JPS61294608A - Pcm recording and reproducing device - Google Patents

Abstract

PURPOSE:To reduce disturbance to an audio signal by providing a recording current correcting circuit so that the recording current of the synchronous head part of the FM video signal or luminance signal of a low carrier is less than the recording current of any other part. CONSTITUTION:Recording current frequency characteristics of the video signal are flattened to reduce the influence of the FM luminance signal of the low carrier upon a PCM audio signal to be modulated. The circuit composed of an input signal line 79, a transistor (TR) 80, resistances 81, 82, and 85, a coil 83, and a capacitor 84 is provided so as to reduce the influence of the video signal and the recording current frequency characteristics are corrected by a resonance frequency determined by the coil 83 and capacitor 84 and resonance characteristics determined by a resistance 85, etc. Thus, a PCM-modulated audio signal or digital data is recorded on the video signal one over the other while the disturbance of the video signal is reduced, thereby obtaining an audio signal or digital data of high quality.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a PCM recording and reproducing apparatus, and particularly to a PCM recording and reproducing apparatus suitable for multiplex recording a PCM audio signal or digital information on a video signal.

[Background of the invention]

Conventionally, as an audio signal recording method for home VTRs with the aim of improving sound quality, the method described in the IEICE technical research report MR85-20 (1985) by Miura et al. entitled ``System Development of HiFi VH8 VTR'' As described in the literature, a method is adopted in which an FM audio signal is multiplexed on a video signal track for recording a video signal using a rotating audio head dedicated for recording an audio signal. However, with the spread of digital audio disc players using compact discs and the start of high-quality digital audio broadcasting through satellite broadcasting, the era has come when it is necessary to digitize even higher-quality recordings of VTRs.

[Purpose of the invention]

In response to the demands of the times, an object of the present invention is to enable digital recording in a home VTR, and to provide a method for recording a digital recording medium that does not cause mutual interference with video signals.
An object of the present invention is to provide a commercial recording sickle reproducing device.

[Summary of the invention]

The present invention converts an audio signal into a PCM digital signal, and then converts the signal modulated by the input PCM digital signal into the occupied band of a low carrier FM luminance signal and a low frequency converted chroma signal. outside, or with a gap between the occupied bands of both, and
The signal modulated by the PCM digital signal is recorded and reproduced on the same video track or on the same video track using a magnetic head with a different azimuth angle from the magnetic head that records and reproduces the low carrier wave F'M luminance signal and the low frequency conversion chromaticity signal. It is something that is recorded and played back in parallel. Alternatively, the above-mentioned frequency multiplexing and azimuth angle difference are used in combination to record and reproduce video and audio while reducing mutual interference.
The modulation method of the signal modulated by the PCM digital signal is a four-phase differential PSK modulation method.

Furthermore, the frequency characteristics of the video signal are corrected to reduce interference with the audio signal.

[Funny example of invention]

An embodiment of the present invention will be described below with reference to FIG. 1st
In the figure, 1 is a video signal input terminal, 10 is a low-pass filter (LPF) that separates and extracts the luminance signal, 11 is a frequency (FM) modulator that inputs the luminance signal, and 12 is a chromaticity signal that is separated and extracted. 1s is a frequency converter for low-pass conversion of the chromaticity signal, 14 is a frequency converter (F
M) an adder that adds the modulated luminance signal and the low-frequency converted chromaticity signal; 15 is a recording amplifier; 169 is an equalization circuit;
16a and 16b are recording and reproducing heads for video signals; 2;
is an audio signal input terminal, 20 is an A/'D converter, 2
1 is a digital processing circuit, 22 is a PSK modulation circuit, 23
24a and 24b are recording amplifiers, 24a and 24b are recording and reproducing heads for audio signals, and 30 is a reproduction amplifier 31, which is a bandpass filter for separating and extracting a luminance signal.
FM) demodulation circuit, 55 is a low-pass filter (LPF) that separates and extracts the chromaticity signal, 34 is a frequency conversion circuit, 35 is an adder that adds the luminance signal and chromaticity signal, 5 is a video signal output terminal, 40 is a reproduction amplifier, 68 is a reproduction equalization circuit, 41 is a bandpass filter (BPF) for separating and extracting audio signals, 4
2 is a demodulation circuit, 43 is a digital processing circuit, and 44 is a D/
A converter 4 is an audio signal output terminal.

