JP2001197398A - Device and method for multiplexing/demodulating sound - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the erroneous judgment of a stereo mode and an SAP mode by a USA sound multiple system. SOLUTION: When a PLL circuit 103 is judged to be locked to the carrier of a video signal, the PLL locking detection part 102 of a VIF/SIF demodulation circuit 13 outputs a PLL locking detection signal to a judgement circuit 14. The demodulation part 101 of the VIF/SIF demodulation circuit 13 outputs a sound detection signal to stereo LPF 15 and SAPBPF 16. When the judgment circuit 14 continuously receives the PLL locking detection signal for a prescribed time, it outputs a judgment control signal to a stereo discrimination part 17 and an SAP discrimination part 26. While the judgment control signal is inputted from the judgment circuit 14, the stereo discrimination part 17 judges the presence or absence of a differential signal inputted from stereo BPF 15. While the judgment control signal is inputted form the judgment circuit 14, the SAP discrimination part 26 judges the presence or absence of the SAP signal inputted from SAPBPF 16 or SAPLPF 25.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an audio multiplex demodulation apparatus and method, and more particularly, to an audio multiplex signal of a US audio multiplex broadcast in a mono mode, stereo mode,
The present invention relates to an audio multiplex demodulation apparatus and method capable of demodulation without erroneously determining which of the SAP modes.

[0002]

2. Description of the Related Art Television receivers compatible with audio multiplex broadcasting are becoming popular. Audio multiplex broadcasting in the United States includes monaural signals, stereo signals, and SAP (Su
b Audio Program: Auxiliary audio program). Stereo signals are sent to the left and right speakers
It outputs different audio signals, enabling more realistic audio output than monaural audio. The SAP signal is 2
This is a sub-audio program signal known as bilingual broadcasting. For example, bilingual audio output is enabled by, for example, outputting Japanese from the left speaker and English from the right speaker.

[0003] These audio signals are output from the broadcast station side as different audio modes, respectively, and the user can select and output a monaural mode, a stereo mode, or an SAP mode.

For example, when a user selects a stereo mode and receives a program in the stereo mode, when the broadcast is switched to another program in the monaural mode, the audio multiplexing demodulation device of the television receiver operates in this mode. , And switches to monaural mode to output audio. Further, when the program in the monaural mode ends and the program is switched to the program in the stereo mode again, the audio multiplexing demodulator detects this and can switch the audio output to the stereo mode.

[0005] This mode switching is performed similarly when the SAP mode is selected. For example, when a bilingual movie is being broadcast, when the broadcast is switched to a monaural mode or a stereo mode program, the audio multiplexing demodulator of the television receiver detects the change in this mode, and Or switch to stereo mode and output audio. In addition, the program in monaural mode or stereo mode ends, and SAP
When switching to the broadcast of the mode program, the audio multiplex demodulator detects this, switches the audio output to the SAP mode,
Audio signals can be output in two languages.

[0006]

By the way, the conventional audio multiplex demodulator, when the input of the audio multiplex signal is small due to a weak electric field, for example, broadcasts a monaural signal instead of a stereo signal or an SAP signal. Even when you are
Since the input levels of the stereo signal and the SAP signal have a characteristic of easily following noise, the input level sometimes detects a stereo signal or an SAP signal that should not be originally detected. For this reason, the audio multiplexing demodulation device erroneously detects the stereo mode or the SAP mode in spite of the monaural mode, thereby erroneously selecting the mode. As a result, noise is combined with a monaural signal instead of a stereo signal or SAP signal that has not been transmitted, and thus there has been a problem that abnormal noise is generated.

[0007] Regarding this problem, Japanese Patent Laid-Open Publication No. 2-25047
Japanese Unexamined Patent Application Publication No. 6-1994 discloses that the presence or absence of the second voice carrier is detected, and when it is determined that the second voice carrier does not exist, the monaural mode is forcibly set, thereby causing an erroneous determination of the stereo mode. It is disclosed that the generation of sound is suppressed.

