JP2000299824A - Multi-voice demodulator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multi-voice demodulator where a noise canceller with respect to a television voice-multiple signal is effectively activated. SOLUTION: This multi-voice demodulator is a multi-voice demodulator having a noise canceller, and band elimination filters 5, 16 to eliminate a sub voice carrier are placed to a pre-stage of main voice and sub voice signal gate circuits 7, 17 to decrease a change in a storage level by the sub voice carrier so as to reduce a noise by the holding operation in the case of the holding. Furthermore, the band elimination filter 5 to eliminate the sub voice carrier signal is placed to a pre-stage of a noise detection section 39 to detect a noise even when there exists the sub voice carrier.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an audio multiplex demodulator for use in a television receiver or the like.

[0002]

2. Description of the Related Art In recent years, the number of opportunities for mounting a television receiver on a car has been increasing. However, when a normal television receiver is mounted on a car, a television sound signal is remarkably generated due to various pulse noises. to degrade. The pulse noise includes ignition noise from an automobile engine, antenna switching noise generated when switching an antenna by a diversity system, multipath noise, and the like.

[0003] On the other hand, FMs similarly mounted on automobiles
A radio broadcast receiver has conventionally been provided with a function of a noise canceller capable of removing pulse noise. With this noise canceller, FM radio broadcasts can be heard with little deterioration in sound quality due to pulse noise.

Conventionally, television receivers for automobiles have
In order to remove the pulse noise, a noise canceller equivalent to the noise canceller used in the FM radio broadcasting was used.

[0005] However, in television broadcasting, the above-mentioned noise canceller is used in monaural broadcasting.
Although a pulse noise removal effect equivalent to that of FM radio broadcasting can be obtained, a sufficient effect of removing pulse noise cannot be obtained in stereo broadcasting or bilingual broadcasting, and this is an obstacle to good TV audio reception in an in-vehicle TV. Was. The reason is that the sub audio signal of FM radio broadcasting is DSB (double sideband) modulation without subcarriers,
This is because television audio broadcasting is a system in which subcarriers exist.

Hereinafter, a description will be given of the elimination of pulse noise in a conventional on-vehicle television receiver. FIG. 4 is a block diagram showing an audio processing unit (audio multiplex demodulator) of a conventional in-vehicle television, in which a mixer, a local oscillator and a detector at the preceding stage are not shown.

In FIG. 4, reference numeral 1 denotes a voice multiplexed signal input terminal. 2 and 3 are audio output terminals, respectively. 4
Is an input buffer amplifier. Reference numeral 38 denotes a sub audio demodulation unit that detects a sub audio from the audio multiplex signal. Reference numeral 13 denotes a bandpass filter for detecting a sub audio signal. Reference numeral 14 denotes a sub sound detection circuit. Reference numeral 15 denotes a low-pass filter for reducing residual carriers leaking to the output when demodulating (detecting) the sub-sound.
20 and 21 are de-emphasis circuits. Reference numeral 18 denotes a discrimination signal detection unit that detects an audio multiplex discrimination signal for discriminating whether the audio signal is monaural, stereo, or bilingual broadcast. Reference numeral 19 denotes an output signal processing unit that performs a matrix process on the main sound and the sub sound according to the judgment result of the judgment signal detecting unit 18. Reference numeral 39 denotes a noise detection unit that detects a noise component superimposed on the audio multiplex signal. Reference numeral 8 denotes a high-pass filter for detecting a noise component of the audio multiplex signal.
9 is an AGC amplifier. Reference numeral 10 denotes a pulse noise detection circuit that detects pulse noise. Reference numeral 11 denotes a waveform shaping circuit that receives the output of the noise detection unit and generates a switching signal. Reference numeral 6 denotes a low-pass filter for delaying a signal.
Reference numeral 7 denotes a gate circuit which passes or cuts off the audio multiplex signal at the output of the waveform shaping circuit 11 and holds the level at the time of cutoff.

The mixer mixes the received high-frequency television signal with the local oscillation signal and converts the signal into an intermediate frequency signal. The local oscillator supplies the mixer with the local oscillation signal, and the detector outputs the signal from the mixer. The amplified intermediate frequency signal is amplified and detected to output an audio multiplex signal.

