JPS63209003A - Magnetic recording method - Google Patents

Abstract

PURPOSE:To decrease the occurrence of cross modulation component between multiple signals by multiplexing plural different kinds of signals including frequency-modulated signals in terms of frequency and impressing a high frequency bias so as to supply a recording signal to a magnetic recording head. CONSTITUTION:A color video signal is separated to a luminance signal and a carriage chrominance signal by a low pass filter 5 and a band-pass filter 8 and FM-modulated luminance signal and the carriage chrominance signal converted in terms of low pass are inputted in a synthesizing unit 11 with respectively occupying separate bands. Then both signals are multiplexed in terms of frequency and amplified in a recording amplifier 12 to be inputted in a synthesizing unit 13. Meanwhile, a signal which gives a high frequency bias magnetic field generates the frequency equal to several fold frequency of the maximum frequency of the recording signal in a bias oscillator 15, which is amplified in an amplifier 14 and inputted in the synthesizing unit 13. The frequency multiplexed signal superposed on the high frequency bias is given to a rotary head 16 and recorded in a video track on a magnetic tape 17. Thus, cross modulation more between both signals can be remarkably decreased since the input/ output relation of an electromagnetic conversion system becomes nearly linear.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a magnetic recording/reproducing apparatus such as a video tape recorder, and particularly to a magnetic recording apparatus suitable for frequency modulating a video signal and recording it on the same track of a magnetic tape by frequency multiplexing. It is about the method.

2. Description of the Related Art Conventional magnetic recording devices, such as rotary head video tape recorders (hereinafter referred to as VTRs), use frequency modulation and frequency multiplexing techniques as effective means for recording video signals.

For example, the color under one type (for example, National Technical Revo), which is often used in home VTRs, Vol.
, 19. In Na 3 P2O6-P214), the video signal is separated into a luminance signal and a carrier color signal, and the luminance signal is frequency modulated (FM) L, and the color signal is low frequency converted and magnetically modulated using the frequency arrangement shown in Figure 5. A rotating magnetic head is used to record a signal for each field on a track on the tape. Although this color under-one type method can be said to be an excellent method in that it makes effective use of the limited recording band for home VTRs, it has one major problem that limits its performance.

An electromagnetic transducer system consisting of a magnetic tape and a head has nonlinearity that can be expressed as an odd function symmetric about the origin, and produces odd-order distortion including third-order distortion. F in such an electromagnetic conversion system
When a signal obtained by frequency multiplexing the M wave and the low-frequency conversion carrier wave is applied, a cross-modulation moiré component is generated between the two signals. Among the cross-modulation moiré components, the component that is mainly problematic within the band is f, ±2fc ・−・・−−−−−
-(1) fr; FM carrier frequency fc; This is the frequency of the low-pass conversion color subcarrier, and when it is FM demodulated, it becomes a 2fc component and is mixed into the luminance signal, causing mesh-like interference fringes on the playback screen. It becomes unsightly. In order to reduce this interference, in the color under system, the frequency of the low-pass conversion color subcarrier is selected to be two lines offset, so that the component mixed into the FM demodulated luminance signal is two lines offset, and the visual It takes advantage of the mitigation effect. In addition, the 2fc cross-modulation moiré component mixed into the luminance signal is the 2nd level of the mixing level of the low-frequency conversion subcarrier.
It is known that the recording level of the low-frequency conversion subcarrier is determined so that moiré interference does not become a problem on the playback screen. Since the S/N of the color signal in the color under one-sided system depends on the recording level of this low frequency conversion subcarrier, the S/N of the color signal is limited. In the color under one-sided system where FM waves and low-frequency conversion color signals are frequency-multiplexed and recorded in this way, the recording level of the color signal is selected to be low enough that the cross-modulation moiré components generated in the electromagnetic conversion system do not pose a visual problem. As a result, the S/N of the color signal was poor, and the image quality of the color under one-sided system was also a major problem.

A second example of FM frequency multiplexing recording of video signals includes those aimed at high image quality, such as commercial VTRs. (For example, National Technical Report Vol. 2B, k 3
P59-75) As shown in Figure 6, the luminance signal and color signal are recorded in separate channels using two tracks on a magnetic tape, and the luminance signal is FM'd and recorded on the luminance channel.
As for the color signal, two color difference signals are each subjected to FM and recorded in a color channel by frequency multiplexing. In this case, since the luminance channel performs FM recording of only the luminance signal, it is possible to record and reproduce a wider band luminance signal than with the color under system, and it is not interfered with by cross-modulation with the color signal. Furthermore, since the color channel records color signals on an FM basis, it has the characteristic of being able to record and play with a good S/N ratio. However, due to the nonlinearity of the electromagnetic conversion system, cross-modulation interference occurs between both FM signals (Q-FM, I-FM) of the color channel. Therefore, Q-FM and I-FM must be placed with an appropriate frequency interval, and the recording level of both FM waves must also be set taking into consideration the cross-modulation level, thereby ensuring efficiency in frequency band use. There were problems such as poor signal quality and limited S/N.