Japanese Patent Application Laid-Open No. 8-79654 discloses that
When turning on the power switch and changing channels, the stereo signal or SAP signal is used to reduce the effect of electromagnetic waves generated from the horizontal synchronization circuit in the same frequency band on the pilot signal that determines the presence or absence of stereo mode. It is disclosed that a circuit for determining the presence / absence of a signal is turned off to suppress erroneous determination in the stereo mode or the SAP mode.

However, any of the above publications has a problem that erroneous determination cannot be sufficiently suppressed.

[0010] The present invention has been made in view of such a situation, and is intended to sufficiently suppress erroneous determination with a simple configuration.

[0011]

According to a first aspect of the present invention, there is provided an audio multiplex demodulator for detecting a carrier of a signal relating to a video signal corresponding to an input audio signal, and
Detecting means for outputting a control signal; first determining means for determining whether a stereo signal is included in the input audio signal; and determining whether the SAP signal is included in the input audio signal. A second judging means for judging, a first judging control means for controlling the judgment by the first judging means corresponding to the control signal outputted by the detecting means, and a control signal outputted by the detecting means. And a second determination control means for controlling the determination by the second determination means.

[0012] The detecting means further includes a generating means for generating, by a PLL, a signal having a phase synchronized with a carrier wave.
It is possible to detect whether or not is locked.

[0013] The detecting means may output the control signal when the PLL is locked when the locked state of the PLL continues for a predetermined time or more.

[0014] The detection means may detect a level of a chroma signal included in the video signal.

According to a fifth aspect of the present invention, in the audio multiplex demodulation method, a detection step of detecting a carrier of a signal related to a video signal corresponding to the input audio signal and outputting a control signal in accordance with the detection result; A first determination step of determining whether a stereo signal is included in the input audio signal; a second determination step of determining whether an SAP signal is included in the input audio signal; In response to the control signal output in the processing of the step, a first determination control step of controlling the determination in the processing of the first determination step, and in response to the control signal output in the processing of the detection step, The second controlling the determination in the process of the second determining step
And a determination control step.

In the audio multiplex demodulation device according to the first aspect and the audio multiplex demodulation device according to the fifth aspect, a carrier of a signal related to a video signal corresponding to the input audio signal is detected, and the carrier corresponding to the detection result is detected. A control signal is output, it is determined whether the input audio signal includes a stereo signal, it is determined whether the input audio signal includes an SAP signal, and the output control signal is output. In response to the signal, determine whether the input audio signal contains a stereo signal or if the input audio signal
The determination as to whether or not a signal is included is controlled.

[0017]

FIG. 1 is a block diagram showing the configuration of an embodiment of a voice multiplex demodulator to which the present invention is applied. The antenna 11 of the audio multiplex demodulator 1 receives a broadcast signal from a broadcast station (not shown), and receives an RF (Radio Frequency) signal.
The signal is output to the tuner 12 as a signal. Tuner 12
Selects a signal of a predetermined broadcasting station from the RF signals from the antenna 11 and converts the IF (Intermediate Frequency) signal into a VIF / SIF (Video Intermediate Frequency / Sound Int) signal.
output to the demodulation circuit 13.

The demodulation unit 101 of the VIF / SIF demodulation circuit 13
An LL (Phase Locked Loop) circuit 103 is built in, and a signal synchronized with the phase of the carrier of the video signal is generated from the IF signal of the broadcasting station selected by the tuner 12, and this signal is used to generate the video signal and the audio signal. The detection signal (baseband signal) is demodulated, the video detection signal is output to a video processing device (not shown), and the audio detection signal is converted to a stereo LPF (Low
Pass Filter) 15 and SAPBPF (Sub Audio Program Ban)
d Pass Filter) 16.