The received television broadcast is mixed with a local oscillation signal, converted into an intermediate frequency, and then separated into a video signal and an audio intermediate frequency signal. The audio intermediate frequency signal is detected to become an audio multiplex signal, and is input to the audio multiplex signal input terminal 1 in FIG. The audio multiplexed signal passes through a low-pass filter 6 for signal delay, passes through a gate circuit 7 that temporarily holds the signal by an output of a waveform shaping circuit 11 that operates in response to an output of a pulse noise detection circuit 10 described later, and is input. Enter the buffer amplifier 4. The input buffer amplifier 4 is a buffer amplifier inserted so that an audio multiplex signal is appropriately transmitted to a circuit for demodulating an audio signal at a subsequent stage. The output of the input buffer amplifier 4 is divided into three, and is input to a main audio demodulation unit (which indicates a path leading to the de-emphasis circuit 21), a sub audio demodulation unit 38, and a discrimination signal detection unit 18.

In the operation of the main audio demodulator, an audio multiplexed signal passed through the input buffer amplifier 4 is input to the de-emphasis circuit 21. The output of the de-emphasis circuit 21 is input to the output signal processing section 19.

The output of the input buffer amplifier 4 is input to a sub audio demodulator 38. The audio multiplex signal is first input to the band-pass filter 13. The band-pass filter 13 is a filter for passing a sub-sound carrier signal. Usually, a band-elimination filter or a trap filter for reducing the frequency of the audio multiplex discrimination signal or the like and a higher signal component is provided before or after the band-pass filter 13. But may be omitted here. The output of the band-pass filter 13 enters a sub-sound detection circuit 14 to obtain sub-sound by detection. This sub-sound passes through the low-pass filter 15 for reducing the residual carrier signal superimposed on the sub-sound itself, and is input to the de-emphasis circuit 20. When the sub audio signal is FM-modulated, the residual carrier has the largest frequency component twice that of the original sub audio carrier signal. The output of the de-emphasis circuit 20 is input to the output signal processing section 19.

The output of the input buffer amplifier 4 is input to a discrimination signal detector 18. The determination signal detection unit 18
An audio multiplex discrimination signal included in the audio multiplex signal is detected, and the output signal processing unit 19 is controlled. From this determination signal, it is possible to determine whether the received television signal is a monaural broadcast, a bilingual broadcast, or a stereo broadcast.

As described above, the main sound and the sub sound demodulated from the sound multiplex signal are subjected to matrix processing in the output signal processing unit 19 according to the discrimination signal, and the sound output terminals 2 and 3 are monaural, bilingual, Outputs corresponding to each stereo broadcast appear.

Next, the operation of the noise detector 39, the gate circuit 7, the waveform shaping circuit 11, and the low-pass filter 6 will be described with reference to FIG.

[0015] Generally, received television signals include:
Pulse noise such as engine noise such as ignition noise generated from a car, multipath noise, and antenna switching noise due to a diversity system is superimposed. The pulse noise is also included in the audio multiplex signal detected from this television signal. In synchronization with the pulse noise.

In the case of monaural broadcasting, the audio multiplex signal on which the pulse noise is superimposed has a waveform in which the pulse signal 33 is superimposed on the audio signal as shown in FIG. This signal is attenuated by the high-pass filter 8 in the audio band, and becomes as shown in FIG. The signal shown in FIG.
It enters the amplifier 9 and enters the next pulse noise detection circuit 10. Here, the gain of the AGC amplifier 9 is controlled so that the output of the pulse noise detection circuit 10 becomes substantially constant when there is no pulse noise. Here, when a signal on which pulse noise is superimposed enters, if the response speed of the AGC amplifier 9 is made sufficiently slower than the pulse noise,
The output of the AGC amplifier 9 increases from the constant output by the amount of the pulse. This is detected by the pulse detection circuit 10, and a pulse is input to the waveform shaping circuit 11. The waveform shaping circuit 11 generates a gate pulse 35 having a constant pulse width as shown in FIG.

On the other hand, in the audio multiplex signal input to the audio multiplex signal input terminal 1, as shown in FIG. Become like The signal of FIG. 6D is input to the gate circuit 7 and the level of reference numeral 41 in FIG. 6E where pulse noise starts due to the gate pulse 35 of FIG. 6C generated by the waveform shaping circuit 11. It operates as a so-called noise canceller that performs an operation of holding for the time of the gate pulse 35. Reference numeral 37 denotes a portion whose level is kept constant by the holding operation. The pulse width of the gate pulse 35 is at least the waveform 36
Is set so as to be able to hold the level of reference numeral 41 during the period.

[0018]

However, when the received broadcast is a multiplex broadcast, the operation of the conventional noise canceller becomes insufficient due to the presence of the sub-audio carrier signal. This will be described with reference to FIG.

When the broadcast is a multiplex broadcast, the sub audio component is superimposed on the audio multiplex signal, and the output of the high-pass filter 8 is as shown in FIG. In FIG. 5A,
Reference numeral 24 denotes a sub-sound carrier signal, and reference numerals 23 and 41 denote superposed pulse noise.

