JPS60223005A - Recording and reproducing device of double channel sound signal - Google Patents

Abstract

PURPOSE:To obtain a recording/reproducing device of double channel sound signal which can obtain reproduction sound signals of high quality without deteriorating the picture quality and also has interchangeability with a monaural sound recording system, by compressing the dynamic range of the difference signal of a stereo sound signal with noise reduction and then giving FM modulation to said dynamic range. CONSTITUTION:For the stereo sound signals supplied through input terminals 29 and 32 in a recording mode, both sum and difference signals are produced for right and left signals by a matrix circuit 37. These sum and difference signals are supplied to LPFs 73 and 74 to receive the band limitation. The band-limited difference signal has its dynamic range compressed to half by a noise reducer NR40. Thus the maximum deviation of the difference signal is reduced less than that of the sum signal. This reduces an occupied band for record of sound signal and prevents th deterioration of picture quality. The interchangeability with a monaural system is maintained as a recording system for both sum and difference signals.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a two-channel audio signal recording and reproducing device that is compatible with a monaural audio signal recording and reproducing device, and particularly to a magnetic recording and reproducing device that records and reproduces audio signals together with video signals using a rotating head. The present invention relates to a two-channel audio signal recording and reproducing device suitable for.

[Background of the invention]

Conventionally, in video signal magnetic recording and reproducing devices (hereinafter abbreviated as VTR), video signals are FM-modulated and then alternately recorded by a rotating magnetic head as video tracks tilted at a constant angle with respect to the running direction of the magnetic tape. Generally, audio signals are recorded on audio tracks parallel to the running direction of the magnetic tape using a fixed audio recording head.

Therefore, in order to record a multi-channel audio signal 1, such as a stereo audio signal, the number of audio recording fixed heads corresponding to the number of channels is used.

The audio track parallel to the magnetic tape running direction is of the form Fv l
ii'l 1m 1r 1By the way, the above VTR
In order to increase the recording density and extend the recordable time, a method is used in which the magnetic tape running speed is slowed down and the video track width is narrowed. For this reason, the relative speed between the magnetic tape and the fixed head for audio recording is 4.5 in the cassette tape recorder. It is much slower than yscm15 and drops to about 16n/S, for example. As a result, the frequency band of the reproduced audio signal is drastically reduced, and furthermore, the wow and flutter characteristics are also deteriorated, causing serious problems in terms of sound quality. He's talented.

If the gap width of the audio recording fixed head is narrowed in order to improve the reproduced audio frequency band, five seats will deteriorate.

As one of the methods for preventing these deteriorations in sound quality, a method has been devised in which an audio signal is FM-modulated and superimposed on a video track using a one-rotation head (hereinafter referred to as an audio signal superimposition recording method).

What are the characteristics of the recording method for superimposing audio signals on video tracks?

(1) Good wow and flutter characteristics because it is less affected by time axis fluctuations due to uneven tape running speed.

(2) The reproduction frequency band does not depend on the tape running speed, and a wide band is possible.

etc. can be mentioned.

An example of a monaural audio signal superimposition recording method will be described with reference to FIGS. 1 and 2. In FIG. 1, a monaural audio signal is input from an input terminal 1 during recording, and is pre-emphasized in a pre-amplifier circuit 2. The output of the pre-emphasis circuit 2 is debiased to a maximum deviation of ±100 KHz by a debiasing adjuster 3.
After being adjusted, the signal is FM modulated by an FM modulator 4. The FM modulated audio signal is passed through a band pass filter (BPF) 5.
After removing unnecessary band components, the level adjuster 6 adjusts the recording level. FM with adjusted recording level
The modulated audio signal is added by the adder 7 to the FM modulated luminance signal and the low frequency converted chromaticity signal inputted from the input terminal 9 and the pilot signal for tracking control inputted from the input terminal 8. Thereafter, the video is recorded on the magnetic tape 11 as alternately inclined video tracks by rotating heads 10 and 12 having different azimuth angles. Here, the carrier frequency A of the FM modulator 4 is 1.5 MHz, and the spectra of the video signals Y and C input from the input terminal 9 and the pilot signal P input from the input terminal 8 are shown in FIG. As shown.

Next, the reproduction system will be briefly explained. Signals reproduced from the magnetic tape 11 by the rotary head 10.12 are amplified by the preamplifier 15.24 and converted into a series of reproduction signals by the changeover switch 26, one of which is sent from the output end 25 to a tracking control circuit (not shown). as well as.

The signal is output to a video signal reproducing circuit (not shown).

