JPH0366065A - Audio signal reproducing device - Google Patents

Abstract

PURPOSE:To prevent noise from occurring by outputting only a 1st audio signal, i.e. a main audio signal or a signal of the sum of stereo sounds from an audio signal processing means when an inconsistency is generated in a detected result between a 1at detecting means and a 2nd detecting means. CONSTITUTION:A carrier wave level of an audio FM (AFM) signal is detected by envelope detecting circuits 42 and 43 respectively and outputted to sample- and-hold (S/H) circuits 44 and 45 and comparators 54 and 55. Carrier wave levels of the AFM signal are sampled and held (S/H) by the circuits 44 and 45 and supplied to the comparators 52 and 53, and when a difference between their levels is large, a high level is outputted. And, when levels of the comparators 54 and 55 are large, a high level is outputted. Then, outputs of the comparators 52-55 becomes read addresses of a ROM 50. Consequently, when a mode data output of the ROM 50 is not clear by the detecting means, only the main audio signal is outputted, thus preventing noise from occurring.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an audio signal reproducing device, and more particularly to an audio signal reproducing device capable of reproducing a plurality of types of two-channel audio signals.

[Future technology]

In recent years, camera-integrated video tape recorders have also
Stereo audio is being promoted, but conventionally 1.5 MH
Even in VTRs that recorded monaural audio signals with FM modulation using a carrier wave of A method is adopted in which the sum signal of the L channel and the R channel is recorded, and a 1.7 MHz FM modulated carrier wave is newly provided to record the difference signal between the L channel and the R channel.

A VTR that records stereo audio signals using this type of sum-difference method.
In this case, when trying to record so-called main and sub-audio signals, such as Japanese on the L channel and English on the R channel, where left and right audio signals are recorded independently, the recorded signal is a stereo audio symbol. It is necessary to determine whether the signal is a main or subphonetic symbol and whether or not to pass it through the matrix circuit.

[Problem to be solved by the invention] Manually switching the processing as described above becomes complicated and causes confusion, and if the switching is performed incorrectly, the playback quality in particular will be significantly impaired. Because of this problem, it has been desired to automatically switch the processing mode. In order to perform such switching of processing modes, identification information for identifying the type of audio signal must be recorded in some form on the recording medium, and the switching described above must be performed in accordance with this 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 a dedicated recording and reproducing means. Therefore, it is conceivable to multiplex such identification information into the audio signal, but the audio signal itself does not have any redundant portion, and even if the identification information is multiplexed as described above, there is a possibility that it will be detected incorrectly. If this false detection occurs, it will appear as large noise in the reproduced audio.

In view of the above-mentioned problems, the present invention provides audio signal reproduction that can prevent the occurrence of noise due to erroneous detection of whether a two-channel audio signal is a stereo audio signal or a main/sub audio signal. The purpose is to provide equipment.

[Means for solving problems]

According to the present invention, the first aspect of the present invention is to provide a first audio signal which is a sum signal of stereo audio signals or a main audio signal, and a difference signal between the stereo audio signals or a sub audio signal. In a device capable of reproducing the stereo audio signal or the main and sub audio signals from a recording medium on which a certain second audio signal is respectively recorded, information multiplexed on the reproduced first audio signal. a first detecting means for detecting that the first and second audio signals are the main and sub audio signals based on the information multiplexed on the reproduced second audio signal; a second detection means for detecting that the second audio signal is the main and sub-audio signal; and a first and second audio signal reproduced according to the outputs of the first and second detection means. audio signal processing means for processing and outputting a stereo audio signal or the main and sub audio signals, and when the detection results of the first detection means and the second detection means contradict each other, the audio signal processing means The configuration is such that only the first audio signal is output.

