JPS61288583A - Recording and reproducing system for stereo sound signal in video tape recorder - Google Patents

Abstract

PURPOSE:To attain recording and reproduction of a stereo sound signal with high sound quantity without crosstalk or deterioration in distortion factor due to a matrix circuit by recording and reproducing a stereo sound signal recorded with frequency multiplex with a video signal in a form of a sum signal and a subtraction signal so as to record and reproduce the stereo sound signal of a sound multiplex television broadcast without passing through a matrix circuit. CONSTITUTION:The sum signal (L+R) and the subtraction signal (L-R) of stereo sound signals outputted from a demodulator 4 of a sound multiplex television tuner 6 are extracted as it is as a recording sound signal at recording and recorded with a video signal V outputted similarly from the demodulator 4 with frequency multiplex, and they are fed as they are to an RF converter 22 at reproduction and converted into the RF signal of the same form as the sound multiplex television broadcast signal together with the reproduced video signal V fed to the RF converter 22 similarly and fed properly to a television receiver from an output terminal 25.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a video tape recorder that frequency-multiplexes a video signal and a two-channel stereo audio signal, records and reproduces the same, and records the output from an audio multiplexing television tuner. The present invention relates to a recording and reproducing method for stereo audio signals suitable for reproduction.

[Background of the invention]

As a device that records and reproduces video signals and audio signals on a recording medium, it frequency modulates the luminance signal of the video signal and
The conveyed color signal is low frequency converted and recorded on a video track inclined at a constant angle in the longitudinal direction of the magnetic tape. There is a so-called video tape recorder (hereinafter referred to as VTR),
With the progress of high-density recording technology in recent years, the tape running speed has tended to become extremely slow. Recording and playback of high quality sound is increasingly required. Especially when it comes to recording and playing back audio signals.

Conventional video tape recorders generally use a fixed head to perform recording and playback on audio tracks along the sides of the magnetic tape, but in this recording and playback system, the tape running speed is limited.

When the speed is extremely slowed down, wow and flutter characteristics occur.

It has become difficult to obtain sufficient playback quality in terms of playback 8/N, playback frequency characteristics, etc., and it has become impossible to record and play back stereo audio signals with satisfactory sound quality, which is a strong demand for high-fidelity. I'm sorry.

Therefore, in order to solve this problem, as shown in, for example, Japanese Patent Laid-Open No. 58-136192, left and right channel signals of a stereo audio signal are frequency-multiplexed with a video signal and recorded using a video track. A method for reproducing it was proposed.

In this method, the right channel signal (
R signal) and left channel signal (L signal) are each frequency-modulated, and are frequency-multiplexed with the luminance signal of the video signal, which is separately frequency-modulated, and the carrier chrominance signal, which is low-frequency converted, and recorded. It has become.

Now, let us consider the case where the above recording and reproducing method is applied to recording and reproducing stereo audio signals and video signals obtained by receiving audio multiplexed television broadcasting. As you know,
The frequency spectrum of the audio signal in audio multiplex television broadcasting is determined as shown in Figure 9. When the audio signal is a stereo audio signal, the main channel audio signal is a combination of the L signal and the R signal. The sum signal and the sub-channel signal are obtained by frequency modulating the subcarrier (31.5 kHz) using the difference signal between the L signal and the R signal. This audio multiplex signal is generally restored to the original audio signal by a demodulator having a configuration as shown in FIG. 10 provided in an audio multiplex television tuner. T, that is, in FIG.

An FM-detected audio multiplex signal is input from the terminal 102, and the input signal includes a subchannel signal and a pilot signal (
Bandpass filter 10 that only passes the filter (see Fig. 9)
3 and is supplied to the de-emphasis circuit 111. The signal that has passed through the de-emphasis circuit 111 passes through a low-pass filter 112 that passes only the main channel signal, and is input to a switch 115.