The other is input to JIPF+4 and only the reproduced FM modulated audio signal is extracted. The extracted reproduced FM modulation signal is FM demodulated by an FM demodulator (15Vc), and then carrier leakage etc. are removed by a low pass filter (LPF) 16. noise or dropout noise during the noise generation period,
Noise correction is performed by holding the previous value. here,
The head switching point is detected by the edge detection circuit 22 catching the edge of the rotating head switching signal input from the input end 22, and the dropout is detected by envelope detection of the output of the BPF 14- by the dropout detection circuit 19. . After the head switching point signal and the dropout detection signal are added by an adder 21, the pulse width is expanded by a pulse width expansion circuit 27 only during the transient period of noise generated due to band limitation.

The hold circuit 17 is controlled by the output signal of the pulse width expansion circuit 27. The demodulated audio signal subjected to noise correction by the hold circuit 17 is de-emphasized by the de-emphasis circuit 1B, and outputted from the output terminal 25 as a reproduced audio signal with reduced noise.

In the monaural audio signal recording and playback system explained above,
S, 7H1 frequency characteristics, wow, fushi, ivy age Jl! 1:
21 However, the above system is a recording/playback system for monaural audio signals, and multi-channel recording of audio signals is not possible. This is what the times demand.Therefore, it may be possible to achieve two-channel recording of audio by simply using two sets of the above-mentioned monaural systems.However, simply using two sets of monaural systems would not allow the recording of audio signals. The recording bandwidth will be more than twice that of a monaural recording system.If we consider the above-mentioned system, a monaural audio recording system will require 500 fRz as the audio signal wiring bandwidth, and a two-channel system will require a recording bandwidth of 500 fRz. 600KEz is required.

As a result, in a two-channel system that simply uses two monaural systems, the recording band occupied by the video signal becomes narrower, resulting in deterioration in image quality such as resolution deterioration. Also, 2
Channel recording systems also need to be compatible with monophonic systems.

[Purpose of the invention]

An object of the present invention is to avoid deterioration of image quality.

It is an object of the present invention to provide a two-channel audio signal recording and reproducing device that can obtain high-quality reproduced audio signals and is compatible with monaural audio recording systems.

[Summary of the invention]

In the present invention, the sum signal and the difference signal of stereo audio signals are
Since the difference signal generally has a small amount of information and a small dynamic range, the recording band occupied by the audio signal can be narrowed by making the deviation of the difference signal smaller than that of the sum signal. Based on the basic concept of compatibility with monaural audio and prevention of image quality deterioration. However, when the deviation of the difference signal is reduced, it becomes less susceptible to adjacent crosstalk noise generated by crosstalk signals from adjacent tracks and buzz generated by the sideband of the video signal, resulting in a reduction in high-quality playback sound quality. You won't be able to get it. By the way, the adjacent crosstalk noise N is the crosstalk signal level from the adjacent track U, the signal level from the track to be traced, and the instantaneous difference frequency between the D signal and the skipping signal is Δ.
・If it is -.

A' OcU/D・Δru −c, o, 6Δrnt −
It can be expressed as 00,-0-(1). Here t represents time. Therefore.

In the present invention, by compressing the dynamic range of the difference signal using noise reduction and then performing FM modulation, the instantaneous difference frequency of equation (1) is effectively increased without increasing the maximum deviation. △・- tends to be outside the audible band or become white noise5
k to reduce adjacent crosstalk noise. moreover.

If the sidebands of the FM modulated luminance signal or the low-frequency conversion chromaticity signal leak in, modulation noise and the like can also be reduced by the compression/expansion effect of the noise reduction.

Therefore, in the present invention, a sum signal and a difference signal of stereo audio signals are obtained, at least the dynamic range of the difference signal is compressed by noise reduction, and then the sum signal and the difference signal are FM-modulated with different carriers and recorded. Moreover, by making the deviation of the difference signal smaller than the deviation of the sum signal, a two-channel audio recording system is constructed that is compatible with a monaural system and prevents image quality deterioration such as resolution deterioration.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings. Fourth
The figure shows that an FM-modulated luminance signal, a low-frequency-converted chromaticity signal, an FM-modulated audio signal, and a pilot signal for tracking control are sequentially recorded on the same video track by rotating heads with different azimuth angles, and This is an example of a configuration in which the present invention is applied to an audio processing system of a VTR in which a PCM audio signal whose time axis has been compressed and the pilot signal are recorded in the overlap portion of the video track.

Fig. 4 Ki6, when recording, input ends 29', 50
Stereo audio signals inputted from the stereo audio signal, that is, the right side signal and the left side signal, are inputted to the matrix circuit 37 through switches 50 and 51. In the matrix circuit 57, an addition signal of the right side signal and the left side signal, so-called a sum signal, and a subtraction signal, so-called a difference signal are created, and these sum signal and difference signal are inputted to the LPF 75.74 through the switches 58 and 59. Note that if the signal input to the input terminals 29 and 52 is not a stereo audio signal but a bilingual Japanese signal such as Japanese and English, the switches 50 and 51.58
, 59 are operated by a control signal input from the input terminal 28.