In the conventional voice multiplex demodulator configured as described above, the pulse noise 23 is detected by the noise detection unit 39, and a gate pulse having a constant pulse width is generated by the waveform shaping circuit 11, and the period of the gate pulse is determined. In the case where the audio multiplexed signal is held by the middle gate circuit 7, since the auxiliary audio carrier signal is present, when the holding operation is started at the center of the auxiliary audio carrier signal, the gate is switched as shown in a portion 25 in FIG. As a result, the noise output of the audio output is reduced as indicated by a portion 26 in FIG.

However, when the holding operation starts near the upper limit of the sub audio carrier signal as shown in a part 27 of FIG. 5D, the audio output becomes a pseudo audio noise component as shown in a part 28 of FIG. Is generated. Also, when the signal is held near the lower limit of the sub-sound carrier signal as in the part 29 in FIG. 5F, pseudo sound noise as in the part 30 in FIG. 5G is generated.

The sub-sound carrier signal has a considerably high level when the sub-speech is FM-modulated, and the pseudo-speech noise is at a level which is not negligible compared to the original sound signal. Although the high-frequency part of the audio multiplex signal is reduced to some extent by the low-pass filter 6, several tens k
Since the sub audio carrier signal having a frequency of Hz affects the demodulated audio signal, it cannot be reduced significantly, and this effect cannot be avoided.

In the case where the pulse amplitude is small and not large compared to the sub-sound carrier signal as in the pulse noise 41 in FIG. It is difficult to separate the noise from the noise, and in this case, the pulse cannot be detected.
The noise canceller does not operate as in the part 42 of (c), (e), and (g), and noise is output to the audio output.

As described above, in the conventional configuration, pseudo noise is generated at the time of noise cancellation in the state where the sub audio carrier signal exists. In addition, there is a problem that pulse noise cannot be detected due to the sub-sound carrier signal.

An object of the present invention is to solve the above-mentioned conventional problem, and an object of the present invention is to provide an audio multiplex demodulator capable of excellent noise cancellation even in the presence of a sub audio carrier signal.

[0026]

In order to achieve this object, an audio multiplex demodulator according to the first aspect of the present invention includes a noise detection section for detecting a noise component superimposed on an audio multiplex signal, and a noise detection section. And a second waveform shaping circuit for generating a switching signal in response to the output of the second audio shaping circuit, a sub audio carrier removing circuit for reducing or eliminating a sub audio carrier signal superimposed on the audio multiplex signal, and a first waveform shaping circuit , A first gate circuit for holding the output of the sub-sound carrier removal circuit in response to the output of the sub-speech carrier removing unit, a sub-sound demodulation unit for detecting the sub-sound from the audio multiplex signal, and a residual carrier component superimposed on the output of the sub-sound demodulation unit A residual carrier removing circuit for reducing or removing the signal; a second gate circuit for receiving the output of the second waveform shaping circuit and holding the output of the residual carrier removing circuit;
A discrimination signal detection unit for detecting a speech multiplex discrimination signal from a speech multiplex signal, and an output signal for outputting a main sound and a sub-sound or a stereo signal from the outputs of the first and second gate circuits in accordance with the output of the discrimination signal detection unit And a processing unit.

According to the configuration of the audio multiplex demodulator according to the first aspect, the sub audio carrier removing circuit and the residual carrier removing circuit are respectively provided before the first and second gate circuits, and receive the output of the noise detecting section. Since the first and second gate circuits are controlled by the first and second waveform shaping circuits for generating the switching signal, the first and second gate circuits are provided even when the sub audio carrier signal and the residual carrier signal are present. Can reduce the sub audio carrier signal and the residual carrier signal that are input to the sub-carrier, and can reduce pseudo audio noise due to the holding operation.

According to a second aspect of the present invention, there is provided an audio multiplex demodulator.
A sub-sound carrier removal circuit for reducing or removing a sub-sound carrier signal superimposed on the sound multiplexed signal, a noise detection unit for detecting a noise component superimposed on an output of the sub-sound carrier removal circuit, and an output of the noise detection unit. A waveform shaping circuit for receiving and generating a switching signal, a gate circuit for receiving an output of the waveform shaping circuit and holding an audio multiplex signal, and a sub audio demodulation unit for detecting a sub audio from the audio multiplex signal output from the gate circuit. A discrimination signal detection unit for detecting a speech multiplex discrimination signal from the speech multiplex signal, and a main speech and a sub-speech according to the output of the discrimination signal detection unit from the speech multiplex signal output from the gate circuit and the output signal of the sub speech demodulation unit. Or an output signal processing unit for outputting a stereo signal.

