JPS6366701A - Magnetic recording and reproducing method - Google Patents

Abstract

PURPOSE:To realize a digital VTR whose bit density is higher than that of a usual digital VTR by superposing and recording a digital signal with a different recording azimuth in order to superpose on a track where another digital signal is recorded and reproducing the respective signals. CONSTITUTION:In order to be superposed on the track 31b where the digital video signal is recorded, a digital sound signal modulated by recording heads 13 and 15 which have azimuth different from the recording heads 12 and 14 for the digital video signal is recorded in the shallow layer part 31a of a video signal recorded layer and the digital video signal and digital sound signal are separately reproduced by the heads whose azimuths are different each other. Though the digital signal such as a sound PCM signal etc., are newly recorded, the picture quality of the digital video signal is hardly deteriorated with the aid of an error correction. And while keeping the interchangeability with the usual digital VTR, the bit density of the signal in a magnetic tape is made to raise by recording in superposition with the azimuth.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a high-density magnetic recording and reproducing method that multiplexes two channels of digital signals on a magnetic layer such as a magnetic tape and enables separate reproduction.

Conventional technology Conventional digital video tape recorder (abbreviated as VTR)
In this field, a method has been developed for exchanging color video signals to digital signals and recording and reproducing them on magnetic tapes and the like. For example, Journal of the Television Society, Vol. 39 1
'h4 (1985), pages 312-316, and is a helical scan type digital VTR having a guard band in the recording track pattern. In other words, conventional digital VTR
In this case, the signal recording density on the magnetic tape is low due to the presence of the guard band.

With reference to the drawings below, the above-mentioned conventional digital VT
An example of R will be explained.

FIG. 2 is an example of a digital signal recording track pattern in a conventional digital VTR. In Figure 2, 2
01, 202 and 203 are track patterns recorded by magnetic heads, respectively. In Figure 2, 2
8 is the track pitch, 29 is the track width, and 30
is a guard band. In conventional digital VTRs, a guard band exists as described above, and the recording density is lower than that of a recording system without a guard band. Furthermore, in conventional digital VTRs, in order to increase the recording density, the recording wavelength and recording track width are selected near the high-density recording limit determined by the equipment.

Problems to be Solved by the Invention As described above, in the conventional digital VTR, since a guard band exists in the recording track pattern, the recording density is lower than that of a recording system without a guard band. Generally, recording density is increased by shortening the shortest recording wavelength of the recording signal to increase the recording linear density, or by narrowing the recording track width to increase the recording track density, but in conventional digital VTRs, These recording wavelengths and track widths are used near the high-density recording limit determined by the equipment. In other words, due to the shortest recordable and reproducible wavelength determined by the magnetic head and magnetic tape, and the narrowest track width determined by mechanical precision and servo system response, conventional digital VTRs are unable to record at high recording densities that exceed the limit determined by these. This is a fundamental problem in that it is impossible to record and reproduce digital signals.

In view of the above-mentioned problems, the present invention provides a digital VTR with higher recording density than conventional digital VTRs by superimposing and reproducing two digital signals using magnetic heads with different azimuths. be.

Means for Solving the Problems In order to solve the above problems, in the present invention, another digital signal is recorded in a different recording azimuth so as to overlap the track on which the digital signal is recorded, and each signal is recorded. By reproducing data, it becomes possible to realize a digital VTR with higher recording density than conventional digital VTRs.

Effect: The recording and reproducing method described above improves the recording density and enables recording and reproducing of two-channel digital signals.

For example, it is possible to exchange a video signal into a two-channel digital signal and record it, or to exchange a video signal and an audio signal into one-channel digital signal each and record them. Generally, if error correction is performed when recording and reproducing digital signals in a VTR, it is possible to obtain a reproduced signal that is extremely faithful to the input signal, but the present invention makes it possible to realize a highly reliable two-channel digital VTR. .

EXAMPLE Hereinafter, an example of the magnetic recording and reproducing method of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of main parts in one embodiment of the present invention.

In FIG. 1, the video signal input from the video signal input terminal 1 is converted into a PCM signal by the code modulator 3, and after adding an error correction code and a synchronization code, it passes through the LPF 5 as a digital signal and is recorded as a digital video signal. The signal enters the amplifier 8 and is recorded on the magnetic tape by the magnetic head 12, 14 on the rotating cylinder 10 at an appropriate recording level.

When a video signal is converted into a PCM signal, the transmission rate is several tens to hundreds of Mbps. For example, the band of an NTSC color video signal is 4.2 MHz, so the sampling frequency needs to be about 9 MHz or more, the number of quantization bits needs to be 7 bits or more, and if you add a large length such as an error correction code, it becomes a composite signal. Approximately 100Mbps
, the component signal is about 200 Mbps.

However, the transmission rate can be reduced by removing synchronization signals, sub-Nyquist sampling, and reducing the length of the video signal, but for example, in Intelsat communication satellites, the transmission rate can be reduced while maintaining image quality equivalent to current analog transmission. The speed is approximately 30 Mbps. In this embodiment, the digital signal passing through the digital video signal recording amplifier has no DC component and the transmission rate is 100M.
Suppose that it is bps.