Further, as a second invention, a first audio signal that is a sum signal of stereo audio signals or a main audio signal, and a second audio signal that is a difference signal of stereo audio signals or a sub audio signal 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 method for detecting that the first and second audio signals are the stereo audio signal or the main/sub audio signal.
a detection means, a second detection means for detecting whether or not the second audio signal is recorded, and first and second audio signals reproduced according to outputs of the first and second detection means. and audio signal processing means for processing a stereo audio signal or the main and sub audio signals, and the audio signal processing means detects that the first and second audio signals are detected by the stereo audio signal. signal or the main/sub audio signal, and when the second detection means detects that there is no recording of the second audio signal, only the first audio signal is output. It is said that

[Effect]

In the first invention, for example, when the first detection means detects that the main and sub-audio signals are the main and sub-audio signals, and the second detection means detects that the main and sub-audio signals are not the main and sub-audio signals, the stereo audio signal and the main and sub-audio It is not clear which signal is being recorded. In this case, noise is likely to occur no matter which audio signal is processed. Therefore, in the present invention, generation of noise is prevented by outputting only the first audio signal, which is the main audio signal or the sum signal of stereo audio.

Further, in the second invention, although the first detection means detects that the stereo audio signal or the main and sub audio signals are recorded, it is determined that the second audio signal is not recorded. If 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 insufficient. In this case as well, there is a high possibility that noise will occur no matter which audio signal is processed. Therefore, in the present invention, generation of noise is prevented by outputting only the first audio signal, which is the main audio signal or the sum signal of stereo audio.

〔Example〕

Examples of the present invention will be described below.

FIG. 2 is a diagram showing a schematic configuration of a reproduction system of a VTR as an embodiment of the present invention. The VTR of this embodiment FM-modulates and records the left and right sum signals and left and right difference signals of stereo audio signals, or the aforementioned main and sub audio signals, as two-channel audio signals.

Here, the audio FM modulated signal (hereinafter referred to as AFM signal) is magnetically recorded and reproduced in the form of an FM modulated audio signal obtained by FM modulating the audio signal, but the frequency spectrum of the AFM signal is shown in Figure 3. It is as shown.

fl to f4 shown in FIG. 3 are the frequencies of the tracking pilot signal ATF according to the well-known four-frequency system, and f
c is the carrier frequency of the low frequency conversion chroma low number CL, fm and fs are the AFMFM signal FM - m a i n ,
This is the carrier wave frequency of AFM-sub, and the AFM main signal (first audio signal) AFM-main is:
When recording stereo audio signals, the L left channel and R (
A signal obtained by converting the signal of the right) channel into a sum signal of these is recorded, and when recording the main and sub audio signals, the main audio signal, such as Japanese, is recorded.

On the other hand, the AFM sub signal AFM-sub (second audio signal) is used for the L channel and R channel when recording a stereo audio signal.
A signal obtained by converting the channel signal into these difference signals is recorded, and when recording the main and sub audio signals, for example, a sub audio signal such as English is recorded. Note that if this AFM sub signal is not recorded, the AFM main signal is recorded as a monaural audio signal.

fsy is the luminance signal sync chip frequency, fwh
is the peak white frequency. It is well known that these frequency allocations differ depending on the format, such as so-called humband mode and normal mode recording.

FIGS. 4(a) and 4(b) show the AFMFM signals F M -m a i n and A F at the time of recording the main and sub audio signals.
It is a figure which shows the amplitude of the carrier wave of M-sub.

As shown in FIGS. 4(a) and 4(b), the amplitude level of the carrier wave of the AFM signal in the vertical retrace section of the luminance signal is larger than that in the other than the vertical retrace section.

This will be explained below with reference to FIG. In FIG. 2, the signals recorded on the magnetic tape IO are
12 and preamplifiers 13 and 14, these signals are made continuous by a switch circuit 15 switched by a head switching pulse (HSWP) synchronized with the rotational phase of the head 11 and 12 from a terminal 16, and then converted into a band. Pass filter (BPF) I7. Bypass filter (HPF)18. BPF24° is input to BPF25.

The low-frequency color signals separated by BPF17 undergo color signal processing (
Process C) The color signal is processed by the circuit 19 to return it to its original band, and is outputted from the color signal output terminal 21 and inputted 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, outputted from a luminance signal output terminal 24, and inputted to a mixing circuit 22. The output of the mixing circuit 22 is outputted 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 the AFM main signal output from the limiter circuit 27 is FM demodulated by the FM demodulation circuit 29 and demodulated to the original audio signal. is,
It is input to the stereo matrix circuits 3, 3, the a terminal of the switch 31, and the b terminal of the switches 31 and 32.

