JPH07143459A - Second generation edtv audio signal processing unit - Google Patents

Abstract

PURPOSE:To output audio information without unpleasant broken noise specific to a PCM digital audio signal even when a 2nd generation EDTV signal is received in a poor reception state such as C/N deterioration with respect to the 2nd generation EDTV receiver. CONSTITUTION:The processing unit is provided with an orthogonal detection circuit 22 demodulating a PCM audio signal from a 2nd generation EDTV signal received by a tuner 10, a PCM audio signal processing circuit receiving the PCM audio signal to execute various decoding, an FM demodulation circuit 30 demodulating the FM audio signal, a PCM audio/FM audio changeover circuit 50, and a microcomputer 60 detecting the reception state at that time. A PCM audio signal is outputted when the reception state is excellent and an FM audio signal is outputted when the reception state is deteriorated by using an output from the microcomputer 60. Audio information is outputted without unpleasant broken noise specific to a PCM digital audio signal in the case of reception in the deteriorated reception such as low C/N by controlling the changeover circuit 50 in this way.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an audio signal processing device for a second generation EDTV receiver.

[0002]

2. Description of the Related Art The second generation EDTV will be broadcast from 1995 as an improved version of the first generation EDTV.
The feature is that the aspect ratio of video is the same as that of HDTV.
It is the same as 6 to 9 and improves the resolution. On the other hand, the voice is a digital voice (P
(CM audio) 4 channels are transmitted by carrying out carrier suppression modulation of a carrier whose phase is 90 ° different from the image carrier,
It provides high-quality sound equivalent to a CD. Also,
The current NTSC terrestrial broadcasting receiver is compatible so that it can be received, and in the case of voice, analog voice is transmitted by FM modulation as well as PCM voice.

FIG. 4 is a block diagram of a conventional second-generation EDTV receiver. In FIG. 4, 10 is a tuner, and 11
Is a Nyquist filter, 12 is a video detection circuit, 13 is a video signal processing circuit, 40 is a display with an aspect ratio of 16: 9, 14 is a carrier reproduction circuit, 15 is a 90 ° phase shifter,
Reference numeral 21 is a bandpass filter, 22 is a quadrature detection circuit, and 23.
Is a waveform equalization circuit, 26 is a PCM audio signal processing circuit, which includes 24 channel decoders and 25 source decoders, 30 is an FM demodulation circuit for demodulating an FM-modulated analog audio signal, and 50 is PCM / FM voice switching circuit, 60 is a microcomputer, 61 is a preamble detection signal, 71 is a PCM / FM voice switching signal, and 41 is a speaker.

Second-generation EDTV configured as described above
The operation of the receiving device will be described. The second generation EDTV signal selected by the tuner 10 is divided into a video system and an audio system for signal processing. In the video system, the second sideband amplitude modulated second
The video signal of the generation EDTV passes through the Nyquist filter 11, and then the video signal is demodulated by the synchronous detection circuit 12.
It is input to the video signal processing circuit 13. The video signal processing circuit 13 performs processing using the reinforcement signal superimposed from the sending side in order to improve the horizontal and vertical resolution of the letter box type video signal having an aspect ratio of 16: 9, and reproduces a high quality image. To do.