On the other hand, the signal that has entered the bandpass filter 103 is divided into a subchannel signal and a pilot signal 107, and after the subchannel signal is demodulated by the FM demodulator 104,
De-emphasis circuit 105 and hero pass filter 10
6 and is input to switch 114. After the pilot signal 107 is demodulated by an AM demodulator 1081/i, it is input to a circuit 109 that detects whether the audio multiplexed signal is a stereo audio signal or a bilingual audio signal, and is input to a circuit 109 that detects whether the audio multiplexed signal is a stereo audio signal or a bilingual audio signal. If so, switches 114-117
A control signal 110 for switching the bilingual audio signals 1j, etc. to the other terminal is outputted to the terminal exposed to the M-IJ box circuit 113. As a result, when the audio multiplexed signal is a stereo audio signal, the king channel signal from the low-pass filter 112, that is, the stereo sum signal, and the demodulated sub-channel signal, that is, the stereo difference signal from the low-pass filter 106, are sent to the matrix circuit. 113 and is restored to the L signal and 几平, which is then input to terminal 118.1.
19, and when the audio multiplex signal is a two-factor audio signal, the main channel signal and the demodulated sub-channel signal are directly output from the terminal without going through the multi-IJ sock circuit 113. It will be output from 118 and 119.

Now, a conventional configuration in which the stereo audio signal of the audio multiplexed television broadcast obtained in this way is frequency-multiplexed and recorded with a video signal using the recording/reproducing method described above is as shown in FIG. 11, for example. It was something. That is, in FIG. 11, 6 is an audio multiplexing television tuner, and this tuner converts the received signal input from the terminal 1 into a video signal V and a sum signal of the stereo audio signal (
L+l7), difference signal (L-)1. ), and further, the matrix circuit 5 separates the stereo audio signal into an L signal and an R signal and outputs the signals. These R signals are selectively switched to external input stereo audio signals from terminals 2 and 3 by changeover switches 27 and 28 as necessary, and are input to noise reduction encoders 62 and 63. The dynamic range is compressed by encoders 62 and 63 as is well known, and the R signals are then input to frequency modulators 10 and 11 to become FM audio signals each having a different carrier frequency, which are then added together by an adder 32. , an adder 3 via a low-pass filter 12
3.

On the other hand, the adder 33 is also supplied with an FM video signal obtained by frequency modulating the video signal V output from the tuner 6 by the video processing circuit 13.

Here, since the frequency bands of the FM video signal and the FM audio signal are set in advance to be different frequency bands, the signal synthesized by the adder 33 is
A frequency multiplexed signal of an 'M video signal and an F'M audio signal is obtained, and the frequency multiplexed signal is recorded on a video track of the magnetic tape 29 by a head 30 via a recording amplifier 14.

During reproduction, the signal reproduced by the head 30 is amplified by the preamplifier 15, and then passed through the bandpass filter 17.
18 and is input to the video processing circuit 16.

The bandpass filters 17 and 18 separate and extract two different carrier frequencies included in the FM audio signal, and
Demodulators 19 and 20 demodulate the L signal and the ratio signal. The dynamic ranges of these L and R signals are expanded by noise reduction decoders 86 and 87, respectively, and outputted from terminals 23 and 24. They are also input to the matrix circuit 21, and the respective sum signals (L+1
() and difference signals (L-R) are created, and these signals are RF
It is supplied to converter 22. On the other hand, the video processing circuit 16
appropriately demodulates and processes the reproduced FM video signal, and supplies the output video signal V to the RF converter 22. RF
The converter 22 converts the sum signal (L+l()) and the difference signal (
L-)L) and video signal V are converted into an RF flaw signal in the same format as audio multiplex television broadcasting (however, the frequency is equivalent to an empty channel), and the converted signal is supplied from an output terminal 25 to a television receiver.

By the way, in the recording and reproducing method of FIG. 11 explained above,
This is because the ratio signal and L signal, which are stereo audio signals, are independently FM modulated and recorded and reproduced.

During recording, the recorded audio signal is sent to the audio multiplex TV tuner 6.
The L signal and the R signal must be extracted from the R output terminal, that is, via the matrix circuit 5, and during playback, the L signal and the ratio signal of the reproduced stereo audio signal are extracted by the matrix circuit 21. Once the sum signal (
After converting into L-)-R) and difference signal (L-R), R, F
It is necessary to supply the signal to the converter 22 and then return it to the L signal and R signal through the matrix circuit (not shown) on the TV receiver side to which the output from the RF converter is supplied. As a result of passing the stereo audio signal through the circuit, the sound quality was impaired due to increased crosstalk of the stereo audio signal and deterioration of the distortion rate. In addition, when the L signal and R signal are FM-modulated separately and frequency-multiplexed with the video signal, the recording band occupied by the stereo audio signal is relatively wide, so the recording band occupied by the video signal becomes narrow, resulting in high image quality. It also has the disadvantage that it is difficult to obtain.

