JPH0792893B2 - Magnetic recording method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording / reproducing apparatus such as a video tape recorder, and more particularly to a magnetic recording suitable for frequency-modulating a video signal and frequency-multiplexing and recording it on the same track of a magnetic tape. It is about the method.

2. Description of the Related Art In a conventional magnetic recording device, for example, a rotary head type video tape recorder (hereinafter referred to as VTR), frequency modulation and frequency multiplexing techniques are used as effective means for recording a video signal.

For example, the color under method, which is widely used in home VCRs (eg National Technical Report Vol. 19, No.
3 P206-P214), the video signal is separated into a luminance signal and a carrier color signal, the luminance signal is frequency-modulated (FM), the color signal is converted to a low frequency band, and the magnetic tape is arranged by the frequency arrangement as shown in FIG. A rotary magnetic head is used to record a signal for each field on the upper track. It can be said that this color under method is an excellent method in that it effectively uses a limited recording band as a home VTR, but it has one major problem that limits its performance.

An electromagnetic conversion system consisting of a magnetic tape and a head has non-linearity that can be expressed by an odd function that is symmetrical with respect to the origin, and produces third-order distortion and other odd-order distortion. FM to such an electromagnetic conversion system
When a signal in which the wave and the low-frequency conversion carrier are frequency-multiplexed is applied, a cross-modulation moire component is generated between both signals. Of the intermodulation moiré components, the main problem component in the band is f _F ± 2f _C ...... (1) f _F ; FM carrier frequency f _C ; Low-frequency conversion color subcarrier frequency, which is the FM When demodulated, it becomes a 2f _C component and mixes into the luminance signal, causing mesh-like interference fringes on the playback screen, which is unsightly. In order to reduce this interference, in the color under method, the frequency of the low-frequency conversion color subcarrier is selected as 1/4 line offset, and the components mixed in the FM demodulated luminance signal are
1/2 line offset is used to utilize the visual reduction effect. Also, it is known that the 2f _C intermodulation moiré component mixed in the luminance signal is proportional to the square of the mixing level of the low-frequency conversion subcarrier, so that the moiré interference does not become a problem on the playback screen in practice. , The recording level of the low frequency conversion subcarrier is determined. Since the S / N of the color signal in the color under system depends on the recording level of the low frequency conversion subcarrier, the S / N of the color signal is limited.
In the color under system in which the FM wave and the low-frequency conversion color signal are frequency-multiplexed and recorded in this way, it is necessary to select a low color signal recording level within a range where the intermodulation moiré component generated in the electromagnetic conversion system does not cause a visual problem. Therefore, the S / N of the color signal was poor, which was the biggest problem in the image quality of the color under system.

As a second example of FM frequency multiplex recording of video signals,
Some are aimed at high image quality such as VTR. (For example, National Technical Report Vol.28, No.3 P59-75) The luminance signal and the chrominance signal are recorded on separate channels using two tracks on the magnetic tape as shown in FIG. FM is applied to the luminance channel, and two chrominance signals are subjected to FM and recorded on the color channel by frequency multiplexing.
In this case, since the luminance channel FM-records only the luminance signal, it is possible to record and reproduce a luminance signal in a wider band than the color under system, and there is no interference due to intermodulation with the color signal. In addition, since the color channel records the color signal by FM, it is possible to record and reproduce with good S / N. However, due to the non-linearity of the electromagnetic conversion system, both FM signals of the color channels (Q-FM, IF
Intermodulation interference occurs between M). Therefore Q-FM and I-FM
Must be placed with an appropriate frequency interval, and the recording levels of both FM waves must also be set in consideration of the intermodulation level, resulting in poor frequency band utilization efficiency and S / N limitation. There was a problem such as receiving.

Problems to be Solved by the Invention When recording a video signal using frequency modulation and frequency multiplexing technology in a conventional VTR as described above, cross-modulation moire due to non-linearity of the electromagnetic conversion system causes a large deterioration in image quality. Therefore, when trying to avoid it, there were major problems such as poor recording efficiency and insufficient S / N.

Therefore, an object of the present invention is to significantly reduce the occurrence of intermodulation components between multiplexed signals when recording a frequency multiplexed signal containing a frequency modulated wave using a magnetic recording medium,
An object of the present invention is to provide a magnetic recording method capable of easily realizing high-performance recording / reproducing without limiting the band utilization efficiency and the recording level.

Means for Solving the Problems A magnetic recording method of the present invention separates a video signal into a luminance signal and a carrier color signal, frequency-multiplexes a frequency-modulated luminance signal and a low-frequency-converted carrier color signal, and applies a high frequency bias. The recording signal is applied to supply the recording signal to the magnetic recording head, and recording is performed on the same track on the magnetic tape.

