JP2943713B2 - Surround circuit with pseudo stereo function - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surround circuit, and more particularly to mode control of pseudo stereo and surround in a phase shift type surround circuit having a pseudo stereo function.

[0002]

2. Description of the Related Art A conventional surround circuit of this type is disclosed in Japanese Utility Model Laid-Open Publication No. 64-38884. This conventional surround circuit will be described with reference to the drawings.

FIG. 4 is a block diagram showing the configuration of a conventional surround circuit described in the above publication. As shown in the figure, a conventional surround circuit with a pseudo stereo function includes a left channel signal L and a right channel signal R.
And a difference detection circuit 28 for detecting whether the input signal is stereo or monaural, and taking the input signal as it is into the surround detection circuit 27 as it is based on the detection result or through the pseudo stereo sound creation circuit 23. A judgment circuit 29 for judging whether or not the
The switch 9a is controlled by the switch 9a and determines the output destination of an input signal composed of the left channel signal L and the right channel signal R. In this conventional surround circuit, the changeover switch 22 is arranged immediately after the input terminal 21R for the left channel signal L and the input terminal 21L for the right channel signal R.

Next, the operation of such a conventional surround circuit will be described.

A left channel signal L and a right channel signal R
Is input to the difference detection circuit 28,
The difference between the two signals is detected. Then, it is determined by the determination circuit 29 whether or not there is the difference, and the switch 29 is switched by the output 29a.

When a difference is detected as a result of the determination, the changeover switch 22 is controlled to the position indicated by the broken line. As a result, both signals are input to the surround detection circuit 26 via only the buffers 24L and 24R.

On the other hand, if no difference is detected, the changeover switch 22 is controlled to the position indicated by the solid line. Thereby, the right channel signal R is input to the surround detection circuit 26 via the low-pass filter 23A and the buffer 25R,
The left channel signal L is input to the surround detection circuit 26 via the high-pass filter 23B and the buffer 25L.

The signal detected by the surround detection circuit 26 is input to a phase shift circuit 27. The phase shift circuit 27 performs a phase shift, and outputs a surround sound signal 27.
0 is generated.

As described above, a surround sound signal can be generated by automatically setting the pseudo stereo mode according to whether the input signal is stereo or monaural.

[0010]

In the above-described conventional surround circuit, switching between the stereo function and the pseudo stereo function is performed on the left channel signal L and the right channel signal R immediately after the input, and the difference detection circuit is used. And a surround detection circuit are separately provided. Therefore, in order to perform automatic switching between the surround function and the pseudo stereo function, two switching switches are required in addition to the difference detection circuit and the determination circuit, and there is a drawback that the number of parts is large.

Further, when switching control is performed by two changeover switches, the switching timing of both switches may be shifted, and a timing shift may occur between the left channel signal L and the right channel signal R. This shift has the disadvantage that it is output as an unnatural sound in terms of hearing.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned drawbacks of the prior art, and has as its object to reduce the number of parts and to provide a surround sound which does not output unnatural sound during switching control. Is to provide a circuit.

[0013]

A surround circuit according to the present invention comprises a right channel signal and a left channel signal of an input signal.
Includes a differential amplifier that detects the level difference of the signal.
The amplifier is connected to a stereo signal or a mono signal.
Difference detection means for determining whether the input signal is
Shared with level difference detection means as surround detection circuit
It is characterized by becoming . Other Surrounds According to the Invention
The right and left channel signals of the input signal
First differential amplifying means for detecting a level difference between
The input signal is based on the output of the first differential amplifying means of
Determine if the signal is stereo or monaural
Determining means for determining a level difference between a high band and a low band of the input signal;
A second differential amplifying means for detecting the input signal;
If the determination means determines that the input signal is
The output of the differential amplifying means is selected and transmitted, and the input signal is
If the determination means determines that the signal is a monaural signal,
A selecting means for selecting and outputting the output of the second differential amplifying means;
Stage and the first differential amplifier output from the selection means
A surround that creates a surround signal based on the output of the means
Command signal generating means, and the output from the selecting means.
Pseudo-stereo signal based on the output of the second differential amplifying means
And a pseudo-stereo signal generating means for generating
Sign.

In the surround circuit with pseudo-stereo function of the present invention, whether the input is monaural or stereo is detected by the surround detection circuit itself, and switching from the surround circuit to the pseudo-stereo circuit is performed by the input section of the phase shift circuit. Do with. That is, the detected level difference and the created pseudo stereo signal are alternatively input to the phase shift circuit. For this reason, the number of changeover switches can be reduced by one, and the switching timing of the left and right channel signals does not deviate, thereby preventing deterioration of characteristics at the time of switching.
As described above, since the difference detection circuit for the left and right channel signals is shared with the surround detection circuit, the number of circuits can be reduced, and it is possible to prevent a hearing problem due to variation in characteristics of both circuits.

[0015]

Next, embodiments of the present invention will be described with reference to the drawings.