On the other hand, the PCM audio signal transmitted by quadrature modulation is 90 ° with the carrier for video signal demodulation generated by the carrier reproducing circuit 14 after removing unnecessary crosstalk from the video signal by the bandpass filter 21. The quadrature detection circuit 22 synchronously detects carrier waves having different phases. The output signal of the quadrature detection circuit 22 is input to the waveform equalization circuit 23, and transmission distortion such as ghost and crosstalk with the video signal is removed by using the reference signal superimposed on the video signal and the PCM audio signal. . The output signal of the waveform equalizing circuit 23 is input to the PCM voice signal processing circuit 26, and is subjected to channel coding (channel coding) and source coding (voice signal coding) to decode PCM data, and then D / It is converted into analog voice by the A conversion circuit. The channel decoder 24 performs error correction decoding and deinterleaving to reproduce a bit stream whose data is compressed to about 1/6 based on the specifications of MPEGII, and the source decoder 25 uses the channel decoder 24.
The audio data compressed to about 1/6 is decoded by using the bit stream reproduced in step 1 as an input. The output signal of the source decoder 25 is the D / of the PCM audio signal processing circuit 26.
It is input to the A converter and analog voice is generated. Also,
The FM sound transmitted by the simulcast is demodulated by the FM demodulation circuit 30. The PCM voice and FM voice reproduced as analog signals in this way are input to the PCM / FM voice switching circuit 50, and the preamble (the signal for determining the phase of the symbol of the PCM voice is output from the channel decoder 24 for channel coding. The signal added by the PCM voice is detected by the detection signal 61. The microcomputer 60 detects the presence or absence of the PCM voice by the detection signal 61 and controls the PCM / FM voice switching circuit 50 to generate the PCM voice. When broadcast, PCM audio is output, and when PCM audio is not broadcast, FM audio is output.

[0006]

The audio signal of the second-generation EDTV is transmitted by high-efficiency coded digital audio (PCM audio) 4 channels by carrying out carrier suppression modulation of a carrier having a 90 ° phase difference from the image carrier. It provides high-quality sound similar to that of a CD. Such a digital voice can obtain high sound quality without any problem in a normal reception state. However, when the reception state is deteriorated due to C / N deterioration or the like, a sharp voice breakdown state occurs unlike FM voice, which is excessive. Noise is generated, causing a great deal of discomfort to the receiver and adversely affecting the speaker. For this reason, when the PCM voice is corrupted, it is difficult to listen as it is, and mute (voice suppression) is performed, so that it is impossible to obtain voice information.

In view of the above problems, the present invention provides a second generation EDT.
An object is to be able to output voice information without unpleasant noise in a broken state even when V is received in a bad receiving state such as C / N deterioration.

[0008]

A second-generation EDTV audio signal processing apparatus of the present invention for solving the above-mentioned problems includes a video signal detection circuit for demodulating a video signal from a signal amplitude-modulated by the video signal, and a video signal. A quadrature detection circuit that demodulates a PCM audio signal in which a carrier wave that is orthogonal to a carrier wave is subjected to carrier wave suppression amplitude modulation, and an output of the quadrature detection circuit and an output of the video signal detection circuit are input, and a video signal and an audio PC
A channel equalization circuit that removes transmission line distortion based on a reference signal inserted in the M signal and a PCM audio signal after the waveform equalization are input, and channel coding (transmission is performed on the transmission side. Path coding) and source coding (speech signal coding) respectively, and performs D / A conversion on the PCM sound signal processing circuit, and FM for demodulating the PCM sound signal and analog sound transmitted by FM modulation as simulcast. A demodulation circuit and a PCM / F which receives the output of the PCM audio signal processing circuit and the output of the FM demodulation circuit
The M audio switching circuit is provided, and (1) by controlling the PCM / FM audio switching circuit using the detection signal of the synchronization state at the time of source coding decoding, C / N deterioration or the like occurs when the second generation EDTV broadcast is received. When the bit error rate is deteriorated and the PCM voice is broken down, it is characterized by switching to the FM voice without sudden breakage.

(2) A bit error rate detection circuit for detecting a bit error rate by using a synchronous code added for each voice frame in the source coding is added to the source coding decoding circuit in the PCM voice signal processing circuit. Then, using the output signal of the bit error rate detection circuit, the PCM / FM
By controlling the audio switching circuit, the second generation EDT
When receiving V broadcast, if the PCM voice is broken due to the deterioration of the bit error rate due to C / N deterioration, etc., there is no sudden breakage F
It is characterized by switching to M voice.

