JPH0750897

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DESCRIPTION JPH0750897
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
audio signal amplifier, and more particularly to howling of a microphone.
[0002]
2. Description of the Related Art In general, in a broadcast studio, a recording studio, a music
performance hall or the like, a microphone is used to enlarge the sound or extract only a
necessary sound. When using this microphone, an audio signal amplifier as shown in FIG. 18 is
required.
[0003]
This conventional device comprises a microphone 2, a head amplifier 4, a microphone amplifier
6, a power amplifier 8, a speaker 10, a howling cut filter 12, and a changeover switch 14. A
microphone volume is connected to the output of the head amplifier 4 and a master volume is
connected to the output of the microphone amplifier 6.
[0004]
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In this case, the entire device loop is in a positive feedback state due to the amplification degree
of the device, the distance between the microphone 2 and the speaker 10, and the reflected
sound from the peripheral wall of the reproduction sound field, and a kind of oscillation
phenomenon at a predetermined high frequency. (Howling) may occur. In this case, an offensive
high-pitched "key" is output from the speaker 10. Once this howling occurs, it continues to be
output as it is without taking any action.
[0005]
One of the methods of not outputting the howling is to manually turn the switch 14 to S1 and
turn on the fixed howling cut filter 12 to remove the howling (the high frequency band
concerned) from the audio signal. . However, since this method does not stop howling occurrence
itself, once the howling cut filter 12 is turned on, it is usually left as it is.
[0006]
However, the above-mentioned audio signal amplifier has the following problems.
[0007]
When howling is forcibly stopped by a method such as the amplification degree of the amplifiers
4, 6, 8 being lowered, etc. When the forgetting of returning the howling cut filter 12 to OFF is
kept and it is kept in the ON state There is.
In this case, the audio signal is always removed in the band of the howling cut filter 12, and there
is a problem that the high frequency characteristic of the microphone 2 is deteriorated.
[0008]
In addition, since howling occurs in a series of different frequency bands, it is necessary to widen
the removal band of the howling cut filter 12, and there is also a problem that the deterioration
of the frequency characteristic of the microphone is even greater. .
[0009]
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An object of the present invention is to solve the above-mentioned problems and to effectively
eliminate howling while minimizing deterioration in sound quality.
[0010]
An audio signal amplifier according to claim 1 is an audio signal amplifier comprising an audio
input means, an amplifier, and an audio output means, wherein a predetermined high frequency
component is applied to a predetermined portion of the apparatus. A plurality of high band
removal filter means for removing the predetermined high band component of the audio signal,
and for each of the predetermined high band frequencies corresponding to the high When the
amplitude of the audio signal exceeds the predetermined reference amplitude by comparing the
amplitudes of the audio signal passed by the high-pass filter means with the predetermined
reference amplitude. And a plurality of control means for operating the corresponding highfrequency removal filter means so as not to operate the corresponding high-frequency removal
filter means when the amplitude of the audio signal does not exceed the predetermined reference
amplitude. It is characterized by comprising a.
[0011]
The audio signal amplifier device according to claim 2 is the audio signal amplifier device
according to claim 1, wherein the control means is configured to remove the high-pass filter
when the number of times the amplitude of the audio signal exceeds the predetermined reference
amplitude exceeds a predetermined number. It is characterized in that it keeps operating.
[0012]
An audio signal amplifier according to claim 3 is characterized in that, in the audio signal
amplifier according to claim 1, each high-pass removing filter means is connected in series.
[0013]
The audio signal amplification device according to claim 4 is an audio signal amplification device
comprising an audio input means, an amplifier and an audio output means, provided in series at
predetermined high frequency parts in a predetermined part of the device, A plurality of high
band removal filter means for removing the predetermined high band component, and a plurality
of high band removal filter means provided corresponding to the predetermined high band
frequency corresponding to the high band removal filter means for passing the predetermined
high band component of the audio signal High-pass filter means compares the amplitude of the
audio signal passed by the high-pass filter means with a predetermined reference amplitude, and
if the amplitude of the audio signal exceeds the predetermined reference amplitude, the
corresponding high-pass removal A plurality of control means for operating the filter means so
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as not to operate the corresponding high-frequency removal filter means when the amplitude of
the audio signal does not exceed the predetermined reference amplitude, and any of the plurality
of control means When Kaniyori each high band elimination filter means is operated, it is
characterized in that the gain of the amplifier provided with a loop coupling adjustment means
for reducing by a predetermined value.
