JP2559564B2 - Video tape recorder - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a two-channel audio signal recording / reproducing device which is compatible with a monaural audio signal recording / reproducing device, and more particularly to a two-channel audio signal recording / reproducing device using a rotary head. The present invention relates to a video tape recorder that records and reproduces video along with video signals. In a conventional video tape recorder (hereinafter referred to as VTR) which is a magnetic recording / reproducing apparatus for a video signal, the video signal is FM-modulated and then magnetic tape is recorded by two rotary magnetic heads. In general, the audio signals are alternately recorded on the video tracks inclined by a certain angle with respect to the traveling direction, and the audio signal is recorded on the audio tracks parallel to the traveling direction of the magnetic tape by the audio recording fixed head. Therefore, in order to record a multi-channel audio signal, for example, a stereo audio signal, an audio track parallel to the running direction of the magnetic tape is formed by a fixed number of audio recording heads corresponding to the number of channels. I try to record it. By the way, in the VTR, as a method of increasing the recording density and lengthening the recordable time, a method of slowing the magnetic tape running speed and narrowing the width of the video track is used. However, according to this method, the relative speed between the magnetic tape and the fixed head for voice recording is significantly slower than 4.75 cm / sec in the cassette tape recorder, for example, about 1 cm / sec. As a result,
The frequency band of the reproduced audio signal is greatly reduced, and further wow and flutter characteristics are deteriorated, which causes a serious problem in sound quality. Further, there is a method of narrowing the gap width of the fixed head for audio recording in order to improve the frequency band of the reproduced audio signal.
N will be deteriorated. In addition, one of the methods for preventing such sound quality deterioration
As one, FM modulation of the audio signal, the rotary head,
A method of superimposing recording on a video track (hereinafter referred to as an audio signal superimposing recording method) has been devised. The characteristics of the audio signal superposition recording method are: (1) Wow and flutter characteristics are good because they are not easily affected by fluctuations in the time axis due to tape running speed irregularities. (2) The reproduction frequency band does not depend on the tape running speed, and can be broadened. And the like. An example of the monaural audio signal superposition recording method will be described with reference to FIGS. 6 and 7. However, in FIG. 6, 1 is an input terminal, 2 is a pre-emphasis circuit, 3
Is a deviation adjustment circuit, 4 is an FM modulator, 5 is a band pass filter (hereinafter referred to as BPF), 6 is a level adjuster, 7 is an adder, 8 and 9 are input terminals, 10 and 12 are rotary heads, 11 is Magnetic tape, 13 is a preamplifier, 14 is a BPF, 15 is an FM demodulator, 16 is a low pass filter (hereinafter referred to as LPF), 17 is a hold circuit, 18 is a dephasing circuit, 19 is a dropout detection circuit,
20 is an edge detection circuit, 21 is an adder, 22 is an input terminal, 23 is an output terminal, 24 is a preamplifier, 25 is an output terminal, 26 is a changeover switch, and 27 is a pulse width expansion circuit. In FIG. 6, during recording, a monaural audio signal is input from the input terminal 1 and subjected to pre-emphasis processing by the pre-emphasis circuit 2. Pre-emphasis circuit 2
The output audio signal is subjected to deviation adjustment by the deviation adjuster 3 so that the maximum deviation becomes ± 100 KHz, and then FM-modulated by the FM modulator 4. FM
The FM-modulated audio signal output from the modulator 4 is BPF5.
After the unnecessary band component is removed by, the recording level is adjusted by the level adjuster 6. The FM-modulated audio signal whose recording level is adjusted is input to the FM terminal of the adder 7 from the input terminal 9.
After the modulated luminance signal and the low-frequency conversion carrier color signal (hereinafter referred to as video signal Y / C) and the tracking control pilot signal input from the input terminal 8 are added, the rotary heads 10 and 12 having different azimuth angles are used. Recording is performed on inclined video tracks that are alternately formed on the magnetic tape 11. Here, the carrier frequency A of the FM modulator 4
Is 1.5 MHz, and FIG. 7 shows the spectrum of the video signal Y / C input from the input terminal 9 and the pilot signal P input from the input terminal 8. Next, the reproducing system will be briefly described. In FIG. 6, the signals reproduced from the magnetic tape 11 by the rotary heads 10 and 12 are amplified by the preamplifiers 13 and 24, and then converted into a series of continuous reproduced signals by the changeover switch 26. It is supplied to a control circuit (not shown) and a video signal reproduction circuit (not shown), and on the other hand, supplied to the BPF 14 for reproduction FM.