The operation will be explained below. Video signal is LPF10BPF1
2, the luminance signal is separated into 9 chromaticity signals, and then FM modulated 61
19 are FM-modulated and low-frequency converted into bands as shown in FIG. The signals are equalized by an equalization circuit 69 for correcting recording characteristics, and recorded on a tape by two opposing heads 16a and L6b having an azimuth angle of ±6°, for example, for recording and reproducing video signals. During reproduction, the signals reproduced by the heads 16a and 16b are amplified by the reproduction amplifier 30, and then the signals are each amplified by the reproduction amplifier 30. L P FM3 separates the luminance signal 1 chromaticity polarization, and the FM demodulator 529 and frequency converter 34 return each to the pre-recording video frequency band, and add 'x, @
35, it is demodulated into a video signal.

On the other hand, the audio signal is once demodulated into a digital signal by an A/D converter 20, and then a synchronization signal and a correction code are added to it by a digital processing circuit 21, and interleaving is performed.
After 'C, the signal is input to the PSK modulation circuit 22. In the PSK modulation circuit 22, the modulated signal is recorded as shown in FIG.
A gap is provided as shown in the figure, and the signal is modulated so as to fit into the gap, and after being amplified by the recording amplifier 25, the opposite
Two heads 24a and 24b perform deep recording on the tape in advance of the video signal.

During playback, the audio signal playback head 24a, 2
The 1g signal reproduced by the G11 circuit 42.4b is amplified by the reproduction amplifier 40, and the audio modulation signal is extracted by the BPF 41. A digital processing circuit 45 demodulates the original digital signal, and a D/A converter 44 demodulates the original audio signal.

When an audio signal is recorded as a digital signal at any time in this way, it is not affected by distortion of the recording medium, and high-quality audio transmission becomes possible.

Here, a four-phase PSK method is an example of a modulation method for modulating a PCM audio signal into a narrow signal band.

This modulation circuit 22. The configuration of the demodulation circuit 42 is shown in FIG. 3 and FIG. 4. In FIG. 5, 50 is a serial/parallel conversion circuit for digital signals, 51 is a differential encoder, and 5
2 is a balanced modulator, and 53 is an oscillator.

54 is a 90° phase shifter, 55 is an adder, and 56 is a BPF. In Fig. 4, 60FiBPF, 61 a balanced modulator, 62 a carrier recovery circuit, 63 a 90° phase shifter, 64a and 64b LPFs, 65 a data recovery circuit, 66 a differential decoder, and 67 a demodulator. This is a parallel-to-serial conversion circuit that converts parallel data into serial data.

The operation of the modulation circuit 22 will be explained below. Nine digital processing circuit output terminals 6 are output from the digital processing circuit 21.
The PCM audio data is replaced with parallel data in 2-bit units by the serial-parallel conversion circuit 50. This signal is generated by the differential encoder 51, and for the 2-bit data value, 0°, 90'>, 180°, 27
It is converted into a signal with a phase change of 0°. This signal is input to the balanced modulator 52 using the oscillation frequency of an oscillator 55 having a stable oscillation source such as a crystal as a carrier signal.

After balanced modulation, the signals are added by an adder 55 to generate a four-phase differential PSK signal, band limited by a BPF 56, and output from the digital modulation circuit ratio cuff.

The reproduction demodulation circuit 42 reproduces serial data during recording from the four-phase differential PSK signal.