Matrix circuit 37 is bypassed. The sum signal and the difference signal are band-limited to 20A#z at LP7''75°74.The band-limited difference signal is subjected to noise reduction (
NR) 40, the dynamic range is compressed by 172 VC. The characteristics of this NR4o are shown in Figure 5.1. As mentioned above, since there is no correlation between audio signals between adjacent tracks, NR40 compresses the dynamic range of the difference signal and creates an effective deviation. By increasing the difference frequency Δ·U shown in equation (1), it is likely to be outside the audible band or become white noise. Moreover, due to the effect of increasing the effective deviation of the NR, there is no deterioration in the reproduced sound quality even if the maximum deviation is smaller than the sum signal, so the audio recording occupied band can be made smaller. Therefore, the bandwidth is about 1.5 times that of a monaural system, and compared to a two-channel system that simply uses two monaural systems, there is less deterioration in image quality such as resolution deterioration, and high reproduced image quality can be obtained. The difference signal compressed by NR40 is as follows.

Maximum deviation is ±50KH with level adjuster 41
After z K IN adjustment, the carrier center frequency is 1.7
FM modulation is performed by the FM modulator 46 of M1b. After unnecessary band components are removed from the FM-modulated difference signal by the BPF 44, the recording level is adjusted by the level adjuster 45, and the signal is input to the adder 7. on the other hand.

After the sum signal passes through the pre-emphasis circuit 2, the maximum deviation is adjusted by ±100 AHZK with the level adjuster 5, and then it is converted to an FM signal with a carrier frequency of 1.5M1iz.
The signal is FM modulated by a modulator 4. After unnecessary band components are removed from the FM-modulated sum signal by a BPF 5, the recording level is adjusted by a level adjuster 6, and the signal is input to an adder 7. F&modulation harmonic signal, FM modulation difference signal, pH modulation luminance signal and low frequency conversion chromaticity signal input from input terminal 9.

After the pilot signal for tracking control inputted from the input terminal 8 is added by the adder 7, the added signal is inputted to the switches 48 and 49 through the recording amplifier 47. On the other hand, the PCM audio signal recording system.

The audio signals inputted from the input terminals 29 , 52 , 55 , 54 are selected by the switches 55 , 56 operated by the audio signal selection signal inputted from the input terminal 60 . The selected audio signal is band limited by L P F 200 , 5 [10 and passed through a converter 52 . The PCB signal processing circuit 55 generates a PCM audio signal whose time axis is compressed to about 176.

This time-base compressed PCM audio signal is added with a pilot signal in an adder 400, and then input to switches 48 and 49 through a recording amplifier 54.

Here, as shown in Fig. 5, the magnetic tape is wrapped around the rotating cylinder approximately 220 degrees, and one rotation head 10 degrees 12 is 1
The switches 48 and 49 are operated by a head switching signal input from the input end 22 to switch one of the rotating heads 10 and 12 shown in FIG. It is controlled to switch at a point of 50°,
During the 60° period, the PCM audio signal is transmitted to the rotating head I.
During the remaining period, the addition signal of the pH modulated luminance signal, the low frequency conversion chromaticity signal, the FM audio signal, and the pilot signal is transmitted to the rotary head and recorded on the magnetic tape 11. be done. The track locus recorded on the magnetic tape is as shown in FIG. Further, the recorded signal spectrum is as shown in FIG.

Next, the reproduction system will be explained. In FIG. 4, the reproduction signal reproduced from the magnetic tape 11 by the rotary heads 10 and 12 is amplified by the preamplifier 15, 24, and then
Switches 55 and 56 separate the signal into a series of reproduced signals consisting of a video signal, an FM modulated audio signal, and a pilot signal, and a PCM audio signal compressed by one time axis. Of these, the PCM audio signal that has been compressed by one time axis is outputted from an output terminal 57 to a PCM signal demodulation processing circuit (not shown) V:.

In addition, a series of reproduction signals consisting of a video signal, an FM modulated audio signal, and a pilot signal, one of which is BjFl and one of which is 61VC
The other signal is output from the output terminal 58 to a video signal reproduction circuit (not shown) and a tracking control circuit (not shown). Here, the switches 55 and 56 are controlled by a head switching signal inputted from the input terminal 22. BPF1
In 4.61.

Only the FM modulation harmonic signal and the FM modulation difference signal are extracted from the series of reproduced signals. The extracted reproduced FM harmonic signal is
The FM demodulator 15 demodulates the signal into a sum signal. The demodulated sum signal is input to the hold circuit 17 after carrier leakage and the like are removed by the LPF 16 . The hold circuit 17 includes a dropout detection circuit 19 and an edge detection circuit 2.
Dropout noise and head switching point noise detected at 0 are compensated for by holding the values before the noise generation period using control signals obtained from the adder 21 and the pulse width expansion circuit 27. The noise-compensated output signal of the hold circuit 17 is subjected to an L, PF 75 in which FM modulation difference signal components and the like are removed, and the band is limited to 20 KHz. L
The reproduced sum signal, which is the output of the P F 75, passes through the de-emphasis circuit 1B, and then passes through the switch 66 and is input into the matrix circuit 68.