In order to solve this drawback, for example, as shown in FIG. 12, the matrix circuit 26 and 10 are added to the configuration of FIG.
Add 0 and paste from tuner 6.

It is also possible to convert the R signal again into a sum signal (L+R) and a difference signal (L-R) and record it, and then convert it back to the R signal after playback, but in this case, the stereo audio signal Although the recording occupied band can be made narrower than in the case of FIG. Since the multi-IJ Fuchs paths 26 and 100 are added to the signal, the crosstalk and distortion rate of the stereo audio signal become even worse than in the case of the 11th case, which is undesirable.

[Purpose of the invention]

An object of the present invention is to solve the above-mentioned problems, and to record and reproduce stereo audio signals and video signals output from an audio multiplexing television tuner by frequency multiplexing the stereo audio signals with high sound quality. To provide a recording and reproducing system for stereo audio signals in a video tape recorder, which allows recording and reproducing without deteriorating the image quality of video signals.

[Summary of the invention]

In order to achieve this objective, the present invention provides a video signal and a left and right
In a video tape recorder that frequency-multiplexes the stereo audio signals of channels and records and plays them, the stereo audio signals are received from the audio multiplexing TV chainer in the form of the sum signal and difference signal of the left and right channel signals before passing through the matrix circuit. The extracted stereo audio signal is frequency-multiplexed with the video signal and recorded as it is, and the reproduced stereo audio signal is supplied to the RF converter together with the reproduced video signal in the form of the sum signal and difference signal. This makes it possible to record and play back stereo audio signals obtained from an audio multiplexing television channel without passing them through a matrix circuit, thereby preventing sound quality deterioration caused by the matrix circuit. By performing frequency multiplex recording with the signal, the recording band is made relatively narrow, and therefore the video signal can be recorded in high image quality without sacrificing the recording band. do.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention,
Since it has almost the same configuration as the configuration explained in FIG. 11, corresponding components are given the same reference numerals as in FIG.
Unlike the case shown in the figure, during recording, the sum signal (L+1(,) and difference signal (L-)L) of the stereo audio signals output from the demodulator 4 of the audio multiplex TV tuner 6 is extracted as is as the recorded audio signal. It is also frequency-multiplexed with the video signal V output from the demodulator 4 and recorded, and during playback, the reproduced audio signal, that is, the sum signal (L+R) of the stereo audio signal and the difference signal (L- R) is supplied as is to the RIF converter 22, and the same (RF
Together with the reproduced video signal V supplied to the converter 22, it is converted into an F signal having the same format as the audio multiplexed television broadcast signal, and is supplied from an output terminal 25 to a television receiver or the like as appropriate.

As is already clear, according to the configuration of this embodiment, the stereo audio signal obtained from the audio multiplexing television tuner is summed without going through a matrix circuit, unlike the examples explained in FIGS. 11 and 12. Since recording and reproduction are performed in the form of a signal and a difference signal, there is no deterioration in sound quality, and there is no loss in image quality of the stereo audio signal and the video signal that is frequency multiplexed and recorded.

In addition, in the embodiment 2 of FIG. 1, the external input terminals 2 and 3
The stereo audio signals (L, R signals) inputted from the audio TV chainer 6 are converted into a sum signal and a difference signal by the matrix circuit 101 so that they can be recorded in the same format as the audio signals from the audio TV changer 6. In addition, when the reproduced stereo voice signal is supplied to the external circuit from the terminals 23 and 24, the matrix circuit 102
The sum signal (L + R) and the difference signal (L - R) are obtained by
It is designed to convert into an R signal and output it.

Next, an example of the structure of the main circuit portion used in the embodiment of FIG. 1 will be explained with reference to FIGS. 2 to 5.

