JPH06315198A - Voice outputting circuit - Google Patents

Abstract

PURPOSE:To provide a voice outputting circuit in which an always optimal stereo effect can be obtained even when a listener listens to an acoustic equipment or a video equipment or the like at any front and back position. CONSTITUTION:This circuit is equipped with attenuators 7R and 7L for right and left channel systems which extract right and left channel system voice signals as mutual additional signals, and control each signal level, phase control circuits 8R and 8L for the right and left channel systems which control the phases of the signals which are controlled in level by the both attenuators 7R and 7L, and microcomputer 9 which controls the level attenuating amounts of the both attenuators 7R and 7L, and the phase shift amounts of the both phase control circuits 8R and 8L based on listening position information for right and left channel system speakers 1R and 1L. Then, a signal phase- controlled by the phase control circuit 8R for the right channel system is inverted in phase, and added to the left channel system voice signal, and the signal phase-controlled by the phase control circuit 8L for the left channel system is inverted in phase, and added to the right channel system voice signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an audio output circuit suitable for use in audio equipment, video equipment and the like for stereo reproduction.

[0002]

2. Description of the Related Art Conventionally, as audio equipment for stereo reproduction, there are a system component, a CD radio cassette recorder (a tape recorder with a radio in which a compact disc player is incorporated), and the like. In a system component in which the mosquito, amplifier, tape deck, etc. are separated from each other, the left and right speakers are placed in the left and right in front of the listener (ideally, to obtain the optimum stereo effect. In front of the listener, 3 left and right respectively
Arrange at a total angle of 60 ° that spreads by 0 °),
It is designed for stereo playback.

However, in reality, the left and right channel speaker is an amplifier or a taper because the indoor space is narrow and the wiring process to the left and right channel speaker is troublesome.
The reality is that they are used adjacent to both sides of the rack part with built-in decks, etc., in a layout similar to that of a CD radio-cassette with a built-in speaker, which impairs the spread of sound. I couldn't get enough stereo effect. For example, as shown in FIG. 9, when the listener P is listening at a distance L1 from the audio device 1 having the left and right channel speaker 1L, 1L arranged on both sides, the left and right channel speaker 1L. 1R is located at an angle that spreads by θ1 to the front and left sides of the listener P, respectively, but when the distance from the audio device 1 becomes L2, the horizontal spread angle becomes θ2 (θ1> θ2). , The farther the distance is, the less the sound spreads, and the stereo effect fades.

Therefore, some audio output circuits have been devised so that a sufficient stereo effect can be obtained even in listening with such a speaker arrangement. For example, in FIG.
As shown in 0, the left and right channel audio signals are taken out as additional signals to each other, and the signal levels thereof are controlled by the left and right channel attenuators 2L and 2R, respectively, and then leveled by the left channel attenuator 2L. The phase of the controlled signal is inverted and added to the right channel audio signal by the adder 3R, and the right channel attenuator 2R is added.
The phase control of the signal is inverted by the adder 3L and added to the left channel audio signal by the adder 3L to be led to the left and right channel speakers 1L and 1R, respectively, to give a sense of sound spread and a stereo effect. I try not to damage it significantly.

With this arrangement, for example, when the listener P is listening at a distance L3 from the acoustic device 1 as shown in FIG. 11, the audio signal at the position of the listener P (for convenience of explanation) , The right channel audio signal only), the right channel audio signal from the right channel speaker 1R is represented by a plus vector F1 from the listener P to the right channel speaker 1R. By representing the inverted right channel audio signal from the left channel speaker 1L by the negative vector F2, the composite vector F3 of these vectors F1 and F2 indicates the direction of the sound. Therefore, in this case, the listener P feels that the right channel speaker 1R is located on the front right side of the dotted line position (the spread angle is θ3 ′). The same applies to the left channel speaker 1L.

When the distance of the listener P from the audio equipment 1 becomes L2, the vector F4 of the right channel audio signal from the right channel speaker 1R and the vector F4 from the left channel speaker 1L are inverted. A synthetic vector F6 with the vector F5 of the right channel audio signal indicates the direction of the sound. That is, the actual right channel speaker 1R
Is located at the divergence angle θ2, but it seems that the right channel speaker 1R is located at the position of the chain double-dashed line (the divergence angle is θ2 ′) on the front right side of the listener P. Therefore, a feeling of expanse of the minute sound is obtained.