According to the configuration of the audio multiplex demodulator according to the second aspect, a sub-audio carrier removing circuit is provided at a stage preceding the noise detecting section, and is gated by a waveform shaping circuit which receives an output of the noise detecting section and generates a switching signal. Since the circuit is controlled, the sub-sound carrier signal input to the noise detection unit can be reduced even when a sub-sound carrier signal is present. The noise can be detected, and the noise canceller can be effectively operated even when the sub audio carrier signal exists.

According to a third aspect of the present invention, there is provided an audio multiplex demodulator.
A sub-sound carrier removal circuit for reducing or removing a sub-sound carrier signal superimposed on the sound multiplexed signal, a noise detection unit for detecting a noise component superimposed on an output of the sub-sound carrier removal circuit, and an output of the noise detection unit. First and second waveform shaping circuits for generating a switching signal in response to the
A first gate circuit for receiving the output of the first waveform shaping circuit and holding the output of the sub audio carrier removal circuit, a sub audio demodulator for detecting the sub audio from the audio multiplex signal, and an output of the sub audio demodulator. A residual carrier removing circuit for reducing or removing the superimposed residual carrier component, a second gate circuit for receiving the output of the second waveform shaping circuit and holding the output of the residual carrier removing circuit, and audio multiplexing from the audio multiplex signal A discriminating signal detecting unit for detecting a discriminating signal; and an output signal processing unit for outputting a main sound and a sub-sound or a stereo signal in accordance with the output of the discriminating signal detecting unit from the outputs of the first and second gate circuits. I have.

According to the configuration of the audio multiplex demodulator according to the third aspect, the sub audio carrier removing circuit is provided before the first gate circuit and the noise detecting section, and the residual carrier removing circuit is provided before the second gate circuit. And the first and second gate circuits are controlled by the first and second waveform shaping circuits that generate the switching signal in response to the output of the noise detection unit. Is present, the sub audio carrier signal and the residual carrier signal input to the first and second gate circuits can be reduced, and pseudo audio noise due to the holding operation can be reduced. Also, the sub-sound carrier signal input to the noise detection unit can be reduced, and even when the pulse noise is not large compared to the sub-sound carrier signal, the pulse noise can be detected. However, the noise canceller can be operated effectively.

[0032]

DESCRIPTION OF THE PREFERRED EMBODIMENTS [First Embodiment] An audio multiplex demodulator according to a first embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing a configuration of a voice multiplex demodulator according to a first embodiment of the present invention, and the illustration of a mixer, a local oscillator, and a detector at the preceding stage is omitted. In FIG. 1, components having the same functions as those in FIG. 4 are denoted by the same reference numerals. Reference numeral 5 denotes a band elimination filter as a sub audio carrier removing circuit for reducing or removing a sub audio carrier signal superimposed on the audio multiplex signal. Reference numeral 16 denotes a band elimination filter as a residual carrier elimination circuit for reducing or eliminating the residual carrier signal superimposed on the output of the sub audio demodulation unit. It should be noted that a trap filter can be used instead of the band elimination filter as the sub audio carrier elimination circuit or the residual carrier elimination circuit. Reference numerals 11 and 12 denote first and second waveform shaping circuits which receive the output of the noise detection unit 39 and generate a switching signal. Reference numeral 7 denotes a first gate circuit that receives the output of the first waveform shaping circuit 11 and holds the output of the band elimination filter 5. A second unit 17 receives the output of the second waveform shaping circuit 12 and holds the output of the band elimination filter 16.
Gate circuit. Note that, in the claims, it is described that the sub audio carrier and the residual audio carrier are reduced or eliminated, but the effect is exerted according to the reduction amount. The same applies to the following embodiments.

In the audio multiplex demodulator having the above configuration, as shown in FIG. 1, an audio multiplex signal is input from an audio multiplex signal input terminal 1 and noise is detected by a noise detecting section 39. Gate pulses are generated by the second waveform shaping circuits 11 and 12, and the first and second gate circuits 7 and 17 are driven by these gate pulses. The audio multiplexed signal input from the audio multiplexed signal input terminal 1 passes through the input buffer amplifier 4 and is input to the band elimination filter 5, and its output passes through the low-pass filter 6 for signal delay to the first signal. The gate circuit 7 is entered. The output of the first gate circuit 7 is used as an output signal processing unit 1 as a main audio signal.
9 is input. Here, if the frequency to be removed by the band elimination filter 5 is set to the sub audio carrier frequency, the output of the band elimination filter 5 can greatly reduce the sub audio carrier signal.