(3) By adding an S / N detection circuit for detecting the video signal S / N by using the output of the video signal detection circuit as an input, and using the output voltage of the S / N detection circuit due to C / N deterioration. By controlling the PCM / FM voice switching circuit, when the second generation EDTV broadcast is received, when the bit error rate is deteriorated due to C / N deterioration and the PCM voice is broken,
It is characterized in that it switches to FM voice without sudden failure.

[0011]

The present invention has the above-mentioned configuration and has the second generation EDT.
Control signal (synchronous state detection signal, bit error rate, C / N) that can judge the PCM voice signal reception state in V reception
By controlling the PCM / FM voice switching circuit by using the CD when the reception condition is good.
(Compact disc) High-quality PCM sound is output, and when receiving in a state where the reception condition deteriorates due to low C / N or the like, by selecting FM sound, a failure state peculiar to PCM digital sound can be obtained. It is possible to output voice information without unpleasant noise.

[0012]

Embodiment 1 First, an embodiment of the first invention will be described with reference to FIG. FIG. 1 is a block diagram of a second generation EDTV audio signal processing device showing an embodiment of the first invention.
In FIG. 1, the same parts as those in the conventional example of FIG. 4 are designated by the same reference numerals. In FIG. 1, 70 is a synchronization state detection signal output from the source decoder.

The operation of the first embodiment of the first invention thus constructed will be described. The second selected by tuner 10
The generation EDTV signal is divided into a video system and an audio system for signal processing. In the video system, the video signal of the second side EDTV whose residual sideband amplitude has been modulated passes through the Nyquist filter 11 and then is demodulated by the synchronous detection circuit 12 and input to the video signal processing circuit 13. Video signal processing circuit 1
In No. 3, in order to improve the horizontal and vertical resolution of the letter box type video signal having an aspect ratio of 16: 9, processing is performed using the reinforcement signal superimposed from the sending side to reproduce a high quality image.

On the other hand, in the audio system, the PCM audio signal transmitted by quadrature modulation removes unnecessary crosstalk from the video signal by the bandpass filter 21, and then the carrier wave for demodulating the video signal generated by the carrier wave reproducing circuit 14. And the quadrature detection circuit 22 synchronously detects carrier waves having different phases by 90 °. The output signal of the quadrature detection circuit 22 is a waveform equalization circuit 23.
The transmission distortion such as ghost or crosstalk with the video signal is removed by using the reference signal input to the video signal and the PCM audio signal. The output signal of the waveform equalization circuit 23 is input to the PCM voice signal processing circuit 26, and after channel coding (transmission line coding) and source coding (voice signal coding) of PCM data is decoded, the PCM voice signal is output. It is converted into analog voice by the D / A conversion circuit of the signal processing circuit 26. That is, the channel decoder 24 performs error correction decoding and deinterleaving to reproduce a bit stream whose data is compressed to about 1/6 based on the specifications of MPEGII, and the source decoder 25 reproduces it in the channel decoder 24. The audio data compressed to about ⅙ is decoded by using the bit stream as an input. The output signal of the source decoder 25 is input to the D / A converter of the PCM audio signal processing circuit 26 and analog audio is generated. The FM voice transmitted by simulcast is demodulated by the FM demodulation circuit 30. The PCM audio and FM audio reproduced as analog signals in this way are input to the PCM / FM audio switching circuit 50 and controlled as follows.

First, the microcomputer 60 recognizes that the PCM audio is being broadcast by the preamble detection signal 61 output from the channel decoder 24, and then detects the synchronization state of the source coding decoding output from the source decoder 25. From the signal 70, the microcomputer 60 recognizes that the reception state is good or bad, and based on that, the microcomputer 60
Outputs the PCM / FM voice switching signal 71, and PCM /
The FM voice switching circuit 50 is controlled. During PCM voice broadcasting,
When the reception state is good, PCM sound is output, and when the reception state is bad, FM sound is output. In this way
When receiving in a state where the reception condition deteriorates due to low C / N etc.,
It is possible to output voice information that is free from unpleasant noise in a broken state peculiar to PCM digital voice.

