JP3082919B2 - Audio signal playback device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an audio signal reproducing apparatus, and more particularly to an audio signal reproducing apparatus capable of reproducing a plurality of types of two-channel audio signals.

[Future technology]

In recent years, audio stereo has been promoted in camera-integrated video tape recorders.
VTR that recorded a monaural audio signal by FM modulation with a carrier wave of
In order to maintain stereo compatibility while maintaining the compatibility with the conventional one, the sum signal of the L channel and the R channel is recorded on the above-mentioned 1.5 MHz FM modulated carrier, and the frequency is further increased by 1.7 MHz.
And a method of recording a difference signal between the L channel and the R channel by newly providing an FM modulated carrier.

VTR that records such a sum-and-difference stereo audio signal
In the case of recording a so-called main / sub audio signal in which left and right independent audio signals such as Japanese are recorded on the L channel and English are recorded on the R channel, the recorded signal is a stereo audio signal. It is necessary to determine whether the signal is a main or sub audio signal or not, and determine whether or not to pass through the matrix circuit.

[Problems to be solved by the invention]

Performing the switching of the processing as described above manually increases the complexity and confusion.If the switching is performed erroneously, there is a problem that the reproduced sound quality is particularly remarkably impaired. It was desired to switch.
In order to switch the processing mode, identification information for identifying the type of the audio signal must be recorded in a recording medium in some form, and the switching must be performed in accordance with the identification information.

However, recording and reproducing such identification information separately from the audio signal is not preferable because it hinders high-density recording and requires dedicated recording and reproducing means. Therefore, it is conceivable that such identification information is multiplexed into the audio signal. However, the audio signal has no surplus portion in the signal itself, and may be erroneously detected even when the identification information is multiplexed as described above. If this erroneous detection occurs, the reproduced voice will appear as a large noise.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems, and has been made in consideration of the above-described problem. It is intended to provide a device.

[Means for solving the problem]

According to the present invention for such a purpose, according to the first invention, a first audio signal which is a sum signal or a main audio signal of a stereo audio signal and a difference signal or a sub audio signal of the stereo audio signal are used. In a device capable of reproducing the stereo audio signal or the main / sub audio signal from a recording medium in which a certain second audio signal is respectively recorded, the information multiplexed with the reproduced first audio signal First detecting means for detecting that the first and second audio signals are the main and auxiliary audio signals based on the second and reproduced second audio signals.
A second detection unit for detecting that the first and second audio signals are the main and sub audio signals based on information multiplexed on the audio signal of the first and second, and an output of the first and second detection units. Audio signal processing means for processing the first and second audio signals reproduced according to the above and outputting the stereo audio signal or the main / sub audio signal, wherein the audio signal processing means is provided with the first detection means Is configured to output only the first audio signal when the detection results of the second detection means are inconsistent.

Further, as a second invention, a first audio signal which is a sum signal or a main audio signal of the stereo audio signals, and a second audio signal which is a difference signal or a sub audio signal of the stereo audio signals are respectively recorded. In a device capable of reproducing the stereo audio signal or the main / sub audio signal from a recording medium, a first device for detecting that the first and second audio signals are the stereo audio signal or the main / sub audio signal Detecting means; second detecting means for detecting the presence or absence of recording of the second audio signal; and first and second audio signals reproduced according to the outputs of the first and second detecting means. Audio signal processing means for processing to output a stereo audio signal or the main and sub audio signals, wherein the audio signal processing means is configured such that the first detection means detects that the first and second audio signals are the stereo audio signals. Or performs detection of the main a sub-audio signal, and said second detecting means said second
When it is detected that no audio signal is recorded, only the first audio signal is output.

[Action]

In the first invention, for example, when the first detecting means detects that the signal is the main and sub sound signal, and the second detecting means detects that the signal is not the main and sub sound signal, the stereo sound signal and the main and sub sound signal are detected. It is not clear which of the signals is being recorded. In this case, there is a high possibility that noise will be generated even if processing corresponding to any of the audio signals is performed. Therefore, in the present invention, generation of noise is prevented by outputting only the first audio signal which is a sum signal of the main audio signal or the stereo audio.

