JP3284747B2 - Sound field control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sound field control apparatus for performing a surround process on a stereo signal composed of left and right two channels.

[0002]

2. Description of the Related Art There is a sound reproducing apparatus which has a surround effect and has a reduced vocal level and is not localized rearward. For example, Japanese Patent Application Laid-Open No. 5-49100 has been proposed.

An example will be described below with reference to FIG. In FIG. 8, 1 is a right (R) channel signal input terminal, 2 is a left (L) channel signal input terminal,
Is a (LR) signal detection circuit, 4 is a low-pass filter,
5 is a phase delay circuit, 6 and 7 are adders, 8 is an inverting amplifier,
9 is an L-channel power amplifier, 10 is an R-channel power amplifier, 11 is an L-channel speaker, 1
2 is an R channel speaker, 13 is an (L + R) signal detection circuit, 14 is a band pass filter, and 15 and 16 are adders.

The (LR) signal detected by the (LR) signal detection circuit 3 is passed through a low-pass filter 4 and then delayed by a phase delay circuit 5 (hereinafter, delayed (LR) ) Signal is expressed as (LR) ′), a surround signal (hereinafter referred to as an S signal), and the L channel is added in normal phase to the adder 6. For the R channel,
In order to disperse the localization, the signals are subjected to antiphase addition in the adder 7 via the inverting amplifier 8.

The (L + R) signal detected by the (L + R) signal detection circuit 13 passes through a band-pass filter 14 that passes only the mid-range, and then (the (L + R) signal that has passed through the band-pass filter is converted to (L + R) ') And a center signal (hereinafter referred to as C signal).
Adders 15 and 16 add positive-phase signals to the L channel and the R channel.

As a result, L + (LR) '+ (L +
R) ′ is reproduced from the speaker 11 via the L-channel power amplifier 9 as a sound from the front left, and R− (L
−R) ′ + (L + R) ′ is reproduced as a sound from the front right by the speaker 12 via the power amplifier 10 for the R channel.

[0007]

However, in the above-mentioned conventional configuration, (L +
R) 'signal is always output as C signal,
When the sound originally should be localized to the left, that is, when the input R signal is 0, the R-channel power amplifier 10 outputs R- (L-
R) ′ + (L + R) ′ = L ′ + L ″ (L ′ represents an L signal passed through a phase delay circuit, and L ″ represents an L signal passed through a band-pass filter), and the right speaker is output. Also outputs an input L signal. Therefore, the sound image is not localized to the left. The same applies to the sound to be localized to the right. That is, there is a disadvantage that the left-right directionality inherent in the stereo signal is impaired.

The present invention solves the above-mentioned conventional problems. By extracting an original C signal, it is possible to reproduce left and right directionality while maintaining vocal clarity, and a circuit for that purpose is provided. An object of the present invention is to provide a sound field control device that can be easily configured.

[0009]

[Means for Solving the Problems]

(Means 1) In order to achieve the above object, a sound field control device of the present invention comprises a detection circuit for detecting an L channel input signal and an R channel input signal, respectively, and a level for determining the magnitude of the output of each of the detection circuits. When it is determined that one of the level detectors and each level detector is small (L + R)
A switch that switches so as not to pass a signal output and a switch control circuit that controls the switch are added to the conventional configuration.

(Means 2) In order to achieve the above object, a sound field control device of the present invention comprises a detection circuit for detecting an L channel input signal and an R channel input signal, respectively.
A volume control amplifier (hereinafter referred to as VCA) for lowering the signal level when the output difference between the two detection circuits is large (L + R) and a VCA control circuit for controlling the VCA are added to the conventional configuration.

(Means 3) In order to achieve the above object, the sound field control device of the present invention comprises a detection circuit for detecting the (L-R) signal and the (L + R) signal, and a circuit for detecting the (L + R) signal. When the output level is lower than the output of the (L-R) signal detection circuit, a switch that switches so as not to pass the (L + R) signal and a switch control circuit that controls this switch are added to the conventional configuration.