Only the modulated audio signal is extracted. This reproduction F extracted
The M-modulated audio signal is FM-demodulated by the FM demodulator 15, and carrier leaks are removed by the LPF 16, and then supplied to the hold circuit 17. The hold circuit 17 performs noise correction by holding the previous value during a noise generation period such as noise or dropout noise generated due to carrier discontinuity at the head switching point. Here, the head switching point is set by detecting the edge of the rotary head switching signal input from the input terminal 22 by the edge detection circuit 20, and the dropout is BPF1 by the dropout detection circuit 19.
4 output signal is detected by envelope detection. After the head switching point signal and the dropout detection signal are added by the adder 21, the pulse width expansion circuit 27 expands the pulse width for the transient period of noise generated by band limitation. The hold circuit 17 is controlled by the output signal of the pulse width expansion circuit 27. The demodulated audio signal whose noise has been corrected by the hold circuit 17 is de-emphasized by the dephasing circuit 18, and is output from the output terminal 25 as a reproduced audio signal with reduced noise. In the monaural audio signal recording / reproducing system described above, high quality reproduction sound quality can be obtained in all aspects such as S / N, frequency characteristic, wow and flutter characteristic. However, the above system is a recording / reproducing system for monaural audio signals.
Multi-channel recording of audio signals is a requirement of the times. Therefore, it is conceivable to achieve two-channel recording of audio by simply using two sets of the above monaural system. However, if only two monaural systems are used, the recording occupied bandwidth of the audio signal needs to be twice or more that of the monaural recording system. Taking the above system as an example, a monaural audio recording system requires 300 KHz as a recording occupied band of an audio signal,
Therefore, in the case of 2 channels as described above, 6
00 KHz is required. As a result, in a 2-channel system using only two monaural systems, the recording occupied band of the video signal must be narrowed, resulting in deterioration of image quality such as deterioration of resolution. In addition, the two-channel recording system must be compatible with the monaural system. An object of the present invention is to solve the above problems, suppress deterioration of image quality, obtain a high-quality reproduced audio signal, and maintain compatibility with a monaural audio recording system. It is to provide a recorder. In order to achieve the above object, the present invention obtains a sum signal and a difference signal of a stereo audio signal and compresses at least a dynamic range of the difference signal by a noise reduction circuit. , The sum signal and the difference signal are FM-modulated by different carriers and recorded, and the maximum deviation of the difference signal is made smaller than the deviation of the sum signal. According to the present invention, a sum signal and a difference signal of a stereo audio signal are FM-modulated and recorded, and generally, the difference signal has a small amount of information and a small dynamic range. The basic concept is to make the recording occupied band of the audio signal narrower by making the deviation of (1) smaller than the deviation of the sum signal, and aim at compatibility with monaural and prevention of image quality deterioration. However, if the deviation of the difference signal is reduced, the difference signal becomes weak against the adjacent crosstalk noise generated by the crosstalk signal from the adjacent track and the buzz sound generated by the side band of the video signal. Playback sound quality cannot be obtained. By the way, the adjacent crosstalk noise N is
The crosstalk signal level from the adjacent track is U, the signal level from the track to be reproduced and scanned is D,
If the instantaneous difference frequency between the D signal and the U signal is Δω, it can be expressed as N∝U / D · Δω · cos Δωt (1). Here, t is time. Therefore, in the present invention, the difference signal is compressed in its dynamic range by using a noise reduction circuit and then FM-modulated so that the deviation is effectively increased without increasing the maximum deviation. And the instantaneous difference frequency Δω in the above equation (1)
The adjacent crosstalk noise is reduced by making the noise easily out of the audible band and white noise. Further, sideband leakage of the FM-modulated luminance signal and the low-frequency conversion chromaticity signal, modulation noise, and the like can be reduced by the compression / expansion effect of the noise reduction circuit. In this way, it is possible to prevent the deterioration of the image quality such as the deterioration of the resolution while preventing the deterioration of the S / N of the difference signal, and to achieve the compatibility with the monaural system by the sum signal. Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a video tape recorder according to the present invention, in which an FM-modulated luminance signal, a low-frequency conversion carrier color signal, an FM-modulated audio signal, a pilot signal for tracking control, and an azimuth angle. VTR audio processing in which different rotary heads sequentially record the same video track of the magnetic tape and the time-axis compressed PCM audio signal and the pilot signal are recorded in the overlapping portion of the video track. 1 shows an example of the configuration of a system. However, in the figure, 28,
29 is an input terminal, 30 and 31 are switches, 32-34 are input terminals, 35 and 36 are switches, 37 is a matrix circuit, 38 and 39 are switches, 40 is a noise reduction circuit (hereinafter referred to as NR), and 41 is a level. Regulator, 4
2 is an input terminal, 43 is an FM modulator, 44 is a BPF, 45
Is a level adjuster, 47 is a recording amplifier, 48 and 49 are switches, 52 is an A / D converter, 53 is a PCM signal processing circuit, 54 is a recording amplifier, 55 and 56 are switches, 57,
Reference numeral 58 is an output terminal, 59 is a pulse width expansion circuit, 60 is an input terminal, 61 is a BPF, 62 is an FM demodulator, and 63 is an LP.