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

Referring to FIG. 1, a surround circuit according to an embodiment of the present invention is a pseudo circuit including a differential amplifier 1, a high-pass filter 7, a low-pass filter 8, and a differential amplifier 9 functioning as a surround detection circuit. A stereo creation circuit, a changeover switch 2 including a well-known analog switch or the like, a phase shift circuit 3, an inverting amplifier 4, adders 5 and 6,
It comprises a full-wave rectifier 10, a DC smoothing circuit 11, and a stereo signal discriminating circuit comprising a comparator (comparison circuit) 12.

The input terminal LIN is a left channel signal input terminal, the input terminal RIN is a right channel signal input terminal, the output terminal LOUT is a left channel signal output terminal, and the output terminal ROUT is a right channel signal output terminal. .

The operation of the present surround circuit having such a configuration will be described with reference to FIG. FIG. 2 is a waveform diagram showing the operation of each part of the surround circuit of FIG. FIG. 1 shows an input signal Lin of an input terminal LIN , an input signal Rin of an input terminal RIN , an output signal 1a of a differential amplifier 1, an output signal 10a of a full-wave rectifier circuit 10, a DC smoothing circuit 11
And the output signal 12a of the comparator 12
a is shown.

In the figure, input signals of a left channel signal L and a right channel signal R are input to a differential amplifier 1 serving as a surround detection circuit in the case of stereo, and a difference signal 1a between the signal L and the signal R is generated. .

In the case of a monaural source, if the signal is directly input to the differential amplifier 1, the output will be lost. Therefore, the signal passed through the high-pass filter 7 and the low-pass filter 8 is input to the differential amplifier 9, and a difference signal 9a is generated. The cut-off frequency of the high-pass filter 7 is set to about several tens of Hz, and the cut-off frequency of the low-pass filter 8 is set to about several kHz.

When the difference signals 1a and 9a are input to the phase shift circuit 3, their phases are changed. The phase-changed signal 3 a is added to the left channel signal L by the adder 5. As a result, the left channel signal L becomes a new left channel signal to which the indirect sound is added, and the output terminal L
Output from OUT .

On the other hand, the signal 4a obtained by further inverting the phase-changed signal 3a by the inverting amplifier 4 is added to the right channel signal R by the adder 6. That is, the signal 3a is subtracted from the right channel signal R. As a result, the right channel signal R becomes a new right channel signal to which the indirect sound is added, and is output from the output terminal ROUT .

In the phase shift circuit 3, the pole frequency 100H
A phase shift of about z is performed.

Here, in the present surround circuit, in order to determine whether the input signal is stereo sound or monaural sound, the differential amplifier 1 serving as a surround detection circuit is also used as a difference detection circuit, and the difference between the signal L and the signal R is used. The signal 1a is detected. That is, the differential amplifier 1 is shared by the surround detection circuit and the difference detection circuit.

The signal 1a detected by the differential amplifier 1 is full-wave rectified by the full-wave rectifier circuit 10, and the output signal 1a
0a is smoothed by the DC smoothing circuit 11 to DC. As a result, the AC level of the difference signal 1a between the signal L and the signal R is converted into the DC level signal 11a.

The comparator 12 compares the output signal 11a of the DC smoothing circuit 11 with a predetermined threshold level. The comparator 12 determines whether the original signal is a monaural sound or a stereo sound based on the magnitude of the output signal 11a, and switches the switching circuit 2 based on the output signal 12a.
Is controlled by switching. That is, in the case of stereo sound, the switching circuit 2 is controlled to the position indicated by the broken line so that the signal 1a from the differential amplifier 1 becomes the input signal of the phase shift circuit 3. On the other hand, in the case of monaural sound, the switching circuit 2 is controlled to the position indicated by the solid line so that the signal 9a from the differential amplifier 9 becomes the input signal of the phase shift circuit 3.

In short, in the surround circuit, whether the input is monaural or stereo is detected by the surround detection circuit itself, and switching from the surround circuit to the pseudo stereo circuit is performed by the input section of the phase shift circuit. It is. More specifically, the differential amplifier 1 is connected to the signal L and the signal R
And a surround detection circuit, and switching between the surround circuit and the pseudo stereo circuit is performed only by the changeover switch 2 arranged at the input section of the phase shift circuit 3. As described above, since the switching between the surround circuit and the pseudo stereo circuit is performed by a single switch, the number of switches can be reduced by one compared with the conventional configuration, and the switching timing is not shifted, thereby deteriorating the switching characteristics. Can be prevented.

Next, another embodiment of the present invention will be described. FIG. 3 is a block diagram showing another embodiment of the surround circuit according to the present invention, and the same parts as those in FIG. 1 are denoted by the same reference numerals. 3, the surround circuit according to the present embodiment is different from that of FIG. 1 in that a Schmitt circuit 13 is used instead of the comparator 12.

That is, in the circuit of FIG. 1, in order to determine whether the input signal is a stereo sound or a monaural sound,
The difference signal between the signal L and the signal R is determined using the full-wave rectifier circuit 10, the DC smoothing circuit 11, and the comparator 12. In contrast, in the circuit of FIG. 3, a Schmitt circuit 13 is used instead of the comparator 12.