Further, in the second invention, it is determined that there is no recording of the second audio signal even though the first detecting means detects that the stereo audio signal or the main / sub audio signal is recorded. If it is detected, it is expected that the detection result of the first detection means is incorrect or that the recording of the second audio signal is not sufficient. Also in this case, there is a high possibility that noise will be generated even if processing corresponding to any of the audio signals is performed. In the present invention, a first audio signal which is a sum signal of a main audio signal or a stereo audio signal is used.
By outputting only the audio signal of, the generation of noise is prevented.

〔Example〕

 Hereinafter, an example of the present invention will be described.

FIG. 2 is a diagram showing a schematic configuration of a reproduction system of a VTR as one embodiment of the present invention. The VTR according to the present embodiment performs FM modulation recording of the left and right sum signals and left and right difference signals of the stereo audio signals or the above-described main and sub audio signals as two-channel audio signals.

Here, the audio FM modulation signal (hereinafter AFM signal) is magnetically recorded and reproduced in the form of an FM modulated audio signal obtained by FM-modulating the audio signal, and the frequency spectrum of the AFM signal is shown in FIG. As shown.

F1 to f4 shown in FIG. 3 are the frequencies of the pilot signal ATF for tracking according to the well-known four-frequency system, fc is the carrier frequency of the low-frequency conversion chroma signal CL, and fm and fs are the AFM signals AFM-main and AFM-. The carrier frequency of the sub is AFM main signal (first audio signal) AFM-main is a signal obtained by converting the signal of the L left channel and the signal of the R (right) channel into a sum signal thereof when recording a stereo audio signal. When the main audio signal is recorded, a main audio signal such as Japanese is recorded.

On the other hand, an AFM sub-signal AFM-sub (second audio signal) is a signal obtained by converting a signal of the L channel and an R channel into a difference signal between these signals when recording a stereo audio signal. A secondary audio signal such as English is recorded. If the AFM sub-signal is not recorded, the AFM main signal is recorded as a monaural audio signal.

fsy is the luminance signal sync tip frequency, and fwh is the peak white frequency. It is well known that these frequency allocations are different depending on a format such as a so-called high band mode and a normal mode recording.

FIGS. 4A and 4B are diagrams showing the amplitudes of the carrier waves of the AFM signals AFM-main and AFM-sub at the time of recording the main and sub audio signals.

As shown in FIGS. 4 (a) and 4 (b), the amplitude level of the carrier of the AFM signal in the vertical blanking interval of the luminance signal is larger than that in the non-vertical blanking interval.

Hereinafter, description will be made with reference to FIG. In FIG. 2, signals recorded on the magnetic tape 10 are reproduced through rotating heads 11 and 12 and preamplifiers 13 and 14. These signals are synchronized with the rotating phases of the heads 11 and 12 from the terminal 16. After being made continuous by a switching circuit 15 switched by a changed head switching pulse (HSWP), a band-pass filter (BPF) 17, a high-pass filter (HPF) 18, a BPF 24, and a PBF 25
Is input to

The low-frequency color signal separated by the BPF 17 is subjected to color signal processing (C
Process) The color signal is returned to the original band by the process (circuit) 19 and the like, and is output from the color signal output terminal 21 and input to the mixing circuit 22.

The FM modulated luminance signal separated by the HPF 18 is subjected to processing such as FM demodulation by a luminance signal processing (Y process) circuit 20 and output from a luminance signal output terminal 24 and a mixing circuit.
Entered in 22. The output of the mixing circuit 22 is output from an output terminal 23 as a composite video signal.

The AFM main signal separated by the BPF 25 is input to the mode detection circuit 30 and the limiter 27, and is input to the limiter circuit.
The AFM main signal output from 27 is FM-demodulated by the FM demodulation circuit 29 to be demodulated into the original audio signal, and is input to the stereo matrix circuit 33, the terminal a of the switch 31, and the terminal b of the switches 31, 32.

The AFM sub-signal separated from BPF26 is the mode detection circuit
30 and the signal input to the limiter 28, the signal input to the limiter 28 is demodulated into the original audio signal FM-demodulated by the FM demodulation circuit 30, and the signals are inputted to the matrix circuit 33 and the switch circuit 32.
Input to the terminal.

