JPH0793883A - Voice processing circuit and voice reproducing device - Google Patents

Abstract

PURPOSE:To eliminate a needless low frequency region noise and to emphasize only voice keeping variation of voice quality to the minimum. CONSTITUTION:A left voice signal and a right voice signal are supplied to an adder 3 and a subtracter 4. An output of the adder 3 is supplied to a low frequency cut filter 5 having a first cutoff frequency, and an output of the subtracter 4 is supplied to a low frequency cut filter 6 having a second cutoff frequency. An output of the low frequency cutoff filter 5 and an output of the low frequency cutoff filter 6 are supplied to an adder 7 and a subtracter 8 respectively.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an audio processing circuit and an audio reproducing apparatus capable of reducing noise and emphasizing only audio when recording with a camera-integrated VTR or tape recorder.

[0002]

2. Description of the Related Art An audio recording / reproducing apparatus capable of recording audio, such as a tape recorder and a camera-integrated VTR, is widely used. In the audio recording / reproducing apparatus, the tone quality of each of the left audio signal L and the right audio signal R is adjusted by a tone control circuit for each channel. However, such sound quality adjustment may disturb the sound quality balance. Also, when voice is recorded using a stereo microphone and the recorded voice is reproduced, for example, the voice of a person located in the center may be difficult to hear due to ambient noise. In this case, even if the sound quality is adjusted for each channel, the reproduced sound of the surrounding sound also changes, so that the desired sound cannot be easily heard.

Therefore, for example, an audio processing circuit as shown in FIG. 3 can be considered. That is, in FIG. 3, the left audio signal L is supplied to the adder 44 and the mid-range extraction amplifier 43 via the input terminal 41. Also, the right audio signal R
Is supplied to the adder 45 and the mid-range extraction amplifier 43 via the input terminal 42. The mid-range extraction amplifier 43 is
A circuit for extracting and amplifying the audio signal component of the sum audio signal (L + R) (the signal in the center area where the audio to be recorded) has a frequency band substantially equal to the human audio frequency band from the input audio signals L and R. is there. Mid-range extraction amplifier 4
The outputs of 3 are supplied to adders 44 and 45, respectively.

The output of the adder 44 is amplified by the amplifier 48 after the low frequency component is cut by the low frequency cut filter 46, and is supplied to the output terminal 50. Also, adder 4
The low-frequency cut filter 47 cuts the low-frequency component of the output of the signal No. 5, and the output of the output terminal 5 is amplified by the amplifier 49.
1 is supplied. In this way, it is possible to cut out the low range noise and output only the voice.

[0005]

In the voice processing circuit as described above, if low-pitched noise such as wind noise is completely cut, the change in the sound quality of low-pitched voice (such as male voice) becomes considerably unnatural. Will end up. Therefore, in the voice processing circuit shown in FIG. 3, the cutoff frequency of bass noise is set so as to realize both the bass cut amount and the sound quality change. As a result, the amount of noise cut and the change in sound quality are both inadequate. Also, the circuit configuration becomes complicated.

Therefore, an object of the present invention is to emphasize only voice and to suppress unnecessary changes in sound quality while removing unnecessary low frequency noise, and to easily configure a voice processing circuit and voice reproduction. To provide a device.

[0007]

According to a first aspect of the present invention, there is provided a first adder circuit and a first subtractor circuit to which a left audio signal and a right audio signal are supplied, and an output of the first adder circuit. A first low frequency component attenuation circuit supplied, a second low frequency component attenuation circuit supplied with the output of the first subtraction circuit, and a first low frequency component attenuation circuit
And a second subtraction circuit to which the output of the low-frequency component attenuation circuit and the output of the second low-frequency component attenuation circuit are supplied, and the cutoff frequency of the first low-frequency component attenuation circuit. Is different from the cutoff frequency of the second low-frequency component attenuation circuit.

According to a third aspect of the present invention, there is provided a reproducing circuit group for reproducing a right audio signal and a left audio signal recorded on a recording medium, and a noise attenuating circuit for removing noise in a signal outputted from the reproducing circuit group. The noise attenuating circuit comprises a first adding circuit and a first subtracting circuit to which a left audio signal and a right audio signal are supplied, and a first low-frequency component to which an output of the first adding circuit is supplied. An attenuation circuit, a second low frequency component attenuation circuit to which the output of the first subtraction circuit is supplied, an output of the first low frequency component attenuation circuit and an output of the second low frequency component attenuation circuit are supplied. The audio reproducing device includes a second adding circuit and a second subtracting circuit.