[0014]
According to the first aspect of the present invention, when the predetermined high frequency
component is generated in the audio signal, the high frequency removal filter means is operated
to remove the predetermined high frequency component.
Then, when the predetermined high frequency band component is stopped, the high frequency
band removing filter can be prevented from operating to prevent the deterioration of the high
frequency band characteristic and improve the sound quality.
[0015]
Further, by providing a plurality of high-pass removing filter means, only the high range of the
specific range is removed, so that the high range component of the audio signal is prevented
from being removed over a wide range, and the sound quality is improved. it can.
[0016]
According to the audio signal amplifying device of the second aspect, the control means keeps
the high-frequency removing filter means operating only when the number of times the
amplitude of the audio signal exceeds the predetermined reference amplitude exceeds the
predetermined number. Do.
Therefore, it is possible to prevent the high frequency removal filter means from remaining in
operation by the predetermined high frequency component generated only momentarily.
[0017]
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According to the audio signal amplifier of claim 3, each high-pass removing filter means is
connected in series.
Therefore, even when a plurality of predetermined high frequency components occur at the same
time, the high frequency removal filter means can remove them.
[0018]
According to the audio signal amplifier of claim 4, when a plurality of predetermined high
frequency components occur in the audio signal, each high frequency removal filter means
operates to remove the predetermined high frequency components.
Then, when each high band removal filter means is operated, the gain of the amplifier is lowered
by a predetermined value by the loop coupling degree adjusting means.
Therefore, it is possible to prevent the predetermined high frequency components from being
generated again in succession.
[0019]
DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows the basic configuration of an
audio signal amplifier 5 according to an embodiment of the present invention.
This device 5 is an audio signal amplifying device comprising an audio input means 20 for
inputting an audio signal, an amplifier 22 for amplifying an audio signal, and an audio output
means 24 for outputting an audio signal, and comprises the following means .
[0020]
A plurality of high frequency band removal filter means 26 are provided between the amplifier
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22 and the audio output means 24 for each predetermined high frequency band, and remove the
predetermined high frequency component of the audio signal.
A plurality of high pass filter means 30 are provided for each of the predetermined high
frequency band corresponding to the high frequency removal filter means 26, and passes the
predetermined high frequency component of the audio signal.
[0021]
The plurality of control means 28 compare the amplitude of the audio signal passed by the highpass filter means 30 with the predetermined reference amplitude, and when the amplitude of the
audio signal exceeds the predetermined reference amplitude, the control signals C1 and C2 ,...,
CN to output the corresponding high-pass removal filter means 26 so that the corresponding
high-pass removal filter means 26 is not operated when the amplitude of the audio signal does
not exceed the predetermined reference amplitude. Do.
[0022]
FIG. 2 shows a block diagram of the apparatus 5 in the case where each means of FIG. 1 is
configured by specific hardware.
This device 5 comprises a microphone 2 as sound input means, a head amplifier 4 as amplifier, a
microphone amplifier 6 and a power amplifier 8, a speaker 10 as sound output means, and
howlings of different frequency bands as multiple high band removal filter means. Cut filter 50
(in this example, four of 501, 502, 503, 504), band pass filters (BPF) 55 (551, 552, 553, 554)
which are a plurality of high pass filter means, control circuits 60 (601, 602, 603, 604) which
are a plurality of control means, changeover switch 70 (Terminals 700, 701, 702, 703, 704) are
provided.
[0023]
The BPF 551 is connected to the control circuit 601, and the terminal 701 of the changeover
switch 70 is connected by the output of the control signal C1 generated by the control circuit
601, and the howling cut filter 501 is connected. Further, the control circuit 602 is connected to
the BPF 552, and the terminal 702 of the changeover switch 70 is connected by the output of the
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control signal C2 generated by the control circuit 602, and the howling cut filter 502 is
connected. The same applies to the BPFs 503 and 504.
[0024]
The audio signal input to the microphone 2 is amplified and output from the speaker 10 through
the head amplifier 4, the microphone amplifier 6, and the power amplifier 8 because the terminal
700 of the changeover switch 70 is connected in the normal case. .
