JPS63133788A - Magnetic recording and reproducing device - Google Patents

Abstract

PURPOSE:To obtain a reproduced picture having no moire by linearly or non- linearly controlling the quantity of the attenuation of the prescribed frequency component of a reproduced signal according to the level of the chrominance sub-carrier frequency component of a reproduced signal after an FM demodulation. CONSTITUTION:An FM signal reproduced by a reproducing head 1 is amplified in a head amplifier 2, FM demodulated in a demodualtor 5, and thereafter inputted to an adaptive filter 4 through an LPF 6. The output of the LPF 6 is inputted to a detection circuit 3. The detection circuit 3 is constituted of a BPF for passing the chrominance sub-carrier frequency and a detector and the level of the chrominance sub-carrier frequency component is detected therein. This level signal is applied to the adaptive filter 4 as a control signal and the quantity of the attenuation of the prescribed frequency component is controlled according to said level signal in the adaptive filter 4.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a magnetic recording and reproducing apparatus such as a video tape recorder (VTR).

Conventional technology Video signals such as those used for home use, such as NTS
C-signal VTRs include the color under method, which converts the color signal to a reduced value and then superimposes it with an FM-modulated luminance signal, and the direct FM method, which modulates the video signal as it is by FM.
In addition, there is a component method in which two brightness signals are recorded and reproduced on separate tracks.

Here, in the direct FM method, since the color signal exists in the high range of the video signal frequency, it has a problem that other methods do not have with regard to moiré caused by unnecessary components due to aliasing of the FM sideband during FM modulation and demodulation. There is. Since moiré is well known, its explanation will be omitted.

Problems to be Solved by the Invention In the direct FM system, there was a problem of deterioration of reproduced image quality due to moiré.

Means for Solving the Problems In order to solve the above problems, the present invention provides a method for converting a video signal having a color signal subcarrier frequency fs to a carrier frequency fc.
In a magnetic recording and reproducing device that performs recording and reproducing with M modulation,
During reproduction, a predetermined frequency component f of the reproduced signal after FM demodulation is determined according to the level of the fs frequency component of the reproduced signal after FM demodulation.
The attenuation amount of n is controlled linearly or nonlinearly. Here, the predetermined frequency component element n is fn=|2×fc−nxfsl (however, n=2°3
, 4. 5...).

According to the above-described structure, the present invention reproduces the original signal as it is for a screen having a small color signal of the reproduced video signal, that is, a signal with low color saturation, and reproduces the original signal as it is for a screen having a large color signal, that is, a screen where moiré is usually noticeable. By attenuating unnecessary frequency components that cause moire, a playback screen free of moire can be obtained.

Example Below, regarding a magnetic recording and reproducing device according to an example of the present invention,
This will be explained with reference to the drawings.

FIG. 1 is a block diagram of one embodiment of the present invention. The FM signal reproduced by the reproduction head 1 is amplified by the head amplifier 2, and inputted to the adaptive filter 4 through the demodulator DEM5 and the low-pass filter 6, and is also inputted to the detection circuit 3. Adaptive filter 4 controlled by detection circuit 3
The output is output from the output terminal 7.

Next, the operation will be explained using the spectrum diagram shown in FIG.

When the signal fs is FM modulated with the FM carrier frequency fc, F
As shown in the figure, the M sideband exists at a frequency of lfc±nfsl.In this figure, the signal that becomes a moiré component within the signal band after demodulation is f, = lfc-3fsl.
and fi:+= l 3 f c -3fsl and
i! After Jl, both are considered to become unnecessary components of fn=12fc-3fsl. Therefore, by attenuating these frequency components in the subsequent stage of the demodulator, moiré can be suppressed.

However, it is not desirable to always attenuate the frequency component of fn because it also attenuates the signal component. Therefore, by detecting the level of the color signal frequency fs after demodulation and adaptively determining the attenuation amount of fn in a linear or nonlinear manner according to the level, it is possible to Plays the original signal as is,
For screens with large color signals, that is, screens where moire is usually noticeable, it is possible to obtain a reproduced screen without moire by attenuating unnecessary frequency components that cause moire. Next, a detailed circuit of the detection circuit 3 is shown in FIG. As shown in A, it may be simply configured with a BPF 8 that passes the color signal frequency fS and a detector 9, or as shown in B, the detected output may be compared with a reference level, and the waveform may be shaped before being output. Next, a detailed circuit of the adaptive filter 4 is shown in FIG.

Turn on the trap circuit as shown in FIG. 4A.

A configuration in which it is turned off may be sufficient. It is clear that the resonant frequency of the trap here is the unnecessary frequency fn. Furthermore, in order to perform nonlinear operation in order to minimize the deterioration in image quality, a configuration similar to a commonly used noise canceller is used as shown in Figure 4B, and the limiter's limit range is determined based on the signal from the detection circuit. It is effective to change the value of the mixing coefficient or to change the value of the mixing coefficient. Here, it is clear that the BPF 13 is a filter that passes the frequency fn in order to attenuate it.

Furthermore, in addition to the configuration shown in the embodiment, a low-pass filter may be placed after the adaptive filter, for example.

Further, various types of adaptive filters other than the circuit shown in FIG. 4 can be considered, as long as they attenuate a predetermined frequency relative to the video signal level.

Effects of the Invention As described above, the present invention provides a magnetic recording and reproducing apparatus that performs recording and reproducing by FM modulating a video signal having a color signal subcarrier frequency fs at a carrier frequency fc.
A predetermined frequency component fn of the reproduced signal after FMfi modulation according to the level of the fs frequency component of the reproduced signal of l, tWIHl.
By linearly or nonlinearly controlling the amount of attenuation, it is possible to effectively attenuate unnecessary frequency components that become moiré components and drastically reduce moiré on the playback screen.It is especially effective when used in direct FM VTRs. There is.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a magnetic recording/reproducing device according to an embodiment of the present invention, and FIG. 2 is a block diagram of the same FM according to an embodiment of the present invention.
3 is a detailed block diagram of the detection circuit of FIG. 1, and FIG. 4 is a detailed block diagram of the adaptive filter of FIG. 1. 3...detection circuit, 4...adaptive filter, 5...demodulation circuit! , 8.13...bandpass filter, 9...detector, 10...
... Comparator, 14... Limiter circuit, 15.
... Coefficient circuit, 16 ... Subtractor. Name of agent: Patent attorney Toshio Nakao (1 person) Figure 2 b fl・fc-fs f3' /fc-3・fs/ fn fs fFigure 4

Claims (3)

[Claims] (1) In a magnetic recording and reproducing device that records and reproduces a video signal having a signal frequency fs by FM modulating it with a carrier frequency fc, the reproduction after FM demodulation is performed according to the level of the fs frequency component of the reproduced signal after FM demodulation during reproduction. A magnetic recording/reproducing device characterized in that the amount of attenuation of a predetermined frequency component fn of a signal is controlled linearly or nonlinearly. (2) The magnetic recording and reproducing apparatus according to claim (1), wherein the signal frequency fs is a color signal subcarrier frequency. (3) The predetermined frequency component fn is fn=|2×fc−n
×fs| (where n=2, 3, 4, 5...). The magnetic recording and reproducing apparatus according to claim (1).