A PLL lock detection unit 102 built in the VIF / SIF demodulation circuit 13 determines whether or not the PLL circuit 103 is locked. When it is determined that the PLL circuit 103 is locked, a detection signal (PLL lock detection Signal) to the determination circuit 14. When the determination circuit 14 continuously detects the PLL lock detection signal for a predetermined time or more, the determination circuit 14 outputs a determination control signal to the subsequent stereo determination unit 17 and the SAP determination unit 26.

The stereo LPF 15 passes only a low frequency band including a difference (L−R) signal and a monaural (L + R) signal of the audio detection signal, and outputs the signal to the stereo discrimination unit 17. Further, the SAPBPF 16 allows only the frequency band of the SAP signal of the input voice detection signal to pass, and the FM (Frequency
output to the detector 24 and the SAP discriminator 26. That is, this stereo LPF 15 and SAPBPF
Reference numeral 16 divides the input audio detection signal into a monaural signal and a difference signal band and a SAP signal band.

When receiving the judgment control signal input from the judgment circuit 14, the stereo judgment section 17 outputs a stereo LPF.
The ST (Stereo) INDICATOR 18 is turned on when the difference signal is detected, that is, in the stereo mode, and the mode controller 31 Send the signal detection signal. Further, when not receiving the determination control signal from the determination circuit 14, the stereo determination unit 17 regards this as noise even if it has received the difference signal,
It is determined that the mode is not the stereo mode (monaural mode), the ST INDICATOR 18 is turned off, and the differential signal detection signal is not output to the mode controller 31. Further, the stereo discriminating unit 17 compares the input monaural signal and the difference signal with a subsequent MAINLPF (MAIN Low Pass Filter) 19 and S
Output to UBBPF (SUB Band Pass Filter) 21.

The ST INDICATOR 18 is an LED (Light Emissio)
n) (not shown) or the like, and turns on or off an LED based on a control signal from the stereo determination unit 17 to indicate whether the mode is the stereo mode.

The MAINLPF 19 extracts a monaural signal (main audio signal) having a low frequency from the signals input from the stereo discriminating unit 17, removes unnecessary frequency parts, and outputs the signal to the de-emphasis unit 20. The de-emphasis unit 20 performs de-emphasis processing on the input monaural audio signal and outputs the monaural audio signal to the audio matrix 30.

The SUBBPF 21 extracts a difference signal from the signals input from the stereo discriminating unit 17 and outputs the difference signal to an AM (Amplitud) signal.
e Modulation) output to the detector 22.

The AM detector 22 performs AM detection on the signal input from the SUBBPF 21, extracts an L signal and an R signal, and
23. The SUBLPF 23 removes unnecessary portions of the L signal and the R signal input from the AM detector 22, and outputs the same to the switch terminal 28a.

An FM (Frequency Modulation) detector 24
Performs FM detection of the SAP signal input from SAPBPF16,
Output to LPF25. The SAPLPF 25 removes an unnecessary portion from the SAP signal as the FM detection signal input from the FM detector 24, and removes an SAP discrimination unit 26 and a switch terminal 28.
b.

The SAP discriminating unit 26, like the stereo discriminating unit 17, determines whether the signal input from the SAPBPF 16 or the SAPLPF 25 includes the SAP signal when receiving the judgment control signal from the judgment circuit 14. If the SAP signal is detected from any of them, that is, if the SAP mode is set, the SAP INDICATOR 27 is turned on, and the SAP signal detection signal is sent to the mode controller 31. Further, when the SAP determination unit 26 does not receive the determination control signal from the determination circuit 14, even if the SAP signal is received, the SAP determination unit 26 regards the SAP signal as noise and determines that the SAP signal is not received. Then, the SAP INDICATOR 27 is turned off, and the SAP signal detection signal is not output to the mode controller 31.