In the magnetic recording method of the present invention, the color signal of the video signal is formed into two color difference signals, the two color difference signals are frequency-modulated and frequency-multiplexed, and a high-frequency bias is applied to the recording signal to the magnetic recording head. It is not supplied, but is recorded on the same track on the magnetic tape.

Action High-frequency bias in magnetic recording has the effect of improving the non-linear distortion of the electromagnetic conversion system. This is effective even when the video signal is handled because the high-frequency bias frequency is recognized even at several tens of MHz. Therefore, if a high-frequency bias is used to record a frequency-multiplexed signal of multiple different types of signals including frequency-modulated signals, the intermodulation moire between the two signals will not be high-frequency bias because the input / output relationship of the electromagnetic conversion system is close to a straight line Compared with the case of direct recording in, the amount is significantly reduced.

Examples Examples of the present invention will be described below with reference to the drawings. FIG. 1 is a rotary head type which is an embodiment of the present invention.
It is a figure which shows the video signal recording frequency allocation of VTR. Among the video signals, the carrier color signal 1 is converted into the low frequency band and occupies the band shown in the figure, and the frequency-modulated FM luminance signal 2 is recorded using the band shown in the figure. The band used for these video signals is the same band as the color VTR which has been widely used in the past. Now, in the color under system of this type, as described above, the cross modulation based on the non-linearity of the electromagnetic conversion system is a problem. FIG. 1 shows that a high-frequency bias 3 is applied to record the video signal in order to reduce the cross modulation. High-frequency bias in magnetic recording is a technique commonly used in audio tape recorders, etc., and electromagnetic recording is performed by using the linear region of the hysteresis loop instead of leaving residual magnetization in the non-linear region of the initial magnetization curve. This is a recording method that can significantly improve the nonlinear distortion of the system. However, in recording video signals,
High frequency bias recording is used in that the DC component is essentially transmitted and that the FM luminance signal 2 has already acted as a high frequency bias for recording the low frequency conversion carrier color signal 1 in the color under system. Didn't. In this example, focusing on the fact that the high-frequency bias is effective in reducing nonlinear distortion even in the high-frequency region of several tens of MHz,
A common high frequency bias (about 30 MHz) is applied to the FM luminance signal 2 and the low-frequency conversion carrier color signal 1 to bring the characteristics of the electromagnetic conversion system close to a straight line and reduce the intermodulation moiré between both signals. As a result, cross-modulation moire mixed in the demodulated luminance signal is significantly reduced, and a high-quality luminance signal is reproduced.
Further, since the cross-modulation component is small, the recording level of the low-frequency conversion carrier color signal 1 can be set higher than that of the conventional FM luminance signal, and the S / N of the color signal can be improved.
The recording current value of the luminance signal can be smaller than the conventional value due to the bias effect.

FIG. 2 is a circuit diagram of a recording system main part circuit according to an embodiment of the present invention. In the figure, a color video signal including a luminance signal and a carrier color signal is applied to a terminal 4. This color video signal has a low pass filter (LPF) 5 and a band pass filter (B
The PF) 8 separates the luminance signal and the carrier color signal. The luminance signal output from the low-pass filter 5 is FM-modulated by the FM modulator 6, band-limited by the high-pass filter (HPF) 7 so as to include the lower sideband, and then provided to the combiner 11. The carrier color signal frequency converter 9 and the low-pass filter 10 which are the outputs of the band pass filter 8 frequency-convert the frequency of the FM luminance signal so that it is lower than the lower side band of the FM luminance signal, and the resultant signal is added to the synthesizer 11. The FM intensity signal and the low-frequency converted carrier color signal are input to the synthesizer 11 in such a form that they occupy separate bands, and both signals are frequency-multiplexed and amplified by the recording amplifier 12, Entered in 13. On the other hand, a signal which gives a high frequency bias magnetic field generates a frequency corresponding to several times the maximum frequency of the recording signal in the bias oscillator 15, is input to the synthesizer 13 amplified by the amplifier 14, and the frequency allocation shown in FIG. Will be realized. The frequency multiplexed signal superimposed on the high frequency bias by the synthesizer 13 is given to the rotary head 16 and recorded on the video track on the magnetic tape 17. The signal thus recorded can be reproduced as a video signal by passing through a reproduction system similar to that used conventionally. The reproduction signal level recorded by applying a high frequency bias is slightly different from that of conventional recording, but the luminance signal passes through the limiter and the carrier color signal passes through the automatic chroma level control (ACC). Can be played back as is, and performance can be improved while maintaining compatibility with tapes.