[0025]
Here, it is assumed that the device 5 is in a positive feedback closed loop state and howling of the
microphone 2 occurs.
Once this howling occurs, its amplitude is successively amplified and continues to oscillate, so the
power amplifier 8 is saturated and becomes a signal of high frequency and large amplitude. This
howling becomes a specific frequency depending on the amplification degree of the device, the
distance between the microphone 2 and the speaker 10, and the like.
[0026]
For example, as shown in FIG. 3A, when howling P2 of center frequency f2 occurs, howling P2 is
first given to each BPF 55.
[0027]
Here, FIG. 4 a shows the pass frequency band of the BPF 55.
The center frequency of the BPF 551 is f1, the center frequency of the BPF 552 is f2, the center
frequency of the BPF 553 is f3, and the center frequency of the BPF 554 is f4. Therefore,
howling P 2 in this example is taken out only from BPF 552 (101 in the figure) and input to
control circuit 602.
[0028]
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Next, in the control circuit 602, as shown in FIG. 3b, it is determined whether the amplitude of
the howling P2 exceeds the reference amplitude K or not. Then, if the reference amplitude K is
exceeded, the control signal C2 is generated based on the howling P2. The terminal 702 of the
changeover switch 70 is connected by the output of the control signal C2, and the howling cut
filter 502 is connected.
[0029]
Here, FIG. 4 b shows the removal passband of the howling cut filter 50. As shown in this figure,
the center frequency f1 (removed band) of the howling cut filter 501 is set to be the same as the
center frequency f1 (pass band) of the BPF 551 of FIG. The same applies to the cut filter 503 and
the BPF 553 and the howling cut filter 504 and the BPF 554.
[0030]
Thereby, the howling P2 of the center frequency f2 extracted from the BPF 552 is removed by
the howling cut filter 502 (shown in FIG. 3) having a removal band of the center frequency f2
(FIG. 3C). Howlings P1, P3, and P4 extracted from the BPFs 551, 553, and 554 are similarly
removed.
[0031]
Next, the control circuit 60 that outputs the control signal C will be described. As shown in FIG. 5,
the control circuit 60 includes control signal generation circuits 66 (start signal generation
circuit 62 and end signal generation circuit 64) and continuous signal generation circuits 68 for
each of the control circuits 601, 602, 603, and 604. The start signal generation circuit 62
compares the amplitude of the audio signal with a predetermined reference amplitude, and
generates the start signal of the control signal C when the amplitude of the audio signal exceeds
the predetermined reference amplitude. The end signal generation circuit 64 generates an end
signal of the control signal C which is terminated for a predetermined time from the start signal.
Thus, control signals C (C1, C2, C3, C4) are generated for each of the control circuits 60 (601,
602, 603, 604).
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[0032]
This control signal C is inputted to the changeover switch 70 in FIG. 2, and the howling cut filter
50 is turned on a predetermined time (0.6 seconds in this example) after the generation of the
howling P, and then the predetermined time (in this example) Turn off after 1.8 seconds). 6
shows the start signal generation circuit 62, and FIG. 7 shows the end signal generation circuit
64. Further, FIG. 8 shows a signal continuous generation circuit 68.
[0033]
Hereinafter, the operation of the device 5 will be described with reference to the time chart of
FIG. First, in the start signal generation circuit 62 of FIG. 6, the start signal of the control signal C
is generated.
[0034]
The voice signal is integrated by the rectifying and integrating circuit 102 and then provided to
the comparator 104. The threshold value of the comparator 104 is set to be larger than that of a
normal audio signal, and when howling P does not occur, the comparator 104 outputs nothing.
Here, when howling P occurs (FIG. 9a), a waveform as shown in FIG. 9b is outputted from the
rectifying and integrating circuit 102. Then, the waveform is shaped by the comparator 104 and
rises about 0.2 seconds after the generation of the howling P (a shown in FIG. 9). Next, this signal
is inverted by the inverter 106 and then applied to the integrating circuit 108, the comparator
110, the inverter 112 and then to the integrating circuit 114, the comparator 116 and the
inverter 118, and similarly about 0.2 seconds each in total. .4 seconds later (Figs. 9d, 9e). As a
result, a howling P is generated from the toggle flip flop (toggle FF) 120, and a signal M rising
(.beta. Shown in the drawing) with a delay of about 0.6 seconds is extracted (FIG. 9e). This signal
β is used as the start signal of the control signal C.