(Means 4) In order to achieve the above object, a sound field control device of the present invention comprises a detection circuit for detecting an L channel input signal and an R channel input signal, respectively;
A VCA that controls the gains of the L and R signals in accordance with the difference between the outputs of the two detection circuits,
An adder for adding the output of CA to obtain a C signal;
Is added to the conventional configuration.

[0013]

[Action]

(Operation 1) According to the configuration of the means 1, when either the input level of the L channel input signal or the R channel input signal is lower than the specified level, it is determined that there is no C signal, and no (L + R) signal is output. Therefore, the sound to be localized to the left is localized to the left, and the sound to be localized to the right is the same.

(Function 2) Due to the configuration of the means 2, the level of the (L + R) signal decreases as the difference in volume level between the L-channel input signal and the R-channel input signal increases, and where the difference is sufficiently large. , The level of the (L + R) signal becomes 0 and the level of the C signal becomes 0. Therefore, the sound to be localized to the left is accurately localized to the left, and the sound to be localized to the right is the same.

(Function 3) According to the configuration of the means 3, (L +
When the level of the (R) signal is lower than the level of the (LR) signal, it is determined that there is no C signal, and the (L + R) signal is not output. Therefore, the sound that should be localized to the left is accurately localized to the left,
The same applies to the sound to be localized to the right.

(Function 4) According to the configuration of the means 4, when the volume level of the L-channel input signal is sufficiently higher than the volume level of the R-channel input signal, the gain of the VCA controlling the L signal gradually decreases to 0,
At the same time, the gain of the VCA that controls the R signal gradually increases to 2. At this time, the C signal is 2R,
At this time, the volume of the C signal is sufficiently smaller than that of the L signal, so that the sound image is accurately localized to the left. Conversely, when the volume level of the R channel input signal is sufficiently higher than the volume level of the L channel input signal, V
The gain of CA gradually decreases to 0, and at the same time, the gain of VCA controlling the L signal gradually increases.
Becomes The C signal at this time is 2L, but since the volume of the C signal at this time is sufficiently smaller than the R signal, the sound image is accurately localized to the right.

[0017]

【Example】

(Embodiment 1) Hereinafter, a sound field control device according to a first embodiment of the present invention will be described in detail with reference to FIGS. In the description of the drawings, the same elements as those in FIG. 8 will be denoted by the same reference numerals, and redundant description will be omitted.

FIG. 1 is a block diagram showing a basic configuration of a sound field control device according to a first embodiment of the present invention. In FIG. 1, 17 is an L-channel input signal detection circuit, 18 is an R-channel input signal detection circuit, 19 is an L-channel level detector, 20 is an R-channel level detector, 21 is a switch control circuit, and S1 is a switch. is there.

The (LR) signal detected by the (LR) signal detection circuit 3 passes through a low-pass filter 4 and is then delayed by a phase delay circuit 5 so as to be a surround signal. The in-phase addition is performed by the adder 6.
The R channel is subjected to reverse phase addition by an adder 7 via an inverting amplifier 8 to disperse the localization.

The input stereo L and R signals are detected by detection circuits 17 and 18, respectively, and level detectors 19 and 20 output High if the output level of the detection circuits 17 and 18 exceeds a specified level. Is output, and if not exceeded, Low is output. This prescribed level can be appropriately set according to the purpose of use. Outputs of the level detectors 19 and 20 (hereinafter, | l |, | r |) are input to the switch control circuit 21. The switch control circuit 21 outputs | l |, |
ON / OFF of switch S1 by combination of r |
Control.

The (L + R) signal detected by the (L + R) signal detection circuit 13 passes through the band-pass filter 14, becomes (L + R) ', and is input to the switch S1.
The switch S1 includes a band-pass filter 14, an adder 15,
16 and only when ON (L +
R) ′ is output to the adders 15 and 16, and nothing is output when it is OFF. FIG. 2 shows a truth table of the switch control circuit 21.
Is shown. In FIG. 2, reference numerals 19 and 20 denote level detectors.
Whether the volume levels of the L and R channels are High or Low is input to the switch control circuit 21. The switch control circuit 21 determines that the combination of | l | and | r |
Only in the case of h, the switch S1 is turned ON. That is, the switch S1 outputs (L + R) 'as the C signal only when the volume levels of the L channel and the R channel are both higher than the specified level. Only at this time, an adder 1 is added to the L and R channels as a C signal from which (L + R) 'is extracted.
5 and 16 are added in the normal phase.