F and 64 are hold circuits, 65 is a noise reduction circuit, 66 and 67 are switches, 68 is a matrix circuit,
69 and 70 are switches, 71 and 72 are output terminals, 73-
Reference numeral 76 is an LPF, reference numerals 200 and 300 are LPFs, and reference numeral 400 is an adder. In FIG. 1, the input terminal 2 is used for recording.
When a stereo audio signal is input from 9, 32, the right side signal and the left side signal of this stereo audio signal are switched by the switch 3
It is supplied to the matrix circuit 37 via 0 and 31, and a sum signal and a difference signal of the right side signal and the left side signal are formed. These sum signal and difference signal are passed through the switches 38 and 39 to the LP
It is supplied to F73 and F74. When the input signals from the input terminals 29 and 32 are not stereo audio signals but bilingual signals such as Japanese and English, the switch 3 is used.
0, 31, 38, 39 are switched by the control signal input from the input terminal 28 and bypass the matrix circuit 37. The sum signal and the difference signal are limited to the band up to 200 KHz by the LPFs 73 and 74, respectively. The band-limited difference signal has its dynamic range compressed to 1/2 at NR40. FIG. 2 shows the characteristics of this NR40. As described above, since the audio signals between the adjacent tracks have no correlation, the dynamic range of the difference signal is compressed by NR40 to increase the effective deviance, and thus the difference frequency in the above expression (1) is increased. Δω tends to be out of the audible band and white noise. Further, due to the effect of effectively increasing the deviation of the NR 40, even if the maximum deviation of the difference signal is made smaller than that of the sum signal, the reproduced sound quality is not deteriorated, so that the audio recording occupied band can be made small. Therefore, the bandwidth is about 1.5 times that of a monaural system, and image quality deterioration such as resolution deterioration is less than in a two-channel system that simply uses two sets of monaural systems, and high reproduction image quality can be obtained. The difference signal whose dynamic range is compressed by the NR 40 is FM-modulated by the FM modulator 43 having a carrier center frequency of 1.7 MHz after the maximum deviation is adjusted to ± 50 KHz by the level adjuster 41. FM
The FM modulation difference signal output from the modulator 43 is BPF4
After the unnecessary band component is removed at 4, the recording level is adjusted at the level adjuster 45 and supplied to the adder 7. On the other hand, the sum signal output from the LPF 73 is processed by the pre-emphasis circuit 2, the maximum deviation is adjusted to ± 100 KHz by the level adjuster 3, and the FM modulator 4 having a carrier frequency of 1.5 MHz. F
M-modulated. The FM modulation sum signal output from the FM modulator 44 has its recording level adjusted by the level adjuster 6 after the unnecessary band component is removed by the BPF 5, and is supplied to the adder 7. In the adder 7, the FM modulation sum signal and the FM modulation difference signal are added to the video signal Y / C input from the input terminal 9 and the tracking control pilot signal input from the input terminal 8. The addition signal output from the adder 7 is sent to the switch 4 via the recording amplifier 47.
It is supplied to 8,49. The addition signal of the FM modulation sum signal and the FM modulation difference signal is hereinafter referred to as FM modulation audio signal. On the other hand, in the PCM audio signal recording system, the audio signals input from the input terminals 29, 32 or the input terminals 33, 34 are operated by the switches 35, 36 operated by the audio signal selection signal input from the input terminal 60. Selected,
The selected audio signal is band-limited by the LPFs 200 and 300, converted into a PCM audio signal by the A / D converter 52, and further, the time axis is about 1 by the PCM signal processing circuit 53.
Compressed to / 6. This time-base compressed PCM audio signal is added with a pilot signal by an adder 400,
It is supplied to the switches 48 and 49 via the recording amplifier 54. Here, as shown in FIG. 3, the magnetic tape 1
1 is wound around a rotary cylinder by about 200 °, and rotary heads 10 and 12 are arranged on the rotary cylinder at angular intervals of 180 °. The switches 48 and 49 are controlled by a head switching signal input from the input terminal 22 so as to switch when one of the rotary heads 10 and 12 rotates about 30 ° from the point of entry into the magnetic tape 11. The time-axis-compressed PCM audio signal is supplied to the rotary heads 10 and 12 during the rotation period of 30 °, and the addition signal from the adder 7 is supplied to the rotary heads 10 and 12 during the remaining rotation period. As a result, the magnetic tape 11 will be displayed on the magnetic tape 11 as shown in FIG.