The AFM sub-signal separated from the BPF 26 is input to the mode detection circuit 30 and the limiter 28, and the limiter 2
The signal input to 8 is FM demodulated by the FM demodulation circuit 30 to the original audio signal, and is input to the a terminal of the matrix circuit 33 and the switch circuit 32.

When a stereo audio signal is recorded, the switch circuits 31 and 32 transmit the stereo audio signal demodulated by the matrix circuit 33 to each C terminal according to a 2-bit mode detection signal outputted from the mode detection circuit 36, which will be described later. When the main and sub audio signals are recorded 4), the audio signals output from the FM demodulation circuits 29 and 30 are outputted to the output terminals 34 and 35 via the a terminals without going through the matrix circuit 33. By outputting to the output terminals 34 and 35, the stereo audio signal and the main and sub audio signals are selectively output as appropriate.

In addition, the switch 31. When both terminals 32 and 32 are connected to the b terminal, an AFM main signal, that is, a monaural audio signal, is output from the terminals 34 and 35, and when they are connected to the d terminal, no audio signal is output to the terminals 34 and 35.

The mode detection circuit 36 in FIG. 2 will be explained in detail below.

FIG. 1 is a diagram showing a specific example of the configuration of the mode detection circuit shown in FIG. 2. FIG. 40 and 41 in the figure are BPF25 in Figure 2, respectively.
．． This is a terminal to which the AFM signals separated by 26 are input, and these AFM signals are respectively input to the envelope detection circuit 42.
．． 43. Envelope detection circuit 42.43
detects the level of the carrier wave of the AFM signal. The output signal of the envelope detection circuit 42 is sample-and-hold (S/H).
) circuit 44 and a comparator 54, and the output signal of the envelope detection circuit 43 is supplied to an S/H circuit 45 and a comparator 55.

The S/H circuits 44 and 45 each S/H the carrier wave level of the AFM signal within the vertical retrace period, and this sampling pulse is generated by the timing signal generation circuit 49 in synchronization with H3WP from the terminal 48. Ru.

The levels output by the S/H circuits 44 and 45 are supplied to comparators 52 and 53, respectively, and if the difference level between them is greater than a predetermined threshold level vth, the comparators 52 and 53 output the levels. 53 outputs a logical high level (Hi). That is, when the main and sub audio signals are recorded, the outputs of the comparators 52 and 53 become Hi.

On the other hand, the output of the envelope detection circuit 42.43 is supplied to a comparator 54.55 so that the carrier level of the AFM signal reaches a predetermined threshold level vth2. It is detected whether it is larger than vth3. When the carrier wave level is higher than the threshold level, that is, when the carrier wave level of the AFM signal is sufficiently large, the outputs of the comparators 54 and 55 become Hi.

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

Table 1 In Table 1, “0” is a logical low level (Lo)
, "t" corresponds to Hi. Mode data md, which is the output of this ROM 50, becomes control data for the switches 31 and 32 in FIG. 2 via the terminal 51. That is, as shown in Table 1, when md is "00", switches 31 and 32 are connected to the d terminal, and similarly when md is "01", "lO" and "11"
”, switches 31 and 32 are connected to the S, C, and A terminals.

Here, the idea behind determining this md will be explained. First, if the output d3 of the comparator 54 is Lo, it means that there is no recording of the stereo audio sum signal and the main audio signal, so it is impossible to obtain a normal audio output. both di and d2 are H
Even if it is i, switches 31 and 32 are connected to the d terminal to prohibit audio output. When d3 is Hi and the output d4 of the comparator 55 is LO, it is impossible to reproduce 2-channel audio and only monaural audio can be output. Therefore, even if di and d2 are both Hi, the switch 31 .32
is connected to the b terminal, and monaural audio signals are output from both terminals 34 and 35.

Next, d3. A case where both d4 are Hi will be explained.

