JPH08196000A - Audio circuit - Google Patents

Abstract

PURPOSE: To provide a means for compensating the capacity shortage of a speaker box and the characteristic decline of a speaker and reproducing low-frequency sound with presence in the sound circuit of a television or the like. CONSTITUTION: The respective signals of L2 and R2 are mixed in a mixing amplifier 21, amplified to a level optimum for the sound system of a television receiver and outputted as the signals M1. Low-band components are extracted by optional (f) characteristics by a filter 22 and the signals M1 are outputted as the signals M2. The signals M2 are outputted as the signals M3L and M3R by a distributor 23, are superimposed on the respective signals of L2 and R2 branched from a sound control part 2 by the mixing amplifier 24 and the mixing amplifier 25, are inputted to a power amplifier 8 as the signals L4' and R4', are amplified, and drive a speaker 9 and the speaker 10 respectively as output signals L5 and R5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an audio circuit for enhancing a low frequency characteristic in a so-called general audio field such as an audio circuit of a television receiver.

[0002]

2. Description of the Related Art Conventional audio circuits such as television receivers fall into the category of general audio, not so-called high-fidelity audio. Therefore, the sound is a so-called radio cassette tape recorder level sound. On the other hand, however, in the market, more powerful AV (audio / visual) software is required for the audio output of general AV equipment.

In action movies and the like, which occupy most of AV software, the sound contains a lot of low frequency components, and it is required to enhance the power and presence by sufficiently reproducing the low frequency components. There is.

Due to the boom of karaoke, home karaoke for enjoying karaoke at home by connecting an LD player for karaoke or a video tape recorder for karaoke to the television receiver is in the limelight. Is required.

Further, from a global point of view, depending on the country / region, a sound that emphasizes high and low tones, which is so-called "don't miss", is preferred.

On the other hand, in the market of television receivers, further cost reduction is required, and the speaker at the final stage of audio output is also the target, which is a different direction from the market movement. For this reason, miniaturization and weight reduction are progressing, and the low frequency characteristics of the audio frequency characteristics (hereinafter referred to as f characteristics) of the speaker tend to be deteriorated.

In order to solve this problem, a method of increasing the low frequency component of voice by an electric circuit to increase the volume feeling of the low frequency region has been generally used.

A conventional low frequency emphasizing audio circuit will be described with reference to FIG. Referring to FIG. 7 which is a block diagram of an audio circuit in which the low frequency band of the conventional example is enhanced, TV audio input signals TV-L, TV
-R and the video / audio input signals AV-L and AV-R are switched and output as output signals L1 and R1. The output of the AV switch (AVSW) 1 is bass, treble, balance and volume for these signals L1 and R1. , Surround, etc. and outputs as signals L2, R2 are connected to the input of the audio control unit 2. The control unit 3 is connected so as to instruct the AVSW 1 to switch and to perform various controls to the audio control unit 2 by command signals.

The output signal L2 of the voice control unit 2 is divided into two,
One is directly connected to the input of a mixing amplifier 6 which mixes the input signals, and the other is directly connected via a bandpass filter (BPF) 4 which extracts an arbitrary low frequency region from the input signal and outputs it as a signal L3. Similarly, one of the output signals R2 of the voice control unit 2 is input to the input of the mixing amplifier 7 which mixes the input signals directly through the BPF 5 which extracts an arbitrary low frequency region from the input signal and outputs it as the signal R3. Connected. The outputs of the mixing amplifiers 6 and 7 are input to a power amplifier 8 which amplifies the signals L4 and R4 and outputs them as signals L5 and R5, and the amplified outputs are connected to a left speaker (SP) 9 and a right SP10. It

The operation of the conventional audio circuit configured as described above will be described below. The input signals TV-L and TV-R or the input signals AV-L and AV-R are switched by the AVSW1 by the switching signal from the control unit 3 and output as the signals L1 and R1. Signal L1,
R1 is processed by the audio control unit 2 by various control signals for controlling bass, treble, balance, volume, surround, etc. from the control unit 3 and output as signals L2 and R2.

The signals L2 and R2 are each branched into two, and B
Arbitrary low frequency components are extracted by PF4 and BPF5 and output as signals L3 and R3. The original signals L2 and R2 are mixed by mixing amplifier 6 and mixing amplifier 7 and output as signals L4 and R4. This enhances the low frequency components of the original signal. Signals L4, R4
Is amplified by the power amplifier 8 as signals L5 and R5, and reproduced as low-frequency emphasized sound from the speakers 9 and 10. FIG. 8 shows an example of the f characteristic of the conventional audio circuit.