When no pulse noise is superimposed on the audio multiplex signal, the main audio signal is transmitted to the subsequent stage without being affected by the band elimination filter 5, but when the pulse noise is superimposed, the main audio signal is transmitted. The audio multiplexed signal is held in the first gate circuit 7 for a certain period of time by the gate pulse. In this configuration, the signal input to the first gate circuit 7 is a signal having a low level of the sub audio carrier signal as shown in FIG.
In the case where the holding operation is performed, pseudo voice noise can be greatly reduced as shown in a portion 31 in FIG. In this case, the sub audio carrier frequency is about 31.5 kHz for an audio multiplex signal in Japan. This band elimination filter 5
If the recent semiconductor technology is used, the attenuation of the voice band can be reduced by 1 d
B, and the attenuation of the removal frequency can be easily reduced to -30 dB or less.

The output of the input buffer amplifier 4 is input to a sub-sound detector 38, where the sub-sound is detected and input to the band elimination filter 16, and the output of the band elimination filter 16 is supplied to the second gate circuit 17. Output signal processing unit 19
Is input to Here, if the elimination frequency of the band elimination filter 16 is set to the residual carrier frequency included in the output of the sub audio demodulator 38, the residual carrier signal included in the auxiliary audio can be significantly reduced.

When no pulse noise is superimposed on the audio multiplex signal, the sub audio signal is output from the band elimination filter 16.
However, when pulse noise is superimposed, the second gate circuit 17 holds the audio multiplex signal for a certain period of time when the pulse noise is superimposed. When this holding operation is performed, pseudo audio noise can be significantly reduced as in the portion 32 in FIG. In this case, the residual carrier frequency is twice as large as the sub audio signal frequency when the sub audio signal is an FM modulation wave, and is about 63 kHz when the audio multiplex signal is in Japan.

The output signal processor 19 outputs the main / sub audio or the left / right or monaural audio output through the de-emphasis circuits 20 and 21 according to the result of the discrimination signal detector 18. As in this configuration, the output signal processing unit 1
9 can be arranged at the subsequent stage for the following reason. That is, since the sub-audio carrier signal and the residual carrier signal included in the main audio and the sub-audio are reduced by the band elimination filter 5 and the band elimination filter 16, the substantial amplitude of each audio signal is reduced. Output signal processing unit 1 with not so large input dynamic range
This is because the main and sub-speech can be directly input to the sub-voice 9. As a matter of course, as shown in FIG. 4, the de-emphasis circuits 20 and 21 may be located before the output signal processing unit 19.

According to the audio multiplex demodulator of the first embodiment, the band elimination filter 5 for removing the auxiliary audio carrier and the band for removing the residual carrier are provided before the first and second gate circuits 7 and 17. Since the first and second gate circuits 7 and 17 are controlled by the first and second waveform shaping circuits 11 and 12 which respectively provide the removal filter 16 and generate the switching signal in response to the output of the noise detection unit 39, Even when a sub audio carrier signal and a residual carrier signal are present, the sub audio carrier signal and the residual carrier signal input to the first and second gate circuits 7 and 17 can be reduced, and pseudo audio noise due to the holding operation can be reduced. it can.

That is, since the holding operation by the noise canceller is performed on the audio multiplexed signal including the sub audio carrier signal on which the pulse noise is superimposed while excluding the sub audio carrier signal, the pseudo operation by the holding operation is performed. An audio multiplex demodulator capable of reducing audio noise can be realized. In addition, since a holding operation by a noise canceller is performed on a sub-audio signal including a residual carrier signal in a state where the residual carrier signal is removed, an audio multiplex demodulator capable of reducing pseudo audio noise due to the holding operation can be realized. It is.

[Second Embodiment] Hereinafter, a second embodiment of the present invention will be described.
An audio multiplex demodulator according to the embodiment will be described with reference to the drawings.

FIG. 2 is a block diagram showing a configuration of an audio multiplex demodulator according to a second embodiment of the present invention, and the illustration of a mixer, a local oscillator and a detector at the preceding stage is omitted. In FIG. 2, components having the same functions as those in FIG. 4 are given the same numbers. Reference numeral 23 denotes a band elimination filter as a sub audio carrier removal circuit for reducing a sub audio carrier signal superimposed on the audio multiplex signal. Note that a trap filter can also be used as the sub audio carrier removal circuit.