In this case, if dl=d2, the reliability of this information is extremely high. Therefore, if di and d2 are both Hi,
Switches 31 and 32 are connected to the a terminal, and the FM demodulation circuit 2
The main and sub audio signals output from terminal 34.9.30 are output from terminal 34. 3
Output from 5. If di and d2 are both Lo, both switches 31 and 32 are connected to the C terminal, and the L channel of the stereo audio output by the matrix circuit 33 is
The R channel signal is output from terminals 34 and 35. However, in the case of dl#d2, the reliability of this information is low, and there is a possibility that incorrect processing will be performed even if measures are taken for either the main/sub audio signal or the stereo audio signal. If incorrect processing is performed, unlistenable audio will be output. Therefore, in this example, in the case of d16d2, the output signal of the FM demodulation circuit 29, that is, the sum signal of the stereo audio or the main audio signal of the main and sub audio is outputted from the terminals 34 and 35 as a monaural audio signal. At this time, display section 3
8 indicates whether the output audio signal is a stereo signal, a monaural signal, or a main/sub signal according to the 2-bit mode information md.

According to the above-mentioned configuration, if it cannot be determined whether a stereo audio signal or a main/sub audio signal is being recorded, a monaural audio signal is output. Even if it is determined that the main and sub audio signals are recorded based on the carrier wave level of the period, if the carrier wave level of the AFM sub signal is insufficient, a monaural audio signal will be output, so no harsh noise will be output. do not have.

In the above-described embodiment, the FM carrier level during the vertical retrace period was set high when recording the main and sub-audio signals.
Increase the FM carrier level when recording stereo audio signals,
The reproduction system may also be configured to detect that a stereo audio signal is recorded.

〔Effect of the invention〕

As explained above, according to the present invention, there is provided an audio signal reproducing apparatus that can prevent the occurrence of noise in the event that the determination as to whether a two-channel audio signal is a stereo audio signal or a main/sub audio signal is erroneously determined. can get.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of the configuration of a mode detection circuit of a VTR according to an embodiment of the present invention, FIG. 2 is a diagram showing a schematic configuration of the entire reproduction system of a VTR according to an embodiment of the present invention, and FIG. Diagram showing the frequency spectrum of the recorded signal, No. 4
The figure is a diagram for explaining the carrier wave level of a recorded FM modulated audio signal. In the figure, 10 is a magnetic tape, 11. 12 is a rotating head;
25, 26 are band pass filters, 27.28 are limiters, 29.30 are FM demodulation circuits, 31.32 are changeover switches, 33 are matrix circuits, 34. 35 is an audio output terminal, 36 is a mode detection circuit, 38 is a display section, 42,
43 is an envelope detection circuit, 44 and 45 are sample and hold circuits, 50 is a ROM, and 52, 53, 54° and 55 are comparators.

Claims (2)

[Claims] (1) From a recording medium on which a first audio signal that is a sum signal of stereo audio signals or a main audio signal and a second audio signal that is a difference signal of stereo audio signals or a sub audio signal are respectively recorded, The device is capable of reproducing the stereo audio signal or the main/sub audio signal, wherein the first and second audio signals are reproduced as the main/sub audio signal based on information multiplexed on the reproduced first audio signal. a first detection means for detecting that the second audio signal is a signal; and a first detection means for detecting that the second audio signal is a signal;
a second detection means for detecting that the audio signal is the main/sub audio signal; and processing the first and second audio signals reproduced according to the outputs of the first and second detection means. and audio signal processing means for outputting a stereo audio signal or the main and sub audio signals, and when the detection results of the first detection means and the second detection means are inconsistent, the audio signal processing means An audio signal reproducing device characterized in that it outputs only one audio signal. (2) From a recording medium on which a first audio signal that is a sum signal of stereo audio signals or a main audio signal and a second audio signal that is a difference signal of stereo audio signals or a sub audio signal are respectively recorded. A device capable of reproducing the stereo audio signal or the main/sub audio signal, and a first detection means for detecting that the first and second audio signals are the stereo audio signal or the main/sub audio signal. and a second detection means for detecting whether or not the second audio signal is recorded, and processing the first and second audio signals reproduced according to the outputs of the first and second detection means. an audio signal processing means for outputting a stereo audio signal or the main and sub audio signals, and the audio signal processing means is configured to detect whether the first and second audio signals are the stereo audio signal or the main/sub audio signal. It is characterized by outputting only the first audio signal when it is detected that the audio signal is a main/sub audio signal, and the second detection means detects that there is no record of the second audio signal. audio signal reproducing device.