JPH0754610B2 - PCM recording method, recording device and recording / reproducing device - Google Patents

Description

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

[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, with the spread of digital audio disc players using compact discs 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]

An object of the present invention is to provide a PCM recording method, a recording device, and a recording / reproducing device that enable digital recording in a home VTR and do not cause mutual interference with a video signal in response to the demands of such times. It is in.

[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 is outside the occupied band of a video signal, or a low carrier FM luminance signal and low frequency conversion chromaticity. It is used to record or reproduce by frequency multiplexing in the occupied band of the signal, and the signal modulated by the PCM digital signal is recorded or reproduced as the video signal or the low carrier FM luminance signal and the low frequency conversion chromaticity signal. The magnetic head is one for recording or recording / reproducing with magnetic heads having different azimuth angles.

Alternatively, the above-mentioned frequency multiplexing and azimuth angle difference are used together to reduce the mutual interference between video and audio and record and reproduce. Further, the modulation method of the signal modulated by the PCM digital signal is an offset four-phase phase modulation (hereinafter referred to as O-QPSK modulation) method, preferably an offset four-phase differential phase modulation (hereinafter referred to as O-QDPSK modulation). It is a method.

Further, this modulated signal is band-limited by a band-pass filter (hereinafter referred to as BPF) and its amplitude is limited by a limiter for recording.

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 for separating a luminance signal, 11 is an FM modulator for inputting a luminance signal, 12 is a BPF for separating a chromaticity signal, and 13 is a low-frequency conversion for the chromaticity signal. Frequency converter, 14 is an adder for adding the FM-modulated luminance signal and the low-frequency converted chromaticity signal, 15 is a recording amplifier, 16a and 16b are video signal recording / reproducing heads, and 2 is an audio signal input Terminal, 20 is an A / D converter, 21 is a digital processing circuit, 22 is an O-QPSK modulation circuit, 23 is BPF, 24 is a limiter, 25 is a recording amplifier, 26a and 26b are audio recording / playback heads, and 30 is Reproduction amplifier, 31 BPF separating the luminance signal, 32 FM demodulation circuit, 33 LPF separating the chromaticity signal,
34 is a frequency conversion circuit, 35 is an adder for adding a luminance signal and a chromaticity signal, 3 is a video signal output terminal, 40 is a reproduction amplifier,
41 is a BPF for separating an audio signal, 42 is an O-QPSK demodulation circuit, 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 the LPF10 and BPF12, and then FM modulated and low-frequency converted into the bands shown in FIG. Recording is performed on the tape by the two recording heads 16a and 16b. Head 1 during playback
The signals reproduced by 6a and 16b are separated into a luminance signal and a chromaticity signal by BPF31 and LPF33, respectively, and FM demodulator 32 and frequency converter 34
To return to the video frequency band before recording and adder 35
To demodulate into a video signal.

On the other hand, the audio signal is once converted into a digital signal by the A / D converter 20, and then the digital processing circuit 21 adds a synchronizing signal and a correction code, and interleaves the signal.
Input to the SK modulation circuit 22. The second in the O-QPSK modulation circuit 22
As shown in the figure, O-QPSK modulation is performed so that the spectrum falls within the occupied band of the low-frequency conversion chromaticity signal and the low carrier FM luminance signal in the recording signal spectrum. And this O
-Before video recording on the video track by using the dedicated audio heads 26a and 26b that limit the bandwidth and amplitude of the QPSK modulated signal by the BPF 23 and the limiter circuit 24 and have different azimuth angles from the video heads 16a and 16b. And record.
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 dedicated audio heads 26a and 26b is subjected to O-QPSK after extracting the audio modulation signal with 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.

Thus, once the audio signal is converted into a digital signal and recorded, it is not affected by the distortion of the recording medium, and high-quality audio transmission is possible. Furthermore, the digital signal is O-QPSK modulated, and both the bandwidth and the amplitude are limited and recorded to reduce interference with the video signal and to reproduce the C / N ratio of the reproduced O-QPSK modulated signal. Can be improved. Hereinafter, this will be described in detail.

FIG. 3 shows an example of actual measurement of recording current vs. reproduction output level characteristics of the audio dedicated heads 26a and 26b. Generally, in the magnetic head, the reproduction output level increases in proportion to the recording current up to a certain level, but there is a saturation point that 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) method used in various fields as a digital modulation method is substantially equivalent to the amplitude modulation (AM) method,
There was a problem that the side lobe spreads due to this saturation.

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 and the distortion due to the saturation is adopted. The occurrence of 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 amplitude fluctuation 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 is not spread even if the waveform is clipped. Therefore, even if the digital audio signal is recorded by using this system, the interference to the video signal is hardly given.