First, the signal at the four-phase difference #PSK signal input terminal 9 is input to an input waveform equalization circuit 60 to correct deterioration of frequency characteristics on the tape. Here, a transmission characteristic that does not cause code amount interference, such as a squared cosine characteristic, is selected.

The four-phase differential PSK signal from which the luminance signal and chromaticity signal components have been removed is used to regenerate a carrier signal in a carrier regeneration circuit, and a signal having a phase shift of 90 degrees from this signal is input to a balanced modulator 61. Each output of the balanced modulator 61 is connected to an LPF 64.
The data is demodulated into 2-bit data via the data reproducing circuit 65. This signal is input to the differential encoder 51 and the differential decoder 66 which performs the inverse conversion, and the 2-bit data after decoding is input to the parallel-to-serial conversion circuit 67, and the serial signal at the time of recording is output from the digital demodulation circuit. It is played back from terminal 8.

As explained above, the PCM audio signal is transferred to the spectral gap between the chromaticity signal and the luminance signal using a four-phase differential PS.
By performing K modulation and multiplex recording, it is possible to provide a recording and reproducing device for higher quality audio signals in a home VTR.

Also, in FIG. 1, the audio signal is sent to the A/D converter 20.
The signal is converted into a digital signal and input to the digital processing circuit 21. However, in the case of digital information such as voice or facsimile that has already been digitized, it is conceivable to directly input it to the digital processing circuit 21 and record it digitally. An example of digital data is shown in FIG. This data starts with a synchronization signal, then control data,
Audio signal data, independent data other than the audio signal, and finally a correction code when an error occurs are added. 12
This is a PCM audio format for GH2 band satellite broadcasting. The transmission bit rate of this signal is 2.048 Mbpa, and when four-phase differential PSK modulation is performed, the band after the modulation is approximately IMHz.

Therefore, if the carrier frequency is selected to be around 16 MHz, for example, the spectral band of the audio signal during tape recording will be 11 to 2.1 MHz. As a result, PCM audio can be recorded and reproduced with less interference with the luminance signal and chromaticity signal of the video signal.

As another example, the format processed and generated in the digital signal processing circuit 21 is, for example, the "Activities of the DAT Council" written by Ryuji Iwashita in the magazine "Denshi" Vol. 24, No. 10 (1982). When using the configuration of the PCM area of the rotating head DAT format described in the article titled ``, the transmission bit rate of the recording signal is approximately 2.6 MbPB, and it is possible to transfer data without using 4-phase PSK modulation. In this case, the band after modulation is approximately 1.5 MHz.0 Therefore, if the carrier frequency is set to, for example, around 2 MHz, the frequency spectrum band of the audio signal during tape recording becomes i5 Mllz-2-65Ml (z. As a result,
Audio signals can be recorded and reproduced while reducing mutual interference with the luminance signal and chromaticity signal of the video signal.

Furthermore, in order to reduce interference with the color and luminance signals of this video, it is recommended to limit the signal band with a BPF of 56.41 during recording and playback.An example of such a BPF is shown in Figure 6.The carrier frequency and BP F56.41
The center frequencies of the four-phase differential PSK signals are made to match, and the bandwidth is limited to reduce interference from the four-phase differential PSK signal to the video signal.

In this way, the audio signal is sent to the audio dedicated head 2.
4a and 24b, the top and bottom of the same video track are preceded by an audio signal in parallel, and after deep recording,
A low carrier FM luminance signal and a low frequency converted chromaticity signal are recorded by video heads 16a and 16b.

Here, as shown in Fig. 2, the recording occupied band of the audio signal is placed outside the occupied band of the low carrier FM luminance signal and the low frequency conversion chromaticity signal, or in the gap between both, and the azimuth angle is By recording and reproducing different dedicated audio signals using the magnetic heads 24a and 24b, mutual interference between the video signal and the audio signal can be reduced.

