standard room.
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[0035]
Further, since the above-described simulation is performed by the calculation of the CPU 40, the
processing time can be significantly shortened as compared with the case of actual measurement.
For example, assuming that it takes only time T to measure one frequency characteristic, the
processing time is n · T when the frequency characteristic is measured for n PEQs. On the other
hand, in the embodiment described above, the time involved in the simulation is extremely small
compared to the measurement time T. Therefore, the processing time can be reduced to 1 / n. In
particular, since noise is generated from the speaker 26 during the measurement period, the user
feels uncomfortable when the howling prevention device 2 is used as a karaoke device, but in
this embodiment, the measurement time is short. Therefore, the discomfort in use can be relieved
significantly.
[0036]
<3. Modifications> The present invention is not limited to the above-described embodiment,
and various modifications described below are possible, for example. (1) The correspondence
between the PEQ and the frequency at which the loop gain is maximum may not necessarily be in
the order as in the embodiment. Also, instead of white noise, pink noise or a sweep signal may be
used as a test signal. Since the frequency characteristic changes according to the type of test
signal, a correction curve for correcting the frequency characteristic is stored according to the
type of test signal, and CPU 40 measures the frequency characteristic measured according to the
corresponding correction curve. It is desirable to correct the
[0037]
(2) Also, in the above-described embodiment, A / D and D / A are used to convert to digital in the
apparatus for processing, but processing as analog using a switched capacitor filter etc. Is also
possible.
[0038]
(3) Also, in the above-described embodiment, the position of the microphone 27 is fixed at one
place and measured, but in a karaoke box or the like, a singer may sing duet or the like.
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In such a case, since the microphones 27 are used at a plurality of points, it may happen that the
howling can not be sufficiently suppressed. In the embodiment described above, frequency
characteristic data to be set in each of the PEQ 311 to PEQ 31 n is generated and stored by the
measurement results of the first point and simulation. Also, it is possible to calculate frequency
characteristic data corresponding to the second point by moving the microphone 27 from the
first point to the second point and performing the measurement and simulation of the frequency
characteristic described above. In this modification, by comparing the frequency characteristic
data at the first point and the frequency characteristic data at the second point, frequency
characteristic data capable of suppressing howling regardless of whichever the microphone 27 is
used is generated. . Hereinafter, the operation of the modification will be described with
reference to FIG.
[0039]
In the initial state, the frequency characteristic data of the PEQ 311 to PEQ 31 n indicate default
values, and the frequency characteristic of each of the PEQ 311 to PEQ 31 n is flat. In this state,
the microphone 27 is positioned at the first point to perform measurement and simulation of
frequency characteristics. As a result, frequency characteristic data SET11, SET12,..., SET1n are
set to each of the PEQ 311 to PEQ 31n. In this case, the frequency characteristic data is
composed of, for example, the suppression gain and the center frequency of the equalizer.
Further, since the frequency characteristic data is set in order from the largest peak of the loop
gain, the suppression gain is large in the order of SET11, SET12,..., SET1n.
[0040]
Next, the user moves the microphone 27 from the first point to the second point, where
measurement and simulation of frequency characteristics are performed. Then, frequency
characteristic data SET21, SET22,... SET2n are obtained. The CPU 40 performs the suppression
gain comparison based on these data and SET11, SET12,..., SET1n obtained at the first point.
Then, sorting is performed in descending order of suppression gain, and n pieces of data are
identified from the largest. For example, assuming that the suppression gain corresponding to
SET 21 is intermediate between the suppression gain corresponding to SET 11 and the
suppression gain corresponding to SET 12, and the suppression gain corresponding to SET 22 is
smaller than the suppression gain corresponding to SET 1 n, each PEQ 311 The frequency
characteristic data to be set to the PEQ 31n are SET11, SET21, SET12,..., SET1n-1, as shown in
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the figure.
[0041]
Thus, the frequency characteristic data of the first point is stored, the position of the microphone
27 is moved to the second point, the frequency characteristic data is obtained again, the two are
compared, and the peak at which the howling is most likely to occur Since equalization is
performed sequentially from the frequency, it becomes possible to effectively suppress howling
at a plurality of points. Of course, howling of the third point, the fourth point... May be
suppressed by repeatedly executing the above processing.
[0042]
As described above, according to the present invention, it is possible to sufficiently prevent
howling in a room having complicated frequency characteristics and to significantly reduce the
processing time therefor.
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