JPH0754608B2 - PCM recording method and recording / reproducing apparatus - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a PCM recording / reproducing apparatus, and more particularly to a PCM for a video signal.
The present invention relates to a PCM recording / reproducing device suitable for multiple recording of audio signals or digital information.

[Background of the Invention]

Conventionally, as a method for recording an audio signal of a home-use VTR for the purpose of improving sound quality, a technical research report of the Institute of Electronics and Communication Engineers
MR83-20 (1983) "HiFi V" by Miura and 5 others
As described in the document entitled "HS VTR System Development",
A method of multiplexing FM audio signals by using a dedicated rotary audio head for recording audio signals on a video signal track for recording video signals is adopted. However, a digital audio disc that uses a compact disc. With the spread of players and the start of broadcasting high-quality digital audio by satellite broadcasting, VTR has become an era in which digitization is required for higher quality recording.

[Object of the Invention]

It is an object of the present invention, in response to the demands of such an era, to enable digital recording in a domestic VTR and, in that way, a PCM that does not interfere with the video signal.
It is to provide a recording / reproducing apparatus.

[Outline of Invention]

The present invention, after converting an audio signal or information to a PCM digital signal, or a signal modulated by an input PCM digital signal, outside the occupied band of the video signal,
Alternatively, the signal is frequency-multiplexed and recorded and reproduced in the occupied band of the low carrier FM luminance signal and the low frequency conversion chromaticity signal, and the signal modulated by the PCM digital signal is a video signal or the low carrier FM luminance signal and low Record the gamut conversion chromaticity signal. The reproducing magnetic head is a magnetic head for recording and reproducing with a magnetic head having a different azimuth angle. Furthermore, the frequency multiplexing and the azimuth angle difference are used together to reduce the mutual interference between video and audio and record and reproduce. Furthermore, as the modulation method of the signal modulated by the PCM digital signal, the code change points are
Offset-type 4-phase PSK that phase-modulates two orthogonal carriers with two data strings that differ by two data cycles
(Hereinafter abbreviated as O-QPSK) method.

Example of Invention

An embodiment of the present invention will be described below with reference to FIG. First
In the figure, 1 is a video signal input terminal, 10 is an LPF that separates a luminance signal, 11 is an FM modulator that receives a luminance signal as input, 12
Is a BPF for separating the chromaticity signal, 13 is a frequency converter for converting the chromaticity signal into the low frequency range, 14 is an adder for adding the FM-modulated luminance signal and the low-frequency converted chromaticity signal, and 15 is Recording amplifiers, 16a and 16b are video recording / playback heads, 2 is an audio signal input terminal, 20 is an A / D converter, 21 is a digital processing circuit, 22 is an offset type 4-phase PSK (O-QPSK) modulation circuit, 2
3 is a recording amplifier, 24a and 24b are recording / playback heads dedicated to audio signals, 30 is a playback amplifier, and 31 is a BP for separating a luminance signal.
F and 32 are FM demodulation circuits, 33 is a frequency conversion circuit that separates chromaticity signals, 34 is a frequency conversion circuit, 35 is an adder that adds luminance signals and chromaticity signals, 3 is a video signal output terminal 40 is a reproduction amplifier, and 41 is O −
Separate QPSK-modulated digital audio signal
BPF, 42 are O-QPSK demodulation circuits, 43 is a digital processing circuit, 44 is a D / A converter, and 4 is an audio signal output terminal.

The operation will be described below. The video signal is separated into a luminance signal and a chromaticity signal by LPF10 and BPF12, and then FM modulated by the FM modulator 11 and frequency converter 13 into bands as shown in FIG.
Two heads for low-frequency conversion and opposite video recording 16
It is recorded on the tape at a and 16b. Head 16a, 1 during playback
The signal reproduced in 6b is separated into a luminance signal and a chromaticity signal by BPF31 and LPF33, respectively, returned to the video frequency band before recording by FM demodulator 32 and frequency converter 34, and demodulated to a video signal by adder 35. To do.