FIG. 2 shows the basic configuration of a matrix circuit, including an adder 39 that adds two input signals from terminals 35 and 36, and a subtractor that subtracts the input signal at terminal 35 from the input signal at terminal 36. It consists of 40 vessels. Left and right channel signals of stereo audio signals are output from terminals 35 and 36.
, the sum signal (L + R,) is obtained from the output terminal 37 of the adder 39, and the sum signal (L + R,) is obtained from the output terminal 38 of the subtracter 40.
The difference signal (L-)1. ) is obtained. Conversely, the sum signal (L+R) and the difference signal (L-R
), output terminals 37 and 38 each output 2L.

2R1, that is, left and right channel signals of stereo audio signals.
You can get a difference.

FIG. 3 shows a specific example of the configuration of the MA I-IJ socks path, in which operational amplifiers 45 and 46 and resistors R1''2
+ '3 + '4 and R5 constitute the adder 39 in FIG. 2, and the operational amplifier 47 and the resistor '6 + R7+
8 and R9 constitute the subtracter 40 in FIG. 2. The voltage follower circuits of operational amplifiers 43 and 44 supply the audio input signals from the terminals 35 and 36 to the adder and subtracter with low impedance. This is a buffer circuit for the output voltage of the output terminal 37 of the adder.
:1's, the input voltage from terminals 35 and 36 is "1 +
If it is '2, then the resistance value is '1 = '2 = '3 r几4=
Should I choose average 5? 3 z PI + 22 is obtained. The operation of the subtracter is such that the input signal from the terminal 35 is applied to the inverting input side of the operational amplifier 470, and the input signal from the terminal 36 is applied to the non-inverting input side.
80 subtractor output voltage? 4 is.

So, the resistance value is 6”? ! ``8'''9
If you choose IF5 =? 2-? It becomes H. Such matrix circuits are used as matrix circuits 5, 101, 102, etc. in the embodiment of FIG.

FIG. 4 shows the frequency modulator 10 in the embodiment of FIG.
11, the input signal from the terminal 60 (
A sum signal or a difference signal of the stereo audio signals output from the noise reduction encoders 62 and 63 in FIG. 1 is supplied to the vCO control circuit 64. vCO control circuit 64
are a VCO (voltage controlled oscillator) 65, a frequency dividing circuit 66, a frequency comparator 67, a reference frequency oscillator 70, a frequency dividing circuit 69
Together with the loop filter circuit 68, it constitutes an automatic frequency control circuit (AFC circuit). When there is no input signal from terminal 60, output terminal 61 outputs a VCO 65 equal to the reference frequency set by reference frequency oscillator 70.
The oscillation frequency output can be obtained.

When the signal from the terminal 60 is input, the vCO control circuit 6
4, the oscillation frequency of the VCO 65 is shifted from the reference frequency according to the amplitude of the input signal, so that the output terminal 61
A signal having a frequency shift according to the input signal amplitude, that is, a signal obtained by FM modulating the input signal is obtained.

FIG. 5 shows the FM demodulators 19, 2 in the embodiment of FIG.
0, a reproduced FM audio signal (FM stereo sum signal or difference signal) inputted from a terminal 71 is amplified to a constant amplitude by an automatic gain control circuit (AGC) 72.

The wave is shaped into a rectangular wave by the limiter circuit 73 and the phase detection circuit 7
is supplied to one input terminal of 4.

On the other hand, the circuit block 103 includes an AFC circuit (a fourth
The circuit shown in the figure can be used as is, and the constituent circuit elements are shown using the same symbols as in Figure 4), and the VC
The output of O65 is input to the other input terminal of phase detection circuit 74. The phase detection circuit 74 compares the phases of the FM audio signal and the output signal of the VCO 65, and feeds back the error output to the adder 104 of the AFC circuit 103, and also supplies it to the vCO control circuit 64 via the low-pass filter 75. It looks like this.

The related configuration of the phase detection circuit 74 and the AFC circuit 103 forms a so-called automatic phase control circuit (APC), which allows the vC065 to synchronize its oscillation phase with the FM audio signal. However, since the control signal therefor, that is, the output change of the phase detection circuit 74, corresponds to the frequency change of the FM audio signal, it is necessary to extract it from the low-pass filter 75.

A demodulated output of the FM audio signal can be obtained.

