JPS62249594A - Magnetic recording and reproducing method - Google Patents

Abstract

PURPOSE:To erase/re-record a digital signal only by executing the phase correcting, etc. of a video signal by using a single frequency signal which is generated at the time fo reproducing a digital signal which si recorded so as to overlap a track of a video signal recording medium. CONSTITUTION:A video signal inputted from a terminal 1 is separated into a brightness signal and a color signal by a video signal processing circuit 3, amplified 4, and recorded in a magnetic tape by magnetic heads 11 and 13 mounted on a rotary cylinder 9. A sound signal inputted from a terminal 4 is digitized by a code modulator 5, subjected to a LPF 6, 4-phased-phase- modulated by a phase modulator 7, and further, amplified 8, and recorded in the shallow layer part of a track in which video signals are recorded by magnetic heads 12 and 14. A video signal and a sound signal reproduced by magnetic heads are respectively amplified 15 and 16, and inputted to a phase error correcting circuit 17 and a phase demodulator 18. The circuit 18 executes four- phased phase-demodulation to input the single frequency signal having reference phase to a phase error detector 19, where a detected phase error is used for phase correction 17. A demosulated 18 signal is decoded 21, and an original sound signal is restored.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a high-density, high-performance magnetic recording and reproducing method that multiplexes video signals and audio signals on a magnetic layer such as a magnetic tape and enables separate reproduction. It is something.

2. Description of the Related Art In conventional magnetic recording and reproducing devices, such as rotating head video tape recorders (hereinafter referred to as VTRs), luminance signals and color signals forming video signals are recorded on a video trunk, and audio signals are recorded on a separate audio trunk. Information is recorded on almost the entire surface of the magnetic tape using so-called azimuth recording, in which the azimuth angles of two rotating heads for recording video signals are different. There are almost no gaps. For this reason, the current state of the industry is to focus on improving recording density by shortening wavelength recording and narrowing tracks.

Recently, with the aim of improving the performance of VTR audio signal recording,
A method of recording a frequency-modulated audio signal along with a video signal on a TR video track has been put into practical use (for example, rVHS Hi-Fi VTRJ, Shuzo Machi et al., Na
ttonal Technical Report.

voL, 30. Nl I Feb, 1984).

FIG. 2 shows the frequency allocation in this recording method, and FIG. 3 shows the recording state in the depth direction of the magnetic tape.

In FIG. 2, 25 is a luminance signal including a frequency-modulated synchronization signal, and 26 is a low-band-converted carrier color signal.

27 is a signal obtained by frequency modulating (FM) an audio signal,
The audio signal is recorded in a band between the low frequency conversion carrier color signal 26 and the FM luminance signal 25 by an audio dedicated head at an azimuth angle different from that of the video signal head.

As is clear from FIG. 3, the FM audio signal is recorded in the deep layer 2 of the magnetic layer with a large recording current before the video signal.
8b, and the video signal is then recorded on the surface layer 28a of the magnetic layer. Note that 28C is a non-recording layer of the magnetic layer, and 29 is a base film.

In the case of such a conventional example, since the audio signal is recorded in FM, the S/N ratio is high and the quality is good, and the sound quality does not deteriorate even if the tape running speed is slowed down.
It can be said that this is one of the effective methods for recording TR. Moreover, it is noteworthy that it utilizes the deep layer of the magnetic tape magnetic layer, which was not previously used.

The problem that the invention seeks to solve Such conventional VTRs have several problems.

First, it is necessary to supply a large current to the recording head in order to record the FM audio signal deeply, and the frequency band that can be recorded is limited to a relatively low range due to space loss. .

As a result, it has become impossible to develop code modulation (PCM) recording, which has higher quality than FM recording of audio signals (FM
Since the audio signal is recorded in the low frequency range using a large current, the interference of the audio signal recorded deep in the video signal cannot be ignored when playing back the video signal.
Large current supply circuits for recording audio signals have become larger.
Moreover, the large current has a negative effect on other video circuits. Second, it is impossible to perform after-recording.

Conventionally, in a VTR, video and audio are recorded on separate tracks, so it is possible to record the audio later while playing the video, so-called after-recording. However, as is clear from Figure 3, since the audio signal is recorded deep, if it is erased or re-recorded, the video signal will also disappear, making after-recording impossible.