Here, 4L and 4R are left and right channel input terminals for inputting left and right channel audio signals, respectively.
L and 5R are left and right channel volume volumes for adjusting the level of the left and right channel audio signals to which additional signals have been added.
The left and right channel output amplifiers 6L, 6R are provided.
Then, there is also one in which such an additional signal to the left and right channel audio signals is delayed and added to give a sound field feeling (surround feeling) that is further enveloped in sound.

[0008]

However, in such a conventional audio output circuit, although a sound expansive feeling and a sound field feeling surrounded by the sound can be obtained, a vague sound image is seen from the viewpoint of sound image localization. Moreover, the sound image moved and became unstable depending on the listening position of the listener. for that reason,
It was very tired to listen for a long time, and I could not say that a sufficient stereo effect could be obtained. For example, as can be seen from FIG. 11, the distance of the listener P from the audio device 1 is L2 and L3.
And, the size and angle θ of the composite vectors F6 and F3.
2 ′ and θ3 ′ are also greatly changed, and the stereo effect and the sound pressure level are greatly changed depending on the position of the listener P. The present invention has been made in view of the above points, and an object of the present invention is to provide an audio output circuit capable of always obtaining an optimum stereo effect without being affected by a listening position or the like. Is.

[0009]

In order to achieve the above-mentioned object, in the present invention, a left channel audio signal is taken out as an additional signal and phase-inverted into a right channel audio signal,
Further, in the audio output circuit which takes out the right channel audio signal as an additional signal and inverts the phase to add it to the left channel audio signal respectively, the level and phase of the additional signal to the left and right channel audio signals are set to the left and right channel system speed. The control means is provided for controlling based on the listening position information for the mosquito. For example, the control means controls so that the level of the additional signal becomes 0.52 times the original signal level and the phase thereof is shifted by 75 °.

Specifically, the control means takes out the left and right channel audio signals as additional signals from each other, and controls the signal levels of the left and right channel attenuators, respectively, and the levels are controlled by both attenuators. A phase control circuit for the left and right channel systems, which controls the phase of each signal,
And a control circuit for controlling the level attenuation amount in both attenuators and the phase shift amount in both phase control circuits based on the listening position information for the left and right channel system speakers, respectively.
The signal controlled by the phase control circuit for the left channel system is phase-inverted into a right channel audio signal, and the signal controlled by the phase control circuit for the right channel system is phase inverted to the left channel system. It is designed to be added to each audio signal.

Further, a left channel system delay circuit for delaying the left channel system audio signal and a right channel system delay circuit for delaying the right channel system audio signal are provided, and the delayed left channel system audio signal is provided with the right channel system. The signal phase-controlled by the system phase control circuit is phase-inverted and added, and the delayed right-channel audio signal is phase-inverted by the signal controlled by the left-channel system phase control circuit. It was done like this.

The control means takes out the left and right channel audio signals as additional signals from each other and inverts the phase of one of them to add them, and the difference between the left and right channel audio signals output from the adder. Attenuator that controls the signal level, phase control circuit that controls the phase of the signal whose level is controlled by this attenuator, level attenuation amount in the attenuator and phase shift amount in the phase control circuit And a control circuit for controlling each of the left and right channel system speakers based on the listening position information, and for the channel system audio signal whose phase has been inverted at the time of addition, the phase-controlled signal is phase-inverted. In addition, the signal whose phase is controlled by the phase control circuit is added to the channel audio signal whose phase is not inverted during addition without phase inversion. A.

Further, a left and right channel system delay circuit and an attenuator for delaying and level controlling the left and right channel system audio signals to which the signals from the phase control circuit are respectively applied are provided, and the left and right channel system attenuators are provided. The level attenuation amount in the attenuator is controlled according to the level attenuation amount in the attenuator.