On the other hand, the BPF 61 extracts only the FM modulation difference signal. The extracted FM modulation difference signal is demodulated by an FM demodulator 62, carrier leakage etc. are removed by an LPF 65, and
This becomes a reproduced difference signal. The reproduction difference signal is noise-compensated by holding the previous value in the hold circuit 64 based on the output signal of the pulse width expansion circuit 59 during the period in which dropout noise and head switching point noise occur. The noise-compensated reproduced difference signal is limited to the same band as the input band to the recording system NR40 by the LPF 76, expanded to the original dynamic range by the NR65, and then input to the matrix circuit 68 through the switch 67. do. In addition, the above NR
By the operations of 40 and 65, noise such as adjacent crosstalk noise and video buzz is reduced, and a high quality difference signal is obtained. Therefore, by the operation of the matrix circuit 6B, a reproduced right side signal and a reproduced left side signal having higher quality than the sum signal and the difference signal are obtained, and these reproduced stereo audio signals are transmitted to the switch 69.
, 70 and are output from output ends 71 and 72. Here, if the audio signal at the time of recording is a bilingual Japanese audio signal,
A switch 6 operated by a control signal input from the input terminal 42
Matrix circuit 6 by 6, 67, 69, 70
He will be released by bypassing the day.

As explained above, in the present invention, by compressing the dynamic range of the difference signal by NRVc and increasing the effective deviation, the maximum deviation of the difference signal is smaller than the deviation of the sum signal, and the audio signal recording occupied band is reduced. By making it narrower, one image quality deterioration is prevented. Additionally, compatibility with monaural systems is ensured using sum/difference signals as a recording system.

Although noise reduction is not used in the sum signal system in this embodiment, it is clear that even higher quality reproduced audio can be obtained by employing noise reduction. Also.

When using NR for the sum signal system, it is not necessary to have the same characteristics as the NR for the difference signal system, and it is sufficient to use an NR that corresponds to the characteristics of the recording system. Furthermore, in the above-described embodiments, the 1-discrimination pilot may be superimposed and recorded outside the audio band for discriminating the bilingual language, and the reproduction system matrix may be controlled depending on the presence or absence of this discrimination pilot. In this case, it is desirable to superimpose the discrimination high lot on the difference signal system from the viewpoint of sound quality, such as interference with the monaural system. Further, the 1-discrimination pilot signal may be applied to a system other than the above-mentioned audio signal recording system, such as a system in which it is superimposed on a part of a video signal system, or a system in which it is superimposed on a part of an inclined recording track.

〔Effect of the invention〕

As stated above, according to the present invention, (1) By compressing the dynamic range of the difference signal by noise reduction and then performing FM modulation, the effective deviation is increased and high-quality audio and recording bandwidth are achieved. Narrowing the band.

(2) As a result, it is possible to prevent image quality deterioration such as resolution deterioration, which requires widening the recording band of the video signal.

(5) It is configured to record a sum signal and a difference signal.

Compatibility of monaural systems can be ensured.

There are many benefits, and the effects are great.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a conventional monaural magnetic recording/reproducing device, Fig. 2 is a recording spectrum diagram of Fig. 1, Fig. 6 is an NR characteristic diagram, and Fig. 4 is a two-channel audio signal recording according to the present invention. FIG. 5 is a plan view of the cylinder explaining the relationship between the rotary cylinder and the magnetic tape, FIG. 6 is a pattern diagram of the magnetic tape, and FIG. 7 is a recorded signal spectrum diagram. . 57, 68...matrix, 40, 65...NR. 4.45...FM modulator. 15, 62...FM demodulator. Representative Patent Attorney Akio Takahashi] Figure Z Figure 5 Figure 6 Figure 7 7 2 3 4 Evening 6

Claims (1)

[Claims] Magnetic recording in which a frequency modulated video signal and a frequency modulated audio signal are sequentially recorded and reproduced on the same magnetic tape using rotary heads with different azimuth angles as a recording trajectory inclined at a constant angle with respect to the tape running direction. At the time of recording, the playback device obtains a sum signal of the right side signal and left side signal of the stereo audio signal and a difference signal between the right side signal and the left side signal, and then compresses at least the dynamic range of the difference signal. When recording and reproducing, the dynamic range compressed during recording is expanded to its original characteristics, and then the sum signal and the difference signal are added and subtracted to reproduce the right side signal and left side signal of the stereo audio signal. A two-channel audio signal recording and reproducing device.