The purpose of the present invention is to solve the problems of conventional VTRs, and to provide wideband PCM signals such as PCM signals in which audio signals are encoded in the shallow part of the analog signal track where video signals etc. are recorded. For example, by recording the digital signal in synchronization with the video signal and restoring the digital signal using the synchronization signal of the video signal, the VT
It is an object of the present invention to provide a magnetic recording and reproducing method that enables high-density recording of R and also enables erasing and re-recording of only digital signals recorded in shallow layers.

Means for Solving the Problems The magnetic recording and reproducing method of the present invention records a digital signal such as a phase-modulated PCM audio signal so as to overlap a track on which a video signal is recorded, and when reproducing the reproduced digital signal. signal with a single frequency (single carrier signal)
is generated, and the phase information of the single frequency signal is used to correct the phase or time axis of the video signal to improve the image quality of the reproduced video signal, and it is also possible to record and reproduce PCM audio signals, etc. That is. In the embodiment, a case has been described in which a digital signal is recorded in a shallow layer of a magnetic tape, but a similar effect occurs when a digital signal is recorded in a deep layer.

Function: The above-mentioned recording and reproducing method makes it possible to reproduce high-quality signals such as PCM audio signals as well as high-quality video signals, and it is also possible to erase and re-record only digital signals, so it is widely used as a high-density recording method. Application is possible.

EXAMPLE An example of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of main parts in one embodiment of the present invention. In FIG. 1, a video signal inputted from a video signal input terminal 1 reaches a recorded video signal processing circuit 3, where the video signal is separated into a luminance signal and a color signal. Then, a mixed signal of the frequency-modulated luminance signal and the low-converted chrominance signal enters the video signal recording amplifier 4, and the magnetic head 1) on the rotary cylinder 9 at an appropriate recording level. 13 on the magnetic tape.

The audio signal manually inputted from the audio signal input terminal 2 is linearly quantized and pulse encoded in the code modulator 5, and after adding an error correction code and a synchronization code, it passes through the LPF 6 as a digital signal and undergoes phase modulation. The signal is subjected to quadrature phase keying (QPSK) in the unit 7.

When the sampling frequency of the audio signal is 43 kHz, 16-bit linear quantization is performed on two channels, and 40% redundancy is added, the digital signal transmission rate is approximately 2.3 megabits per second (Mbps). be.

Bandwidth of 2.3Mbps signal in baseband is 1.15MH
z, even if this signal is QPSKed, the band (-3
dB) may be 1.15MHz. The PSK center frequency output from the phase modulator 7 is 2MHz and the band is approximately 1.15MHz.
The QPSK digital signal of z is set at a recording level lower than normal in the audio signal recording amplifier 8, and is recorded by the magnetic head 12, 14 in the shallow part of the track where the video signal is recorded.

FIG. 4 is a recording state diagram in the depth direction of the magnetic layer.

When video signals are recorded on magnetic tape using a rotating head in the conventional manner, the depth of the recording layer is 0.25 of the recording wavelength.
~0.3 times, and 0.3 to 0 for current consumer VTRs.
．． This means that data is recorded to a depth of 8 .mu.m, and since the thickness of the magnetic layer 30 of a general magnetic tape is 2 to 4 .mu.m, a non-recording layer 30c exists as shown in FIG. The conventional example described in FIGS. 2 and 3 utilizes a portion of this non-recording layer, but essentially only signals with long wavelengths (low frequency band) can be recorded. The shallow layer of the tape magnetic layer is suitable for recording broadband signals, and in fact, video signals are recorded only on the very surface.

The present invention focuses on the fact that recording and reproducing digital signals does not require the same S/N ratio as recording and reproducing analog signals, and records broadband digital signals in the shallow part of the recording layer 30b where video signals are recorded. , a digital signal recording layer 30a.

For reproducing digital signals, if the S/N is 15 dB, 10
The code error rate becomes approximately -S, approaching a practical value. It is sufficient if an S/N of 20 to 30 dB can be secured with a margin. Therefore, a modulated digital signal to be recorded in a shallow layer may be recorded at a depth such that the S/N satisfies the above value.

If a video signal is to be recorded at the optimum recording current (the recording current value that maximizes the reproduction output), the recording current for the digital signal may be 2 or less. Naturally, the modulated digital signal is shallowly recorded after the recorded video signal, so the playback output of the video signal decreases, but the extent of this is small because the recording current of the digital signal is small, and the recording current Taking the value as an example, it stays within about 1 dB. Moreover, since the noise due to the surface nature of the tape is recorded in the shallow layer of the digital signal, it is less likely to be directly involved in the reproduction of the video signal, and modulation noise is reduced, so the actual S/N drop in the video signal is further reduced. . In this way, the S/ of the previously recorded video signal is
It is possible to suppress N degradation to a small level and to modulate and record a digital signal having a practical bit error rate on top of a video signal.