[0035]
Next, the end signal generation circuit 64 of FIG. 7 generates an end signal of the control signal
C. The circuit 64 includes a first stage circuit 82 and a second stage circuit 84. First, in the first
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stage circuit 82, the output of FIG. 9c is given to the integrating circuit 124 via the inverter 122
and integrated according to a predetermined time constant (FIG. 9f). Then, it is given to the
comparator 126 to obtain the signal R (FIG. 9g). This signal R is applied to the discharge circuit
130 through the integration circuit 128. In the discharge circuit 130, after a predetermined time,
the voltage of the capacitor of the integration circuit 124 is discharged to turn the signal R from
ON to OFF (FIG. 9h). On the other hand, the differentiating circuit 132 creates a signal S for
producing an end signal (which rises 0.2 seconds after howling P is generated) (FIG. 9i). This
signal S and the signal R of the comparator 126 are applied to the OR 134 (FIG. 9j). The output of
OR 134 is applied to toggle FF 136 to produce signal T (FIG. 9k). Then, the inverted signal U (FIG.
9m) of the signal T is applied to the reset flip flop (reset FF) 138. Thereafter, the output of the
reset FF 138 (FIG. 9n) and the signal U are applied to the AND 140 to obtain the signal V (FIG.
9o). Next, this signal V is input to the second stage circuit 84.
[0036]
In the second stage circuit 84, the signal V is applied to the integration circuit 142 and the
comparator 144. This output (FIG. 9p) is applied to the integrating circuit 146, the discharging
circuit 148, and the differentiating circuit 150, similarly to the first stage circuit 82. This output
signal and the signal S of FIG. 9i are applied to the OR 152. Then, the signal W output from the
toggle FF 154 rises at the signal S and becomes a signal (γ shown in the drawing) after a
predetermined time (2.2 seconds) (FIG. 9 q). This signal γ is used as the end signal of the control
signal C.
[0037]
The signal W is a reset signal of the toggle FF 120 (see FIG. 6). As a result, the howling P is
generated from the toggle FF 120, and rises about 0.6 seconds later (β in the figure), and then
falls 1.8 seconds (γ in the figure) to output the control signal C (FIG. 9r). As described above, the
control signal C is generated.
[0038]
For example, when the generated howling P2 passes through the BPF 552 and is input to the
control circuit 602, the control signal C2 is output, the terminal 702 of the changeover switch 70
is connected, and 0.6 seconds from the generation of the howling P2. The howling P2 is removed
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after turning on the howling cut filter 502 (PE in the dotted line in FIG. 9a). After 1.8 seconds, the
howling cut filter 502 is turned off. At this time, when none of the control signals C1, C2, C3 and
C4 is output, C0 is output from the OR 172 in the circuit shown in FIG. 10, and the terminal 700
of the changeover switch 70 is connected. Therefore, since the audio signal does not pass
through the howling cut filter 50 after the howling P is cut, the high frequency component of the
audio signal is not removed, and the sound quality can be improved.
[0039]
When the generation of howling P continues, the signal continuity creating circuit 68 of FIG. 8 is
used. The circuit 68 includes toggle FFs 156, 158, 160, 162, an OR 164, and an inverter 166.
The inverted signal QB of the output Q of the toggle FF 120 is applied to the toggle FFs 156, 158,
160, 162 connected in series (four in this example). This output and the output Q of the toggle
FF 120 are applied to the OR 164, and as shown in FIG. 11, a signal in which the control signal C
continues four times is produced. As a result, when howling P occurs four times consecutively, it
is determined that the howling is not sudden, and the howling cut filter 501 is forced to be in the
ON state, and the following howling is cut.
[0040]
Here, in the case where a plurality of howlings having different frequency bands occur
simultaneously, a plurality of howling cut filters may be selected using a switch that connects a
plurality of them simultaneously instead of the switch selectively selected like the changeover
switch 70 of FIG. It is also conceivable to operate 50 simultaneously to eliminate howling.
[0041]
For example, it is assumed that howling of the bands of the center frequency f2 and the center
frequency f4 occurs simultaneously.