In the FM demodulator with such a configuration, the reference frequency oscillator 7
Since the AFC operation of the AFC circuit 103 based on the 00 oscillation output is also performed, the demodulation center frequency is always stable without being affected by temperature changes, etc.
It has the characteristics that it can be made without adjustment.

Now, the demodulated output of the FM audio signal taken out from the low-pass filter 75 is input to a hold circuit 84 in this configuration example.

The hold circuit 84 captures the temporary loss (dropout) of the reproduced signal due to the alternating operation switching period of the two rotary heads in the VTR or damage to the tape by holding the previous value. One of the signals controlling the hold circuit 84 is generated from the rising and falling parts of the rotary head switching signal input from the terminal 78, and the other is generated from the rising and falling parts of the rotary head switching signal input from the terminal 78.
The output signal of VCO65 is passed through D type flip-flop 7.
The FM audio signal from the AGC 72 is synchronously detected by the synchronous detection circuit 77 using a signal whose phase is shifted by 90 degrees by 6, and the output is passed through the dropout detection circuit 80. These control signals are supplied to the monomulti 83 via the adder 82, and the output thereof causes the hold circuit 84 to hold the previous value for a predetermined period corresponding to the temporary loss of the reproduced audio signal. The output of the detection circuit 77 is also supplied to the AGC 72, and the AGC
It is designed to control movement.

Furthermore, in order to prevent large noise from being output to the audio output when the audio signal is missing for a long time, such as when no FM audio signal is input from the terminal 71,
The output of the synchronous detection circuit 77 is input to a mute detection circuit 81 that detects audio signal loss for a predetermined period of time or longer, and a mute circuit 85 is operated based on the detected output. The signal passing through the mute circuit 85 is outputted from the terminal 88 as a demodulated audio signal, and then the signal is outputted from the terminal 88 as a demodulated audio signal.
Modifications of the illustrated embodiment will be described with reference to FIGS. 6 to 8.

FIG. 6 shows how the video signal V and audio signal L+I (,, L-) on the input side in FIG. This allows the user to choose whether to remove the
In addition to the configuration of the embodiment shown in the figure, selector switches 90, 91.9
2 is provided. As is clear from the figure, the changeover switches 90 and 91 switch between the audio signals L-1-R, LR, output from the audio multiplex television tuner 4 (demodulator) or the matrix circuit 101, and the noise reduction of the reproduction circuit. The RF converter 2 selectively switches between the reproduced audio signals L+R and LR output from the decoders 86 and 87.
2 and is supplied to the matrix circuit 102. Similarly, the changeover switch 92 selectively switches between the video signal V output from the audio multiplex television tuner 4 and the reproduced video signal V output from the video processing circuit 16 and supplies the signal to the RF' converter 22. Therefore, these changeover switches 90 to 9
By switching 2 in conjunction with each other, for example, during the playback operation of a VTR, the reproduced video signal and audio signal can be switched, and at other times, the video signal and its audio signal output from the TV tuner 4 or the output from the matrix circuit 101 can be switched. You can selectively listen to the audio signals that are sent to you.

Figure 7 shows an example in which the configuration of Figure 6 is further modified to suit the US audio multiplex television broadcasting system. As in the above case, it is transmitted in the form of a sum signal and a difference signal of the left and right channels, but the difference signal is subjected to noise reduction to compress its dynamic range, and this is inversely converted on the receiving side. It's starting to go back. In order to accommodate such a system, the modified example shown in FIG.

Among the stereo audio signals output from the TV chainer 4 (demodulator), the difference signal (LR) to which noise reduction has been applied is as follows.

After the dynamic range is restored to its original state through the noise reduction decoder 95, the selector switch 28
Noise reduction encoder 63 of the recording circuit via
It is designed to be input. Also, during playback, the playback difference signal output from the noise reduction decoder 87 (
The signal (L) is supplied to the RF converter 22 after being subjected to noise reduction through a noise reduction encoder 97, thereby obtaining a broadcast wave that conforms to the above method.