[0014]

As described above, the level and phase of the additional signal to the left and right channel audio signals are controlled by using the attenuator and the phase control circuit based on the listening position information for the left and right channel speaker. A stable sound image and a sufficient sense of sound spread can be provided without being affected by the listening position and the like, and an optimum stereo effect can always be obtained. In addition, by delaying not the additional signal but the left and right channel audio signals to which the additional signal is added, a sound field feeling with a broad sound can be obtained with a high degree of freedom in design. It will be. Furthermore,
By using the difference signal of the left and right channel audio signals as the additional signal, the signal processing time is shortened,
Also, the circuit configuration becomes simple.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. The same parts as those of the conventional one are designated by the same reference numerals and the description thereof will be omitted. In this embodiment, the position and phase of the additional signal to the left and right channel system audio signals are used as the listening position information for the left and right channel system speaker (the plane on which the left and right channel system speakers are arranged (in this case, the acoustic device).
To the listener and the distance information between the left and right channel speakers) so that the optimum stereo effect can be obtained no matter where the listener listens to the audio equipment. It is the one.

Specifically, the left and right channel audio signals which are converted into digital signals by the A / D converter and are input to the left and right channel input terminals 4L and 4R as shown in FIG. Left and right channel attenuators 7L and 7R for controlling the signal levels respectively
And the left and right channel system phase control circuits 8L and 8R for controlling the phases of the signals whose levels have been controlled by both attenuators 7L and 7R, respectively, and the level attenuation amount and both phase control at both attenuators 7L and 7R. A control circuit 9 (for example, a microcomputer) for controlling the phase shift amounts in the circuits 8L and 8R respectively based on the listening position information for the left and right channel system speakers 1L and 1R, and a digital signal from the left channel system input terminal 4L. A left channel delay circuit 10L for delaying the converted left channel audio signal, a right channel delay circuit 10R for delaying the digitally converted right channel audio signal from the right channel input terminal 4R, and this delay A left channel that inverts and adds the signal whose phase is controlled by the right channel phase control circuit 8R to the generated left channel audio signal. R-system adder 11L, a right-channel adder 11R that adds the delayed right-channel audio signal to the delayed right-channel audio signal by inverting the phase of the signal whose phase is controlled by the left-channel system phase control circuit 8L, and adding them together. Bowl 11
Left and right channel system D / A converters 12L and 12R for converting the left and right channel system audio signals to which the additional signals have been added respectively in L and 11R into the original analog are provided.

Here, 13 is a distance measuring circuit for measuring the distance from the audio equipment 1 to the listener P. For example, the distance information signal sent by the listener P operating a remote control transmitter. Is received, the distance to the listener P is measured and input to the microcomputer 9. It should be noted that the distance between the left and right channel system speakers 1L and 1R can be manually input by the listener, but in this case, the left and right channel system speakers 1L and 1R.
C is a speaker integrated type that is adjacent to both sides of the rack.
It is known because it has the same arrangement form as the D radio-cassette, and is stored in advance in the data ROM or the like.

Therefore, the microcomputer 9 determines the distance from the audio device 1 to the listener P and the left and right channel system speed.
Using the distance between 1L and 1R as listening position information,
The level and the phase of the additional signal that gives the optimum stereo effect at each listening position are calculated, and both attenuators 7 and 7 are calculated.
Level attenuation at L and 7R and both phase control circuits 8L and 8R
And the amount of phase shift at.

For example, as shown in FIG. 2, when the listener P is listening at a distance L3 from the acoustic device 1, the spread angle θ of the left and right channel system speakers 1L, 1R.
Since 3 is 30 ° or more, the magnitude of the additional signal vector F2 is set to zero because it is possible to obtain a sufficient stereo effect with only the right channel audio signal vector F1. Then, the distance from the audio device 1 becomes L4, and the vector angle (right channel system speed) of the right channel system audio signal.
When the spread angle θ of the power 1R becomes 30 ° or less, the combined vector F9 of the vector F7 of the right channel audio signal and the vector F8 of its additional signal is the same as the vector F7 of the right channel audio signal at an angle of 30 °. The level and phase of the vector F8 of the additional signal, that is, the angle and the magnitude are set so that Similarly, even if the distance of the listener P becomes L2, the combined vector F6 of the vector F4 of the right channel audio signal and the vector F5 of its additional signal is the same as the vector F4 of the right channel audio signal at an angle of 30 °. The angle and the magnitude of the vector F5 of the additional signal are set so that the magnitude becomes the magnitude. In this way, no matter where the listener P listens to the acoustic device 1 at any of the front and rear positions, the left and right channel speaker 1 is always set at a position of 30 ° in the front and left and right directions.
It feels like there is L, 1R, and an ideal stereo effect can be obtained.