Furthermore, by equalizing the output signal of the recording amplifier circuit 15 by the equalization circuit 169, it is possible to reduce the interference of the video signal with the audio signal. In the case of overwriting by recording the modulated luminance signal in this embodiment In general, the playback output level of a previously recorded deep-recorded PCM audio signal causes deterioration in frequency characteristics due to the surface layer erasing effect caused by overwriting. 'M7 figure is
The frequency characteristics of the overwritten v4PCM audio signal are measured. In Figure 7, 69
is the frequency characteristic before overwriting, and 70 is the frequency characteristic after overwriting. Therefore, in order to correctly demodulate the modulated PCM audio signal, it is necessary to optimally compensate for the deterioration in frequency characteristics due to this overwriting, that is, the deterioration corresponding to the output ratio of 70 and 69.

FIG. 8 shows an embodiment of this reproduction equalization circuit 68. 71 is a reproduction equalization circuit input terminal, and this input signal and the outputs of delay elements 72 and 75 are sent to coefficient circuits 74 to 76.
By inputting the signals into the signals and adding them in the adder circuit 77, the deterioration of the frequency characteristics is corrected, and the output cuff 8 is obtained.

Furthermore, in the case of this embodiment, first the audio signal is recorded by the audio head, and then the video signal is recorded by the video recording head. By recording in this order, the surface layer portion of the audio signal is erased, and the video signal is recorded on the surface layer portion. Conventionally, regarding the recording state on magnetic tape, there is a document titled "Short wavelength recording characteristics during non-bias recording" by Kengo Muramatsu in Materials MR75-28 (19b) of the Magnetic Recording Study Group of the Institute of Electronics and Communication Engineers. It is described in FIG. 2, wavelength vs. recording depth characteristics. As is clear from the same paper, it can be seen that the degree of surface layer erasure increases as the frequency becomes lower or the recording current becomes larger.

Here, the low carrier FM luminance signal in the video signal is obtained by frequency modulating the luminance signal, and is modulated such that the synchronization signal part has a lower frequency and the brighter the luminance, the higher the frequency. This is shown in the recorded signal frequency spectrum of FIG.

Furthermore, the recording current has frequency characteristics that are greater than the characteristics of the recording head, and the value is steeper at lower frequencies.

Therefore, when recording with the device of this embodiment, the reproduced signal of the modulated PCM audio signal will undergo amplitude modulation by the low carrier FM luminance signal 1, that is, the cancellation effect of the synchronization signal part in the modulated luminance signal. Since the signal is large, it is subjected to amplitude modulation according to the same signal.

The reproduced signal waveform of the modulated PCM audio signal amplitude-modulated by the modulated video signal is as shown in FIG. 9, and the divided signal frequency spectrum is as shown in FIG. 10a. Here, the recording current frequency characteristics of the low carrier wave FM luminance signal recording head are shown by the solid line in FIG.

As shown in FIG. 2, the low carrier FM luminance signal is obtained by FM modulating the luminance signal, and is modulated to, for example, the synchronization signal portion F13.4MtLz. Therefore, from FIG. 2 and FIG. 11, in the modulated luminance signal, since the frequency of the synchronizing signal portion is low and the recording current is large φ, the erasure time of the modulated PCM audio signal becomes large.

In order to reduce the degree of erasure caused by such a synchronization equal part, it can be realized by changing the recording current frequency characteristic, for example, by flattening it to a characteristic as shown by the broken line in FIG. 11, for example.

41011g shows this effect, which is the frequency spectrum of the audio head reproduction signal when a 17 MHz signal is recorded with the audio head and then a video signal is recorded with the video head.

Here, FIG. 12 (2) and FIG. 10 (a) show the frequency spectrum of a reproduced signal when a modulated video signal is recorded with the characteristics of the video head shown by the solid line in FIG. 11.

