JPS6019190B2 - Magnetic recording and reproducing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic recording and reproducing method, and more particularly to an improvement in a reproduction signal processing method in a low frequency conversion recording and reproducing method for color television signals.

In recent years, most home magnetic recording and reproducing apparatuses (hereinafter referred to as VTRs) use a low frequency conversion recording and reproducing method.

This separates an NTSC color television signal into a luminance signal and a carrier chrominance signal, and converts the carrier chrominance signal into a low frequency signal of, for example, 767 KHz, as the first signal, and the luminance signal as an angle-modulated signal, for example, as a second signal that is FM-modulated. and create the first signal.
The signal and the second signal are combined and recorded by a video head. In this method, the carrier color signal frequency recorded is lower than that of the direct FM method used for broadcasting or industrial purposes, so the low frequency conversion method is less likely to cause time axis fluctuations (hereinafter referred to as jitter) of the carrier color signal. It is a fraction of the cost, and relatively stable color reproduction is possible with a simple circuit. However, this low-frequency conversion method is subject to band limitations due to the separation of the luminance signal and the carrier color signal, and although there are problems such as low resolution, it has sufficient bandwidth for home use. Conventionally, the carrier color signal converted to a low frequency band may deteriorate the response characteristics of the APC circuit (automatic phase control circuit) of the reproduction processing circuit due to distortion of the tape head or the generation of noise mainly caused by the tape head. VT due to incorrect control
There were problems such as poor residual jitter (color convergence) and color unevenness in the R output.

However, the distortion and noise of only the color signal causes color unevenness in only a portion, and does not cause any problems on the screen. However, the reproduced burst signal of the low-frequency conversion carrier color signal has a wave number of only about 1.5 to 2.0 cycles, and is affected by noise from the tape head and distortion of the electromagnetic conversion system.

The affected burst signal is further limited in coverage by filters in the color signal processing circuit (for example, filters 15, 20, 26, etc. in FIG. 2), so the envelope of the burst signal has a round shape, and Near the beginning and end of the burst signal, there is a transient due to the deterioration of the group delay characteristic of the filter, and the phase is no longer the original one. Therefore, due to these various factors, residual jitter occurs in the APC circuit in the VTR, causing color unevenness and hue shift from line to line. Moreover, a VTR like this
If the output is input to a monitor television receiver or a general color television receiver, the burst gate circuit of the television receiver will extract the burst signal. Since the burst gate pulse is created from the signal, the position of the burst gate pulse slightly changes left and right relative to the position of the burst signal, and the envelope of the burst signal is rounded as mentioned above, so the burst signal amplitude changes. Alternatively, burst signals with different phases due to the influence of the filter are extracted, and the APC malfunctions due to the influence of noise, causing problems such as large hue unevenness and hue shift on the screen. Moreover, since the APC circuits of VTRs and television receivers exhibit complexly different responses, there is a drawback that hue unevenness and hue shift are serious. The present invention has been made in view of the above-mentioned points, and has a very simple configuration, in which a burst signal of 3.58M used for jitter correction is used for the burst signal of the VTR playback output.
By replacing the crystal oscillator output with a stable ratio with a new burst signal obtained by gating, a burst signal of constant amplitude and constant phase of 7 to 8 cycles is formed.
To provide a magnetic recording and reproducing method that eliminates problems such as the APC circuit of the television receiver being affected by noise and distortion, and that allows stable images without color unevenness or hue unevenness to be obtained on the television screen. It is something to do. An embodiment of the present invention will be described below based on the drawings.

In FIG. 1, an NTSC color television signal input from an input terminal 1 is separated into a luminance signal and a carrier color signal by a low-pass filter 2 and a high-pass filter 6. The separated luminance signal is subjected to FM modulation by an FM modulator 3, and the FM spectrum of the band used for recording the carrier color signal is removed.It is passed through a pass filter or trap 4.
The signal is amplified by a recording amplifier 5 and added to an adder 11. On the other hand, after the separated carrier color signal is made to a constant level by an automatic gain control circuit AGC7, a crystal oscillator 9 is generated by a frequency converter 8.
The signal is frequency-converted with the output signal of , and passed through a low-pass filter 10 for taking the difference between the two signals to convert it to a low frequency. Here, the carrier color signal frequency converted to low frequency is fs=767K
Let it be Hz. The low frequency converted transport chrominance signal fs and the luminance FM signal are added by an adder 11 and recorded from the video head 12'. In FIG. 2, a signal recorded like the spectrum in FIG. fS is separated, and the separated luminance FM signal is passed through a limiter circuit 16 that removes amplitude fluctuations due to head/tape touch unevenness, head fluctuation, etc., demodulated by an FM demodulator 17, and applied to an adder 22.