(Embodiment 2) Next, an embodiment of the second invention will be described with reference to FIG. FIG. 2 is a block diagram of a second generation EDTV audio signal processing device showing an embodiment of the second invention. In FIG. 2, the same parts as those in the conventional example of FIG. 4 are designated by the same reference numerals. In FIG. 2, reference numeral 51 is a bit error rate detection circuit that detects a bit error rate by using a synchronization code added for each audio frame of a bit stream, and 72 is a PC output from the bit error rate detection circuit.
This is an M voice suppression signal.

The operation of the embodiment of the second invention having the above-described structure will be described. The analog audio signal output from the PCM audio signal processing circuit 26 and the FM demodulation circuit 30 is input to the PCM / FM audio switching circuit 50, while in the bit error rate detection circuit 51, one frame of the bit stream decoded by the channel decoder 24. A bit error rate representing the current reception state is detected using the synchronization code added for each, and the PCM voice suppression signal 72 is output to the microcomputer 60 when the error rate at which PCM voice starts to break down is reached. . The PCM / FM voice switching circuit 50 is controlled as follows.

First, the microcomputer 60 recognizes from the preamble detection signal 61 output from the channel decoder 24 that PCM voice is being broadcast, and then the microcomputer 60 outputs 72 from the bit error rate detection circuit 51.
The PCM voice suppression signal is recognized. Based on that, the microcomputer 60 outputs the PCM / FM voice switching signal 71,
It controls the PCM / FM voice switching circuit 50. During PCM audio broadcasting, PCM audio is output when the reception status is good, and FM audio is output when the reception status is poor. In this way, when the signal is received in a state where the reception state is deteriorated due to low C / N or the like, it is possible to output the voice information without the unpleasant noise in the breakdown state peculiar to the PCM digital voice.

(Embodiment 3) Next, an embodiment of the third invention will be described with reference to FIG. FIG. 3 is a block diagram of a second generation EDTV audio signal processing device showing an embodiment of the third invention. 3, the same parts as those in the conventional example of FIG. 4 are designated by the same reference numerals. In FIG. 3, reference numeral 52 denotes an S / N detection circuit that detects the video signal S / N by using the output of the video signal detection circuit as an input, and extracts a signal outside the frequency band of the video signal to detect the peak value. Video signal S /
A DC voltage proportional to N is output. 53 is S
The voltage comparator receives the output voltage of the / N detection circuit 52 as an input and compares it with a certain reference voltage. Reference numeral 73 is a PCM voice suppression signal output from the voltage comparator.

The operation of the third embodiment of the present invention having the above-described structure will be described. The analog audio signal output from the PCM audio signal processing circuit 26 and the FM demodulation circuit 30 is input to the PCM / FM audio switching circuit 50, while S /
The N detection circuit 52 receives the output of the video signal detection circuit 12 as an input and detects the video signal S / N associated with C / N as a DC voltage. The output signal of the S / N detection circuit 52 is input to the voltage comparator 53, and the output voltage of the S / N detection circuit 52 for C / N at which PCM voice starts to break down is compared with a reference voltage, and then PCM voice suppression is performed. The signal 73 is output to the microcomputer 60. The PCM / FM voice switching circuit 50 is controlled as follows.

First, the microcomputer 60 recognizes from the preamble detection signal 61 output from the channel decoder 24 that PCM audio is being broadcast, and then the microcomputer 60 outputs the PCM audio suppression signal 73 output from the voltage comparator 53. Recognize. Based on that, the microcomputer 60
The CM / FM voice switching signal 71 is output to output PCM / FM.
The voice switching circuit 50 is controlled. During PCM audio broadcasting, PCM audio is output when the reception status is good, and FM audio is output when the reception status is poor. In this way, low C
If the reception condition deteriorates due to / N, etc., the PC
It is possible to output the voice information without the unpleasant noise in the broken state peculiar to the M digital voice.