The conventional method as described above is disclosed in
It is also proposed in Japanese Patent No. 49092. In addition, there has been proposed a method for correcting deterioration of a voice signal during transmission by voice control for monaural voice when the voice band is limited to 0.3 to 3.4 KHz like a telephone line (Japanese Patent Laid-Open No. 123543/1989). Issue). However, no specific correction means is specified.

Further, as a conventional example, JP-A-5-11510.
No. 0 gazette proposes a voice emphasizing circuit that makes it easier to hear the voice of the person in the center, but in order to obtain the effect of emphasizing the midrange rather than the bass, the lower range is further claimed in claim 2. A cut circuit is provided, not for bass enhancement.

[0014]

However, the bass enhancement effect is insufficient with the configuration of the conventional audio circuit as shown in FIG. 7 described above. Further, there has been a problem that a sufficient low range feeling cannot be obtained due to f special deterioration due to speaker cost reduction or speaker box capacity reduction due to slimmer TV.

The f-characteristic indicated by the solid line in FIG. 8 is on an electric circuit, and there is also a problem that the f-characteristic of the audio output becomes further disadvantageous due to the addition of the peculiar f-characteristic of the speaker.

It is an object of the audio circuit of the present invention to solve the above problems of the conventional example and to provide an audio circuit capable of obtaining a more effective bass enhancement effect.

[0017]

To achieve the above object, the audio circuit of the present invention has, as a first configuration, a mixing means for mixing a first audio signal and a second audio signal, and the mixing means. A filter for outputting a fourth audio signal extracted from the third audio signal output from the means with an arbitrary frequency characteristic having an optimum f0 value and Q value for a speaker to be used with a specific frequency in the bass range as a reference; Distribution means for distributing at least two of the fourth audio signal as a fifth audio signal, the first audio signal, the second audio signal and the fifth audio signal distributed by the distribution means, respectively. And a superimposing means for superimposing. As a result, there is a characteristic that reproduction with rich low frequencies is possible.

In contrast to the first configuration, control means for performing on / off control or signal level control on the fourth audio signal is provided, and a specific frequency having an arbitrary frequency characteristic to be added to the fourth audio signal. By making it possible to arbitrarily select the signal level of the range, it is possible to make a selection according to the user's preference.

As a second structure, in comparison with the first structure, a full-wave rectified signal is output between the filter as the first filter and the distribution means to output a doubled frequency of the original signal. The wave rectification means and the output signal of the full-wave rectification means with an arbitrary frequency as a reference and a sixth frequency characteristic
It is also possible to adopt a configuration in which a second filter for outputting as the audio signal of is added.

Further, as a modification of the second configuration, with respect to the first configuration, an output signal of the first filter is amplified between the first filter and the distribution means to obtain a fifth audio signal. Amplifying means for outputting, full-wave rectifying means for full-wave rectifying the output signal of the first filter and outputting as a sixth audio signal having a frequency twice the original signal, output signal of the amplifier and full-wave rectifying means. Signal switching means for switching the output signal of the signal to output as a seventh audio signal, first control means for controlling the switching of the signal switching means, and an arbitrary frequency for the output signal of the signal switching means. A second filter that outputs an eighth signal with an arbitrary frequency characteristic as a reference,
It is also possible to add a second control means for performing on / off control or signal level control to the output signal of the second filter.

In the above construction, the switching means may be replaced by a mixing means for mixing the fifth signal of the amplifying means and the sixth signal of the full-wave rectifying means and outputting the mixed signal as the seventh signal. .

[0022]

According to the first aspect of the present invention, the L and R signals are mixed, and an arbitrary low frequency range component is extracted by a filter having an arbitrary frequency characteristic, divided into two by the distribution means, and overlapped by the superposition means. By superimposing only the low frequency component on the original L and R signals while ensuring the separation of the original L and R signals, the audio signal having a sense of volume in the low frequency region is reproduced.

In the second structure, in the low frequency range where it is difficult to output from a small speaker, the overtone is emphasized by the full-wave rectification means to emphasize the bass feeling, and in the case where a switching circuit is provided, the bass is emphasized by an amplifier. It is possible to easily switch between the low-frequency overtone emphasis and the full-wave rectification means. In addition, in the configuration in which the output of the full-wave rectification means and the amplifier are mixed, the effects of both the bass enhancement and the bass overtone enhancement are combined, and both are optimal bass enhancement according to the inch configuration of the TV receiver or the speaker used. Acts to reproduce the audio signal for.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An audio circuit according to an embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of an audio circuit according to the first embodiment of the present invention. The first embodiment of the present invention will be described below with reference to FIG. In FIG. 1, components having the same reference numerals as those in FIG. 7 of the conventional example have the same functions, and detailed description thereof will be omitted.