Problems to be Solved by the Invention As described above, when attempting to record video signals using frequency modulation and frequency multiplexing techniques in a conventional VTR, cross-modulation moiré due to the nonlinearity of the electromagnetic conversion system causes a significant deterioration in image quality. Therefore, if attempts were made to avoid this, there were serious problems such as poor recording efficiency and inability to obtain a sufficient S/N ratio.

Therefore, an object of the present invention is to significantly reduce the occurrence of cross-modulation components between multiplexed signals when recording frequency multiplexed signals including frequency modulated waves using a magnetic recording medium.
It is an object of the present invention to provide a magnetic recording method that can easily realize high-performance recording and reproduction without imposing restrictions on band utilization efficiency or recording level.

Means for Solving the Problems The magnetic recording method of the present invention frequency-multiplexes a plurality of different signals including frequency-modulated signals, applies a high-frequency bias, and supplies a recording signal to a magnetic recording head. This system is configured to frequency multiplex record different types of signals on the same track on a magnetic tape.

The high frequency bias in operational magnetic recording has the effect of improving nonlinear distortion in the electromagnetic conversion system, and this effect is observed even when the high frequency bias frequency reaches several tens of MHz, so it is also effective when handling video signals. Therefore, if a frequency-modulated signal is frequency-multiplexed with multiple dissimilar signals remaining, and recorded using a high-frequency bias, the input-output relationship of the electromagnetic conversion system is close to a straight line, so the cross-modulation moiré between both signals will be eliminated by the high-frequency bias. This is a significant reduction compared to the case of direct recording without any.

EXAMPLES Hereinafter, examples of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing the video signal recording frequency allocation of a rotating head type VTR which is an embodiment of the present invention. Among the video signals, the carrier color signal 1 is low-pass converted and occupies the illustrated band, and the frequency-modulated FM luminance signal 2 is recorded using the illustrated band. The band used for these video signals is the same band as that of color VTRs, which have been widely used in the past. Now, as mentioned above, in this type of color under one-sided system, there is a problem of cross modulation based on the nonlinearity of the electromagnetic conversion system. FIG. 1 shows that the video signal is recorded by applying a high frequency bias 3 in order to reduce this cross-modulation.

High-frequency bias in magnetic recording is a technology commonly used in audio tape recorders, etc., and uses 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 conversion system. However, in recording video signals, essentially the DC component must be transmitted 1°, and color undercoding is one-sided. In □゛, high-frequency bias recording is not used because the FM luminance signal 2 already acts as a high-frequency bias on the low-frequency conversion carrier color signal 1, and so on.
6. In this example, we focused on the fact that the high frequency bias is effective in reducing nonlinear distortion even in the high frequency region of several tens of M Itz, and we applied a high frequency bias (approximately 30 M llz) is applied,
This is to bring the characteristics of the electromagnetic conversion system closer to a straight line and reduce cross-modulation moiré between both signals. As a result, cross-modulation noise mixed into the demodulated luminance signal is significantly reduced, and a high-quality luminance signal is reproduced.

Furthermore, 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. Note that 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 main part of a recording system 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 is separated into a luminance signal and a carrier color signal by a low pass filter (LPF) 5 and a band pass filter (BPF) 8. The luminance signal that is the output of the low-pass filter 5 is subjected to FM modulation by an FM modulator 6, band-limited by a bypass filter (HPF) 7 so as to include the lower sideband, and then applied to a synthesizer 1). The carrier chrominance signal, which is the output of the bandpass filter 8, is frequency-converted by a frequency converter 9 and a low-pass filter 10 so that the frequency is lower than the lower band of the FM luminance signal, and is applied to the synthesizer 1). The FM luminance signal and the low-frequency converted carrier chrominance signal are input to the synthesizer 1) in a form that each occupies separate bands,
Both signals are frequency multiplexed and amplified by a recording amplifier 12,
It is input to the synthesizer 13. - The signal that provides the force cylinder frequency bias magnetic field is generated by the bias oscillator 15 at a frequency equivalent to several times the maximum frequency of the recording signal, amplified by the amplifier 14 and input to the synthesizer 13, and then generated at the frequency shown in FIG. Allocation is realized. The frequency multiplexed signal superimposed on the high frequency bias by the synthesizer 13 is applied to the rotary head 16 and recorded on a video track on the magnetic tape 17.

A video signal can be reproduced from the signal recorded in this manner by passing it through a reproduction system similar to that conventionally used. Note that the playback signal level recorded by applying a high frequency bias is slightly different from that of conventional recording, but since the luminance signal passes through a limiter and the m color feed (K signal passes through automatic chroma level control (ACC)), it is different from conventional recording. It is possible to playback using the same playback system as is, and performance can be improved while maintaining tape compatibility.