In contrast, Fig. 12 ■ and Fig. 10 (b) show the 11th
This is the frequency spectrum when the signal is recorded with the characteristics shown by the broken line in the figure.◎ As shown in Figures 10 and 12, the effect of the synchronization signal in the luminance signal is can be reduced by approximately 5 dB.

As described above, by flattening the recording current frequency characteristics of the video signal, the influence of the low carrier FM luminance signal on the modulated PCM audio signal can be reduced.

Next, a circuit for obtaining characteristics shown by the broken line in FIG. 11 in order to reduce the influence of the video signal will be described.

First, a circuit having characteristics such as those shown by the broken line in FIG. 11 is inserted between the video heads. This ninth specific circuit example is shown in FIG. The circuit shown in FIG. 13 provides the characteristics shown by the broken line in FIG. 11, and the overall characteristics shown by the broken line in FIG. 14.

In Fig. 13, 79 is an input signal line, 80 is a transistor, 81.82.85#Pi low resistor, 83 is a coil,
A capacitor 84 corrects the recording current frequency characteristics based on the resonance frequency determined by the coil 83 and the capacitor 84 and the resonance characteristics determined by the resistor 85 and the like.

Next, when an audio recording signal is superimposed on a video recording signal and recorded at the same time, the audio recording signal is recorded using the video recording signal current as a bias current, so the audio recording signal is played back depending on the frequency and recording current of the video recording signal. The output is subject to change.

Generally, since the FM carrier frequency at the synchronization leading edge of the video signal is low, overbiasing occurs and the reproduction output of the audio recording signal decreases. To compensate for this, a video recording signal current correction circuit is inserted into the video recording signal system as in the above embodiment.

〔Effect of the invention〕

According to the present invention, it is possible to multiplex and record a PCM-converted audio signal or digital data with a video signal while reducing interference with the video signal, and a high-quality audio signal or digital data can be obtained.

[Brief explanation 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, and Fig. 3 is a diagram showing a spectrum of a tape recording signal.
4 is a diagram showing a 4-phase differential PSK demodulation circuit, FIG. 5 is a diagram showing an example of the structure of recorded digital data, FIG. 6 is a diagram showing BPF characteristics, and FIG. 7 is a diagram showing a modulation circuit. 8 is a diagram showing the reproduction frequency characteristics after deep recording and overlapping, FIG. 8 is a diagram showing the configuration of the reproduction equalization circuit, and FIG. 9 is a signal waveform diagram.
FIG. 10 is a reproduced signal frequency spectrum diagram of a modulated audio signal, FIG. 11 is a recording current frequency characteristic diagram, FIG. 12 is a reproduced signal frequency spectrum diagram, and FIG. 15 is an equalization circuit diagram. 11...FM modulator 32...FM demodulator 16
a, 16b, 24a, 24b - recording/reproducing head 20...A/D converter 44...D/A converter 21.43...digital processing circuit 22...modulation circuit 42...demodulation circuit 68・
... Reproduction equalization circuit 169...Equalization circuit Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 - Lunar amnesty Figure 7 Moon wave number band (MHz) Figure 8 Animal 9 Figure I Figure 10 Figure (b 11 Figure A Sasuka - C 112 Figure ○n

Claims (1)

[Claims] To record a PCM audio signal or digital data on a magnetic tape together with a video signal, the PCM audio signal or digital data is encoded and modulated into an audio recording signal, and the video signal is modulated into a low carrier FM video signal. Alternatively, the video recording signal is modulated into a low-carrier FM luminance signal and a low-range chromaticity signal, and these audio recording signals and video recording signals are frequency-multiplexed and recorded simultaneously on a magnetic tape, or this audio recording signal is In an apparatus that first records a signal with an audio-only head and then records the video recording signal with a video-only head having a different azimuth angle from the audio-only head, the synchronization of the low carrier FM video signal or the low carrier FM luminance signal is performed. A PCM recording device characterized in that a recording current correction circuit is provided in the video recording signal system so that the recording current at the leading end is smaller than the recording current at other parts.