The reason why the SAP discriminating unit 26 detects not only the output from the SAPBPF 16 but also the presence or absence of the output from the SAPLPF 25 is that the monaural signal is output even if the stereo mode is erroneously set to the monaural mode. On the other hand, when it is determined that the SAP signal is not detected, the mode controller 31 controls the matrix circuit 30 so that the SAP signal is not reproduced, and the audio output in the SAP mode is completely cut off. This is to improve the detection accuracy compared to the difference signal.

The SAP INDICATOR 27 is a ST INDICATOR 18
In the same manner as described above, it is composed of an LED (not shown) or the like, and turns on or off the LED based on the control signal from the SAP discriminating unit 26, and displays the state of the SAP mode.

The switch 28 is a mode controller 31
By switching the connection between the switch terminals 28a and 28b, a signal to be sent to the subsequent stage is defined as a differential signal.
Switch to one of the SAP signals.

The noise removing unit 29 removes noise of the differential signal or SAP signal input via the switch 28 and outputs the result to the audio matrix 30. The audio matrix 30 synthesizes a monaural signal input from the de-emphasis unit 20 and a difference signal input from the noise removal unit 29 by calculation based on a control signal from the mode controller 31, and outputs an Lch (Left channel: left speaker) The output signal is divided into an output terminal signal and an Rch (Right channel: right speaker output terminal) signal. Alternatively, a monaural signal is output as an Lch signal, and the audio signal output from the SAPLPF 25 is output as an Rch signal.

The mode controller 31 outputs to the audio matrix 30 a control signal corresponding to the audio mode selected by the user using an operation device (for example, a touch panel or a remote controller) (not shown). On the basis of the difference signal detection signal and the SAP signal detection signal from the SAP discrimination unit 26, a control signal is output to the audio matrix 30 for control.

Next, the operation when the audio multiplex demodulation device 1 outputs an audio signal will be described. The process is started when the user instructs to receive a broadcast signal. Step S
In 1, the tuner 12 generates an IF signal of a selected broadcasting station from the RF signal input from the antenna 11, and
Output to the F / SIF demodulation circuit 13.

In step S 2, the demodulation unit 101 of the VIF / SIF demodulation circuit 13 uses the signal synchronized with the carrier of the video signal reproduced by the PLL circuit 103 to input the signal.
The IF signal is demodulated into a video detection signal and an audio detection signal, and the video detection signal is output to a video processing unit (not shown), and the audio detection signal is output to the stereo LPF 15 and the SAPBPF 16. Also stereo L
The PF 15 and the SAPBPF 16 convert the audio detection signal input from the VIF / SIF demodulation circuit 13 into a stereo determination unit 17 and an SAP determination unit for each band shown in the baseband spectrum of the audio multiplex system in the United States shown in FIG. 26
Output to That is, the stereo LPF 15 extracts a monaural signal having a frequency equal to or lower than 3f _H (= 3 × 15.734 kHz) and a difference signal from the input audio detection signal, and outputs the extracted signal to the stereo determination unit 17. extracts SAP signal over a frequency 3f _H outputs the FM detector 24 and SAP determination unit 26. Further, the FM detector 24 includes the SAPBPF 16
, And performs SAP detection processing, and outputs the SAP signal to SAPLPF25. SAPLPF25 is input FM detection processing
The SAP signal is output to the SAP discrimination unit 26 and the switch terminal 28b.

In step S3, the PLL lock detector 102 of the VIF / SIF demodulation circuit 13 determines whether or not the PLL circuit 103 is locked to the carrier of the video signal. In step S4, a PLL lock detection signal is output to the determination circuit 14.

In step S5, the judgment circuit 14
It is determined whether or not the PLL lock detection signal has been continuously detected for a predetermined time. If it is determined that the PLL lock detection signal has been continuously detected for a predetermined time or more, in step S6, the stereo determination unit 17 and the SAP A determination control signal is output to the determination unit 26.

In step S7, the stereo discriminating unit 1
7 determines whether a difference signal of a predetermined level or more is detected while the determination control signal is being input from the determination circuit 14, and if detected, proceeds to the process of step S8.