Specifically, if the distance to the listener P is L and the distance between the left and right channel system speakers 1L, 1R is W, the left and right channel system speakers to the front and left of the listener P are shown. The spread angle θ of 1L and 1R can be obtained by θ = tan ⁻¹ {L / (W / 2)}, and from this, the phase and level of the additional signal, that is, the angle and magnitude of the additional signal vector from the antiphase can be calculated. become. For example, as shown in FIG. 3, a vector Fm of the right channel audio signal from the right channel speaker 1R and an inverted right channel audio signal from the left channel speaker 1L, that is, an additional signal vector Fs. , And the case of only the right channel audio signal, the angle Φ and the magnitude | Fs | are Φ = 180 ° −90 ° −2θ− (30 ° −θ) / 2 = 75 ° −3θ / 2 | Fs | = | Fm | × 2 × sin {(30 ° −θ) /
2} is obtained (however, θ ≦ 30 °).

When obtained in this way, the composite vector of the vector of the right channel audio signal and the vector of the additional signal is the same as the vector of the right channel audio signal regardless of where the listener P hears it. The size is such that the sound can be heard from the direction of the spread angle of 30 °. For example, when the vector angle of the right channel audio signal is 30 ° (the spread angle θ of the right channel speaker) as shown in FIG. 4, the additional signal vector F11 is Φ = 30 °, | F.
11 | = 0, the combined vector F12 has the same angle and the same magnitude as the vector F10 of the right channel audio signal. Further, as shown in FIG. 5, when the vector angle of the right channel audio signal is 0 °, the additional signal vector F
14 is Φ = 75 °, | F14 | = | F13 | × 0.52
Therefore, the synthesized vector F15 has the same magnitude as the vector F13 of the right channel audio signal, and the spread angle 30
The angle is such that sound can be heard from the direction of °. still,
The same applies to the case of the left channel audio signal.

FIG. 6 shows a flow chart of the control operation of the microcomputer 9 as described above. First, the microcomputer 9 starts the control operation based on a control program stored in a program ROM or the like, and step # 5, the distance W between the left and right channel system speakers 1L and 1R is set to the data ROM in this case.
And the distance L to the listener P is read from the distance measuring circuit 13 in step # 10. Then, it is determined whether or not the distances W and L read in the next step # 15 are the same as the values used for the previous control, and if they are the same, the control state of the previous time can be maintained. It will end. If they are not the same, the process proceeds to step # 20 to obtain the spread angle θ of the left and right channel system speakers.

Then, in step # 25, it is determined whether or not θ is 30 ° or more, and if it is determined to be large, the process proceeds to step # 30 to obtain the angle Φ of the additional signal vector. Then, in step # 35, the magnitude | Fs | is obtained, and in the next step # 40, the level attenuation amounts at the left and right channel system attenuators 7L and 7R and the left and right channel system phase control circuits 8L and 8R are set. After performing control with the phase shift amount of, the control operation ends. If it is determined in step # 25 that θ is 30 ° or more, the process proceeds to step # 45 and the magnitude of the additional signal vector | Fs |
After setting 0 to zero, the process proceeds to step # 40.

Next, FIG. 7 shows another embodiment in which reverberation processing is applied to each of the additional signals to the left and right channel audio signals to give a further sense of depth.
4L and 14R are reverberation circuits for the left and right channel systems.
L and 15R are phase control circuits 8L and 8 for the left and right channel systems.
Left and right channel reverberation adders for adding signals from a feedback controller, which will be described later, to the signals phase-controlled by R, 16L and 16R are reverberation adders 15L,
Left and right channel reverberation delay circuits for delaying the signals from 15R respectively, and 17L and 17R are reverberation delay circuits 16
The feedback signals from the L and 16R are fed back, that is, attenuated to a predetermined level and then fed to the reverberation adders 15L and 15R. The feedback attenuators, 18L and 18R are left and right channel phase control circuits 8L and 8R. The left and right channel system reverberation circuits 14L and 14R are added to the left and right channel system reverberation circuits, respectively.