In the audio multiplex demodulator having the above configuration, an audio multiplex signal is input from the audio multiplex signal input terminal 1 and input to the band elimination filter 23 as shown in FIG. If the removal frequency of the band elimination filter 23 is set to the sub-audio carrier frequency, the sub-audio carrier signal of the audio multiplexed signal input to the noise detection unit 39 is greatly reduced. Here, when pulse noise is superimposed on the audio multiplex signal, the frequency component corresponding to the sub-audio carrier frequency of the pulse noise is attenuated by the band elimination filter 23. Since the frequency spectrum includes many higher frequency components than the sub-sound frequency, the pulse is not attenuated by the band elimination filter 23, and the noise detection unit 39 at the subsequent stage can perform noise detection without any trouble.

According to the audio multiplex demodulator of the second embodiment, the band elimination filter 23 for removing the sub audio carrier is provided in the preceding stage of the noise detection section 39, and the output of the noise detection section 39 is received to switch the switching signal. Since the gate circuit 7 is controlled by the waveform shaping circuit 11 that generates
Noise detection unit 3 even when a sub-voice carrier signal exists
9 can be reduced, the pulse noise can be detected even when the pulse noise is not large compared to the sub audio carrier signal, and the noise canceller can be used even when the sub audio carrier signal exists. It can be operated effectively.

In other words, even if the noise level of the audio multiplex signal including the sub audio carrier signal on which the pulse noise is superimposed is not higher than that of the sub audio carrier signal, the audio carrier signal is removed through the band elimination filter 23. Therefore, it is possible to realize an audio multiplex demodulator capable of performing good noise detection.

[Third Embodiment] A voice multiplex demodulator according to a third embodiment of the present invention will be described with reference to the drawings.

FIG. 3 is a block diagram showing a configuration of a voice multiplex demodulator according to a third embodiment of the present invention. A mixer, a local oscillator, and a detector at the preceding stage are not shown. 3, components having the same functions as those in FIG. 4 are denoted by the same reference numerals. Reference numeral 5 denotes a band elimination filter as a sub audio carrier removal circuit for reducing or removing a sub audio carrier signal superimposed on the audio multiplex signal.
Reference numeral 16 denotes a band elimination filter as a residual carrier elimination circuit for reducing or eliminating the residual carrier signal superimposed on the output of the sub audio demodulation unit 38. It should be noted that a trap filter can be used as the sub audio carrier removing circuit instead of the band removing filter. Reference numerals 11 and 12 denote first and second waveform shaping circuits which receive the output of the noise detection unit 39 and generate a switching signal. Reference numeral 7 denotes a first gate circuit that receives the output of the first waveform shaping circuit 11 and holds the output of the band elimination filter 5. 17 is the second
And a second gate circuit that receives the output of the waveform shaping circuit and holds the output of the band elimination filter 16.

In the audio multiplex demodulator having the above configuration, as shown in FIG. 3, an audio multiplex signal is input from the audio multiplex signal input terminal 1, passes through the input buffer amplifier 4, and is output by the band elimination filter 5. The voice carrier signal is reduced, noise is detected by the noise detection section 39, and gate pulses are generated by the first and second waveform shaping circuits 11 and 12, and the first and second gate circuits 7 are formed by these gate pulses. , 17 are driven.

In this configuration, if the elimination frequency of the band elimination filter 5 is set to the sub-audio carrier frequency, the sub-audio carrier signal of the audio multiplexed signal input to the noise detector 39 is greatly reduced.

Here, when pulse noise is superimposed on the audio multiplex signal, the band elimination filter 5 attenuates the frequency component corresponding to the sub audio carrier frequency of the pulse noise. Since the frequency spectrum contains many higher frequency components than the sub-sound frequency, the pulse is not attenuated by the band elimination filter 5 and the noise detection unit 39 at the subsequent stage can detect noise without any trouble.

The audio multiplexed signal input from the audio multiplexed signal input terminal 1 passes through the input buffer amplifier 4 and is input to the band elimination filter 5, and its output passes through the low-pass filter 6 for signal delay. The first gate circuit 7 is entered. The output of the first gate circuit 7 is input to the output signal processing section 19 as a main audio signal. Here, if the frequency to be removed by the band elimination filter 5 is set to the sub audio carrier frequency, the output of the band elimination filter 5 can greatly reduce the sub audio carrier signal.

When no pulse noise is superimposed on the audio multiplex signal, the main audio signal is transmitted to the subsequent stage without being affected by the band elimination filter 5, but when the pulse noise is superimposed, the main audio signal is transmitted. The audio multiplexed signal is held in the first gate circuit 7 for a certain period of time by the gate pulse. In this configuration, the signal input to the first gate circuit 7 is a low signal of the sub-sound carrier signal as shown in FIG. 5 (h). Pseudo voice noise can be greatly reduced like the part 31 of 5 (h). The sub audio carrier frequency in this case is approximately 31.5 k in the case of an audio multiplex signal in Japan.
Hz. The band elimination filter 1 can easily reduce the attenuation of the audio band to 1 dB or less and the attenuation of the elimination frequency to -30 dB or less by using recent semiconductor technology.