Therefore, only when the volume levels of the L channel and the R channel are both higher than the specified level, L +
(L−R) ′ + (L + R) ′ is reproduced as a sound from the front left from the speaker 11 via the L-channel power amplifier 9, and R− (L−R) ′ + (L + R) ′ becomes R
Speaker 1 via power amplifier 10 for channel
The sound is reproduced as sound from the front right of 2.

In this embodiment, for a sound to be localized to the left, (L + R) = L + 0 = L, but (| l |, | r
|) = (High, Low), and the switch S1 is set to O
It becomes FF, C = 0, and the sound is localized to the left. The same applies to the sound to be localized to the right. In the case of a sound that should be localized in the center, such as dialogue, since L = R, (L + R)
≠ 0, and (| l |, | r |) = (High, H
i), and (L + R) ′ is output as the C signal. As a result, it is possible to reproduce the left and right directionality while maintaining sufficient vocal clarity.

The present invention is not limited to the above-described embodiment, and the C signal output from the switch S1 is changed to the L signal,
It is also possible to prepare a center speaker separately without adding to the R signal, and to use it also at the time of reproducing three speakers that outputs a C signal from the center speaker. Further, in the switch control circuit 21, a modification is possible in which the switch S1 is turned ON even when the volume levels of the L channel and the R channel are both low.

(Embodiment 2) Hereinafter, a sound field control device according to a second embodiment of the present invention will be described in detail with reference to FIGS. In the description of the drawings, FIG.
The same elements as those in FIGS. 2 and 8 are denoted by the same reference numerals, and redundant description will be omitted.

FIG. 3 is a block diagram showing the basic configuration of a sound field control device according to a second embodiment of the present invention. In FIG. 3, 22 is a subtractor, 23 is a VCA control circuit, 24, 2
Reference numerals 5 and 26 are VCAs. The input stereo L and R signals are (L-R) signal detection circuit 3, (L + R) signal detection circuit 13, detection circuits 17 and 18, and VCAs 25 and 26.
Is input to (LR) detected by the signal detection circuit 3 (LR)
After passing through the low-pass filter 4, the signal is delayed by the phase delay circuit 5, and is added as a surround signal by the adder 6 in the positive phase to the L channel. The R channel is subjected to reverse phase addition by an adder 7 via an inverting amplifier 8 to disperse the localization. (L + R) detected by the signal detection circuit 13 (L + R)
R) signal passes through the band-pass filter 14 (L +
R) ', and is input to the VCA 24. VCA24
Is provided between the band-pass filter 14 and the adders 15 and 16, and outputs A · (L + R) ′ (A represents the gain of the VCA 24) to the adders 15 and 16 as a C signal.

The detection circuits 17 and 18 output the volume levels of the stereo L and R signals, respectively, and output the output of the detection circuit 17 (hereinafter referred to as | L |) and the output of the detection circuit 18 (hereinafter referred to as |
R |. ) Is subtracted by the subtractor 22 and | L | − | R
|. | L | − | R | is input to the VCA control circuit 23, and the VCA control circuit 23 outputs a voltage for controlling the level of the VCA 24. FIG. 4A shows a gain characteristic diagram of the VCA 24 by the VCA control circuit 23. In FIG. 4A,
VCA2 of the VCA control circuit 23 when L |-| R | = 0
The output voltage for 4 is the maximum, and the gain of VCA 24 at this time is 1. As the absolute value of | L | − | R | increases from 0, the output voltage of VCA control circuit 23 to VCA 24 decreases, and the gain of VCA 24 decreases. When the absolute value of | L |-| R | exceeds a certain level, the gain of the VCA 24 becomes zero.