As shown in FIG. 5, the above-mentioned added signal is recorded in the 180 ° rotating portion of each track, and the PCM audio signal is recorded in the overlapping portion shown by hatching. As shown in FIG. 5, the band of the FM modulation sum signal and the FM modulation difference signal is between the bands of the FM modulation luminance signal and the low frequency conversion carrier color signal. Next, the reproducing system will be described. In FIG. 1, a reproduction signal reproduced from the magnetic tape 11 by the rotary heads 10 and 12 is amplified by the preamplifiers 13 and 24, and then the video signals Y / C, the FM modulated audio signal, and the pilot signal are generated by the switches 55 and 56. And a PCM audio signal that has been time-axis compressed. The time-axis compressed PCM audio signal is output from the output terminal 57 to a PCM signal demodulation processing circuit (not shown). Here, the switches 55 and 56 are connected to the input terminal 22.
It is controlled by a head switching signal input from the. On the other hand, a series of reproduction addition signals consisting of the video signal Y / C, the FM-modulated audio signal and the pilot signal are supplied to the BPFs 14 and 61 on the one hand, and from the output terminal 58 on the other hand to the video signal reproduction circuit ( (Not shown) and a tracking control circuit (not shown). BPF14
Then, only the FM modulation sum signal of the FM modulation audio signal is extracted from this reproduction addition signal, and only the FM modulation difference signal of the FM modulation audio signal is extracted from the above reproduction addition signal in BPF 61. The reproduced FM-modulated sum signal extracted by the BPF 14 is demodulated into a sum signal by the FM demodulator 15, the LPF 16 removes noise such as carrier leakage, and then supplied to the hold circuit 17. In the hold circuit 17, the dropout noise and the head switching point noise detected by the dropout detection circuit 19 and the edge detection circuit 20 are controlled by the control signals obtained by the adder 21 and the pulse width expansion circuit 27 to obtain the values before the noise occurrence period. Noise is compensated by holding. The noise-compensated output sum signal of the hold circuit 17 is band-controlled to 20 KHz after the FM modulation difference signal component and the like are removed by the LPF 75. The reproduction sum signal output from the LPF 75 is processed by the de-emphasis circuit 18, and then is processed by the matrix circuit 6 via the switch 66.
8 is supplied. On the other hand, the FM modulation difference signal extracted by the BPF 61 is demodulated to the reproduction difference signal by the FM demodulator 62, and the LPF is obtained.
At 63, carrier leaks and the like are removed. Then, the reproduction difference signal is held in the hold circuit 64 on the basis of the output signal of the pulse width expansion circuit 59, and is held at a value before the generation period of the dropout noise and the head switching point noise for noise compensation. The noise compensated reproduction difference signal is L
After being limited to the same band as the input band of the NR 40 in the recording system by the PF 76, it is expanded to the original dynamic range by the NR 65 and supplied to the matrix circuit 68 via the switch 67. By the NRs 40 and 65, noise such as adjacent crosstalk noise and image buzz is reduced, and a high quality difference signal can be obtained. Therefore, in the matrix circuit 68, a reproduced stereo audio signal composed of a reproduced right signal and a reproduced left signal of high quality is obtained from the reproduced sum signal and the reproduced difference signal, and the reproduced right signal and the reproduced left signal are switched. 69, 70
Is output from the output terminals 71 and 72 via. Here, the FM-modulated audio signal to be reproduced is 2
Input terminal 4 if the audio signal is in a different language
The switches 66, 6 are controlled by the control signal input from the switch 2.