In step S8, the stereo discriminating unit 1
7, a difference signal detection signal indicating that a difference signal is input, assuming that the input audio signal is a signal in the stereo mode, turning on the ST INDICATOR 18 and lighting an LED indicating the stereo mode. Is output to the mode controller 31. Further, the stereo determination unit 17
Outputs the monaural signal of the difference signal and the monaural signal input to the stereo discriminating unit 17 to the audio matrix 30 via the MAILPF 19 and the de-emphasis unit 20. Further, the stereo determination unit 17 converts the difference signal into a SUBB signal.
The signal is output to the audio matrix 30 via the PF 21, the AM detector 22, the SUBLPF 23, the switch 28, and the noise removing unit 29. At this time, the mode controller 31 controls the switch 28 to connect it to the switch terminal 28a. Further, the mode controller 31 controls the audio matrix 30 so that the input monaural signal ((L + R)
Signal) and the difference signal ((L-R) signal), and the signal divided by 2 is output to Lch, the difference signal is subtracted from the monaural signal, and the signal divided by 2 is output to Rch, and processed. To end.

In step S3, if the PLL lock detecting unit 102 of the VIF / SIF demodulation circuit 13 determines that the PLL circuit 103 is not locked, the process proceeds to step S3.
Go to 9.

In step S9, the stereo discriminating unit 1
Reference numeral 7 deems that no difference signal is detected (assuming monaural mode), turns off the ST INDICATOR 19, and does not output a difference signal detection signal to the mode controller 32. Also, since the SAP discriminating unit 26 does not receive the judgment control signal similarly to the stereo discriminating unit 17, the SAP INDICATO
R27 is turned off, and the SAP signal detection signal is not output to the mode controller 31. Therefore, the mode controller 3
1 does not receive the difference signal detection signal and the SAP signal detection signal, so that it is determined that the signal in the monaural mode is received, and the audio matrix 30 is controlled so that only the monaural signal input from the de-emphasis unit 20 is output. Output to Lch (left speaker output) and Rch (right speaker output)
The process ends.

If it is determined in step S5 that the PLL lock detection signal has not been detected for a predetermined period of time, the process proceeds to step S9, and the subsequent processes are repeated.

In step S7, the stereo discriminating unit 1
If it is determined that the difference signal has not been detected while the determination control signal is being input from the determination circuit 14, the process proceeds to step S10.

In step S10, the SAP discriminator 26
Detects the presence or absence of the SAP signal input from the SAPBPF 16 or SAPLPF 25 while the determination control signal is input from the determination circuit 14. Proceed to.

In step S11, the SAP discriminator 26
Turns on the SAP INDICATOR 27 and indicates the SAP mode
D is turned on, and at the same time, an SAP signal detection signal indicating that the SAP signal is input is output to the mode controller 31. The mode controller 31 controls the switch 28 to be connected to the switch terminal 28b according to the SAP signal detection signal. The SAP signal subjected to the FM detection processing output from the SAPLPF 25 is output to the noise removing unit 29. The noise removing unit 29 removes a noise component of the input SAP signal and outputs the signal to the audio matrix 30. The mode controller 31 controls the audio matrix 30 to output the monaural signal ((L + R) signal) input from the de-emphasis unit 20 to Lch, and the SAP signal input from the noise removing unit 29 to Rch, The process ends.

In step S10, the SAP discriminator 26
If it is determined that the SAP signal input from the SAPBPF 16 or the SAPLPF 25 is not detected while the determination control signal is input from the determination circuit 14, the process proceeds to step S9.
And the subsequent processing is repeated.

According to the above description, while the discrimination control signal is being input from the discrimination circuit 14, that is, while the carrier of the video signal is locked, the stereo discrimination unit 1 is not used.
By detecting the presence or absence of the difference signal, the detection of the difference signal at the time of the weak electric field, which easily follows the noise, can be prevented, so that the erroneous determination of the difference signal can be prevented.