Therefore, when the volume levels of the L channel and the R channel are the same, the gain of the VCA 24 is 1, and
1 · (L + R) ′ is output as the C signal. At this time, (L + R) ′ is added as an extracted C signal to the L and R channels in the normal phase by adders 15 and 16, and L + R
(L−R) ′ + (L + R) ′ is reproduced as a sound from the front left from the speaker 11 via the L-channel power amplifier 9, and R− (L−R) ′ + (L + R) ′ becomes R
Speaker 1 via power amplifier 10 for channel
The sound is reproduced as sound from the front right of 2.

When the volume level of the L channel is sufficiently higher than the volume level of the R channel, or when the volume level of the R channel is sufficiently higher than the volume level of the L channel, the gain of the VCA 24 becomes 0, the C signal becomes 0 · (L + R) ′ = 0,
No (L + R) signal is output.

In this embodiment, for a sound to be localized to the left, (L + R) = L + 0 = L, but | L | − | R |
>> 0, the gain of VCA24 is 0, and C = A
(L + R) ′ = 0, and the sound is localized to the left. The same applies to the sound to be localized to the right. In the case of a sound to be localized at the center such as a line, since L = R, | L | − | R
| = 0, and the C signal = A · (L + R) ′ = (L +
R) 'is output.

As a result, it is possible to reproduce the left-right directionality while maintaining sufficient vocal clarity.

Further, in this embodiment, when the sound source is left or right, that is, when | L | − | R | ≠ 0, the volume of the C signal (A · (L + R) ′) decreases, and the total volume Lowers, so that VC which amplifies the input L signal and the input R signal
A25 and A26 are used to correct the volume and to emphasize left and right directions. FIG. 4B shows a gain characteristic diagram of the VCAs 25 and 26 by the VCA control circuit 23. In FIG. 4B, when | L | − | R | = 0, the output voltage to the VCAs 25 and 26 of the VCA control circuit 23 is minimum, and the gains of the VCAs 25 and 26 at this time are both 1. | L |
As the absolute value of − | R | increases from 0, the output voltage of VCA control circuit 23 to VCAs 25 and 26 increases, and the gain of VCAs 25 and 26 increases. | L |-
When the absolute value of | R | exceeds a certain level, VCA25,
26 have a gain of 3.

The present invention is not limited to the above-described embodiment. A log conversion circuit is provided at the subsequent stage of the detection circuits 17 and 18, and this output is used as an input to a subtractor, and log | L |-
It is also possible to perform correction by inputting log | R | = log (| L | / | R |) to the VCA control circuit 23. Also VC
Instead of adding the C signal, which is the output of A24, to the L signal and the R signal, it is possible to prepare a center speaker separately and use it during three-speaker playback in which the C signal is output from the center speaker.

Embodiment 3 Hereinafter, a sound field control device according to a third embodiment of the present invention will be described in detail with reference to FIG. In the description of the drawings, FIG.
The same elements as those in FIGS. 3, 4, and 8 are denoted by the same reference numerals,
A duplicate description will be omitted.

FIG. 5 is a block diagram showing a basic configuration of a sound field control device according to a third embodiment of the present invention. In FIG. 5, reference numeral 27 denotes an (L-R) signal detection circuit, and reference numeral 28 denotes (L + R).
Signal detection circuit, 29 is a comparator, 30 is a switch control circuit, 31, 32, 33 are amplifiers, S2 is a switch, 34
Is a power amplifier, and 35 is a center speaker. The input stereo L and R signals are input to the (L-R) signal detection circuit 3 and the (L + R) signal detection circuit 13, respectively. (L−R) detected by the signal detection circuit 3 (L−R)
After passing through the low-pass filter 4, the R) signal is delayed by the phase delay circuit 5 to become (LR) ′, and is added as a surround signal to the L channel by the adder 6 in the positive phase. The R channel is subjected to reverse phase addition by an adder 7 via an inverting amplifier 8 to disperse the localization.

Further, the detected (LR) signal and (L +
R) signals are detected by detection circuits 27 and 28, respectively, and the outputs of the detection circuits 27 and 28 (hereinafter, | LR |, |
L + R |. ) Is input to the comparator 29, and the comparator 29 outputs to the switch control circuit 30 which of the input levels of | LR | and | L + R | is higher. The switch control circuit 30 turns on the switch S2 only when | LR | <| L + R |, and turns off the switch S2 when | LR | ≧ | L + R |.

