JPH0366064A - Audio signal reproducing device - Google Patents

Abstract

PURPOSE:To eliminate an effect of fluctuation of a regenerative output and securely discriminate what kind of an audio signal by obtaining a difference between a carrier wave level of an audio FM signal for one part period and a carrier wave level of the audio FM signal for other part period. CONSTITUTION:A carrier wave level of an inputted audio FM (AFM) signal is detected by envelope detecting circuits 42 and 43. An output of the circuit 42 is supplied to sample-and-hold (S/H) circuits 44 and 45 and a comparator 54, while an output of the circuit 43 is supplied to S/H circuits 46 and 47 and a comparator 55. A carrier wave level just prior to a vertical fly-back interval is sampled and held (S/H) by the circuits 44 and 46, while a carrier wave level in the interval by the circuits 45 and 47, and carrier wave level differences are outputted by differential amplifiers 50 and 51 by subtracting outputs of the circuits 44 and 46 from outputs of the circuits 45 and 47 respectively. Whether main- and sub- audio signals are recorded or not is decided by these carrier wave level differences, so that what kinds of audio signals can securely be decided without being influenced by fluctuation of the regenerative output.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application in Industry A] The present invention relates to an audio signal reproducing device, and particularly to an audio signal reproducing device capable of reproducing a plurality of types of audio signals.

[Prior art] In recent years, even in camera-integrated video tape recorders,
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 Record the sum signal of the L
A method is adopted in which a difference signal between the channel and the R channel is recorded.

A VTR that records stereo audio signals using this type of sum-difference method.
In this case, when attempting 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 independent, the recorded signal is a stereo audio signal. It is necessary to determine whether the signal is a main/sub audio signal and whether or not to pass it through the Maritox circuit.

[Problems 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, in general, audio signals do not have any redundant parts, so it has been difficult to add identification information as described above. Furthermore, it is not preferable to record and reproduce such identification information separately from the audio signal, since this interferes with high-density recording and requires a dedicated recording and reproduction means.

In view of the above problems, an object of the present invention is to provide an audio signal reproducing device that can accurately identify the type of audio signal and perform corresponding processing even if information identifying the type of audio signal is not separately recorded. do.

[Means for Solving the Problem] In one aspect of the present invention, the carrier wave level during a part of the period is determined according to the type of audio signal, and the audio signal is A device for reproducing an audio signal from a recording medium recorded with FM modulation of a signal, comprising a processing circuit for processing the reproduced FM modulated audio signal, and a processing circuit for processing the reproduced FM modulated audio signal during the part of the period. The apparatus is configured to include a control means for controlling the processing circuit based on the difference between the carrier wave level and the carrier wave level of the FM modulated audio signal to be reproduced in another period.

[Function] As mentioned above, by taking the difference in the carrier wave level between some periods and other periods in which the carrier wave is at a level determined according to the type of audio signal, the reproduction output is influenced by fluctuations. It is possible to reliably identify the type of audio signal without any errors. Further, there is no need to make a large difference in the carrier wave level between the above-mentioned part of the period and the other period, and the reproduced audio signal itself can be restored satisfactorily.

[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 one-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 4. It is as shown.

f1 to f4 shown in FIG. 4 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 converted chroma signal CL, fm and f
s is the AFM signal AFM-main, AFM-sub
AFM main signal AFM-ma
When recording a stereo audio signal, in is L (left).
A signal obtained by converting the channel and R (right) channel signals into their sum signal is recorded, and when recording the main and sub audio signals, the main audio signal, such as Japanese, is recorded.

On the other hand, when recording a stereo audio signal, the AFM sub signal AFM-sub records a signal obtained by converting the L channel and R channel signals into their difference signals, and when recording a main and sub audio signal, it records 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.

f sy is the luminance signal sync tip frequency, f
wh is the peak white frequency. It is well known that these frequency allocations differ depending on the format, such as so-called high band mode and normal mode recording.

FIGS. 5(a) and 5(b) are diagrams showing the amplitudes of the carrier waves of the AFM signals AFM-main and AFM-sub during recording of the main and sub audio signals.

As shown in FIGS. 5(a) and 5(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 10 are the rotary head if,1
2 and a preamplifier 13.14, these signals are made continuous by a switch circuit 15 which is switched by a head switching pulse (H3WP) synchronized with the rotational phase of the head 11.12 from a terminal 16. Pass filter (BPF) 17, bypass filter (HP'F) 18, BPF 24, and BPF 25 are manually operated.

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 main vine circuit 27 is FM demodulated by the FM demodulation circuit 29 and demodulated to the original audio signal. and is input to the stereo matrix circuit 33, 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.