The audio signal input from the audio signal input terminal 2 is converted into a 16-bit PCM signal by the code modulator 4, and after adding an error correction code and a synchronization code, it is output as a digital signal.
After passing through PF6, the four-phase phase change AI is applied to the phase modulator 7.
(QPSK). If the sampling frequency of the audio signal is 48 Kllz, 16-bit linear quantization is performed on 2 channels, and a length of 40% is given, the digital signal transmission rail will be approximately 2.3 x Gabisoto/second (Mb).
ps).

Bandwidth of 2.3Mbps signal in baseband is 1.15MH
Since this signal is
B) may be 1.15 MHz. The QPSK digital signal output from the phase modulator enters the digital audio signal recording amplifier 9, the recording level is set lower than normal, and the magnetic head 13.15 records the digital video signal in the shallow part of the track where it has been recorded. recorded.

FIG. 3 is a diagram showing the state of signal recording in the depth direction of the magnetic layer. When video signals are conventionally recorded on magnetic tape using a rotating head, the depth of the recording layer is 0.25 to 0.25 of the recording wavelength.
0.3 times, and recording is performed at this depth even in conventional digital VTRs, and generally the magnetic N31 of magnetic tape
(There is an unrecorded ji31c.) Due to the physical characteristics of various losses in magnetic recording, the shallow part of the tape magnetic layer is suitable for recording wideband signals, and in fact, wideband signals Signal recording is done only on the 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 digital audio signals in the shallow part of the recording JW 31b where digital video signals are recorded. Digital audio signal recording F31
Let it be a. For digital signal reproduction, S/N is 15 dB.
If so, the code error rate would be about 104, which is close to 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 audio signal to be recorded in a shallow layer may be recorded at a depth such that the S/N satisfies the above value. If the band of the digital audio signal is about 1.15 MHz as mentioned above, it is smaller than the band of the digital video signal, so if the digital video signal is recorded at the optimal recording current (the recording current value that maximizes the playback output). For example, the recording current for digital audio signals may be less than that. Naturally, since the modulated digital signal is shallowly recorded after the recorded video signal, the playback output of the digital video signal decreases, but the extent of this is small because the recording current of the digital signal is small, and the above-mentioned recording Taking the current value as an example, it remains 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 digital video signal is even smaller. Become. Since digital video signals are also subjected to error correction during reproduction, they have the characteristic that even slight S/N deterioration causes almost no deterioration of the reproduced video signal. In this way, it is possible to suppress the S/N deterioration of the previously recorded digital video signal and to modulate and record a digital audio signal having a practical bit error rate on top of the digital video signal.

By the way, if the occupied bands of the digital video signal and the digital audio signal are far apart, it is possible to obtain the desired signal by filtering the reproduced signal, but consider cases where the two signals are close to each other or overlap. Therefore, it is necessary to make the azimuth angle of the rotary head for recording and reproducing digital video signals different from the azimuth angle of the rotary head for recording and reproducing digital audio 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.

(dB)・・・・・・・・・・(1) However, Wnidrack width λ: recording wavelength Therefore, the reproduction output of the digital video signal rotary head is based on the signal recorded in the digital audio signal recording layer 31a. It is possible to set the azimuth angle so that only the digital video signal is played back without picking up the signal from the digital video signal recording layer 31b, and the playback output of the rotary head for digital audio signal plays back only the digital audio signal without picking up the signal from the digital video signal recording layer 31b. For example, by making the azimuth angles of the heads for digital video signals and digital audio signals different by 30 degrees, it is possible to share the band for both signals over a band where crosstalk components due to azimuth loss effects are small with a practical track width. It is.

FIG. 4 is a frequency allocation diagram of an embodiment according to the present invention. In this example, the recordable bandwidth is that of a conventional digital VTR.
This is an attempt to realize PCM audio signal recording without changing the PCM audio signal. In this case, it is fully applicable to conventional digital VTRs in which new PCM audio signals can be recorded without expanding the recordable band of VTR electromagnetic loss determined by the magnetic tape and magnetic head. In FIG. 4, 34 is a QPSK digital audio signal. In the embodiment, the baseband digital audio signal is QPSKed and recorded in a shallow layer above the track on which the digital video signal is recorded, but the modulation method for the digital audio signal may be any other method. It can be applied even if

FIG. 5 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.

This is a so-called rotating two-head helical type VTR in which the magnetic tape 25 runs in the direction of arrow 26 and the rotary cylinder 10 rotates at 1201)z in the direction of arrow 1). In this case, the Digimol video signal output terminal 2 is connected to the digital audio signal head 13.
The digital video signal head 14 contacts the tape first.
contacts the tape before the digital audio signal head 15. For example, the azimuth angles of the digital video signal heads 12 and 14 are set to ±6°, and the azimuth angles of the digital audio heads 13 and 15 are set to ±30°. With this configuration, a digital video signal is first recorded on the track on the magnetic tape, and then a digital audio signal is modulated and recorded in the shallow layer by another azimuth head. Regarding the recording current of each head, the digital video signal head 12.14 is set to an optimum recording current, and the digital audio signal recording head 13.15 is set to a recording current smaller than the optimum recording current.