Further, in the present invention, attention is paid to the fact that the spectrum does not spread even if the O-QPSK modulated signal is clipped, and the amplitude fluctuation remaining in the O-QPSK modulated signal is limited by the limiter circuit 23 and recorded at a constant amplitude. I chose As a result, full saturation recording is possible, so that the C / N ratio of the reproduced signal is improved and the code error rate of the demodulated data is reduced.

FIG. 6 is a specific example of the O-QPSK modulation circuit 22 of FIG. 1 and shows an O-QDPSK modulation circuit (offset 4-phase differential phase modulation circuit) which is an example of the O-QPSK modulation circuit. In FIG. 6, 50 is an input terminal for digital data (DATA), 51
Is a clock (DC
K) input terminal, 52 is input digital data 2
Bit parallel data (a circuit for converting into X-DATA, Y-DATA =, 53a, 53b are coded so that the parallel data converted into 2 bits have a code change of each parallel data, that is, a phase change of the modulated wave. A differential encoding circuit, 54 is a delay circuit that can delay one data by 1/2 data cycle, and 55a and 55b are LPs that shape the waveform of a digital signal to limit the band of the modulated wave.
F, 56a and 56b are balanced modulators that modulate a carrier with a waveform-shaped digital signal, 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-
QPSK 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 shows an example of frequency characteristics of the BPF 23. For example, A / D
The code transmission rate of the converted digital audio signal
Assuming 2 Mbits / sec, the minimum required bandwidth for 4-phase PSK modulation is ± 500 KHz. Therefore, if the bandwidth of BPF23 is set to ± 500 KHz and the side lobes of the modulated signal spectrum are completely cut off, there is almost no interference with the video signal.

FIG. 9 is a circuit diagram showing a specific example of the limiter circuit 24. In the figure, the signal input to the input terminal 80 is a resistance
Both the positive and negative amplitudes are limited to the threshold voltage (about 0.7V) of the diode by 81 and the diodes 82 and 83, and the output terminal
It is output from 84. FIG. 9 is a circuit diagram showing another specific example of the limiter circuit 24. Here, transistors 85 and 86 are used.
The limiter effect of the differential amplifier configured by is used.

As described above, various circuit systems can be considered for the limiter circuit 24, but the present invention is not limited to this circuit system, and is characterized in that the limiter circuit is inserted.

FIG. 11 is a block diagram showing a specific example of the O-QDPSK demodulation circuit 42. In the figure, 61 is an input terminal for the reproduced O-QDPSK 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, and 64 is a 90-degree phase shifter. , 65a and 65b are LPFs that remove unnecessary harmonic components generated in the phase detectors 62a and 62b, 66a and 66b are comparators that determine whether the detected signal is positive or negative and convert it to digital signals, and 67a and 67b are comparators. A latch circuit that strobes digital signals from 66a and 66b at the timing of the clock reproduced by the clock reproduction circuit 68, 69 is an inverter circuit, and 70a and 70a
b is a differential decoding circuit for decoding into a data string encoded on the modulator side, 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 demodulated data. This is the output terminal for the bit-synchronized reproduction clock. Figure 12 shows the operation waveforms of these parts. In this way, the input modulated wave is synchronously detected by the reproduced reference carrier, and the detected signal is data strobed by the reproduced clock to obtain I-DATA and Q-DATA. -DATA and Y-DATA are 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 method in which the video signal and the low-frequency conversion chromaticity signal, which have different azimuth angles and which are different in azimuth angle from each other, are over-recorded is shown. 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 / chromaticity time division multiplexing system, the occupied band of the digital audio recording signal may be placed outside the occupied band of the low carrier FM video signal and frequency-multiplexed. When the chromaticity signals are recorded in parallel on different tracks, they may be frequency-multiplexed and recorded so that the occupied bands do not overlap on any one of the tracks.

〔The invention's effect〕

According to the present invention, a PCM audio signal or digital data can be multiplexed and recorded without interfering with a video signal, and the C / N ratio of a reproduced signal can be improved, resulting in high quality. The audio signal or digital data of is 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. O
− Waveform diagram showing the envelope of QPSK modulated wave, FIG.
-Figure showing the spectrum of QPSK modulated wave, Figure 6 shows O-QPSK
FIG. 7 is a configuration diagram of an O-QDPSK modulation circuit showing a specific example of the modulation circuit, FIG. 7 is an operation waveform diagram of the modulation circuit shown in FIG.
The figure shows the frequency characteristics of the BPF on the recording side.
FIG. 11 is a circuit diagram showing a specific example of the limiter circuit, FIG. 11 is a configuration diagram showing a specific example of the O-QDPSK demodulation circuit, and FIG. 12 is an operation waveform diagram of the demodulation circuit shown in FIG. 11 …… FM modulator, 32 …… FM demodulator, 16,17 …… Recording / reproducing head, 20 …… A / D converter, 44 …… D / A converter, 21,43 …… Digital processing circuit, 22 …… O-QPSK modulation circuit, 42 …… O-QPSK demodulation circuit, 23 …… BPF, 24 …… Limiter 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 Ceremony Company Home Appliance Research Laboratory, Hitachi, Ltd.