The switch circuits 31 and 32 switch the matrix circuit 3 when a stereo audio signal is being recorded according to a 2-bit mode detection signal, which will be described later, output from the mode detection circuit 36.
The stereo audio signal demodulated by -3 is output to the output terminals 34 and 35 through each C terminal, and when the main and sub audio signals are recorded, the
The audio signals output from the M demodulation circuits 29 and 30 are outputted to output terminals 34 and 35 via each a terminal. This results in
The stereo audio signal and the main and sub audio signals are selectively output as appropriate. Also, as described below, if the AFM sub signal is not recorded, both switches 31 and 32 are connected to the b terminal, and a monaural audio signal obtained by FM demodulating the AFM main signal is output from the terminals 34 and 35. Ru.

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. 40 and 41 in the figure are respectively BPF25.
This is a terminal into which the AFM signal separated by 26 is input,
These AFM signals are each sent to an envelope detection circuit 42.
43.

Envelope detection circuits 42 and 43 detect the level of the carrier wave of the AFM signal. The output signal of the envelope detection circuit 42 is supplied to sample and hold (S/H) circuits 44 and 45 and a comparator 54, and the output signal of the envelope detection circuit 43 is supplied to S/H circuits 46 and 47 and a comparator 55.

The S/H circuits 44 and 46 are connected to the AF immediately before the vertical retrace period, respectively.
The carrier wave level of the M signal is S/Hed, and this sampling pulse is generated by the timing signal generation circuit 49 in synchronization with H5WP from the terminal 48. On the other hand, S/
H circuits 45 and 47 S/H the carrier wave level of the AFM signal within the vertical retrace period. Sampling pulses to the S/H circuits 45 and 47 are similarly supplied from the timing signal generation circuit 49.

The differential amplifier 50.51 has a level obtained by subtracting the output of the S/H circuit 44.46 from the output level of the S/H circuit 45.47, that is, the carrier wave level of the AFM signal during the vertical retrace period and the AFM signal during other periods. Outputs the level of the difference between the signal and the carrier wave level. The difference levels output by the differential amplifiers 50 and 51 are supplied to comparators 52 and 53, respectively, and when these difference levels are larger than a predetermined threshold level Vthl, the comparators 52 and 53 are set to a logical high level (Hi
) is output. 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 outputs of the envelope detection circuits 42 and 43 are supplied to comparators 54 and 55, and it is detected whether the carrier level of the AFM signal is higher than a predetermined threshold level Vth2°v ths. 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 are high.
It becomes l.

The output of the comparator 52 and the output of the comparator 54 are input to an AND gate 56, and the output of the comparator 53 and the output of the comparator 55 are input to an AND gate 57. The AND gates 56 and 57 invalidate the information from the comparators 52 and 53 that the above-mentioned main and sub audio signals are recorded because it is considered inaccurate when the carrier wave level is low. These and gates 5
When a Hi output is obtained from at least one of 6 and 57, the output of the OR gate 58 becomes Hi, and this mode detection circuit 36 determines that the main and sub audio signals are recorded, and the output of the OR gate 58 becomes Hi. Mode information M from terminal 59
It is output as a.

On the other hand, since the output of the comparator 55 indicates the presence or absence of the AFM sub-signal, if the output of the comparator 55 is at a logical low level (Lo), it is difficult to restore the two-channel audio signal. Therefore, the output of this comparator 55 is also outputted from the terminal 60 as mode information Mb.

In this way, the mote detection circuit 36 outputs 2-bit mode information Ma and Mb.

When the mode information Mb is Lo, regardless of the mode information Ma, the switches 31 and 32 in FIG. The signal is output from output terminals 34, 35 as a monaural audio signal.

On the other hand, when mode information Mb is Hi, it is possible to output a 2-channel audio signal, so mode information Ma is Hi.
Now, the switches 31 and 32 are connected to the a terminals, and the main and sub audio signals output from the FM demodulation circuits 29 and 30 are outputted from the terminals 34 and 35. Further, when the mode information Mb is Hi and the mode information Ma is Lo, the switches 31.32 are connected to the C terminal, and the stereo audio signals output from the matrix circuit 33 are connected to the L channel and R channel signals to the terminals 34.35.
Output from.

At this time, the display section 38 displays the 2-bit mode information Ma, M
According to b, it is displayed whether the output audio signal is a stereo signal, a monaural signal, or a main and sub signal.

With the above-described configuration, whether or not the main and sub-audio signals are recorded is determined by the differential amplifier 50. 51 and the determination is made based on this level, so it is not greatly influenced by the difference in reproduction efficiency of the heads 11 and 13 or the tracking state. Therefore,
The above judgment can be made accurately. Additionally, it is no longer necessary to have a large difference in the carrier level between the vertical retrace period and other periods, and the audio signal during the vertical retrace period is ideally set to have a carrier wave level close to that of other periods. level, so no deterioration of the audio signal occurs.

FIG. 3 is a diagram showing a specific example of the configuration of the mode detection circuit. In the figure, like in FIG. 1, the same reference numerals are given to the constituent elements, and explanations thereof will be omitted. In the detection circuit of FIG. 3, the output signals of envelope detection circuits 42 and 43 are supplied to one end of capacitors 61 and 62. Capacitor 81.62
The other end is connected to an inverting amplifier 63.64, and a switch 65 is connected between the output side and the input side of the inverting amplifier 63.64.
．． A short circuit can be made by turning on 66.