An AV switch (AVS) for switching between the TV audio input signals TV-L, TV-R and the video audio input signals AV-L, AV-R and outputting them as output signals L1, R1.
The output of W) 1 is connected to the input of the audio control unit 2 which controls the signals L1 and R1 such as bass, treble, balance, volume and surround and outputs as signals L2 and R2.

The output of the audio control section 2 which outputs each signal of L2 and R2 is connected to the input of the mixing amplifier 21 which mixes the input signals and amplifies them to an arbitrary level and outputs as the signal M1. Output is the input signal M1
F0 (resonant frequency of low frequency) for arbitrary low frequency component
Is connected to the input of a filter 22 which extracts a signal having a value and a Q value and outputs it as a signal M2, the output of which is the input signal M
2 is connected to the input of a distributor 23 which separates signals 2 as the signals M3L and M3R so as not to affect the next stage. The output signal M3L and the output signal L2 of the voice control unit 2 are mixed and mixed and output. The output signal M of the distributor 23 is connected to the input of the mixing amplifier 24 which outputs the signal L4 ′.
3R and the output signal R2 of the voice control unit 2 mix the input signals and output a mixed output signal R4 '.
5 inputs. The outputs of the mixing amplifiers 24 and 25 are connected to the input of the power amplifier 8.

The control unit 26 has a function equivalent to that of the control unit 3 of the conventional example shown in FIG. 7 such as outputting a switching instruction to the AVSW 1 and performing various controls to the audio control unit 2 by command signals. The device 23 is configured to perform mute control or stepwise or continuous level control on the audio mixed signal M2 as required.

The operation of the first embodiment of the present invention constructed as above will be described below. Similarly to the conventional example, L2 output via the AVSW1 and the audio control unit 2,
Each signal of R2 is branched and one set is input to the mixing amplifier 21.

The signals of L2 and R2 are supplied to the mixing amplifier 2
The signals are mixed at 1, amplified to an optimum level for the audio system of the television receiver, and output as a signal M1. A low-frequency component of the signal M1 is extracted by the filter 22 with an arbitrary f characteristic, and the signal M1 is extracted.
It is output as 2. The signal M2 is output as the signals M3L and M3R signals by the distributor 23, and superimposed on the signals L2 and R2 branched from the audio control unit 2 by the mixing amplifier 24 and the mixing amplifier 25, and the signals L4 ′ and R4 ′.
Is input to and amplified by the power amplifier 8 as an output signal L
5, the speaker 9 and the speaker 10 are driven as R5. At this time, the control unit 26 performs mute control on the distributor 23 to select whether to add enhanced bass to the outputs of the speakers 9 and 10. Alternatively, the degree of enhancement of the bass range in the output from the speakers 9 and 10 can be adjusted by performing the stepwise or continuous level control as needed. This operation may be performed not only in the distributor 23 but also between the mixing amplifier 21 and the distributor 23.

The low frequency components of the input L and R signals are L and
Whichever is included in R, it is mixed by the mixing amplifier 21 and is distributed to the L and R signals again by the distributor 23 and is reproduced from both speakers, so that the volume of the low range reproduced is increased, and a richer bass enhancement. Is done. The low-frequency signal distributed to the L and R signals is filtered by the filter 22.
Is a region where the directivity in the sense of hearing is weak, and the sense of stereo separation in the sense of hearing is not disturbed. However, since they are reproduced at the same level from the left and right speakers, the volume feeling in the low range becomes extremely rich.

Next, a second embodiment of the present invention will be described with reference to FIG. Note that components having the same reference numerals as those in FIG. 1 and FIG. 7 have the same functions, and detailed description thereof will be omitted.

In the present embodiment, between the filter 22 and the distributor 23 of FIG. 1 of the first embodiment, a switching unit 27 for selecting a processing means of a signal from the filter 22 and a second filter 31 are provided. Is added. That is, the switching unit 27 amplifies the signal M10 from the filter 22 to an arbitrary level and outputs it as a signal M11, a full-wave rectifier circuit 29 that full-wave rectifies the signal M10 from the filter 22 and outputs it as a signal M12, Signals M11 and M12
A switch (SW) 30 for switching and outputting as a signal M13. The output signal M13 of the switching unit 27 passes through a filter 31 for extracting an arbitrary low frequency range from the signal M13 and then outputs a signal M2. Is input to the distributor 23.