FIG. 3 is a diagram showing a video signal recording frequency allocation of a 2-channel color signal FM multiplex system which is another embodiment of the present invention. The luminance signal of the video signal is frequency-modulated and recorded in the luminance signal channel 21, and the chrominance signal is frequency-modulated for each of the two color difference signals, frequency-multiplexed as indicated by 22 and 23, and the high-frequency bias 24 is superimposed and recorded. To be done. Since two FM waves 22 and 23 are frequency-multiplexed in the color signal channel, if recorded as it is, the intermodulation moiré component between both signals will mix in both signal bands and cause interference, but recording by applying a high frequency bias. By doing so, the linearity of the electromagnetic conversion system is improved, so that the generation of intermodulation components between both signals is significantly suppressed.
Therefore, it is not necessary to arrange the two FM-generated color signals at intervals, and by using them, the color signal band can be made wider and the FM deviation can be increased to improve S / N. it can. It is also possible to record another signal such as an audio signal that has been frequency-modulated or code-modulated in the frequency region 25 generated by arranging the two color signals close to each other.

FIG. 4 is a circuit diagram of the recording system main part of this embodiment. Terminal
The video signal applied to 26 is separated by a signal separator 27 into a luminance signal Y and two color difference signals I and Q. The luminance signal Y is FM-modulated by the FM modulator 28, passes through the recording amplifier 29, and then the rotary head.
It is supplied to 30 and recorded on the luminance signal track of the magnetic tape 40. The color difference signals I and Q are generated by the FM modulator 34 and
The signal is FMed at 31, is input to the combiner 33 through the bandpass filter 35 and the lowpass filter 32, and is frequency-multiplexed. Two
The frequency-multiplexed signal of the two FM waves is passed through the recording amplifier 36 and combined.
It is applied to 37 together with the output of the bias oscillator 38 and is subjected to high frequency bias. The color signal on which the high frequency bias is superimposed is supplied to the head 39 and recorded on the color signal track of the magnetic tape 40. The reproduction can be realized with almost the same structure as the reproduction channel of the conventional 2-channel color signal FM multiplex system. In this way, if a high frequency bias is introduced into the recording of the frequency multiplexed signal of two FM waves, the band utilization efficiency and the performance can be improved.

EFFECTS OF THE INVENTION As is apparent from the above description, according to the present invention, a plurality of heterogeneous signals including a frequency-modulated signal are frequency-multiplexed and a high frequency bias is applied to supply a recording signal to a magnetic recording head. Since the different signals are frequency-multiplexed and recorded on the same track on the magnetic tape, the intermodulation component between the plural recorded signals can be made extremely small by the high frequency bias effect, and the moiré interference by itself. Etc. can be reduced. Further, since the intermodulation component is small, it is not necessary to take special frequency allocation to avoid intermodulation moire, and the band utilization efficiency is improved. As a result, the recording method has an excellent feature that not only the bandwidth of the recording signal can be expanded and the S / N can be improved, but also another signal can be recorded.

[Brief description of drawings]

FIG. 1 is a frequency allocation diagram according to an embodiment of the present invention, FIG. 2 is a configuration diagram of a recording system main part thereof, FIG. 3 is a frequency allocation diagram according to another embodiment of the present invention, and FIG. FIG. 5 and FIG. 6 are schematic diagrams of the main part of the recording system, and are frequency allocation diagrams of the color under system used in the conventional home VTR and the two-channel color signal FM multiplex recording system used in the commercial VTR. Is. 1 ... Low-pass conversion carrier color signal, 2 ... FM luminance signal, 3 ...
High frequency bias, 15 …… bias oscillator, 14 …… bias amplifier, 13 …… synthesizer, 21 …… FM luminance signal, 22 …… FM
Color signal (I), 23 ... FM color signal (Q), 24 ... high frequency bias, 38 ... bias oscillator, 37 ... synthesizer.

Claims (2)

[Claims] 1. A video signal is separated into a luminance signal and a carrier color signal, a frequency-modulated luminance signal and a low-frequency-converted carrier color signal are frequency-multiplexed, and a high-frequency bias is applied to supply a recording signal to a magnetic recording head. A magnetic recording method characterized in that recording is performed on the same track on a magnetic tape. 2. A color signal of a video signal is shaped into two color difference signals, the two color difference signals are frequency-modulated and frequency-multiplexed, and a high frequency bias is applied to supply the recording signal to a magnetic recording head. None, a magnetic recording method characterized by recording on the same track on a magnetic tape.