This Schmitt circuit has two types of thresholds to be compared, and when the level of the input signal becomes larger than the large threshold, the output signal changes to the high level and becomes smaller than the small threshold. Sometimes, the output signal changes to a low level. That is, in this Schmitt circuit, the threshold value has a hysteresis characteristic.

With this change, in the present surround circuit, it is possible to prevent the adverse effects caused by the incorporation of noise and to reduce the signal L.
A more stable operation can be performed even for a stereo source having a small difference between the signal and the signal R.

As described above, in the present surround circuit, the switch for switching between the surround function and the pseudo stereo function is provided not at the input terminals of the signals L and R but at the input of the phase shift circuit. Therefore, a circuit that detects the difference between the signal L and the signal R is also used as a surround detection circuit,
Automatic switching between surround function and pseudo stereo function,
It can be realized with fewer circuits and components than before.

In the present surround circuit, since a single changeover switch is provided immediately before the phase shift circuit, the signal L
It is possible to switch between the surround function and the pseudo stereo function without shifting the switching timing between the signal and the signal R.

The present invention can take the following aspects in connection with the description of the claims.

(1) A surround circuit including surround signal creating means for creating a surround signal by shifting the phase of the input left and right channel signals, wherein the level is used to detect a level difference signal between the left and right channel signals. Difference detection means, means for generating a pseudo stereo signal based on the left and right channel signals, and selection means for selectively inputting the level difference signal and the pseudo stereo signal to the surround signal generation means. Surround circuit characterized.

(2) The selection means is a full-wave rectifier for full-wave rectifying the waveform of the level difference signal, a smoothing means for DC-smoothing the full-wave rectified output, and compares the smoothed output with a predetermined threshold. The surround circuit according to (1), further comprising: comparing means for selectively outputting the level difference and the pseudo stereo signal in accordance with a result of the comparison.

(3) The surround circuit according to (2), wherein the comparing means has a hysteresis characteristic in the threshold value.

[0039]

As described above, according to the present invention, by providing a switch for switching in the input section of the phase shift circuit, the difference detection circuit for input signals and the surround detection circuit can be shared, and the surround function and the pseudo stereo function can be achieved. Has the effect that automatic switching can be realized with fewer circuits and components than in the past. Further, by providing a single changeover switch immediately before the phase shift circuit, there is an effect that the surround function and the pseudo stereo function can be switched without shifting the switching timing of the left and right channel signals. In addition, by using a comparator circuit with a threshold having a hysteresis characteristic to generate a control signal for the changeover switch, it is possible to prevent adverse effects due to noise contamination and to operate more stably even with a stereo source having a small difference between left and right signals. There is an effect that can be performed.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a surround circuit according to an embodiment of the present invention.

FIG. 2 is a waveform chart showing the operation of each unit in FIG.

FIG. 3 is a block diagram showing a configuration of a surround circuit according to another embodiment of the present invention.

FIG. 4 is a block diagram illustrating a configuration of a conventional surround circuit.

[Explanation of symbols]

 1, 9 Differential amplifier 2 Changeover switch 3 Phase shift circuit 4 Inverting amplifier 5, 6 Adder 7 High-pass filter 8 Low-pass filter 10 Full-wave rectifier circuit 11 DC smoothing circuit 12 Comparator 13 Schmitt circuit

Claims (5)

(57) [Claims] 1. A right channel signal and a left channel signal of an input signal.
Including a differential amplifier for detecting the level difference of the channel signal.
Whether the input signal is a stereo signal
A difference detecting means for determining whether the signal is a monaural signal and the input signal;
Level difference detection means as a surround detection circuit for force signals
A surround circuit characterized by being shared by 2. A first differential amplifier for detecting a level difference between a right channel signal and a left channel signal of an input signal.
And the input based on the output of the first differential amplifying means.
Determine if the signal is a stereo signal or a monaural signal
Discriminating means for distinguishing between a high frequency range and a low frequency range of the input signal.
A second differential amplifying means for detecting the differential signal;
If the determination means determines that the signal is a stereo signal,
The output of the first differential amplifying means is selected and transmitted, and
When the determination means determines that the signal is a monaural signal,
Selecting means for selecting and outputting the output of the second differential amplifying means, and the first difference output from the selecting means.
A surround signal generation means for generating a surround signal based on the output of the dynamic amplification means are output from said selecting means
Pseudo stereo based on the output of the second differential amplifying means.
And a pseudo-stereo signal generating means for generating a signal . 3. The surround signal generating means and the pseudo signal
Means for performing a phase shift on the output of the selection means, and adding the phase shift output to one of the right channel signal and the left channel signal and to the other 3. The surround circuit according to claim 2, wherein the means for subtracting the value is shared. 4. The method according to claim 1 , wherein the determining means includes a first differential amplifier.
A full-wave rectifier for full-wave rectifying the waveform of the level difference detected by the stage; a smoothing unit for performing DC smoothing on the full-wave rectified output; and a comparing unit for comparing the smoothed output with a predetermined threshold. The input signal is changed according to the comparison result.
4. The surround circuit according to claim 2, wherein it is determined whether the signal is a leo signal or a monaural signal . 5. The surround circuit according to claim 4 , wherein said comparing means has a threshold having a hysteresis characteristic.