[0009]

The sum signal of the left audio signal L and the right audio signal R is supplied to the adder 3. The difference signal between the left audio signal L and the right audio signal R is supplied to the subtractor 4. The output of the adder 3 is supplied to the low pass cut filter 5. On the other hand, the output of the subtractor 4 is supplied to the low pass cut filter 6. The cutoff frequency and the amplification degree of the low frequency cut filter 5 and the low frequency cut filter 6 are different from each other. Adder 7
In, the output of the low frequency cut filter 5 and the output of the low frequency cut filter 6 are added. Further, in the subtractor 8, the output of the low frequency cut filter 5 and the output of the low frequency cut filter 6 are subtracted.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a voice processing circuit according to the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of a voice processing circuit. In FIG. 1, the left audio signal L is input from the input terminal 1. Further, the right audio signal R is input from the input terminal 2. The left audio signal L is supplied to the adder 3 and the subtractor 4. Similarly, the right audio signal R is also supplied to the adder 3 and the subtractor 4. In the adder 3, a sum sound signal (L + R) (a signal in the center area where the sound to be recorded is located) is generated and output to the low frequency cut filter 5. The amplification factor of the low-frequency cut filter 5 is 2, and the cutoff frequency is 300 Hz. A high cut filter is added to the feedback system of the low cut filter 5. The subtracter 4 generates a difference audio signal (LR) (a signal other than the center area) and outputs it to the low-pass cut filter 6. The amplification factor of the low-frequency cut filter 6 is 1, and the cutoff frequency is 1 kHz.

The sum sound signal (L + R) supplied to the low pass cut filter 5 is 2 (L + R) in a band of 300 Hz or higher.
R), audio signals below 300 Hz are 12 dB / o
Attenuated by ct. The difference audio signal (LR) supplied to the low-pass cut filter 6 is equal to the input audio signal in the band of 1 kHz or more, and the audio signal of less than 1 kHz is attenuated by 12 dB / oct. The output of the low pass cut filter 5 is supplied to the adder 7 and the subtractor 8. Similarly, the output of the low-frequency cut filter 6 is also added by the adder 7
And a subtracter 8. In the adder 7, the two supplied signals are added and output to the 1/2 attenuator 9. The subtractor 8 subtracts the two supplied signals and outputs the subtracted signal to the 1/2 attenuator 10. The left audio signal L attenuated to 1/2 by the attenuator 9 is supplied to the output terminal 11. Also, with the attenuator 10 1
The right audio signal R attenuated to the magnitude of / 2 is output to the output terminal 1
2 is supplied.

When the left audio signal L output from the output terminal 11 is L'and the right audio signal R output from the output terminal 12 is R ', L' = 1 when the cutoff frequency is 1 kHz or higher. / 2 {2 (L + R) + (LR)} = L + 1/2 (L + R) R '= 1/2 {2 (L + R)-(LR)} = R + 1/2 (L + R). As described above, when the cutoff frequency is 1 kHz or higher, the signal component of 1/2 (L + R) is added to the input signal component.

In the vicinity of the cutoff frequency of 500 Hz, the signal (L + R) component supplied to the output terminal 11 is doubled, and the signal (LR) component supplied to the output terminal 12 is 1/4 (-). 12 dB), L '= 1/2 {2 (L + R) +1/4 (LR)} = L / 4 + 7/8 (L + R) R' = 1/2 {2 (L + R) -1/4 ( LR)} = R / 4 + 7/8 (L + R). As you can see, the cutoff frequency is 5
Near 00 Hz, the left audio signal L'and the right audio signal R '
The signal component of is almost (L + R). When the cutoff frequency is 300 Hz or less, the signal components (L + R) and (LR) are attenuated at the same ratio while maintaining this component ratio. Therefore, the absolute value of the entire signal component is attenuated according to the filter characteristic of the signal component (L + R).

As is apparent from the above, it is possible to amplify the signal component (L + R) having a cutoff frequency of less than 1 kHz and cut the signal component (LR). Since most of the components that affect the low-frequency sound quality are included in the signal component (L + R), it is possible to minimize the change in the sound quality by setting the cutoff frequency of the low-frequency cut filter 5 low. On the other hand, wind noise or the like entering the microphone has no correlation with the left audio signal L and the right audio signal R, and is included in the (LR) signal component. Than this,
By setting the cutoff frequency of the low-frequency cut filter 6 to be high and sufficiently attenuating the low-frequency component, such noise can be removed almost completely.