The output of the input buffer amplifier 4 is input to a sub-sound detector 38, where the sub-sound is detected and input to the band elimination filter 16, and the output of the band elimination filter 16 is supplied to the second gate circuit 17. Output signal processing unit 19
Is input to Here, if the elimination frequency of the band elimination filter 17 is set to the residual carrier frequency that appears in the output of the sub audio detector 38, the residual carrier signal that appears in the auxiliary audio can be significantly reduced.

When no pulse noise is superimposed on the audio multiplex signal, the sub audio signal is
However, when pulse noise is superimposed, the second gate circuit 17 holds the audio multiplex signal for a certain period of time when the pulse noise is superimposed. When this holding operation is performed, pseudo speech noise can be greatly reduced as shown in FIG. In this case, the residual carrier frequency is 2 of the sub audio signal frequency when the sub audio signal is an FM modulated wave.
The largest is about 6 in the case of audio multiplex signals in Japan.
3 kHz.

The output signal processor 19 outputs the main / sub sound or the left / right or monaural sound output through the de-emphasis circuits 20 and 21 according to the result of the discrimination signal detector 18. As in this configuration, the output signal processing unit 19
Can be arranged at the subsequent stage for the following reason. That is, since the sub-audio carrier signal and the residual carrier signal included in the main audio and the sub-audio are reduced by the band elimination filter 5 and the band elimination filter 16, the substantial amplitude of each audio signal is reduced. Output signal processing unit 1 with not so large input dynamic range
This is because the main and sub-speech can be directly input to the sub-voice 9. Naturally, as shown in FIG. 4, the de-emphasis circuits 20 and 21 may be located before the output signal processing unit 19.

According to the audio multiplex demodulator of the third embodiment, the band elimination filter 5 for removing the auxiliary audio carrier and the band for removing the residual carrier are provided before the first and second gate circuits 7 and 17. Since the first and second gate circuits 7 and 17 are controlled by the first and second waveform shaping circuits 11 and 12 which respectively provide the removal filter 16 and generate the switching signal in response to the output of the noise detection unit 39, Even when a sub audio carrier signal and a residual carrier signal are present, the sub audio carrier signal and the residual carrier signal input to the first and second gate circuits 7 and 17 can be reduced, and pseudo audio noise due to the holding operation can be reduced. it can.

In other words, even if the noise level of the audio multiplex signal including the sub audio carrier signal on which the pulse noise is superimposed is not higher than that of the auxiliary audio carrier signal, the audio carrier signal is removed through the band elimination filter. Therefore, it is possible to realize a voice multiplex demodulator capable of performing good noise detection. In addition, since the holding operation by the noise canceller is performed on the sub audio signal including the residual carrier signal in a state where the residual carrier signal is removed,
An audio multiplex demodulator capable of reducing pseudo audio noise due to the holding operation can be realized.

A band rejection filter 23 for removing a sub-sound carrier is provided at a stage preceding the noise detection unit 39, and the gate circuit 7 is controlled by the waveform shaping circuit 11 which receives the output of the noise detection unit 39 and generates a switching signal. As a result, even if a sub-sound carrier signal is present, the sub-sound carrier signal input to the noise detection unit 39 can be reduced, and even if the pulse noise is not large compared to the sub-sound carrier signal, the pulse noise detection can be performed. This makes it possible to effectively operate the noise canceller even when a sub-audio carrier signal exists.

In other words, since the holding operation by the noise canceller is performed in a state where the sub-sound carrier signal is removed from the sound multiplex signal including the sub-sound carrier signal on which the pulse noise is superimposed, the pseudo operation by the holding operation is performed. An audio multiplex demodulator capable of reducing audio noise can be realized.

Specifically, with this configuration, even if the superposed pulse noise is not large as compared with the sub-sound carrier signal, for example, as in the part 41 of FIG.
Since the pulse noise is detected except for the sub-sound carrier signal, the noise can be detected, and the holding operation is performed in a state where the residual carrier signal is removed. Therefore, the gate circuit output is as shown in a portion 43 of FIG. Thus, it is possible to reduce the pseudo noise of the audio output as shown by a portion 44 in FIG.

[0061]

According to the audio multiplex demodulator of the present invention, it is possible to remove a sub audio carrier signal during a holding operation by a noise canceller from an audio multiplex signal including a sub audio carrier signal on which pulse noise is superimposed. Thus, an audio multiplex demodulator capable of reducing pseudo audio noise can be realized.