The timing signal generating circuit 49 generates a timing pulse for turning on the switch 65, 66 during the vertical retrace period, thereby shorting the outputs of the inverting amplifiers 63, 64. At this time, the input and output levels of the inverting amplifiers 63 and 64 are fixed at O level, and the carrier wave level of the AFM signal during the vertical retrace period is maintained in the capacitors 61 and 62e.

Thereafter, when the switches 65, 66 are released, the true level obtained by subtracting the holding level from the carrier level of the AFM signal is supplied from the capacitor 61, 62 to the inverting amplifier 63, 64. Therefore, inverse amplification! 63 and 64 output a positive level corresponding to the difference level between the carrier wave level of the AFM signal during the vertical retrace period and the currently reproduced carrier wave level, and input it to comparators 69 and 70. Comparators 69 and 70 compare a predetermined threshold level Vthl' with the output level of inverting amplifier 63 and 64, output a logical binary signal, and input it to D@ of D type flip-flops 71 and 72. The clock terminal of the D-type flip-prop 71.7 has H3W.
In synchronization with P, a timing pulse is supplied during a period other than the vertical retrace period, and the logical binary signal is held and output for each vertical retrace period. At this time, from this D-type flip-flop 71.72, the comparator 52.5 shown in FIG.
The same output as in FIG. 3 is obtained, and thereafter, the same processing as in FIG. 1 is performed, and the mode information Ma is also obtained.

Obtain Mb.

In this example, similarly to the detection circuit shown in Fig. 1, it is determined whether or not the main and sub audio signals are recorded depending on the difference in the carrier wave level of the AFM signal between the vertical retrace period and other periods. Therefore, the same effect as the detection circuit shown in FIG. 1 can be obtained.

In each of the embodiments described above, it is determined whether the two-channel audio signal is a main/sub audio signal or a stereo audio signal by detecting a change in the carrier wave level.
It is also possible to adopt a configuration in which the type of modulated audio signal (for example, music and other signals, presence or absence of noise low-frequency processing) is detected by the detection circuits shown in FIGS. 1 and 3, and the content of processing during playback is determined. be.

[Effects of the Invention] As explained above, according to the audio signal reproducing device of the present invention, even if information identifying the type of audio signal is not separately recorded, the type of audio signal can be accurately identified and the corresponding processing can be performed. can be done.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a configuration example of a mode detection circuit of a VTR according to an IM example 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; The figure shows a modification of the mode detection circuit of Fig. 1, Fig. 4 shows a frequency spectrum of a recorded signal, and Fig. 5 shows a diagram for explaining the carrier wave level of a recorded FM modulated audio signal. It is a diagram. In the figure, 10 is a magnetic tape, 11.12 is a rotating head, 2
5.26 is a band pass filter, 27.28 is a limiter, 29.30 is an FM demodulation circuit, 31.32 is a changeover switch, 33 is a matrix circuit, 34.35 is an audio output terminal, 36 is a mode detection circuit, 38 is a Display section, 42.43 is envelope detection circuit, 44, 45, 46.47 is sample and hold circuit, 50.51 is differential amplifier, 52.5
3, 54.55, 69.70 are comparators, 61.6
2 is a capacitor, 63.64 is an inverting amplifier, 65.66
is a switch.

Claims (3)

[Claims] (1) A device that sets the carrier wave level during a part of the period to a level determined according to the type of the audio signal, and reproduces the audio signal from a recording medium in which the audio signal is recorded with FM modulation, a processing circuit that processes the FM-modulated audio signal that has been reproduced; , an audio signal reproducing device comprising control means for controlling the processing circuit. (2) For at least one of the two-channel audio signals, the level of the carrier wave during a part of the period is determined according to the type of the two-channel audio signal, and the two-channel audio signal is FM modulated and recorded. A device for reproducing the two-channel audio signal from a recording medium comprising: a processing circuit for processing the reproduced two-channel FM modulated audio signal; and a processing circuit for processing the reproduced two-channel FM modulated audio signal; An audio signal reproducing device comprising switching means for switching the processing of the processing circuit based on the difference between the carrier wave level of the FM modulated audio signal to be reproduced and the carrier wave level of the FM modulated audio signal to be reproduced in another period. (3) One of the two channels of audio signals is a sum signal or a main audio signal of a stereo audio signal, and the other is a difference signal or a sub audio signal of the stereo audio signal, and the processing circuit is a FM receiver of the two channels. The switching means includes a demodulation circuit that performs FM demodulation of each modulated audio signal, and a matrix circuit to which the two-channel audio signals demodulated by the demodulation circuit are input, and the switching means selects between the two-channel audio signals output from the matrix circuit and the two-channel audio signals output from the matrix circuit. No matrix circuit 2
The audio signal reproducing apparatus according to claim 2, further comprising means for selectively outputting the audio signal of the channel.