When a stereo audio signal is recorded based on a 2-bit mode detection signal, which will be described later, output from the mode detection circuit 36, the switch circuits 31 and 32 output the stereo audio signal demodulated by the matrix circuit 33 to each C terminal. Output to the output terminals 34 and 35 via the, and when the main and sub audio signals are recorded, without passing through the matrix circuit 33, the FM demodulation circuits 29 and 3
The audio signal output from 0 is output to output terminals 34 and 35 via the respective a terminals.
Thus, the stereo audio signal and the main and sub audio signals are selectively output as appropriate.

When both switches 31 and 32 are connected to terminal b, an AFM main signal, that is, a monaural audio signal is output from terminals 34 and 35, and when connected to terminal d, an audio signal to terminals 34 and 35 is output. No output is performed.

Hereinafter, the mode detection circuit 36 in FIG. 2 will be described in detail.

FIG. 1 is a diagram showing a specific configuration example of the mode detection circuit of FIG. In the figure, reference numerals 40 and 41 denote terminals to which AFM signals separated by the BPFs 25 and 26 in FIG. 2 are input, respectively.
The signals are supplied to envelope detection circuits 42 and 43, respectively.
The envelope detection circuits 42 and 43 detect the level of the carrier of the AFM signal. The output signal of the envelope detection circuit 42 is supplied to a sample / hold (S / H) circuit 44 and a comparator 54, and the output signal of the envelope detection circuit 43 is output to an S / H circuit 45
And supplied to the comparator 55.

The S / H circuits 44 and 45 each perform S / H on the carrier level of the AFM signal during the vertical retrace period, and this sampling pulse is formed by the timing signal generation circuit 49 in synchronization with the HSWP from the terminal 48. You.

The level this S / H circuit 44 and 45 outputs are supplied to respective comparators 52 and 53, the comparator 52 and 53 when these differences level is greater than a predetermined threshold level Vth ₁ logically high level (Hi ) Is output. That is, when the main and sub audio signals have been recorded, the outputs of the comparators 52 and 53 become Hi.

On the other hand, the outputs of the envelope detection circuits 42 and 43 are supplied to comparators 54 and 55 to detect whether the carrier level of the AFM signal is higher than a predetermined threshold level Vth2. When the carrier level is higher than the threshold level, that is, when the carrier level of the AFM signal is sufficiently large, the comparator
The outputs of 54 and 55 become Hi.

The outputs d1, d2, d3, d4 of these comparators 52, 53, 54, 55
Is a read address of the read only memory (ROM) 50. The 2-bit data md stored at each address of the ROM 50 is as shown in Table 1.

In Table 1, "0" is a logical low level (Lo),
“1” corresponds to Hi. The mode data md output from the ROM 50 becomes control data for the switches 31 and 32 in FIG. That is, as shown in Table 1, when md is "00", the switches 31, 32 are connected to the d terminal, and similarly, when md is "0".
In the case of 1 "," 10 "," 11 ", the switches 31, 32 are connected to the terminals b, c, a.

Here, the idea determined by the md will be described. First, if the output d3 of the comparator 54 is Lo, it means that there is no recording of the sum signal of the stereo sound and the main sound signal, so that it is impossible to obtain a normal sound output. Even if d1 and d2 are both Hi, the switches 31 and 32 are connected to the d terminal to inhibit audio output. d3 is H
i and the output d4 of the comparator 55 is Lo,
Since two-channel audio cannot be reproduced and only monaural audio can be output, even if d1 and d2 are both Hi, switches 31 and 32 are connected to terminal b and monaural audio signals are output from both terminals 34 and 35. Output.