Claims (15)

[Claims] 1. 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. A first magnetic head having a first azimuth angle which is digitally phase-modulated in a frequency band, limits an occupied bandwidth of the modulated digital information signal, limits an amplitude of the band-limited modulated digital information signal, and has a first azimuth angle. The band-limited and amplitude-limited modulated digital information signal is recorded in the deep layer portion of the magnetic layer of the magnetic tape by the magnetic recording medium, and the magnetic layer surface layer portion above the track thus formed has a second azimuth angle. An offset 4-phase phase is used as a method of recording the video recording signal in a superimposed manner by the magnetic head No. 2 and performing the digital phase modulation. A PCM recording method characterized by using a modulation method. 2. A PCM recording method according to claim 1, wherein an offset four-phase differential phase modulation method is used as the digital phase modulation method. 3. The video recording signal according to claim 1, 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 modulated in the carrier frequency band. A PCM recording method characterized by lowering the carrier frequency band of the luminance signal. 4. The video recording signal according to claim 1, 2 or 3, wherein the video recording signal includes a color signal whose low frequency is converted from a sub-carrier frequency band thereof to a low carrier frequency band. A PCM recording method, characterized in that a carrier frequency band of the modulated digital information signal is set higher than a carrier frequency band of the color signal subjected to the low frequency conversion. 5. The audio signal obtained by analog-to-digital conversion by pulse code modulation as the digital information signal according to claim 1, 2, 3 or 4, is recorded. PCM recording method. 6. A device for multiplex recording 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 information. Means for digitally phase-modulating a signal into a carrier frequency band; band-pass filter means for limiting the occupied bandwidth of the modulated digital information signal; limiter means for limiting the amplitude of the band-limited modulated digital information signal; A first magnetic head having a first azimuth angle and recording the band-limited and amplitude-limited modulated digital information signal in a deep portion of a magnetic layer of the magnetic tape; and a second azimuth angle. A surface portion of the magnetic layer above the track formed by recording the band-limited and amplitude-limited modulated digital information signal PCM recording apparatus, which comprises using a second magnetic head for recording overlapping the video recording signal, said digital phase modulation offset 4-phase phase modulation system as a 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, and the digital phase. The PCM recording device, wherein the 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 means for converting the video signal to the video recording signal according to claim 6, 7 or 8, wherein the sub-carrier frequency band of the color signal is converted to a low carrier frequency band. A PCM recording device, characterized in that the means for performing digital phase modulation 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. The analog-digital conversion means for converting an audio signal into a digital audio signal by pulse code modulation according to claim 6, 7, 8 or 9, wherein the digital audio A PCM recording device characterized by recording a signal as the digital information signal. 11. An apparatus for multiplex recording and reproducing a video signal and a digital information signal on the same track of a magnetic tape, said 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; band-pass filter means for limiting the occupied bandwidth of the modulated digital information signal; limiter means for limiting the amplitude of the band-limited modulated digital information signal. A first magnetic head having a first azimuth angle, recording the band-limited and amplitude-limited modulated digital information signal in a deep portion of a magnetic layer of the magnetic tape, and reproducing the recorded signal. Formed by recording the band-limited and amplitude-limited modulated digital information signal having a second azimuth angle. A second magnetic head for superposing and recording the video recording signal on the surface of the magnetic layer above the track and reproducing the recorded signal; and the modulated digital information signal reproduced by the first magnetic head. A method for demodulating and generating the original digital information signal, and a means for converting the video recording signal reproduced by the second magnetic head into the original video signal are provided as the digital phase modulation / demodulation method. Offset 4
A PCM recording / reproducing 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 recording / reproducing apparatus characterized by using a phase differential phase modulation / demodulation method. 13. The method according to claim 11 or 12, 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 modulating means outputs the modulated digital information signal in a carrier frequency band lower than the carrier frequency band of the modulated luminance signal. 14. The means for converting the video signal to the video recording signal according to claim 11, 12 or 13, wherein the sub-carrier frequency band of the color signal is converted to a low carrier frequency band. Means for outputting 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, the PCM recording / reproducing apparatus. 15. An analog-digital conversion means for converting an audio signal into a digital audio signal by pulse code modulation according to claim 11, 12, 13 or 14, wherein the digital audio is used. 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.