In this case, as shown in FIG. 12A, the howling cut filter 502 and the howling cut filter 504 are
simultaneously connected to the audio signal amplifier circuit by a plurality of changeover
switches 72 connected simultaneously. At this time, as shown in FIG. 12b, the howling cut filter
502 operates to remove the band of the center frequency f2 (shown 103), and as shown in FIG.
12c, the howling cut filter 504 operates to set the center frequency f4. The band may be
removed (shown 104).
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[0042]
However, in practice, in the howling cut filter 502, howling in the band of the center frequency
f2 is removed but howling in the band of the center frequency f4 is passed, and in the howling
cut filter 504, the center frequency f4 is removed. The howling of the band is eliminated but the
howling of the band of the center frequency f2 is passed. As a result, the filter characteristics of
the howling cut filter 50 become flat, and the use of the switch 72 which simultaneously
connects a plurality of howling cut filters 50 does not eliminate howlings of different frequency
bands generated simultaneously. A problem arises.
[0043]
In such a case, by arranging the howling cut filters 50 in series and using the analog switch 74
for each of the howling cut filters 50, the above problem can be solved.
[0044]
FIG. 13 shows an example of the high-pass filter removing means 90 in the audio signal amplifier
circuit according to one embodiment of the present invention.
The howling cut filters 501 to 504 are arranged in series. In this case, as the control signal C, in
addition to the control signals C1 to C4, control signals CB1 to CB4 obtained by inverting the
control signals C1 to C4 by inverters 1801 to 1804 are used.
[0045]
That is, when howling occurs, the control signals C1 to C4 are output to the analog switches 741
to 744, and the howling cut filters 501 to 504 start the band elimination operation. On the other
hand, when the howling does not occur, the control signals CB1 to CB4 are output to the analog
switches 741 to 744, and the howling cut filters 501 to 504 stop the band removing operation.
[0046]
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In the above example, howling cut filter 502 receives control signal C 2 and starts band
elimination operation by analog switch 742, and howling cut filter 504 also receives control
signal C 4 and performs band elimination operation by analog switch 744. Start. Since howling
does not occur in these bands, the howling cut filters 501 and 503 stop the band removal
operation in response to the control signals CB1 and CB3. FIG. 14 shows a state in which two
simultaneously generated howlings are removed. As shown in this figure, howling of the band of
center frequency f2 (shown by 105) and howling of band of center frequency f4 (shown by 106)
are simultaneously removed.
[0047]
Such high-pass filter removing means 90 can remove the howling even when a plurality of
howlings having different frequency bands occur simultaneously.
[0048]
On the other hand, howling has the property of being generated in a chain in different frequency
bands one after another.
[0049]
For example, when howling P2 then P4 occurs, and howling cut filters 502 and 504 are turned
ON to remove howlings P2 and P4, respectively, for example, howling P3 of different frequency
bands is generated in a chain. It is.
[0050]
In such a case, in this embodiment, due to the generation of the plurality of howlings P2 and P4,
the ON state of each of the howling cut filters 502 and 504 is continued so that the howlings P2
and P4 are not output. The ON signal of the filters 502 and 504 lowers the gain of the
microphone amplifier 6 by a predetermined value (1 to 2 dB) to prevent chaining of the howling
P3.
FIG. 15 shows a block diagram of an audio signal amplifier 7 according to an embodiment of the
present invention.
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[0051]
This device 7 comprises a gain reduction signal circuit 65 and an automatic attenuator 92 in
addition to the device 5 of FIG.
The gain reduction signal circuit 65 comprises an OR 94, a delay circuit 96 and a reset FF 98,
and the automatic attenuator 92 comprises an analog switch 76 and resistors R1 and R2.
FIG. 16 shows a time chart representing the operation of the gain reduction signal circuit 65. In
the apparatus 7, a high-frequency removing filter means 90 in which the above-mentioned
howling cut filter 50 is arranged in series is used.
[0052]
First, howling P2 and then P4 occur (Fig. 16a, b). Then, howling cut filters 502 and 504 receive
control signals C2 and C4 (FIGS. 16c and 16d) and are turned ON, and howlings P2 and P4 are
removed. The control signals C2 and C4 are applied to the OR 94 of the gain reduction signal
circuit 65. The output (FIG. 16e) is delayed (for example, several hundreds of msec) by the delay
circuit 96 and given to the reset FF 98. This output (FIG. 16f) is the gain reduction signal GS.