On the other hand, the audio signal is once converted into a digital signal by the A / D converter 20, and then added with a synchronizing signal and a correction code by the digital processing circuit 21, interleaved, and O-QPSK.
Input to the modulation circuit 22. As shown in FIG. 2, the O-QPSK modulation circuit 22 performs O-QPSK modulation so that the spectrum falls within the occupied band of the low band conversion chromaticity signal and the low carrier FM luminance signal in the recording signal spectrum. And this O-
The QPSK modulated signal is recorded on the video track prior to the video recording by using the dedicated audio heads 24a and 24b whose azimuth angles are different from those of the video heads 16a and 16b. The recorded O-QPSK modulated signal is erased at the surface layer portion by the video signal to be recorded later and remains in the deep layer portion.

At the time of reproduction, the signal reproduced by the audio signal heads 24a and 24b is subjected to O-QPSK after extracting the audio modulation signal by the BPF41.
The demodulation circuit 42 and the digital processing circuit 43 demodulate the original digital signal, and the D / A converter 44 demodulates the original audio signal.

In this way, once the audio signal is converted into a digital signal and recorded, higher quality voice transmission is possible without being affected by the distortion of the recording medium. Further, by recording the digital signal by O-QPSK modulation, interference with the video signal can be reduced. Hereinafter, this will be described in detail.

FIG. 3 shows an example of actually measured recording current vs. reproduction output level characteristics of the audio dedicated heads 24a and 24b. In this way, the reproduction output level increases in proportion to the recording current up to a certain level, but there is a saturation point at which it does not increase even if the recording current is further increased. Then, normally, the recording current is set to this saturation point in order to improve the S / N ratio. However, this saturation may distort the recording waveform, generate an unnecessary spectrum, and interfere with the video signal. In particular, the 4-phase PSK (hereinafter referred to as QPSK) system, which is used in various fields as a digital modulation system, is substantially equivalent to the amplitude modulation (AM) system. It was

Therefore, in the present invention, in the QPSK system, by adopting the offset QPSK system in which the code change points of the 2-bit parallel data are modulated by shifting each other by 1/2 data period, the amplitude change of the recording waveform is reduced to cause saturation. The occurrence of distortion was suppressed.

FIG. 4 and FIG. 5 show this state. Fourth
In the figure, A and B are envelope waveforms of O-QPSK and QPSK modulated waves, respectively. As described above, the O-QPSK system has less AM components than the QPSK system. Saturation of these waveforms is equivalent to clipping of the waveforms at the level indicated by the alternate long and short dash line in the figure, for example. FIG. 5 shows the spectrum at this time, the solid line is the O-QPSK spectrum, and the broken line is the QPSK spectrum.
Further, the chain double-dashed line shows the spectrum at the time of non-saturation without clipping, which is the same spectrum in both the O-QPSK and QPSK systems. As described above, the O-QPSK system has an advantage that the spectrum does not spread even if the waveform is clipped. Therefore, even if a digital audio signal is recorded by using this system, the interference with the video signal is hardly given.

FIG. 6 shows a specific example of the O-QPSK modulation circuit 22. In FIG. 6, 50 is an input terminal of digital data (DATA), 51 is an input terminal of a clock (DCK) bit-synchronized with the digital data, and 52 is a parallel data (X-DATA) of the input digital data of 2 bits. , Y-DATA) conversion circuit, 53a and 53b are coded so that the parallel data converted into 2 bits have a code change, in other words, a phase change of the modulated wave has information. A delay circuit that delays one data by 1/2 data cycle, 55a and 55b are LPs that shape the digital signal waveform and limit the band of the modulated wave.
F, 56a and 56b are balanced modulators that modulate a carrier with a digital signal whose waveform is shaped, 57 is a carrier oscillator, 58 is a 90-degree phase shifter for obtaining a quadrature carrier, 59 is an adder, and 60 is O- QPS
This is the K signal output terminal. FIG. 7 is a waveform diagram showing the operation of each part of the modulation circuit 22. As described above, in the O-QPSK method, the amplitude fluctuation is suppressed by shifting the X-DATA and Y-DATA converted into 2 bits in parallel by 1/2 parallel data cycle.