The control unit 32 performs the switching instruction to the AVSW 1, various controls by the command signal to the audio control unit 2, the mute control and the level control for the audio mixed signal in the distributor 23, etc., as shown in the embodiment of FIG. It has the same function as the control unit 26, but in addition to
The difference is that switching control is performed on 30.

With the above-mentioned configuration, the operation will be described below. AVSW1 similar to the first embodiment shown in FIG.
The L2 and R2 signals output via the audio control unit 2 are branched and one set is input to the mixing amplifier 21.

The signals of L2 and R2 are supplied to the mixing amplifier 2
The signals are mixed at 1, amplified to an optimum level for the audio system of the television receiver, and output as a signal M1. A low-frequency component having an arbitrary f characteristic is extracted from the signal M1 by the filter 22 and output as a signal M10.

(Explanation for Signal M11 Side) Control Unit 3
2, the SW 30 in the switching unit 27 causes the input signal M1
First, the case where the switch is switched to the 1 side will be described.

The signal M10 is amplified to an optimum level by the amplifier 28 and becomes a signal M11.
It is output as 13. The signal M13 is further output by the filter 31 as a signal M2 having an arbitrary f characteristic. Similar to the first embodiment, the signal M2 is output as the signals M3L and M3R by the distributor 23 and is superimposed on the original L2 and R2 signals branched from the output of the audio control unit 2 by the mixing amplifier 24 and the mixing amplifier 25, respectively. L4 ', R
4'is input to the power amplifier 8 and amplified to drive the speaker 9 and the speaker 10 as output signals L5 and R5, respectively. The low frequency components of the L and R signals are mixed by the mixing amplifier 2 regardless of whether they are included in the L or R signal, and the signals are distributed again to the L and R signals. Bass emphasis is made.

The low-frequency signal distributed to the L and R signals is obtained by setting f0 (resonance frequency of low frequency) near 100 Hz by the filter 22, which is a region having a weak directivity in the sense of hearing, and is a stereo sense in the sense of hearing. The separation feeling is not hindered. However, since it is reproduced at the same level from the left and right speakers, the volume feeling in the low range becomes very rich.

(Description of Signal M12 Side) Next, a case where the control unit 32 switches the SW 30 to the input signal M12 side in the switching unit 27 will be described.

The signal M10 is full-wave rectified by the full-wave rectifier circuit 29 to have a doubled frequency, and is output as the signal M12. The signal M12 is output as a signal M13 via the SW30, and high-frequency components such as edges are cut off by the filter 31 and output as a signal M2.

An example of this waveform conversion using a sine curve is shown in FIG. (1) is an input sine curve. (2) is the phase of the original sine curve from 180 degrees to 36
The polarity of the waveform of the 0 ° portion is inverted. (3)
Is a signal in which a high frequency component is dropped by a filter and shaped into a frequency twice as high as the sine curve of (1).

Similar to the first embodiment, the signal M2 is output as the signals M3L and M3R by the distributor 23, and the original L2 is output by the mixing amplifier 24 and the mixing amplifier 25.
The signals R4 'and R4', which are superimposed on the R2 signals, are input to the power amplifier 8 and amplified as output signals L5 and R5 to drive the speaker 9 and the speaker 10, respectively. L, R
The low-frequency component of each signal is mixed in the L and R signals by the mixing circuit, and is distributed to the L and R signals again.

The signal M12 side is an effective technique particularly when a speaker with a low f characteristic is used, and it is possible to compensate for the lack of the low frequency range by reproducing the overtone of the low-pitched sound part which is not reproduced by the speaker. The volume of the low frequencies to be reproduced is increased, and richer bass enhancement is performed. The low-frequency signals distributed to the L and R signals are selected by the filter 22 as f0 (resonant frequency in the low frequency range) around 100 Hz, which is a region where the directivity on the auditory sense is weak, and the stereo separation on the auditory sense. Is not hindered. However, since it is reproduced at the same level from the left and right speakers, the volume feeling in the low range becomes very rich.