Here, by making the track width of the digital audio recording head narrower than the track width of the digital video signal head, it is possible to have a stopper effect on the reduction in the reproduction output of the digital video signal. Furthermore, if an azimuth is given to the digital video signal head, high-density recording in a recording format without a guard band is also possible.

Next, we will discuss playback. In FIG. 1, the digital video signal reproduced by the magnetic heads 12 and 14 passes through the digital video signal reproducing amplifier 16, reaches the code decoder 19, undergoes error correction and jitter absorption, is decoded into the original video signal, and passes through the LPF 21. Then, the signal is outputted from the video signal output terminal 23. At the same time, the magnetic head 13.15
The reproduced digital audio signal also reaches the digital audio signal reproducing amplifier 17, where error correction and jitter absorption are performed, and then decoded to the original audio signal, which is outputted from the audio signal output terminal 24 via the LPF 22.

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 digital video signal.

In the embodiment, a case has been described in which a video signal and an audio signal are each converted into a digital signal of one channel and recorded and played back, but it is also possible to convert a video signal into a two-channel digital signal and record it. It is also possible to record and reproduce channel digital signals.

Furthermore, if the frequencies of the basic clocks of the two-channel digital signals are in an integer ratio relationship, there is an advantage that basic clock reproduction becomes easy, especially when reproducing digital signals.

Effects of the Invention As described in detail above, the present invention is capable of recording a digital audio signal modulated by a head having a different azimuth angle from the recording head of the digital video signal so as to overlap the track on which the digital video signal is recorded. A digital video signal and a digital audio signal can be recorded on a layer and played back separately by heads with different azimuth angles, and even though digital signals such as audio PCM signals are newly recorded, A great advantage is that the image quality of digital video signals hardly deteriorates due to error correction.

Further, while maintaining compatibility with conventional digital VTRs, there is an advantage that the recording density of signals on the magnetic tape can be increased by overlapping recording with azimuth.

The digital audio signal recorded in the shallow layer of the magnetic tape can share the band with the digital 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 audio signal for audio PCM recording, and in that case, the performance of the audio signal in terms of S/N, frequency characteristics, distortion rate, wow, flutter, etc. will be significantly improved compared to analog audio. At the same time, after-recording, which was impossible with conventional deep recording of FM audio, is now possible, and digital video with extremely superior image and sound quality is now possible.
TR can be realized.

In other words, both the digital signal recorded on a conventional track and the digital signal superimposed on the shallow part of the track are reproduced and decoded by error correction, and the quality of the decoded signal is extremely faithful to the input signal. can.

[Brief explanation of the drawing]

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, FIG. 2 is a recording track pattern diagram for explaining a conventional example, and FIG. 3 is a diagram for explaining the basic principle of the present invention. FIG. 4 is a diagram showing the recording state in the depth direction of the magnetic layer, FIG. 4 is a graph showing frequency allocation of the device to which the present invention is applied, and FIG. 5 is a configuration diagram of the magnetic head group. 10...Rotating cylinder, 1)...Rotating cylinder rotation direction, 12.14...Digital video signal recording head, 13.15...Digital audio signal Recording head, 25...magnetic tape,
26...Magnetic tape running direction, 27...
・Magnetic head running direction, 28...Track pitch, 29...Track width, 30...Guard band, 3I...Magnetic tape magnetic layer, 31
a...Digicle audio signal recording layer, 31b...
...Digital video signal recording layer, 31c...Non-recording layer, 32...Tape base, 33...
...Digital video signal frequency spectrum, 34...
...Digital audio signal frequency spectrum. Name of agent: Patent attorney Toshio Nakao (1 person) Figure 3 Figure 4 夙う 朕 (NHK) Figure 5

Claims (8)

[Claims] (1) A second magnetic head having a different azimuth angle from that of the first magnetic head records a second digital signal in an overlapping manner on the track on which the first digital signal was recorded by the first magnetic head. Characteristic magnetic recording and reproducing method. (2) The first digital signal and the second digital signal are each a signal obtained by dividing the third digital signal into two channels.
1) The magnetic recording and reproducing method described in section 1). (3) The magnetic recording and reproducing method according to claim (2), wherein the third signal is a digital signal obtained by converting a video signal into a digital signal. (4) A patent characterized in that the first digital signal and the second digital signal are digital signals obtained by converting two or more channels of digital signals into two channels of the first digital signal and the second digital signal. A magnetic recording and reproducing method according to claim (1). (5) The magnetic recording and reproducing method according to claim (1), wherein the first digital signal and the second digital signal are signals obtained by converting a video signal and an audio signal into digital signals, respectively. . (6) The magnetic recording and reproducing method according to claim (1), wherein the basic clock frequency during recording and reproducing of the first digital signal and the second digital signal is an integer ratio. (7) The magnetic recording and reproducing method according to claim (1), wherein the track width of the second magnetic head is narrower than the track width of the first magnetic head. (8) The magnetic recording and reproducing method according to claim (1), wherein the first digital signal does not have a guard band in which no signal is recorded in the recording track pattern.