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DESCRIPTION JPH10145888

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DESCRIPTION JPH10145888
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
howling detection / prevention circuit for detecting and preventing howling and a loudspeaker
using the same.
[0002]
2. Description of the Related Art In louding using a microphone and a speaker, howling occurs
when trying to produce a loud sound. As a method to prevent howling, increase the overall gain
for howling to occur by suppressing the overall gain of the loudspeaker below the level where
the howling does not occur or lowering the gain of the frequency band where the howling begins
to occur Conceivable. Conventionally, in order to prevent howling, a person sets the overall gain
of the loudspeaker while checking the presence or absence of howling to turn the volume to set
the loudspeaker gain to a level at which the howling does not occur, a graphic equalizer or a
notch Methods such as setting the overall gain after reducing the gain of a specific frequency
band using a filter have been taken. And the adjustment of those gains was done to the person's
ear. In addition, when howling occurs, people often rush to the location of the loudspeaker and
deal with it by lowering the volume. In such cases, it takes time to stop howling. , I could not
prevent the discomfort in the meantime.
[0003]
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1
As described above, in the conventional loudspeakers etc., since the setting of the loudspeaker
gain at the time of the prevention of howling is performed manually, there are problems in terms
of accuracy, stability, etc. Also, the operation was complicated. In addition, when howling actually
occurs, there is also a problem that it takes a certain amount of time to deal with it. The present
invention has been made under such a background, and an object of the present invention is to
provide a howling detection / prevention circuit capable of automatically detecting and
preventing howling, and a loudspeaker using the same.
[0004]
A howling detection and prevention circuit according to the present invention is a circuit that
detects howling using an output of a microphone as an input signal, and after dividing an input
signal into a plurality of frequencies, a predetermined sampling period is generated. Using means
for calculating the power of each band for each frequency band divided in units and using the
calculated power value of each band, it is determined whether it is howling along a
predetermined condition while shifting its frequency sequentially And, as a result of the
determination, when howling is detected, it is characterized by comprising means for adjusting
the gain of the frequency band to prevent howling.
[0005]
The howling detection / prevention circuit may further include means for adjusting the gain of
the entire frequency band to prevent howling according to the result of the determination.
[0006]
In addition, the calculation means may calculate the power of each band while taking a moving
average for each frequency band divided in units of predetermined sampling cycles.
[0007]
Further, the determination means may determine whether or not the method is howling based on
the difference between the absolute value of the power of the band to be determined and the
power of the frequency band in the vicinity thereof.
[0008]
Also, a loudspeaker system may be configured by providing a microphone, means for amplifying
the output signal of the howling detection preventing circuit, and a speaker driven by the output
of the amplification means using these howling detection preventing circuits. it can.
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2
[0009]
According to the above configuration, after dividing the input signal into bands, the power of
each band is calculated, and using the power value of each band, the howling condition is
searched while sequentially changing the frequency.
Then, if there is a frequency band that satisfies the howling condition, that band is detected as a
howling frequency band, and howling prevention is performed.
This makes it possible to automatically detect and prevent howling that occurs when the sound
volume is raised above a certain value in a PA (public address) system using a loudspeaker or a
microphone.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will
be described below with reference to the drawings.
FIG. 1 is a block diagram showing a configuration example of a howling detection preventing
circuit according to the present invention and a loudspeaker incorporating the same.
The loudspeaker apparatus 100 shown in FIG. 1 includes a microphone 101, a microphone
amplifier 102 for amplifying and outputting an output signal of the microphone 101, and an A /
D converter (analog / digital converter) for analog / digital converting an output signal of the
microphone amplifier 102. 103) Howling detection / prevention circuit 1 performs signal
processing using the digital output of A / D converter 103 as an input signal and outputs the
signal processing result to D / A converter (digital / analog converter) 104, D / A A power
amplifier 105 amplifies the output signal of the converter 104 according to a gain whose gain is
arbitrarily set by the operator, and a speaker 106 driven by the output signal of the power
amplifier.
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The howling detection / prevention circuit 1 is composed of circuits such as a microcomputer, a
signal processing chip, a memory, a timer, etc. In FIG. 1, its internal configuration is shown
divided into functional blocks.