According to the audio multiplex demodulator of the present invention,
An audio multiplex demodulator capable of detecting noise can be realized even when the noise level of the audio multiplex signal including the sub audio carrier signal on which the pulse noise is superimposed is not higher than that of the auxiliary audio carrier signal. .

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of an audio multiplex demodulator according to a first embodiment of the present invention.

FIG. 2 is a block diagram illustrating a configuration of an audio multiplex demodulator according to a second embodiment of the present invention.

FIG. 3 is a block diagram illustrating a configuration of an audio multiplex demodulator according to a third embodiment of the present invention.

FIG. 4 is a block diagram showing a configuration of a conventional audio multiplex demodulator.

FIG. 5 is a signal waveform diagram for explaining a noise canceller of pulse noise which is an object of the present invention.

FIG. 6 is a waveform diagram illustrating a noise canceller of pulse noise for an audio multiplexed signal on which a sub audio carrier signal is superimposed as an object of the present invention.

[Explanation of symbols] [Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Audio multiplexed signal input terminal 2, 3 Audio output terminal 4 Input buffer amplifier 5, 16, 23 Band elimination filter 6, 15 Low pass filter 7, 17 Gate circuit 8 High pass filter 9 AGC amplifier 10 Pulse noise detection circuit 11 , 12 waveform shaping circuit 13 band-pass filter 14 sub-sound detection circuit 18 discrimination signal detection unit 19 output signal processing unit 20, 21 de-emphasis circuit 38 sub-sound demodulation unit 39 noise detection unit

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5C026 DA04 DA06 DA16 DA17 DA20 5K052 AA01 BB03 BB05 DD21 EE03 EE04 EE12 FF04 FF12 FF24 GG11 GG49 5K068 AA22 BA06 BB01 BC07 CB03 CC13 CC14 DA06 DA07 DA15 DB01 DC01

Claims (3)

[Claims] A noise detection unit for detecting a noise component superimposed on the audio multiplex signal; a first and a second waveform shaping circuit for generating a switching signal in response to an output of the noise detection unit; A sub-audio carrier removal circuit for reducing or removing a sub-audio carrier signal superimposed on a signal; a first gate circuit for receiving an output of the first waveform shaping circuit and holding an output of the sub-audio carrier removal circuit; An auxiliary audio demodulator that detects an auxiliary audio from the audio multiplex signal; a residual carrier removing circuit that reduces or removes a residual carrier component superimposed on an output of the auxiliary audio demodulator; and a second waveform shaping circuit. A second gate circuit for receiving the output and holding the output of the residual carrier removing circuit; and a discrimination signal detection unit for detecting a speech multiplex discrimination signal from the speech multiplex signal. , Sound multiplex demodulator and an output signal processing unit for outputting the main audio and the sub-audio or stereo signal in response from the output to the output of said discrimination signal detector of the first and second gate circuits. 2. A sub audio carrier removal circuit for reducing or eliminating a sub audio carrier signal superimposed on an audio multiplex signal, a noise detection unit for detecting a noise component superimposed on an output of the sub audio carrier removal circuit, A waveform shaping circuit that receives the output of the noise detection unit and generates a switching signal; a gate circuit that receives the output of the waveform shaping circuit and holds the audio multiplex signal; and the audio multiplex signal output from the gate circuit A sub-speech demodulation unit for detecting a sub-speech from a voice signal; a discrimination signal detection unit for detecting a speech multiplex discrimination signal from the speech multiplexed signal; And an output signal processing unit for outputting a main audio and a sub audio or a stereo signal according to the output of the discrimination signal detection unit. Conditioner. 3. A sub audio carrier removal circuit for reducing or eliminating a sub audio carrier signal superimposed on an audio multiplex signal, a noise detection unit for detecting a noise component superimposed on an output of the sub audio carrier removal circuit, First and second waveform shaping circuits for receiving the output of the noise detection unit and generating a switching signal; and receiving the output of the first waveform shaping circuit and holding the output of the sub audio carrier removing circuit. A second gate circuit; a sub-sound demodulator for detecting a sub-sound from the audio multiplex signal; a residual carrier removal circuit for reducing or removing a residual carrier component superimposed on an output of the sub-sound demodulator; A second gate circuit that receives the output of the waveform shaping circuit of (1) and holds the output of the residual carrier removing circuit; and detects a voice multiplex discrimination signal from the voice multiplex signal. Audio multiplexing comprising: a discrimination signal detection unit; and an output signal processing unit that outputs a main sound and a sub-sound or a stereo signal from the outputs of the first and second gate circuits according to the output of the discrimination signal detection unit. Demodulator.