Next, FIG. 8 shows the left and right channel input terminals 4L and 4R in order to shorten the processing time for generating the additional signal.
To D / A converters 12L and 12R, a specific configuration of the digital processing unit 19 is shown, in which left and right channel audio signals are taken out as respective additional signals and one phase is inverted, and in this case, the left channel is output. An adder for inverting and adding the phase of the system audio signal, and 21 is a differential signal of the left and right channel system audio signals output from the adder 20.
9 KHz band (the band where you can feel the stereo effect most in terms of hearing)
A band-pass filter that limits the band to 22. Reference numeral 22 denotes a difference signal (2
Attenuator for controlling the level of (0 to 9 KHz band),
A phase control circuit 23 controls the phase of the signal level-controlled by the attenuator 22 (for example, a coefficient is changed by using a first-order IIR filter), and the level attenuation at the attenuator 22 is performed. The amount and the amount of phase shift in the phase control circuit 23 are the left and right channel system speakers 1L, 1
It is controlled by the microcomputer 9 based on the listening position information for R.

Reference numeral 24 is a reverberation circuit, and 25 is a reverberation adder for adding a signal from a feedback controller, which will be described later, to the signal whose phase is controlled by the phase control circuit 23.
Reference numeral 26 denotes a reverberation delay circuit that delays the signal from the reverberation adder 25, and 27 denotes a signal from the reverberation delay circuit 26.
The feedback attenuator that feeds back, that is, attenuates to a predetermined level and then supplies it to the reverberation adder 25, is an adder for adding the signal from the reverberation circuit 24 to the signal from the phase control circuit 23, and 29L and 29R. And 30L, 30R
Is a left / right channel delay circuit and an attenuator for delaying and controlling the level of the left / right channel audio signals converted to digital from the left / right channel input terminals 4L, 4R, respectively. The gains of both attenuators 30L, 30R are attenuators. It is designed to be controlled according to the level attenuation amount at the switch 22. Reference numerals 31L and 31R denote left and right channel system adders that add the signals from the adder 28 to the delayed and level-controlled left and right channel system audio signals, respectively. The left channel system whose phase is inverted at the time of addition by the adder 20. The signal from the adder 28 is phase-inverted and added to the audio signal,
The signal from the adder 28 is added to the right channel audio signal, which has not been phase-inverted at the time of addition by the adder 20, without phase inversion. Reference numerals 32L and 32R denote left and right channel system output terminals for outputting signals from the left and right channel system adders 31L and 31R to the left and right channel system D / A converters 12L and 12R.

In this way, both output terminals 32L, 3
If the gain of the attenuator 22 is A and the gains of the left and right channel attenuators 30L and 30R are B, the left and right channel audio signals output from the 2R are left channel audio signals = BL-A (RL ) = (A + B) L-AR right channel audio signal = BR + A (RL) = (A + B) R-AL, and the gains A and B are controlled by the microcomputer 9 so that A + B in this equation becomes 1. As a result, a signal similar to that shown in FIG. 7 is output to the left / right channel system D / A converter 12
L, 12R. Here, A is 2 × sin {(30 ° −
θ) / 2}. Although the phase of the left channel audio signal is inverted to obtain the difference signal of the left and right channel audio signals, the phase of the right channel audio signal may be inverted, or a bandpass filter may be used. You may omit the reverberation circuit to give a feeling of depth.

As described above, in this embodiment, the distance from the audio equipment to the listener is measured by using the remote control transmitter, but the listener can input the distance arbitrarily by using the numeric keypad or the like. You can In addition, although the system component type audio equipment is described in the present embodiment, the present invention is not limited to this, and the audio equipment is, for example, a speaker.
It may be an integrated CD radio cassette player or a stereo-type video device, and in short, any device capable of stereo reproduction may be used.
Especially in the case of a small radio-cassette player, etc. where the spacing between the left and right channel speakers is extremely narrow, the distance to the listener and the speaker
The level of the additional signal is 0.52 times the original signal level and its phase is 75 ° without having to measure the distance between each
A sufficient stereo effect can be obtained by setting (or switching by switching) so that the shift is performed.

[0029]

As described above, according to the audio output circuit of the present invention, the level and phase of the additional signal to the left and right channel audio signals are controlled based on the listening position information for the left and right channel speaker. As a result, the optimum stereo effect can be obtained no matter where the listener listens to the audio device at any position before and after. Also, by delaying each of the left and right channel audio signals to which the additional signal is added, it is possible to obtain a sound field feeling with a wide envelope. Further, by using the difference signal between the left and right channel audio signals as the additional signal, it is possible to shorten the signal processing time and simplify the circuit configuration.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of an audio output circuit of the present invention.