FIG. 3 is a diagram showing the video signal recording frequency allocation of two-channel color signal FM multiplexing method according to another embodiment of the present invention. Among the video signals, the luminance signal is frequency-modulated and recorded in the luminance signal channel 21, and the color signal is recorded by frequency-modulating two color difference signals, frequency-multiplexing them as shown at 22 and 23, and superimposing a high-frequency bias 24. be done. The color signal channel has two FM waves 22 and 23 frequency-multiplexed, so if recorded as is, cross-modulation moiré components between both signals will mix into both signal bands and cause interference, but recording can be done by applying a high-frequency bias. By doing so, the linearity of the electromagnetic conversion system is improved, and the generation of cross-modulation components between the two signals can be significantly suppressed. Therefore, there is no need to space the two FM color signals, and if you use this, you can widen the color signal band or increase the FM deviation to improve the S/N. can. It is also possible to record other signals, such as frequency-modulated or code-modulated audio signals, in the frequency region 25 created by arranging two color signals close to each other.

FIG. 4 is a circuit diagram of the main part of the recording system of this embodiment. The video signal applied to the terminal 26 is separated by a signal separator 27 into a luminance signal Y and two color difference signals 2 and Q. The luminance signal Y is FM'd by the FM modulator 28, supplied to the rotary head 30 via the recording amplifier 29, and recorded on the luminance signal track of the magnetic tape 40. The color difference signals (1) and (Q) are FM'd by FM modulators 34 and 31, respectively, and input to a synthesizer 33 via a band pass filter 35 and a low pass filter 32, where they are frequency multiplexed. The frequency multiplexed signals of the two FM waves are applied to the synthesizer 37 together with the output of the bias oscillator 38 via the recording amplifier 36, and are biased at a high frequency. The color signal superimposed with this high frequency bias is sent to the head 39.
and recorded on the color signal track of the magnetic tape 40. Reproduction can be realized with almost the same configuration as a conventional two-channel color signal FM multiplexing reproduction circuit. in this way,
By introducing a high frequency bias into the recording of the frequency multiplexed signal of two FM waves, it is possible to improve band utilization efficiency and performance.

Effect of the invention As is clear from the above description, the present invention has the following features.

A configuration in which a plurality of different types of signals including frequency-modulated signals are frequency multiplexed, a high frequency bias is applied to supply recording signals to a magnetic recording head, and different types of signals are frequency-multiplexed recorded on the same track on a magnetic tape. Therefore, cross-modulation components between a plurality of recorded signals can be made extremely small due to the high frequency bias effect, and moiré disturbance etc. can be reduced by itself. Furthermore, since the cross-modulation component is small, there is no need to take special frequency allocation to avoid cross-modulation moiré, improving band utilization efficiency. As a result, the recording signal bandwidth can be expanded and S
This recording method has excellent features such as not only being able to improve /N but also being able to record other signals.

[Brief explanation of the drawing]

FIG. 1 is a frequency allocation diagram according to one embodiment of the present invention, FIG. 2 is a configuration diagram of main parts of the recording system, FIG. 3 is a frequency allocation diagram according to another embodiment of the present invention, and FIG. 4 is a diagram of frequency allocation according to another embodiment of the present invention. The main part configuration diagram of the recording system, Figures 5 and 6, shows the frequency allocation of the color under one type used in conventional home VTRs and the two-channel color signal FM multiplex recording type used in professional VTRs. It is a diagram. 1...Low frequency conversion carrier color signal, 2...F
M luminance signal, 3...High frequency bias, 15...
...Bias oscillator, 14...Bias amplifier, 13...Synthesizer, 21...FM
g degree signal, 22...FM color signal (1), 23.
...FM color signal (Q), 24...High frequency bias, 38...Bias oscillator, 37...
...Synthesizer. Name of agent: Patent attorney Toshio Nakao Figure 1/! 'I-JL (barrel Hχ) Figure 2 Figure 3

Claims (3)

[Claims] (1) Frequency multiplexing a plurality of different signals including frequency modulated signals, applying a high frequency bias to supply the recording signal to the magnetic recording head, and recording the plurality of signals on the same track on the magnetic tape. A magnetic recording method characterized by: (2) The video signal is separated into a luminance signal and a carrier chrominance signal, the frequency-modulated luminance signal and the low-frequency-converted carrier chrominance signal are frequency-multiplexed, and a high-frequency bias is applied for recording. The magnetic recording method according to scope (1). (3) Shaping the color signal of the video signal into two color difference signals,
The two color difference signals are frequency-modulated and frequency-multiplexed,
The magnetic recording method according to claim 1, wherein recording is performed by applying a high frequency bias.