By the way, if the occupied bands of the video signal and the digital signal are far apart, it is possible to obtain the desired signal from the reproduced signal using a filter, but if we consider the case where the two signals are close to each other or overlap, It is necessary to make the azimuth angle of the rotary head for recording and reproducing video signals different from the azimuth angle of the rotary head for recording and reproducing digital signals. Generally, it is known that if the gap direction of the reproducing head is inclined by θ with respect to the gap direction of the recording head, the following loss will occur.

However, Wnidrack width λ: recording wavelength Therefore, the reproduction output of the video signal rotary head does not pick up the signal recorded on the digital signal recording layer 30a and reproduces only the video signal, and the reproduction output of the digital signal rotary head is The azimuth angle can be set so that only the digital signal is reproduced without picking up the signal from the video signal recording layer 30b. For example, by making the azimuth angles of video and digital heads different by 30 degrees, a practical track width can be achieved.
．． It is possible to share the band of both signals over a band of 5 to 2 MHz or more.

FIG. 5 is a frequency allocation diagram of an embodiment according to the present invention. This example attempts to record PCM audio signals while keeping the recordable band of a conventional VTR.

In this case, VT determined by the magnetic tape and magnetic head
New P without expanding the recordable band of the R electromagnetic conversion system
The VH3 standard VT can record commercial audio signals and has only a relatively narrow recording band.
It is fully applicable to consumer VTRs such as R.

In FIG. 5, 32 is a QPSK digital signal.

In the embodiment, the baseband digital signal is QPSKed and recorded in a shallow layer above the track where the luminance signal is recorded, but the modulation method of the digital signal is that the digital signal of a single frequency is Any other device can be applied as long as the signal can be reproduced.

FIG. 6 is a diagram showing an example of the configuration of a rotary head group for realizing the magnetic recording and reproducing method of the present invention. The magnetic tape 33 travels in the direction of arrow A, and the rotating cylinder 9 travels in the direction of arrow B.
A so-called rotating two-handed helical power type VT that rotates at 0Hz.
It is R. In this case, the video signal head 1) contacts the tape before the digital signal head 13, and the video signal head 12 contacts the tape before the digital signal head 14. For example, set the azimuth angles of 7 do 1) and 12 to ±6° for the video signal, and
The azimuth angles of 3 and 4 are ±30''. With this configuration, the video signal is first recorded on the track on the magnetic tape, and then the digital signal is modulated by another azimuth head in the shallow layer. The recording current of each head is set to the optimum recording current for the video signal head 1), 12, and the recording current smaller than the above optimum recording current for digital signal recording. and record it.

Next, we will discuss playback. In FIG. 1, the magnetic head 1). The video signal reproduced by 13 passes through a video signal reproduction amplifier 15 and reaches a phase error correction circuit.

Also, the audio signal reproduced at the same time is transmitted to the audio signal reproducing amplifier 1.
6, the signal reaches a phase demodulator 18, where it is demodulated into four phases. The four-phase demodulated digital signal is sent to a code decoder 21.
After error correction and shifter absorption are performed, the signal is decoded into the original audio signal, passed through the LPF 22, and outputted from the audio signal output terminal 24. Incidentally, in the phase demodulator 18, a phase comparison reference signal consisting of a single frequency having a reference phase created from the reproduced signal is generated. The third single frequency signal, which serves as a reference for this phase comparison, also has jitter during VTR reproduction, so if the frequency of this single frequency signal is a known value, the amount of jitter can be determined. A single frequency signal serving as a reference for phase comparison is output from the four-phase phase modulator 18 to a phase error detector 19, and the instantaneous phase error of the single frequency signal is detected.

The detected phase error or absolute time error enters a phase error correction circuit 17 and is used to correct the phase error or absolute time error due to jitter of the reproduced video signal. That is, since the time axis correction is applied to the reproduced video signal, the reproduced image quality is greatly improved, and the image quality of the video signal does not deteriorate because of the new recording of the audio signal, but on the contrary, the image quality improves.

Furthermore, since the shifter is removed, it becomes easier to use techniques such as sub-Nyquist sampling that require a precise time axis. The signal is demodulated into a signal and output from the video signal output terminal 23.