FIG. 2 is a diagram showing a right channel audio signal at the listener position.

FIG. 3 is a diagram for explaining a method of obtaining an angle and a magnitude of an additional signal vector at the listener position.

FIG. 4 The spread angle of the right channel speaker is 3
The figure which shows the case of 0 degree.

FIG. 5: The spread angle of the right channel speaker is 0.
The figure showing the case of °.

FIG. 6 is a flowchart explaining the control operation of the microcomputer.

FIG. 7 is a diagram showing another embodiment.

FIG. 8 is a diagram showing another specific example of the configuration of the digital processing unit.

FIG. 9 is a diagram showing a listener position with respect to a conventional audio device.

FIG. 10 is a diagram showing an example of the audio output circuit.

FIG. 11 is a diagram showing a right channel audio signal at the listener position.

[Explanation of symbols]

 1L, 1R Left and right channel system speaker 7L, 7R Left and right channel system attenuator 8L, 8R Left and right channel system phase control circuit 9 Microcomputer 10L, 10R Left and right channel system delay circuit 12L, 12R D / A converter 13 Distance measurement Circuit 14L, 14R Reverberation circuit 20 Adder 22 Attenuator 23 Phase control circuit 28 Adder 29L, 29R Left and right channel delay circuit 30L, 30R Left and right channel attenuator

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical indication H04R 3/12 Z 7346-5H H04S 7/00 F 8421-5H

Claims (6)

[Claims] 1. A left channel audio signal is extracted as an additional signal and phase-inverted to a right channel audio signal, and a right channel audio signal is extracted as an additional signal and phase-inverted and added to a left channel audio signal. An audio output circuit comprising a control means for controlling the level and phase of an additional signal to the left and right channel audio signals based on listening position information for the left and right channel speaker. 2. The left and right channel system attenuator for extracting the left and right channel system audio signals as additional signals from each other and controlling the signal levels thereof respectively, and the signal level-controlled by both attenuators. The phase control circuit for the left and right channel systems that controls the phase of each, and the level attenuation amount in both attenuators and the phase shift amount in both phase control circuits based on the listening position information for the left and right channel system speaker, respectively. A control circuit for controlling the phase of the signal controlled by the phase control circuit for the left channel system is inverted to the audio signal of the right channel system, and the signal controlled by the phase control circuit for the right channel system. The audio output circuit according to claim 1, wherein the phase is inverted and added to each of the left channel audio signals. 3. A left channel delay circuit for delaying a left channel audio signal and a right channel delay circuit for delaying a right channel audio signal are provided, and the delayed left channel audio signal is subjected to the right channel. The signal phase-controlled by the system phase control circuit is phase-inverted and added, and the delayed right-channel audio signal is phase-inverted by the signal controlled by the left-channel system phase control circuit. The audio output circuit according to claim 2, wherein: 4. The difference between the adder that takes out the left and right channel audio signals as additional signals from each other and inverts one phase and adds them, and the difference between the left and right channel audio signals output from the adder. Attenuator that controls the signal level, phase control circuit that controls the phase of the signal whose level is controlled by this attenuator, level attenuation amount in the attenuator and phase shift amount in the phase control circuit And a control circuit for controlling each of the left and right channel system speakers based on the listening position information, and for the channel system audio signal whose phase has been inverted at the time of addition, the phase-controlled signal is phase-inverted. In addition, a signal whose phase is controlled by a phase control circuit is added to the channel system audio signal whose phase is not inverted during addition without phase inversion. The audio output circuit according to 1. 5. A left and right channel system delay circuit and an attenuator for delaying and level controlling the left and right channel system audio signals to which the signals from the phase control circuit are added respectively are provided in front of the left and right channel system attenuators. The audio output circuit according to claim 4, wherein the level attenuation amount in the amplifier is controlled according to the level attenuation amount in the attenuator. 6. The control means makes the level of the additional signal 0.52 times the original signal level, and the phase thereof is 75 °.
2. The control is performed so as to be shifted.
The audio output circuit described in.