FIG. 8 is a block diagram showing a specific example of the O-QPSK demodulation circuit 42. In the figure, 61 is an input terminal for the reproduced O-QPSK signal, 62a and 62b are phase detectors for phase-detecting the reference carrier wave signal and the input modulated wave signal reproduced by the carrier reproduction circuit 63,
64 is a 90-degree phase shifter, 65a and 65b are LPFs that remove unnecessary harmonic components generated by the phase detectors 62a and 62b, 66a and 66b are comparators that determine the positive or negative of the detected signal and convert it to a digital signal ,
67a and 67b are latch circuits that strobe the digital signals from the comparators 66a and 66b at the timing of the clock reproduced by the clock reproducing circuit 68, and 69 are inverter circuits 70a and 70b, which are based on the data string encoded on the modulator side. , A differential decoding circuit for decoding into a data string, 71 is a circuit for converting 2-bit parallel data into original serial data, 72 is an output terminal of demodulated data, and 73 is an output terminal of a reproduction clock bit-synchronized with the demodulated data. Is. FIG. 9 shows the operation waveform of each of these parts. In this way, I-DATA and Q-DATA are obtained by synchronously detecting the input modulated wave with the reproduced reference carrier wave and strobing the detected signal with the reproduced clock, and further performing differential decoding on each of them. X-DATA and Y-
DATA is obtained. Then, by converting these parallel data into serial data, final demodulated data can be obtained.

As described above, as an embodiment of the present invention, the video signal is a low carrier FM.
The case of so-called deep recording system in which video and audio dedicated heads which are luminance signals and low-frequency conversion chromaticity signals and have different azimuth angles from each other are overlapped and recorded is shown. However, the gist of the present invention is to provide a digital audio recording signal. Since the occupied bandwidth is made as narrow as possible to suppress the mutual interference with the video recording signal, the recording method may be normal frequency multiplex recording instead of deep layer recording. When the video signal is of the luminance and chromaticity time division multiplexing system, the occupied band of the digital audio recording signal may be arranged outside the occupied band of the low carrier FM video signal and frequency-multiplexed. When the chromaticity signals are recorded in different tracks in parallel, the chromaticity signals may be frequency-multiplexed and recorded so that the occupied bands do not overlap in any one of the tracks.

〔The invention's effect〕

According to the present invention, it is possible to multiplex and record a PCM-converted audio signal or digital data without interfering with a video signal, and a high quality audio signal or digital data can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing a spectrum of a tape recording signal, FIG. 3 is a diagram showing recording current vs. reproduction output level characteristics of an audio dedicated head, and FIG. Waveform diagram showing the envelope of the modulated wave in the offset QPSK, FIG. 5 is a diagram showing the spectrum of the offset QPSK modulated wave, FIG. 6 is a configuration diagram showing an example of the offset QPSK modulation circuit, and FIG. 7 is shown in FIG. Waveform diagram showing the operation of each part of the circuit, No. 8
The figure is a block diagram showing an example of an offset QPSK demodulation circuit,
The figure is a waveform diagram showing the operation of each part of the circuit shown in FIG. 11 …… FM modulator 16,17 …… Record / playback head 20 …… A / D converter 21,43 …… Digital processing circuit 22 …… Offset QPSK modulation circuit 32 …… FM demodulator 44 …… D / A conversion Unit 42: Offset QPSK demodulation circuit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shoji Kobayashi, 292 Yoshida-cho, Totsuka-ku, Yokohama, Kanagawa Prefecture Home Appliances Research Laboratory, Hitachi, Ltd. (72) Inventor Takao Arai, 292, Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Inside the Hitachi Electric Appliances Research Laboratory (72) Inventor Yasushi Yumi, 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Shares Inside Hitachi Electric Appliances Research Laboratory (72) Kuniaki Miura, 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa (56) References JP 60-1651 (JP, A) JP 60-30241 (JP, A) JP 60-50604 (JP, A)