[0011]
The digital signal input from the A / D converter 103 is input to the band division filter unit 11 in
the howling detection and prevention circuit 1. The band division filter unit 11 is configured of M
(M is an integer of 2 or more) FIR (finite impulse response) band pass filters or IIR (infinite
impulse response) band pass filters set by gradually shifting the center frequency. The input
signal from the A / D converter 103 is divided into a signal in the frequency band of M band and
multiplied by a predetermined gain, and then each band power calculation unit 12 and the
addition unit 13 as signals F1, F2,. Output to Each band power calculator 12 calculates power
values P1, P2,..., PM of the signals F1, F2,..., FM in each band, and determines howling each
calculated power value P1, P2,. Supply to the unit 14. The addition unit 13 adds all the M-band
signals F1, F2,. The howling determination unit 14 determines the generation state of howling
based on the power values P1, P2,..., PM of the signals in each band, and sets the gain for each
band used in the band division filter unit 11 based on the determination result. At the same time,
the gain G for the signal of the entire band used by the overall gain control unit 15 is set. The
overall gain control unit 15 multiplies the set gain G by the addition signal of the entire band,
and outputs the calculation result to the D / A converter 104. With the above configuration, the
howling detection / prevention circuit 1 reduces the gain of the frequency band in the state
where the howling occurs or is likely to occur based on the howling determination result, and
prevents the howling. Further, the howling detection / prevention circuit 1 prevents the howling
by lowering the overall gain G when howling still occurs even when the setting gain for each
band is lowered in this way. This makes it possible to completely prevent howling even when the
operator sets an excessive gain.
[0012]
Next, an example of the internal configuration of each band power calculator 12 shown in FIG. 1
will be described with reference to FIG. The circuit block shown in FIG. 2 is a configuration for
performing power calculation for one band in each band power calculation unit 12, and each
band power calculation unit 12 is configured to include M similar blocks. The configuration
corresponding to one band of band power calculation unit 12 includes an operation circuit 121
including a square unit 121a and an adder / subtractor 121b, and an N tap shift memory 122
having N (N is an integer of 2 or more) taps. ing. Here, it is assumed that the input signal X0 (a
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signal corresponding to one of the signals Fi (i = 1, 2,..., M) in FIG. 1) is supplied at a
predetermined sampling period k (k is an arbitrary integer). Do. In this case, the square unit 121
a obtains the square value X 02 of the input signal X 0, and supplies the obtained result X 02 to
each input terminal of the adder / subtractor 121 b and the N tap shift memory 122. The adder /
subtractor 121b adds the calculated value P obtained in the previous sampling cycle k-1 and the
calculation result X02 of the squarer 121a to the tail end of the N tap shift memory 122 before
shifting the memory (N The value XN2 (A) of the (th tap output) is subtracted to obtain a new
calculated value P. Next, the N-tap shift memory 122 sequentially shifts the stored values of the
N memories, and stores the calculation result X02 of the square unit 121a in the current
sampling cycle k as X12 at the beginning of the memory (B). After repeating the above operation
N times, the calculation result P determined by the adder-subtractor 121b is P = (XN2 + XN-12
+... + X12) + X02-XN2 = XN-12 +... + X12 + X02, and the input signal X0 of the sampling cycle at
that time The square value of the input signal of the past N samples including the square value X
02 of is integrated. As a result, the signal P (a signal corresponding to any one of the signals Pi (i
= 1, 2,..., M) in FIG. 1) supplied from the adder / subtractor 121b to the howling determination
circuit 14 has N input signals X0. The value corresponds to the value obtained by integrating the
instantaneous power of Therefore, it is possible to obtain a value corresponding to a moving
average of N samples of instantaneous power of input signal X0 by multiplying signal P by a
predetermined constant (for example, a value corresponding to the reciprocal of sample number
N). .
[0013]
Next, an example of an internal configuration of the howling determination unit 14 illustrated in
FIG. 1 will be described with reference to FIGS. 3 and 4. FIG. 3 is a diagram showing a circuit
block for determining whether or not howling is occurring in the howling determination unit 14
or a state in which the occurrence is likely to occur. A circuit for selecting, a circuit for setting
each gain used in the band division filter unit 11 and the overall gain control unit 15 based on
the determination result, and the like are provided. In FIG. 3, input signals Pm, Pm-1, Pm + 1, Pm2, Pm + 2 are power signals Pm of any band among power values P1, P2,. The five signals
consisting of the power signals Pm−1, Pm−2, Pm + 1, Pm + 2 of the adjacent two bands on each
side are shown, and the subscript m is a value sequentially shifted from 0 to M. However, in the
case of m = 0, 1 and m = M−1, M, the determination based on the data is performed only on one
side where the data of the corresponding subscript exists. When the signals Pm, Pm-1, Pm + 1,
Pm-2, Pm + 2 are input, the subtraction circuits 140, 141, 142 and 143 respectively output PmPm-1, Pm-Pm + 1, Pm-. The calculation of Pm−2, Pm−Pm + 2 is performed, and the calculated
result is output. Next, the comparison circuits 144, 145, 146, 147 and 148 respectively indicate
whether Pm> TL1, Pm-Pm-1> DIF1, Pm-Pm + 1> DIF1, Pm- A comparison is made as to whether
Pm-2> DIF2 and Pm-Pm + 2> DIF2, and the comparison results (“0” (condition not satisfied) or
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“1” (condition satisfied)) are respectively determined. Output. Here, TL1, DIF1, and DIF2 are
reference values used for comparison, and are set in accordance with the actual use conditions of
the loudspeaker apparatus and the like. Then, the AND circuit 149 obtains the logical product of
the comparison results of each of the comparison circuits 144 to 148, and when all the
comparison conditions are satisfied, it is determined that the howling state or howling is likely to
occur. Output “1”).