Next, a case where both d3 and d4 are Hi will be described. In this case, if d1 = d2, the reliability of such information is extremely high. Therefore, if d1 and d2 are both Hi, the switches 31 and 32 are connected to the terminal a, and the main and sub audio signals output from the FM demodulation circuits 29 and 30 are output from the terminals 34 and 35. If both d1 and d2 are Lo, connect both switches 31 and 32 to the c terminal,
The signals of the L channel and the R channel of the stereo sound output from the matrix circuit 33 are output from the terminals 34 and 35. However, when d1dd2, the reliability of such information is low,
Irrespective of which of the main and sub audio signals and the stereo audio signal is applied, there is a possibility that erroneous processing may be performed. Therefore, in this example, when d1 ≠ d2, FM
The output signal of the demodulation circuit 29, that is, the sum signal of the stereo sound or the main sound signal of the main / sub sound is used as a monaural sound signal.
Output from 34,35. At this time, the display unit 38 displays whether the output audio signal is a stereo signal, a monaural signal, or a main / sub signal in accordance with the two-bit mode information md.

According to the above configuration, when it is not possible to determine whether a stereo audio signal or a main / sub audio signal is recorded, a monaural audio signal is output. Even when it is determined that the main and sub audio signals are recorded from the carrier level of the period, if the carrier level of the AFM sub signal is insufficient, a monaural audio signal will be output, so that unpleasant noise may be output. Absent.
In the above-described embodiment, the FM carrier level during the vertical retrace period is set to be high when recording the main and sub audio signals. However, the FM carrier level is set to be high when recording a stereo audio signal, and the stereo audio signal is used in the reproduction system. It may be configured to detect that is recorded.

〔The invention's effect〕

As described above, according to the present invention, there is provided an audio signal reproducing apparatus capable of preventing the occurrence of noise when the determination of whether a two-channel audio signal is a stereo audio signal or a main / sub audio signal is erroneous. can get.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration example of a VTR mode detection circuit according to one embodiment of the present invention, FIG. 2 is a diagram showing a schematic configuration of an entire reproduction system of a VTR according to one embodiment of the present invention, and FIG. FIG. 4 is a diagram showing a frequency spectrum of a recording signal, and FIG. 4 is a diagram for explaining a carrier level of a recorded FM modulated audio signal. In the figure, 10 is a magnetic tape, 11 and 12 are rotary heads, 25 and 26 are bandpass filters, 27 and 28 are limiters, 29 and 30 are FM demodulation circuits, 31 and 32 are switching switches, 33 is a matrix circuit, 34 , 35
Is an audio output terminal, 36 is a mode detection circuit, 38 is a display section, 4
2, 43 are envelope detection circuits, 44 and 45 are sample and hold circuits, 50 is a ROM, and 52, 53, 54 and 55 are comparators.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-22686 (JP, A) JP-A-63-257959 (JP, A) JP-A-63-213162 (JP, A) JP-A-62-1987 77405 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G11B 20/02 H04N 5/91

Claims (2)

(57) [Claims] 1. A recording medium in which a first audio signal which is a sum signal or a main audio signal of a stereo audio signal and a second audio signal which is a difference signal or a sub audio signal of the stereo audio signal are respectively recorded. A device capable of reproducing the stereo audio signal or the main / sub audio signal, wherein the first and second audio signals are reproduced based on information multiplexed on the reproduced first audio signal. First detecting means for detecting that the signal is a sub sound signal, and the first and second sound signals being the main and sub sound signals based on information multiplexed on the reproduced second sound signal. A first audio signal and a second audio signal that are reproduced in accordance with the outputs of the first and second detection means to process a stereo audio signal or the main / sub audio signal. Output audio signal processing Audio signal processing means for outputting only the first audio signal when the detection results of the first detection means and the second detection means are inconsistent. apparatus. 2. A recording medium in which a first audio signal which is a sum signal or a main audio signal of a stereo audio signal and a second audio signal which is a difference signal or a sub audio signal of the stereo audio signal are respectively recorded. A device capable of reproducing the stereo audio signal or the main / sub audio signal, wherein the first and second audio signals are detected to be the stereo audio signal or the main / sub audio signal. Detecting means; second detecting means for detecting the presence or absence of recording of the second audio signal; and first and second audio signals reproduced according to the outputs of the first and second detecting means. Audio signal processing means for processing and outputting a stereo audio signal or the main and sub audio signals, wherein the audio signal processing means is such that the first detection means outputs the second and second audio signals as the stereo audio signals. Or before Detecting that the signal is a main / sub sound signal, and outputting only the first sound signal when the second detecting means detects that there is no recording of the second sound signal. Audio signal playback device.