In the embodiment, the output of the phase error detector 19 is used to directly correct the time axis of the reproduced video signal, but the output of the phase error detector 19 is also used to perform phase correction of the reproduced color signal that has been low-pass converted. It is also possible to perform time axis correction of the frequency-modulated reproduced luminance signal. That is, the present invention is characterized in that the phase correction or time axis correction of the reproduced video signal can be performed in either the base band or the RF band. For example, when performing phase correction on reproduced color signals that have been low-pass converted, QPS
The carrier wave frequency f1 for performing K is the frequency f of the monochromatic color signal.
By establishing the relationship b and f = -fb (n and m are integers), the configuration of the phase correction circuit can be made simple.

In the case of this embodiment, the digitized audio signal is recorded on the very surface of the magnetic layer, so it can be easily rewritten with a new signal with a weak recording current, and it can also be easily erased. be able to.

If the erasing or re-recording current is set appropriately, it will have almost no effect on the video signal.

Effects of the Invention As detailed above, the present invention is capable of transmitting a digital signal modulated by a head having a different azimuth angle from the recording head of the video signal to the shallow part of the video signal recording layer so as to overlap the trunk in which the video signal is recorded. This allows video signals and digital signals to be recorded and played back separately using heads with different azimuth angles.

Even though the digital signal was recorded, the playback video signal is subjected to time axis correction using a single frequency signal created from the playback audio signal, so the image quality of the playback video signal does not deteriorate, but rather improves. have advantages.

In other words, it is an extremely high-capacity, high-density magnetic recording method that improves the quality of video signals and can also record other digital signals.

The digital signals recorded in the shallow layer of the magnetic tape can share the band with the video signal, making it possible to achieve an extremely wide band, and because it is in the shallow layer, it is easy to erase and rewrite. It has the following characteristics. Therefore, it is easy to use this digital signal for audio PCM recording, and in that case, the S/N, frequency characteristics, distortion rate,
Performance such as wow and flutter has been significantly improved, and
After-recording, which was not possible with conventional FM audio recording, is also possible, making it possible to create a VTR with extremely high sound quality.

[Brief explanation of drawings]

FIG. 1 is a block diagram of the main parts of an apparatus using the magnetic recording and reproducing method according to the present invention, and FIGS. 2 and 3 are a frequency allocation diagram and a recording state diagram in the depth direction of the magnetic tape, respectively, to explain the conventional example. , FIG. 4 is a diagram of the recording state in the depth direction of the magnetic layer to explain the basic principle of the present invention, FIG. 5 is a diagram showing the frequency allocation of the device to which the present invention is applied, and FIG. 6 is the configuration of the magnetic head group. It is a diagram. 9... Rotating cylinder, 25... Luminance signal including frequency modulated synchronization signal, 26...
・Low frequency converted carrier color signal, 27... Signal obtained by frequency modulating the audio signal, 28.30... Magnetic layer, 29.31... Non-recording layer, 32...
・QPSK digital signal, 33...Magnetic tape. Name of agent: Patent attorney Toshio Nakao (1 person) Figure 2 Figure 3 Figure 4 Figure 5 R1 (MHz)

Claims (9)

[Claims] (1) When reproducing a second signal recorded so as to overlap the track on which the first signal is recorded, a third signal with phase information is generated from the reproduced second signal, A magnetic recording and reproducing method characterized in that, when reproducing the first signal, phase information or time axis correction of the first signal is performed using phase information of the third signal. (2) The first signal is a signal composed of a low-frequency converted color signal and a frequency-modulated luminance signal, and the third
2. The magnetic recording and reproducing method according to claim 1, wherein the color signal is phase-corrected by the signal. (3) The first signal is a signal composed of a low-frequency-converted color signal and a frequency-modulated luminance signal, and the third
2. The magnetic recording and reproducing method according to claim 1, wherein the luminance signal is time-base corrected by the signal. (4) The magnetic recording and reproducing method according to claim (1), wherein the first signal and the second signal are recorded and reproduced by heads having mutually different azimuth angles. (5) The magnetic recording and reproducing method according to claim (1), wherein the first signal is recorded before the second signal. (6) The magnetic recording and reproducing method according to claim (1), wherein the first signal is recorded after the second signal. (7) Claim (1) characterized in that the first signal is a video signal and the second signal is a digital signal.
2. Magnetic recording and reproducing method described in Section 1. (8) The magnetic recording and reproducing method according to claim (1), wherein the second signal is a signal obtained by digitizing an audio signal and further phase modulating the signal. (9) The magnetic recording and reproducing method according to claim (1), wherein the second signal is a signal obtained by frequency modulating an audio signal.