In the second embodiment as well, as in the first embodiment, the control unit 32 performs mute control on the distributor 23 to determine whether to add enhanced bass to the outputs of the speakers 9 and 10. You can choose. Alternatively, the degree of enhancement of the bass range in the output from the speakers 9 and 10 can be adjusted by performing the stepwise or continuous level control as needed. This operation may be performed not only in the distributor 23 but also between the mixing amplifier 21 and the distributor 23.

In the second embodiment, the control circuit 32 switches the speaker in accordance with the speaker used in the television receiver or the user's preference by the same circuit, so that more effective bass rich sound reproduction can be performed.

Needless to say, the present invention also includes a case in which the SW 30 is fixedly switched by using a jumper wire or the like instead of the control of the control unit 32 and the SW 30 is substituted.
In some cases, the amplifier 28 and the SW 30 may be omitted and only the full-wave rectifier circuit 29 may be used.

Full-wave rectifier circuit 29 used in the second embodiment
Can be realized by a circuit configuration as shown in FIG. R in FIG.
1, R2, R3, R4, R5, R6 and R7 are resistors, and C1, C2, C3 and C4 are capacitors. IC
1 and IC2 are operation amplifiers, D1 and D2
Is a diode. A jumper wire is used in place of D1 in FIG. 4, D2 is not mounted, R4 is not mounted, and the circuit is changed to that shown in FIG. It goes without saying that cases are included in the present invention.

Next, the operation will be described. FIG. 4 is for converting the sine curve shown in FIG. 3 into double the frequency. The sine curve will be described as an example.

Here, it is assumed that R1 = R4 = R5 = 2R6. The sine curve (1) of FIG. 3 input to the INPUT of FIG. 4 is applied to the (−) input terminal of IC1. IC
The polarity of the signal is inverted at 1 and the diode D1 and D2 cause I
The negative half-wave (positive half-wave at the output terminal of IC1) input to the NPUT terminal becomes zero. This output is applied to the (−) terminal of IC2 via the resistor R6, amplified by gain −2, inverted in polarity, and output. That is, only the positive half-wave of the sine curve (1) input to the INPUT input terminal is output to OUTPUT in the same phase, and the negative half-wave becomes zero.

On the other hand, the sine curve (1) which is input to the INPUT terminal and branched is input to the (−) terminal of the IC2 via R4. A signal generated at the connection point of R5 and R6 is added to the (-) terminal of this IC2 via R6. In this input sine curve, the negative half-wave at the INPUT input terminal is inverted at IC2 and output from the OUTPUT terminal as a positive half-wave of amplitude 1, while the positive half-wave at the INPUT terminal is input from R6. At this point, the polarity is opposite to that of the positive half-wave at the INPUT terminal, so that the amplitude becomes 1 by subtraction.

Therefore, the output signal that is synthesized and output from the OUTPUT terminal is doubled in frequency because the (-) side of the sine curve (1) is folded back to the (+) side as shown in the waveform (2) of FIG. A full-wave rectified waveform is obtained, and by passing this through a low-pass filter, the waveform of sine curve (3) in FIG. 3 is obtained.

FIG. 6 shows a third embodiment of the present invention. Third
In this embodiment, instead of switching the signals M11 and M12 in the second embodiment, the signals M11 and M12 are mixed and the bass is emphasized by setting an arbitrary frequency to f0 in addition to the bass overtone reproduction in the unreproducible region of the speaker. This enables rich bass reproduction in the lower range.

In FIG. 6, those having the same reference numerals as those in FIG. 2 have the same functions, and detailed description thereof will be omitted. Figure 2
In place of the SW30, a mixer 33 for mixing the signals M11 and M12 is provided.

The signal M11 and the signal M12 produced in the same manner as in the second embodiment are mixed by the mixer 33 and two types of bass enhancement are added, so that more deep bass reproduction is possible.

[0055]

As described above, the audio circuit of the present invention is a signal obtained by mixing the L and R signals by the above-mentioned structure and then extracting and amplifying an arbitrary low-frequency component by a filter having an arbitrary f characteristic. , While ensuring the separation of the original L and R signals, by distributing only the low frequency component using the distribution means and superimposing it on the original L and R signals, it is possible to reproduce an audio signal having a sense of volume in the low frequency range. That is an extremely excellent effect.