FIG. 8 shows a further modification of the configuration shown in FIG. 7, in which the decoder 95 and encoder 63 during recording and the decoder 87 and encoder 97 during playback are omitted. In this way, the difference signal (L-R
) will be recorded and reproduced as is and supplied to the RF converter 22, and as in the case of Figure 7, the encoder and decoder for noise reduction will not be repeatedly interposed in the recording and reproduction system of the difference signal. In addition to the absence of a 7-trix circuit, it is possible to record and reproduce stereo audio signals of higher quality. In addition, in the modified example of FIG. 8, with the omission of the encoder and decoder as described above, the difference signal (no noise reduction has been applied) of the externally input stereo audio signal output from the matrix circuit 101 is as follows. A noise reduction encoder 98 is separately provided to enable recording with noise reduction applied, and a separate noise reduction decoder 99 is also provided on the playback output side to adjust the dynamic range of the playback difference signal (L-R). After being restored, it can be supplied to the matrix circuit 102.

Although one embodiment of the present invention and its modified examples have been described above, the present invention is not necessarily limited to these examples. For example, when recording and reproducing a stereo audio signal, it is not necessarily necessary to perform noise retardation, and the stereo audio signal and video signal that are frequency multiplexed do not necessarily have to be FM modulated;
The signal may be modulated using an appropriate modulation format such as pcM.

〔Effect of the invention〕

As explained above, according to the present invention, since the stereo audio signal recorded by frequency multiplexing with the video signal is recorded and played back in the form of a sum signal and a difference signal, the stereo audio signal of audio multiplexed television broadcasting is The signal can be recorded without passing through a matrix circuit, and during playback, it can be supplied directly to the RF converter without passing through a matrix circuit.

Therefore, it is possible to record and play back stereo audio signals with high sound quality without causing crosstalk or distortion rate deterioration due to the matrix circuit, and the difference signal between the stereo audio signals is a relatively low level signal. Therefore,
When this is appropriately modulated and frequency multiplexed with the video signal, the recording bandwidth is narrow, and the recording bandwidth of the video signal is correspondingly wide, making it possible to record and reproduce high-quality video signals. A video tape recorder that solves the above-mentioned problems and has excellent features, such as being able to reduce the number of parts in the stereo audio signal recording/playback circuit system, making it more compact, and lowering power consumption. It is possible to provide a recording and reproducing method for stereo audio signals.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing the basic configuration of the matrix circuit in FIG. 1, FIG. 3 is a circuit diagram showing a specific example of the configuration, and FIG. 4 is a block diagram showing an example of the configuration of the frequency modulator in FIG. 1, and FIG. 5 is a block diagram showing an example of the configuration of the FM demodulator in FIG. FIG. 9 is a block diagram showing a modification of the embodiment shown in FIG. 1, FIG. 9 is a spectrum diagram showing the frequency spectrum of an audio signal in audio multiplex television broadcasting, and FIG. 10 is a block diagram showing a demodulator for audio signals in the audio multiplex television team. 11 is a block diagram showing a conventional example in which a stereo audio signal and a video signal obtained from an audio multiplexing television tuner are frequency-multiplexed and recorded and reproduced, and FIG. 12 is a block diagram showing a modified example thereof. 4...Audio signal demodulator 5, Lot, 102...Matrix circuit 6
...Audio multiplex television team 10.11...Frequency modulator 12...Low pass filter 13, 16...Video processing circuit 14...
・Recording amplifier 15...Preamplifier 17.18...Band pass filter 19.20...FM restorer 22...uF converter 29...Magnetic tape 30...Magnetic head 62.63...・Noise reduction encoder 8
6.87...Katsuo Ogawa, Patent Attorney for Noise Reduction Decoder ~ Figure 2 Figure 3 Figure 4 (2) 5 base k (k) Iz) for bud cI Q knee 1rX>f 7th
0 figure

Claims (1)

[Claims] In a video tape recorder that frequency-multiplexes a video signal and stereo audio signals of two left and right channels, records and plays them back, the stereo audio signal is extracted from the audio multiplexing TV tuner in the form of a sum signal and a difference signal of the left and right channels, and the stereo audio signal is output directly as a video signal. A stereo audio signal recording/reproducing method characterized in that the reproduced stereo audio signal is frequency multiplexed and recorded, and the reproduced stereo audio signal is supplied to an RF converter together with the reproduced video signal in the form of the sum signal and difference signal.