[0053]
Receiving this gain reduction signal GS, the analog switch 76 of the automatic attenuator 92 falls
to the side 762 and the resistance R1 is connected, and the gain of the microphone amplifier 6 is
lowered by 1 to 2 dB. Thereby, it is possible to prevent the howling P3 after the howling P2 and
P4 from being generated in a chain.
[0054]
That is, after howling occurs, the gain of the microphone amplifier 6 is lowered to make the
device 7 change from a closed loop in the positive feedback state to an open loop in the nonfeedback state, and then howlings of different frequency bands occur in succession. I try not to.
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[0055]
Incidentally, instead of the gain reduction signal circuit 65 receiving the output of the control
circuit 60, the circuit 67 as shown in FIG. 17 receiving the direct output from the power
amplifier 8 outputs the gain reduction signal GS when howling occurs. You may
[0056]
Further, in this embodiment, although the automatic attenuator 32 using an analog switch and a
resistor is used, a motor-driven automatic attenuator may be used.
[0057]
In this embodiment, howling is detected based on the output of the power amplifier 8. However,
based on any signal of the microphone 2, the head amplifier 4 or the microphone amplifier 6, for
example, any portion of the signal path is detected. Howling may be detected.
[0058]
Further, in this embodiment, although the high frequency removal filter means is provided
between the amplifier and the audio output means, it may be provided anywhere in the signal
path, for example, between the audio input means and the amplifier. Good.
[0059]
According to the first aspect of the present invention, a plurality of high frequency band removal
filter means (howing cut filters) are provided for each predetermined high frequency band
(howling frequency) in a predetermined portion of the audio signal amplification device. The
predetermined high frequency component (howing) of the audio signal is removed.
The operation of the high frequency removal filter means is controlled by the control means
described later.
A plurality of high pass filter means (BPFs) are provided for each of the predetermined high
frequencies corresponding to the high frequency removal filter means, and passes the
predetermined high frequency components of the audio signal.
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[0060]
A plurality of control means compares the amplitude of the audio signal passed by the high-pass
filter means with a predetermined reference amplitude, and when the amplitude of the audio
signal exceeds the predetermined reference amplitude, the corresponding high-frequency
removal filter The means is operated to perform control so as not to operate the corresponding
high-frequency removal filter means when the amplitude of the audio signal does not exceed the
predetermined reference amplitude.
[0061]
Therefore, when a predetermined high frequency component is generated in the audio signal, the
high frequency removal filter means is operated to remove the predetermined high frequency
component.
Then, when the predetermined high frequency band component is stopped, the high frequency
band removing filter can be prevented from operating to prevent the deterioration of the high
frequency band characteristic and improve the sound quality.
[0062]
Further, by providing a plurality of high-pass removing filter means, only the high range of the
specific range is removed, so that the high range component of the audio signal is prevented
from being removed over a wide range, and the sound quality is improved. it can.
As a result, it is possible to provide an audio signal amplifier that minimizes the deterioration of
sound quality and effectively removes the predetermined high frequency component.
[0063]
In the audio signal amplifying apparatus according to claim 2, the control means keeps the highfrequency removing filter means activated when the number of times the amplitude of the audio
signal exceeds the predetermined reference amplitude exceeds the predetermined number.
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Therefore, it is possible to prevent the high frequency removal filter means from remaining in
operation by the predetermined high frequency component generated only momentarily.
As a result, it is possible to provide an audio signal amplifier that minimizes the deterioration of
sound quality and effectively removes the predetermined high frequency component.
[0064]
The high frequency band removal filter means may be connected in series. Therefore, even when
a plurality of predetermined high frequency components occur at the same time, the high
frequency removal filter means can remove them. As a result, it is possible to provide an audio
signal amplifier that minimizes the deterioration of sound quality and effectively removes the
predetermined high frequency component.
[0065]
According to the fourth aspect of the present invention, when a plurality of predetermined high
frequency components are generated in the audio signal, each high frequency band removal filter
means operates to remove the predetermined high frequency components. Then, when each high
frequency band removal filter means is operated, the gain of the amplifier is lowered by a
predetermined value by the loop coupling degree adjusting means (automatic attenuator).
Therefore, it is possible to prevent the predetermined high frequency components from being
generated again in succession.
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