The (L + R) signal detected by the (L + R) signal detection circuit 13 passes through the band-pass filter 14, becomes (L + R) ', and is input to the switch S2.
The switch S2 passes the (L + R) 'signal only when it is ON, and does not pass it when it is OFF. The switch S
(L + R) 'signal controlled by the C
The signal is reproduced from the center speaker 35 via the power amplifier 34. The C signal extracted at the same time is-
The adder 1 is added to the L and R channels via the 増 幅 器 amplifier 33.
The center signals included in the input L and R signals are removed by addition at 5 and 16. When the switch S2 is OFF, the (L + R) 'signal is not output.

In this embodiment, for a sound to be localized to the left, since R = 0, (L + R) = L + 0 = L, but | LR− = | L + R |, and the switch S2 is turned off.
F is applied, C = 0, and the sound is localized to the left. The same applies to the sound to be localized to the right. In the case of a sound to be localized at the center such as a line, since L = R, | LR− <| L
+ R |, the switch S2 is turned on, and the C signal = (L
+ R) 'is output. As a result, it is possible to reproduce the left and right directionality while maintaining sufficient vocal clarity.

Further, in this embodiment, the switch S2 is turned off.
When F is applied, that is, when | LR | ≧ | L + R |, the C signal becomes 0 and the total volume decreases. Therefore, when the switch S2 is turned off, the input L signal and the input R signal are amplified by the amplifiers 31 and 32. By amplifying the sound by three times, the sound volume is corrected and the left and right directionality is emphasized.

The present invention is not limited to the above-described embodiment, and the C signal output from the switch S2 is changed to the L signal,
By adding it to the R signal, it can be used even during 2-channel reproduction.

Embodiment 4 Hereinafter, a sound field control device according to a fourth embodiment of the present invention will be described in detail with reference to FIGS. In the description of the drawings, FIG.
2, 3, 4, 5, and 8 are denoted by the same reference numerals, and redundant description will be omitted.

FIG. 6 shows a basic configuration of a sound field control device according to a fourth embodiment of the present invention. In FIG. 6, 36 is V
The CA control circuit, 37, 38, 39, 40 are VCA, 41
Is an adder. The input stereo L and R signals are (L
-R) Signal detection circuit 3, detection circuits 17, 18, and V
The signals are input to CAs 37, 38, 39, and 40. (LR)
The (LR) signal detected by the signal detection circuit 3 is passed through a low-pass filter 4 and then delayed by a phase delay circuit 5, and is added as a surround signal to the L channel by an adder 6 in a positive phase. Is done. The R channel is subjected to reverse phase addition by an adder 7 via an inverting amplifier 8 to disperse the localization.

The detection circuits 17 and 18 output the volume levels of the stereo L and R signals, respectively. The output (| L |) of the detection circuit 17 and the output (| R |) of the detection circuit 18 are sent to a subtractor 19. To be | L | − | R |. | L |-| R
Is input to the VCA control circuit 36, and the
The VCA control circuit 36 outputs a voltage for controlling the levels of 8, 39 and 40.

The VCAs 37 and 38 apply the L and R signals to the VC
The signal is amplified according to the output of the A control circuit 36. VC in FIG. 7A
FIG. 4 shows a gain characteristic diagram of the VCAs 37 and 38 by the A control circuit 36. FIG. In FIG. 7A, as the value of | L | − | R | decreases, VCA control circuit 36 outputs a control voltage so that the gain of VCA 37 decreases and the gain of VCA 38 decreases. The gain of the VCAs 37 and 38 changes from 0 to 2, and when | L | − | R | = 0, the VCA
The gains of 37 and 38 are both 1. VCA37, 38
(Hereinafter α · L, (2-α) · R, where α
Is 0 ≦ α ≦ 2 and represents the gain of the VCA 37. ) Is input to the adder 41, and an (α · L + (2-α) · R) signal is detected. The detected (α · L + (2-α) · R) signal passes through the band-pass filter 14, is converted into a C signal, and is output to the adders 15 and 16.