[0022]

As described above, the second generation EDT of the present invention
The V audio signal processing device outputs the PCM audio signal and the FM audio signal broadcast by simulcast, and outputs the PCM audio when the reception condition is good by using the signal indicating the reception condition at that time, and the reception condition is When it is received in a state where the reception state is deteriorated due to low C / N or the like by switching such that FM voice is output when it deteriorates, voice information without unpleasant noise in a broken state peculiar to PCM digital voice. Can be output.

[Brief description of drawings]

FIG. 1 is a second-generation EDTV showing an embodiment of the first invention.
Audio signal processing device configuration diagram

FIG. 2 is a second-generation EDTV showing an embodiment of the second invention.
Audio signal processing device configuration diagram

FIG. 3 is a second-generation EDTV showing an embodiment of the third invention.
Audio signal processing device configuration diagram

FIG. 4 is a block diagram showing a configuration of a conventional second-generation EDTV audio signal processing device.

[Explanation of symbols]

10 Tuner 11 Nyquist Filter 12 Video Signal Detection Circuit 13 Video Signal Processing Circuit 14 Carrier Reproducing Circuit 15 90 ° Phase Shifter 21 Bandpass Filter 22 Quadrature Detection Circuit 23 Waveform Equalization Circuit 24 Channel Decoder (Transmission Channel Code Decoder) 25 Source Decoder (voice signal code decoder) 26 PCM voice signal processing circuit 30 FM demodulation circuit 40 16: 9 display 41 speaker 50 PCM / FM voice switching circuit 51 bit error rate detection circuit 52 S / N detection circuit 53 voltage comparator 60 microcomputer 61 preamble detection signal 70 synchronization state detection signal 71 PCM / FM voice switching signal 72 PCM voice suppression signal output from bit error rate detection circuit 73 PCM voice suppression signal output from voltage comparator

Claims (3)

[Claims] 1. A video signal detection circuit for demodulating a video signal from a signal amplitude-modulated by a video signal, and a quadrature detection circuit for demodulating a PCM audio signal in which carrier suppression amplitude modulation is performed on a carrier orthogonal to the video carrier. And a waveform equalization circuit for removing the transmission path distortion based on the reference signal inserted in the video signal and the audio PCM signal, using the output of the quadrature detection circuit and the output of the video signal detection circuit as inputs. A PCM audio signal that receives the converted PCM audio signal as input and decodes the channel coding (transmission path coding) and the source coding (audio signal coding) performed on the transmission side to perform D / A conversion. Processing circuit and PC
An FM demodulation circuit that demodulates FM audio that is simulcast with M audio and is sent, and a PCM / FM audio switching circuit that receives the output of the PCM audio signal processing circuit and the output of the FM demodulation circuit are provided, and when source coding decoding is performed. A second-generation EDTV audio signal processing device, characterized in that the PCM / FM audio switching circuit is controlled by using the detection signal of the synchronization state. 2. A synchronization code added to each audio frame of a bit stream is used by using an output of a channel decoder in a PCM audio signal processing circuit as an input instead of a detection signal of a synchronous state at the time of source coding decoding. A bit error rate detection circuit for detecting the bit error rate is added, and when the bit error rate deteriorates due to C / N deterioration or the like, a PCM / FM voice switching circuit is used by using the output signal of the bit error rate detection circuit. The second-generation EDTV audio signal processing device according to claim 1, wherein the second-generation EDTV audio signal processing device is controlled. 3. An S / N detection circuit for detecting S / N by using an output of a video signal detection circuit as an input instead of a detection signal of a synchronization state at the time of source coding decoding, and S / N accompanying C / N deterioration. Using the output voltage of the N detection circuit, PCM /
2. The FM voice switching circuit is controlled.
The second-generation EDTV audio signal processing device described.