Claims (20)

[Claims] 1. A device for multiplex recording and reproducing a video signal and a digital information signal on the same track of a magnetic tape, comprising means for converting the video signal into a video recording signal having a predetermined frequency band, and the digital signal. Means for digitally phase-modulating an information signal in a carrier frequency band, having a first azimuth angle, recording the modulated digital information signal in a deep portion of a magnetic layer of the magnetic tape, and reproducing the recorded signal. A signal having a first magnetic head and a second azimuth angle, the video recording signal being superposed and recorded on the surface portion of the magnetic layer above the track formed by recording the modulated digital information signal, and the recorded signal And a second magnetic head for reproducing the modulated digital information signal reproduced by the first magnetic head to reproduce the original digital information. And means for generating a signal, means for converting said video recording signal reproduced by said second magnetic head on the basis of the video signal, offset 4 as a system for the digital phase modulation and demodulation
A PCM recording / reproducing device characterized by using a phase modulation / demodulation method. 2. The offset 4 as a method of the digital phase modulation / demodulation according to claim 1.
A PCM recording / reproducing apparatus characterized by using a phase differential phase modulation / demodulation method. 3. The digital signal processing apparatus according to claim 1 or 2, wherein the means for converting the video signal into the video recording signal includes means for frequency-modulating a luminance signal into a predetermined carrier frequency band. The PCM recording / reproducing apparatus, wherein the phase modulating means outputs the modulated digital information signal in a carrier frequency band lower than the carrier frequency band of the modulated luminance signal. 4. The digital signal processing apparatus according to claim 3, wherein the means for converting the video signal into the video recording signal includes means for converting a sub-carrier frequency band of a color signal into a low carrier frequency band. The PCM recording / reproducing apparatus, wherein the means for phase modulating outputs the modulated digital information signal in a carrier frequency band higher than the carrier frequency band of the color signal converted into the low frequency band. 5. An analog-digital conversion means for converting an audio signal into a digital audio signal by pulse code modulation according to any one of claims 1, 2, 3, and 4, wherein the digital audio A signal is recorded as the digital information signal, and the digital information signal demodulated by the digital demodulating means is digital-analog converted to generate the original audio signal.
PCM recording / playback device. 6. A device for multiplex-recording a video signal and a digital information signal on the same track of a magnetic tape, means for converting the video signal into a video recording signal having a predetermined frequency band, and the digital information signal. Means for digitally phase-modulating the modulated digital information signal in a carrier frequency band, and a first azimuth angle for recording the modulated digital information signal in a deep portion of a magnetic layer of the magnetic tape.
Magnetic head and a second azimuth angle, and the video recording signal is superposed and recorded on the surface portion of the magnetic layer above the track formed by recording the modulated digital information signal, and the recorded signal is reproduced. A PCM recording apparatus characterized by using a second magnetic head and an offset quadrature phase modulation method as the digital phase modulation method. 7. The PCM recording device according to claim 6, wherein an offset four-phase differential phase modulation system is used as the system for digital phase modulation. 8. The method according to claim 6 or 7, wherein the means for converting the video signal into the video recording signal includes means for frequency-modulating a luminance signal into a predetermined carrier frequency band. The PCM recording device, wherein the phase modulating means outputs the modulated digital information signal in a carrier frequency band lower than the carrier frequency band of the modulated luminance signal. 9. The digital signal processing apparatus according to claim 8, wherein the means for converting the video signal into the video recording signal includes means for converting a subcarrier frequency band of a color signal into a low carrier frequency band, The PCM recording device, wherein the means for phase modulating outputs the modulated digital information signal in a carrier frequency band higher than a carrier frequency band of the color signal subjected to the low frequency conversion. 