Therefore, when the volume levels of the L channel and the R channel are the same, the gains of the VCAs 37 and 38 become 1, and the adder 41 outputs 1 · L + (2-1) · R = (L
+ R) is output, and the C signal = (L + R) ′. At this time, (L + R) 'is added as an extracted C signal to the L and R channels in the normal phase by the adders 15 and 16,
L + (LR) '+ (L + R)' is reproduced as sound from the front left of the speaker 11 via the power amplifier 9 for L channel, and R- (LR) '+ (L + R)'
Is reproduced as a sound from the front right of the speaker 12 via the power amplifier 10 for the R channel.

When the volume level of the L channel is sufficiently higher than the volume level of the R channel, VCA
37, the gain of the VCA 38 is 2, the output of the adder 41 is 0 · L + (2-0) · R = 2R, and C = 2R ″ (R ″, L ″ are band-pass filters). Represents the L and R signals that have passed through.), But R << L
Therefore, it becomes Cm ²⁰ . Similarly, when the volume level of the R channel is sufficiently higher than the volume level of the L channel, C = 2L ″, but Cm ²⁰ because of L << R.

Further, in this embodiment, when the sound source is left or right, that is, when | L | − | R | ≠ 0, the volume of the C signal (α · L + (2-α) · R) decreases. VCA which amplifies the L signal and the R signal because the total volume is also lowered
39 and 40 are used to correct the volume and to emphasize the left-right directionality. FIG. 7B shows a gain characteristic diagram of the VCAs 39 and 40 by the VCA control circuit 36. In FIG. 7B, when | L | − | R | = 0, V of the VCA control circuit 36 is
The output voltage for CAs 39 and 40 is the minimum, and the gains of VCAs 39 and 40 at this time are both 1. | L |-
As the absolute value of | R | increases from 0, the output voltage of VCA control circuit 36 to VCA 39, 40 increases, and the gain of VCA 39, 40 increases. | L |-
When the absolute value of | R | exceeds a certain level, VCA38,
The gains of 39 are both 3.

In this embodiment, for a sound to be localized to the left, R = 0, | L |-| R | >> 0, and the C signal (α
L- (2-α) R) = 2R ″ = 0, and the sound is localized to the left. The same applies to the case of localization to the right. In the case of a sound to be localized at the center such as a line, since L = R, | L | − | R | = 0, and C = (L + R) ′ is output. As a result, it is possible to reproduce the left and right directionality while maintaining sufficient vocal clarity.

The present invention is not limited to the above-described embodiment. A log conversion circuit is provided at the subsequent stage of the detection circuits 17 and 18, and its output is used as an input to the subtracter 15, and log | L
| -Log | R | = log (| L | / | R |)
It is also possible to make a correction by inputting to the control circuit 36. Also, a C speaker, which is the output of the band-pass filter, is not added to the L signal and the R signal, but a center speaker is separately prepared, and the C signal can be output from the center speaker when reproducing three speakers.

[0050]

As described above, according to the present invention, in a sound field control apparatus for extracting a C signal from a two-channel stereo input signal and performing sound field processing, the output of the (L + R) signal is controlled using a simple configuration. Thus, there is an effect that the left-right directionality can be reproduced and a more realistic sound field can be reproduced.

[Brief description of the drawings]

FIG. 1 is a block diagram of a sound field control device according to a first embodiment of the present invention.

FIG. 2 is a truth table of a switch control circuit 21 in FIG.

FIG. 3 is a block diagram of a sound field control device according to a second embodiment of the present invention.

4A is a diagram illustrating gain characteristics of the VCA 24 in FIG. 3; FIG. 4B is a diagram illustrating gain characteristics of the VCAs 25 and 26 in FIG. 3;

FIG. 5 is a block diagram of a sound field control device according to a third embodiment of the present invention.

FIG. 6 is a block diagram of a sound field control device according to a fourth embodiment of the present invention.

7A is a diagram showing gain characteristics of VCAs 37 and 38 in FIG. 6; FIG. 7B is a diagram showing gain characteristics of VCAs 39 and 40 in FIG. 6;

FIG. 8 is a block diagram of a conventional surround circuit.