7, 69 and 70 are switched, and the matrix circuit 68 is bypassed. As described above, in this embodiment, the maximum deviation of the difference signal is made smaller than that of the sum signal by compressing the dynamic range of the difference signal and increasing the effective deviation with the noise reduction circuit. However, the recording occupied band of the audio signal can be narrowed, so that the image quality deterioration can be prevented. Compatibility with the monaural system is ensured by using a system that records sum / difference signals. In the above embodiment, the noise reduction circuit is not used in the sum signal system, but it is clear that by using the noise reduction circuit, a higher quality reproduced sound can be obtained. When the noise reduction circuit is used for the sum signal system, it does not have to have the same characteristics as the noise reduction circuit for the difference signal system, and a noise reduction circuit according to the characteristics of the recording system may be used. Further, in the above embodiment, in order to discriminate between two languages, the discrimination pilot may be recorded by being superimposed outside the voice band, and the reproduction system matrix may be controlled depending on the presence or absence of the discrimination pilot. In this case, it is desirable that the discrimination pilot be superposed on the difference signal system from the viewpoint of sound quality such as interference with the monaural system. However, the present invention is not limited to this, and the determination pilot signal may be superposed on a part of the video signal system or a part on the inclined recording track other than the audio signal recording system described above. As described above, according to the present invention, (1) FM modulation is performed after the dynamic range of the difference signal is compressed by the noise reduction circuit, so that effective deviation is achieved. As a result, it is possible to narrow the recording occupied band of high-quality audio (2) As a result, it is possible to widen the recording occupied band of the video signal and prevent deterioration of image quality such as resolution deterioration. (3) Since the configuration is such that the sum signal and the difference signal are recorded, there are many merits such as compatibility of the monaural system can be secured, and the effect is great.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of a video tape recorder according to the present invention. FIG. 2 is a characteristic diagram of the noise reduction circuit in FIG. FIG. 3 is a plan view showing the relationship between the rotary cylinder and the magnetic tape in FIG. FIG. 4 is a track pattern diagram of the magnetic tape in FIG. 5 is a spectrum diagram of the recording signal in FIG. 1. FIG. FIG. 6 is a block diagram of a conventional monaural magnetic recording / reproducing apparatus. 7 is a diagram showing a recording spectrum in FIG. [Description of Reference Signs] 4 FM modulator 9 FM modulation luminance signal and low-frequency conversion carrier color signal input terminals 10 and 12 rotary head 11 magnetic tape 15 FM demodulator 29 and 32 audio signal input terminal 37 matrix circuit 40 noise reduction Circuit 43 FM modulator 62 FM demodulator 65 Noise reduction circuit 68 Matrix circuit

Claims (1)

(57) [Claims] 1. The frequency-modulated luminance signal, the frequency-converted low-frequency-converted carrier color signal below the band of the frequency-modulated luminance signal, and the frequency-modulated luminance signal and the low-frequency-converted carrier color signal are frequency-arranged between the bands. In a video tape recorder for recording a frequency-modulated audio signal of 2 channels on a magnetic tape by a rotary head, a means for generating a sum signal and a difference signal forming a stereo audio signal, and a dynamic range of the sum signal and the difference signal Means for respectively compressing, first frequency means for frequency modulating a first carrier wave with the compressed sum signal, and second frequency means for frequency modulating a second carrier wave with the compressed difference signal. The frequency of the first carrier is set lower than the frequency of the second carrier, and the maximum frequency shift in the first frequency modulation means is the second frequency modulation. Video tape recorders, characterized in that the defined greater than the maximum frequency shift in the stage. 2. In Claim 1, the maximum frequency deviation in the first frequency modulation means is ±
A video tape recorder having a frequency of 100 KHz and a maximum frequency deviation of ± 50 KHz in the second frequency modulation means. 3. The video tape recorder according to claim 1 or 2, wherein the compression ratio of the first and second compression means is 2. 4. A frequency-modulated luminance signal and a low-frequency-converted carrier color signal whose frequency is converted below the frequency-modulated luminance signal band;
In a video tape recorder for recording on a magnetic tape a two-channel frequency-modulated audio signal whose frequency is arranged between bands of the frequency-modulated luminance signal and the low-frequency conversion carrier color signal, the audio signal of the first channel is recorded. First compression means for compressing the dynamic range, second compression means for compressing the dynamic range of the audio signal of the second channel, and frequency modulation of the first carrier wave with the output signal of the first compression means. First frequency modulation means, second frequency modulation means for frequency-modulating the second carrier wave with the output signal of the second compression means, and when a stereo audio signal is input, a sum signal and a difference signal are generated Means for supplying the sum signal to the first compressing means and the difference signal to the second compressing means when a stereo audio signal is input. When a voice signal is input, the first compression means is provided with signal supply means for supplying a main audio signal and the second compression means for supplying a sub audio signal, respectively, and the frequency of the first carrier wave is A video tape characterized in that the frequency is set lower than the frequency of the second carrier wave, and the maximum frequency shift in the first frequency modulation means is set larger than the maximum frequency shift in the second frequency modulation means. Recorder. 5. In Claim 4, the maximum frequency deviation in the first frequency modulation means is ±
A video tape recorder having a frequency of 100 KHz and a maximum frequency deviation of ± 50 KHz in the second frequency modulation means. 6. The video tape recorder according to claim 4 or 5, wherein the compression ratio of the first and second compression means is two.