Further, as in the case of the above-mentioned stereo discriminating section 17, only when the carrier of the video signal is locked, the SA
By detecting the presence or absence of the SAP signal by the P determination unit 27,
By preventing the SAP signal at the time of the weak electric field, which easily follows the noise, from being detected, it is possible to prevent erroneous determination of the SAP signal.

In the above description, the determination circuit 14 outputs a determination control signal based on the PLL lock detection signal detected by the PLL lock detection unit 102, thereby causing the stereo determination unit 17 and the SAP determination unit 26 to operate. Although an example of controlling has been described, for example, in the VIF / SIF demodulation circuit 13,
A level of a chroma signal included in the video signal is detected, and a determination circuit 1 is provided based on the level of the detected chroma signal.
4 may output a determination control signal to control the stereo determination unit 17 and the SAP determination unit 26.

[0049]

According to the audio multiplex demodulation device of the first aspect and the audio multiplex demodulation method of the fifth aspect, a carrier of a signal related to a video signal corresponding to an input audio signal is detected, and the detection result is obtained. In response to, output a control signal, determine whether the input audio signal includes a stereo signal, determine whether the input audio signal includes the SAP signal, and output In response to the control signal, the control unit determines whether the input audio signal includes a stereo signal or determines whether the input audio signal includes an SAP signal. Therefore, it is possible to prevent erroneous determination of the stereo mode or the SAP mode.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of an audio multiplex demodulation device to which the present invention is applied.

FIG. 2 is a diagram illustrating a US audio multiplexing baseband spectrum.

FIG. 3 is a flowchart illustrating an operation of the audio multiplex demodulator of FIG. 1;

[Explanation of symbols]

1 audio multiplex demodulator 11 antenna, 12 tuner, 13 VIF / SIF converter, 14 decision circuit, 15 stereo LPF, 16 SAPBPF, 17 stereo discriminator, 1
8 ST INDICATOR, 19 MAIN LPF, 20 De-emphasis part, 21 SUB BPF, 22 AM detector, 23 SUBLP
F, 24 FM detector, 25 SAPLPF, 26 SAP discriminator,
27 SAP INDICATOR, 28 switch, 29 noise remover, 30 voice matrix, 31 mode controller, 101 demodulator, 102 PLL lock detector, 10
3 PLL

Claims (5)

[Claims] 1. A method for detecting a carrier of a signal related to a video signal corresponding to an input audio signal, and corresponding to a detection result,
Detecting means for outputting a control signal; first determining means for determining whether or not the input audio signal includes a stereo signal; and whether or not the input audio signal includes an SAP signal A second determination unit for determining whether the first determination unit is in response to the control signal output from the detection unit, and a first determination control unit for controlling the determination by the first determination unit. An audio multiplex demodulation device, comprising: a second determination control unit that controls the determination by the second determination unit in accordance with the control signal. 2. The apparatus according to claim 1, wherein said detecting means further includes a generating means for generating a signal having a phase synchronized with said carrier wave by a PLL, and detects whether said PLL is locked or not. An audio multiplex demodulator according to claim 1. 3. The device according to claim 2, wherein the detection unit outputs the control signal when the PLL is locked, when the locked state of the PLL continues for a predetermined time or more. Audio multiplex demodulator. 4. The audio multiplex demodulator according to claim 1, wherein said detecting means detects a level of a chroma signal included in said video signal. 5. A method for detecting a carrier of a signal related to a video signal corresponding to an input audio signal, and corresponding to a detection result,
A detecting step of outputting a control signal; a first determining step of determining whether a stereo signal is included in the input audio signal; and whether a SAP signal is included in the input audio signal. A second determination step of determining whether or not, a first determination control step of controlling the determination in the processing of the first determination step in response to the control signal output in the processing of the detection step; A second determination control step of controlling the determination in the second determination step in response to the control signal output in the detection step.