[0014]
FIG. 4 is a schematic diagram showing an example of the relationship between the comparison
reference values TL1, DIF1, DIF2 shown in FIG. 3 and the input signals Pm, Pm-1, Pm-2, Pm + 1,
Pm + 2. The example shown in FIG. 4 assumes that the power signal Pm in the center frequency
band satisfies the above determination conditions and is in the howling state. The signal of the
frequency band in the state where howling occurs or near that has relatively higher power than
the signal of the frequency band in the vicinity thereof, and the relationship is as shown in FIG. .
This condition, that is, whether or not the power signal Pm in the central frequency band has a
peak with respect to the signal in the adjacent frequency band, for example, for the power signal
Pm in the central frequency band with respect to signals in the respective two bands above and
below that frequency. The difference DIF1 or DIF2 can be detected by checking whether the
power is equal to or more than the difference. Usually, the reference values DIF1 and DIF2 are
set in such a relationship that the reference value DIF1 becomes larger than the reference value
DIF2. However, even if the difference between the power signal Pm in the central frequency band
and the signal in the nearby frequency band is larger than the reference values DIF1 and DIF2,
howling is not detected if the absolute value of the power signal Pm is relatively small. It does not
occur. Regarding this condition, by comparing the power signal Pm with the reference value TL1,
it can be determined by incorporating not only the determination of the difference but also the
determination of the absolute value. Therefore, in the present embodiment, determination as to
whether or not the howling state is based on determination of an absolute value as to whether or
not the power signal Pm is greater than the reference value TL1 and determination of a
difference using the reference values DIF1 and DIF2. It is detected that the frequency band of the
power signal Pm is in the howling generation state only when the above is established.
[0015]
With the above configuration, the howling determination unit 14 shown in FIG. 1 sequentially
determines whether there is a band satisfying the howling condition for all frequency bands
while shifting the center frequency sequentially, and sets the band satisfying the condition as the
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howling frequency band decide. However, as described above, in the case of m = 0, 1 and m =
M−1, M, data is used only for one side that exists, Pm−1 = Pm + 1 or Pm−2 = Pm + 2 Make a
decision by making Then, the gain of the corresponding corresponding band-pass filter in the
band division filter 11 is lowered so as to lower the gain of the frequency band determined as the
howling frequency band. At this time, it is usually possible to prevent the howling by lowering
the gain by about the reference value DIF1 used for the determination of the difference. In
addition, when the howling condition is satisfied in a plurality of bands, the gains of all the bands
that satisfy the conditions are decreased. If the howling state is further detected even after
reducing the gain of each band-pass filter that satisfies the condition, the howling determination
unit 14 reduces the value of the gain used in the overall gain control unit 15. This makes it
possible to completely prevent the occurrence of howling that can not be prevented when the
gain of each divided frequency band is lowered.
[0016]
As described above, according to the present embodiment, the power of a certain time interval is
calculated while moving average for each sampling period for each frequency band, and howling
determination is performed using this, so that the time change of the signal waveform Therefore,
it is possible to prevent the judgment result from being influenced and to make stable howling
judgment. Further, according to this embodiment, the howling determination can be performed in
real time, and the gain for each frequency or the overall gain can be adjusted automatically. Will
be able to do.
[0017]
As described above, according to the present invention, after the input signal is divided into a
plurality of frequencies, the power of each band is calculated for each frequency band divided in
predetermined sampling cycle units, and the frequencies are sequentially determined. Since it is
determined whether or not howling is performed according to a predetermined condition while
shifting, howling can be automatically detected. Then, when howling is detected, the gain of that
frequency band is adjusted to prevent howling, so that it is possible to automatically prevent
howling regardless of the operation of a person.
[0018]
Brief description of the drawings
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[0019]
FIG. 1 is a block diagram showing the configuration of a howling detection preventing circuit and
a loudspeaker according to an embodiment of the present invention.
[0020]
FIG. 2 is a block diagram showing an internal configuration of each band power calculator 12
shown in FIG. 1;
[0021]
FIG. 4 is a block diagram showing an internal configuration of the howling determination unit 14
shown in FIG. 1;
[0022]
FIG. 4 is a schematic diagram for explaining howling determination conditions in the howling
determination unit 14;
[0023]
Explanation of sign
[0024]
DESCRIPTION OF SYMBOLS 1 ... Howling detection prevention circuit, 100 ... Loudspeaker, 101 ...
Microphone, 102 ... Microphone amplifier, 105 ... Power amplifier, 106 ... Speaker, 11 ... Band
division filter part, 12 ... Each band power calculation part, 13 ... Addition part, 14: howling
determination unit, 15: overall gain control unit.
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