Further, by setting the amplification factor of the low-frequency cut filter 5 higher than that of the low-frequency cut filter 6, the signal component (L + R) can be emphasized.
Furthermore, by adding a high cut filter to the feedback system of the low cut filter 5, the signal component (L
+ R) high-frequency amplification is reduced, and signal components (L
By reducing + R, the reduction in auditory crosstalk (stereo feeling) is compensated.

FIG. 2 is a block diagram of an 8 mm VTR reproducing system to which the audio processing circuit according to the present invention is applied. In FIG. 2, the recording signal on the magnetic tape (not shown) read by the rotary head drum 21 is the preamplifier 2
At 2, it is amplified to an amplitude suitable for demodulation. The signal component (L + R) which is the output of the preamplifier 22 is supplied to the band pass filter 23 of 1.5 MHz, for example.
Also, the signal component (LR) which is the output of the preamplifier 22.
Is supplied to the band pass filter 24 of 1.7 MHz, for example. The bandpass filters 23 and 24 are
It is for separating the carrier component from the audio signal component.

The signal with the carrier component removed is (L +
The R) demodulation circuit 25 and the (LR) demodulation circuit 26 are respectively supplied and demodulated. The output of the (L + R) demodulation circuit 25 is supplied to the NR decoder 27. With this,
The output of the (LR) demodulation circuit 26 is supplied to the NR decoder 28. 8 mmA for NR decoders 27 and 28
Noise is reduced and the dynamic range is expanded according to the FM format. NR decoder 2
The output of 7 is sent to the low-frequency cut filter 29 and the NR decoder 2
The outputs of 8 are supplied to the low-pass cut filter 30. The low-frequency cut filter 29 is the adder 3 shown in FIG.
And has characteristics equivalent to those of the low-pass cut filter 5. Further, the low-pass cut filter 30 is the subtractor 4 shown in FIG.
And has characteristics equivalent to those of the low-pass cut filter 6.

The outputs of the low pass cut filters 29 and 30 are supplied to a matrix decoder 31. The matrix decoder 31 includes an adder 7, a subtractor 8, 1 / shown in FIG.
It has characteristics equivalent to those of the 2 attenuator 9 and the 1/2 attenuator 10. The audio signals L and R decoded by the matrix decoder 31 are output signals from the output terminal 3 as audio signals in which low frequency noise is cut and the audio band is emphasized.
2 and 33 respectively output.

[0019]

According to the present invention, the audio signal component (L +
Each of R) and (LR) is passed through a filter having a different cutoff frequency, and each component is amplified with a different amplification degree. As a result, when the left audio signal L and the right audio signal R are reproduced, it is possible to emphasize the audio signal localized in the center and minimize the change in sound quality to remove the low frequency noise. Further, it can be easily configured in terms of circuit.

[Brief description of drawings]

FIG. 1 is a block diagram of a voice processing circuit according to the present invention.

FIG. 2 is an 8 m to which a voice processing circuit according to the present invention is applied.
It is a block diagram of the reproduction system of mVTR.

FIG. 3 is a block diagram of an audio processing circuit used for explaining a conventional technique.

[Explanation of symbols]

 5, 6, 29, 30 Low-pass cut filter 3, 7 Adder 4, 8 Subtractor

Claims (3)

[Claims] 1. A first adding means and a first subtracting means to which a left audio signal and a right audio signal are supplied, and a first low-frequency component attenuating means to which an output of the first adding means is supplied. A second low frequency component attenuation means supplied with the output of the first subtraction means, an output of the first low frequency component attenuation means and an output of the second low frequency component attenuation means. The second addition means and the second subtraction means are provided, and the cutoff frequency of the first low-frequency component attenuating means is different from the cutoff frequency of the second low-frequency component attenuating means. Audio processing circuit. 2. The audio processing circuit according to claim 1, wherein the amplification degree of the first low frequency component attenuating means and the amplification degree of the second low frequency component attenuating means are different. 3. The noise attenuating means comprises reproducing means for reproducing a right audio signal and a left audio signal recorded on a recording medium, and noise attenuating means for removing noise in the signal output from the reproducing means. Is a first adding means and a first subtracting means to which a left audio signal and a right audio signal are supplied, a first low frequency component attenuating means to which an output of the first adding means is supplied, Second low-frequency component attenuating means to which the output of the first subtracting means is supplied, and second output to which the output of the first low-frequency component attenuating means and the output of the second low-frequency component attenuating means are supplied. An audio reproducing device comprising an adding means and a second subtracting means.