Further, by providing a low-frequency overtone emphasis circuit, it is possible to reproduce a harmonic overtone in a frequency range in which the speaker cannot reproduce, thereby enhancing the bass feeling. In addition, a switching circuit and a low-frequency overtone emphasis circuit are provided to easily switch between the low-frequency overtone emphasis circuit and the low-frequency overtone emphasis circuit, or the low-frequency overtone emphasis circuit and the low-frequency overtone emphasis circuit are shared to mix both outputs. For example, by sharing the bass enhancement between the low range and the super low range, a more effective bass enhancement effect can be obtained. In addition, it is possible to obtain an extremely excellent effect that an optimal bass emphasizing circuit can be configured according to the inch configuration of the television receiver or the speaker used.

[Brief description of drawings]

FIG. 1 is a block diagram of an audio circuit according to a first embodiment of the present invention.

FIG. 2 is a block diagram of an audio circuit according to a second embodiment of the present invention.

FIG. 3 is a waveform diagram of full-wave rectification in the same manner as the second embodiment.

FIG. 4 is a circuit diagram of a full-wave rectifier circuit according to the second embodiment.

FIG. 5 is a circuit diagram in which the connection of the full-wave rectifier circuit in the second embodiment is also changed to an amplifier.

FIG. 6 is a block diagram of an audio circuit according to a third embodiment of the present invention.

FIG. 7 is a block diagram of a conventional audio circuit.

FIG. 8 is a frequency characteristic diagram of an output waveform of a conventional example.

[Explanation of symbols]

 21 mixing amplifier 22 filter 23 distributor 24 mixing amplifier 25 mixing amplifier 26 control unit 27 switching unit 28 amplifier 29 full-wave rectifier circuit 30 SW 31 filter 32 control unit 33 mixer

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication H04S 7/00 E

Claims (9)

[Claims] 1. A mixer for mixing a first audio signal and a second audio signal, and a signal in a predetermined low frequency range from a third audio signal output from the mixer, and a fourth audio. A filter that outputs a signal; a distribution unit that distributes the fourth audio signal as at least two as a fifth audio signal; a first audio signal and a second audio signal that are distributed by the distribution unit. An audio circuit, comprising: superimposing means for superimposing the audio signals of 5 on each. 2. The audio circuit according to claim 1, further comprising control means for controlling on / off of the fourth audio signal and outputting to the distribution means. 3. A control means for performing on / off control or signal level control on the fourth audio signal is provided, and a signal level in a specific frequency range having an arbitrary frequency characteristic added to the fourth audio signal is arbitrarily set. The audio circuit according to claim 1, wherein the audio circuit is selectable. 4. A mixing unit that mixes the first audio signal and the second audio signal, and a signal in a predetermined low frequency range is extracted from the third audio signal output from the mixing unit. A first filter for outputting as an audio signal; a full-wave rectifying means for full-wave rectifying the fourth audio signal to obtain a frequency that is twice as high as the original signal and outputting as a fifth audio signal; On the other hand, a second filter that outputs a sixth audio signal with an arbitrary frequency characteristic with an arbitrary frequency as a reference, a distribution unit that divides the sixth audio signal into two, the first audio signal, and the second audio signal. An audio circuit, comprising: a superimposing unit that superimposes the sixth audio signal distributed by the distributing unit on the audio signal. 5. The audio circuit according to claim 4, further comprising control means for performing on / off control or signal level control of the sixth audio signal and outputting the result to the distribution means. 6. The audio circuit according to claim 4, wherein the full-wave rectifying means is used as an amplifier by connecting or disconnecting a peripheral circuit of the full-wave rectifying means. 7. Mixing means for mixing the first audio signal and the second audio signal, and a signal in a predetermined low frequency range is extracted from the third audio signal output from the mixing means. A first filter for outputting as an audio signal; an amplifying means for amplifying the fourth audio signal and outputting as a fifth audio signal; and a full-wave rectification of the fourth audio signal to obtain a frequency twice that of the original signal. Full-wave rectifying means for outputting as a sixth audio signal, signal switching means for switching between the fifth and sixth audio signals and outputting as a seventh audio signal, and switching control for the signal switching means. First control means for performing; a second filter for outputting an eighth audio signal with an arbitrary frequency characteristic based on an arbitrary frequency for the seventh audio signal; Distributing means for performing the first audio signal, Speech circuit and a superimposing means for superimposing each of the eighth sound signal distributed by said distributing means to a second audio signal. 8. The audio circuit according to claim 7, further comprising a second control means for controlling ON / OFF control or signal level control of the eighth audio signal and outputting the eighth audio signal to the distribution means. 9. The audio circuit according to claim 7, further comprising a mixing unit that mixes the fifth signal and the sixth signal and outputs the mixed signal as a seventh signal instead of the switching unit.