[Explanation of symbols]

 Reference Signs List 1 R-channel signal input terminal 2 L-channel signal input terminal 3 (LR) signal detection circuit 4 Low-pass filter 5 Phase delay circuit 6, 7, 15, 16, 41 Adder 8 Inverting amplifier 9, 10, 34 Power Amplifiers 11, 12, 35 Speakers 13 (L + R) signal detectors 14 Bandpass filters 17, 18, 27, 28 Detection circuits 19, 20 Level detectors 21, 30 Switch control circuits 22 Subtractors 23, 36 VCA control circuits 24, 25, 26, 37, 38, 39, 40 VCA 29 Comparator 31, 32, 33 Amplifier S1, S2 Switch

Continuation of front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04S 1/00 H04S 7/00

Claims (4)

(57) [Claims] 1. A circuit for detecting a sum signal (L + R) from a stereo input signal comprising a left (L) channel and a right (R) channel, and a first circuit for detecting a level of the left (L) channel input signal. A detection circuit, a second detection circuit for detecting the level of the right (R) channel input signal, and an input of the output of the first detection circuit to determine whether the level of the input is higher or lower than a specified level A first level detector, a second level detector that receives the output of the second detection circuit as input and performs the same operation as the first level detector,
When the output of the first level detector and the output of the second level detector are input and one of the first level detector and the second level detector is determined to be smaller than a specified level A sound field control device comprising: a switch for switching the sum signal (L + R) so as not to pass therethrough; and a circuit for controlling the switch, wherein the sum signal (L + R) controlled by the switch is used as a center signal. . 2. A circuit for detecting a sum signal (L + R) from a stereo input signal comprising a left (L) channel and a right (R) channel, and a volume control amplifier (Volume) for controlling a level of the sum signal (L + R). Control A
mplifier), a first detection circuit for detecting the level of the left (L) channel input signal, and the right (R)
A second detection circuit for detecting the level of the channel input signal, a subtractor for subtracting the output of the first detection circuit and the output of the second detection circuit, and if the absolute value of the output of the subtractor increases. A circuit for controlling the volume control amplifier so as to lower the output level of the sum signal (L + R) in response thereto, wherein the sum signal (L + R) controlled by the volume control amplifier is used as a center signal. Sound field control device. 3. A circuit for detecting a sum signal (L + R) from a stereo input signal consisting of a left (L) channel and a right (R) channel, and a difference signal (L-R) from the stereo input signal.
R), a first detection circuit for detecting the level of the sum signal (L + R), a second detection circuit for detecting the level of the difference signal (L−R), and the first detection circuit. A comparator that receives the output of the detection circuit and the output of the second detection circuit as inputs, and determines which level is higher, and the output level of the first detection circuit is higher than that of the second detection circuit. A switch for switching the sum signal (L + R) so as not to pass when the output signal is lower than the output level; and a circuit for controlling the switch. The center signal is added to the left (L) channel and right (R) channel input signals, and the center signal is included in the left (L) channel and right (R) channel input signals. Sound field control apparatus characterized by removing the. 4. A first detection circuit for detecting a level of the left (L) channel input signal in a stereo input signal comprising a left (L) channel and a right (R) channel, and a right (R) channel. A second detection circuit for detecting the level of the input signal; and, when the output of the first detection circuit is larger than the output of the second detection circuit, lowering the level of the left (L) channel input signal; A first volume control for controlling the level of the left (L) channel input signal so as to increase the level of the left (L) channel input signal when the output of the second detection circuit is smaller than the output of the second detection circuit. Amplifier (Volume Control A)
and when the output of the first detection circuit is larger than the output of the second detection circuit, the level of the right (R) channel input signal is increased, and the output of the first detection circuit is changed to the second detection signal. A second volume control amplifier for controlling the level of the right (R) channel input signal so as to lower the level of the right (R) channel input signal when the output of the circuit is smaller than the output of the circuit; A control circuit; and an adder for adding the left (L) channel signal and the right (R) channel signal controlled by the volume control amplifier, wherein an output of the adder is used as a center signal. Field control device.