10. An analog-digital conversion means for converting an audio signal into a digital audio signal by pulse code modulation according to any one of claims 6, 7, 8, and 9, wherein the digital audio A PCM recording device characterized by recording a signal as the digital information signal. 11. A video recording signal converted into a video recording signal having a predetermined frequency band, a digital information signal being digitally phase-modulated in a carrier frequency band, and the video recording signal superposed and recorded on a video track of a magnetic tape and the video recording signal. An apparatus for reproducing a modulated digital information signal, comprising: a first magnetic head having a first azimuth angle and reproducing the modulated digital information signal recorded in a deep portion of the video track; A second reproducing means for reproducing the video recording signal which is superposed and recorded on a surface portion of the video track.
Magnetic head, means for demodulating the modulated digital information signal reproduced by the first magnetic head to generate the original digital information signal, and the video signal reproduced by the second magnetic head. An offset 4 is provided as means for converting the original video signal into a digital phase modulation / demodulation method.
A PCM playback device characterized by using a phase modulation / demodulation method. 12. The offset 4 as a method of the digital phase modulation / demodulation according to claim 11.
A PCM playback device characterized by using a phase differential phase modulation / demodulation method. 13. The video recording signal according to claim 11 or 12, wherein the video recording signal includes a luminance signal frequency-modulated in a carrier frequency band, and the means for demodulating the digital phase demodulates the modulated luminance signal. PC for demodulating the digital information signal modulated in a carrier frequency band lower than the carrier frequency band
M playback device. 14. The video recording signal according to claim 13, wherein the video recording signal includes a color signal whose low-frequency is converted from a sub-carrier frequency band to a low-frequency carrier frequency band, and the means for demodulating the digital phase includes A PCM reproducing apparatus characterized in that it demodulates the digital information signal modulated in a carrier frequency band higher than a carrier frequency band of the low-frequency-converted color signal. 15. The audio signal analog-digital converted by pulse code modulation according to any one of claims 11, 12, 13, and 14 is recorded as the digital information signal, and the digital demodulation is performed. The digital information signal demodulated by the means is digital-analog converted, and means for generating the original audio signal is provided.
PCM playback device. 16. A method for multiplex recording a video signal and a digital information signal on the same track of a magnetic tape, wherein the video signal is converted into a video recording signal having a predetermined frequency band, and the digital information signal is carried. The modulated digital information signal is recorded in a deep portion of the magnetic layer of the magnetic tape by the first magnetic head having the first azimuth angle, and the magnetic field above the track formed by the magnetic phase modulation. A PCM recording method characterized in that an offset quadrature phase modulation system is used as a system for superimposing and recording the video recording signal by a second magnetic head having a second azimuth angle on a surface portion of the layer. 17. The PCM recording method according to claim 16, wherein an offset four-phase differential phase modulation system is used as the system for digital phase modulation. 18. The video recording signal according to claim 16 or 17, wherein the video recording signal includes a luminance signal frequency-modulated in a carrier frequency band, and the carrier frequency band of the modulated digital information signal is in the carrier frequency band. A PCM recording method characterized by lowering the carrier frequency band of a modulated luminance signal. 19. The video recording signal according to claim 18, wherein the video recording signal includes a chrominance signal whose low-frequency is converted from a sub-carrier frequency band of the modulated digital information signal to a low-frequency carrier frequency band. A PCM recording method, characterized in that a carrier frequency band is set higher than a carrier frequency band of the color signal subjected to the low frequency conversion. 20. The audio signal which is analog-digital converted by pulse code modulation as the digital information signal according to any one of claims 16, 17, 18 and 19, and is recorded. PCM recording method.