On the other hand, the separated carrier color signal fS is set to a constant level by the AGC circuit 18, frequency-converted by the frequency converter 19 to an APC output signal, which will be described later, and the band-pass filter 2
0, only the difference frequency is extracted. The extracted carrier color signal (3.58M ratio) becomes a signal from which jitter has been removed. Next, the APC circuit will be explained. AGC circuit 1 8
output and the subcarrier frequency of the standard television signal (3.
The frequency converter 24 converts the output fc of the crystal oscillator 25 (5 Hz), and creates fc+fS using the bandpass filter 26 which takes the sum frequency. A burst gate circuit 27 extracts a burst signal from the output of the bandpass filter 26 and applies it to a phase comparator 28 . On the other hand, the output of the crystal oscillator 25 and the output of the variable frequency oscillator 30 (oscillation frequency fS) are added by the frequency converter 29, a continuous wave is created by the bandpass filter 31 which takes the sum frequency, and the continuous wave is combined with the burst gate. If the phase of the reproduced burst signal output from the circuit 27 is compared with the reproduced burst signal by the phase comparator 28, and the variable frequency oscillator 30 is controlled by the error signal, a continuous wave (output 31) whose phase is synchronized with the reproduced burst signal is created. . The output of this bandpass filter 31 is input to the frequency converter 19. For example, if the frequency of the reproduced carrier color signal is fs
+△f (Af is the jitter component), the APC output is f
c+fs+Δf, and when the difference between both signals is taken, it becomes a carrier color signal having a frequency fc that matches the output frequency fc of the crystal oscillator 25 (see Section 3), and the jitter component Δf has been removed. As mentioned earlier, the reproduced burst signal may be affected by tape head distortion or noise, and furthermore, the noise or distortion of the output burst signal or the roundness due to band limitation will also have an adverse effect on the receiver's APC circuit. Therefore, in the present invention, only the burst signal of the jitter-corrected carrier color signal is removed by the burst removal circuit 21,
Add to adder 22. Further, the output of the crystal oscillator 25 is phase-shifted by a phase shifter 32, and a necessary period is extracted by a gate circuit 33 and inputted to the adder 22 as a new burst.
The adder 22 adds the luminance signal, the new burst signal, and the carrier chrominance signal from which jitter and the burst signal have been removed, and outputs the sum to the video output terminal 23. Here, the phase shifter 32 does not necessarily have to be provided. It goes without saying that the mixing level of the new burst can be varied. That is, now the frequency of the output of the frequency converter 18 is , the phase is ◇, the frequency of the output of the oscillator 25 is 2, the phase is J2, the frequency of the output of the oscillator 30 is 3, and the phase is ◇. 3
Assuming that, the frequency of the output of the frequency converter 24 is
10/2, phase difference, 10◇2, and the frequency of the output of the frequency converter 29 becomes 2/10/3, phase difference 2, 1003.

On the other hand, since the APC circuit including the phase comparator 28 controls the frequencies and phases of both the outputs of the frequency converters 24 and 29 to match, that is, w, 2 of 10 = 20 of 3, 01 It is controlled so that ○2=○20◇3.
Therefore, of,=3,◇,:J3.

Therefore, the frequency of the output of the frequency converter 19 is (2 of
3-10, ) = 2, which matches the output frequency of the oscillator 25.

Moreover, the phase of the output of the frequency converter 19 is (g2
Ten? 3-J,)=◇2, which matches the phase of the output of the oscillator 25.

Therefore, the output of the oscillator 25 can be replaced by the burst signal in the output of the frequency converter 19.

Figure 4 shows the waveforms of each part, and A is the bandpass filter 2.
0 is the output, 2 is the output of the burst removal circuit 21, and 3 is the waveform of only the carrier color signal output from the adder 22.

As schematically shown in Figure 4A, when passing through the reproduction system of a VTR, the burst signal becomes rounded because the band is generally limited for reasons such as FM carrier (CW) leakage. Moreover, since jitter is not removed from the reproduced luminance signal, the phase of the burst signal may shift slightly due to burst build-up in the APC circuit of the television receiver, but by replacing the reproduced burst signal with a new burst signal, these problems can be resolved. can be easily resolved. As described above, according to the present invention, distortion of reproduction bursts, color unevenness in the horizontal period due to noise, and hue shift are eliminated, and even when the VTR output is input to a monitor television or a general color television receiver, the VTR and the television receiver are not affected. There is no complicated influence on the APC circuit, and the demodulated screen is free of color unevenness, hue shift, etc.

[Brief explanation of drawings]

The drawings show an embodiment of the present invention; FIG. 1 is a block diagram during recording, FIG. 2 is a block diagram during reproduction, FIG. 3 is a recording spectrum, and FIG. 4 is a waveform diagram. 19,.・・・． Frequency converter, 20...Band pass filter, 21...Burst removal circuit,
22...Adder, 24...Frequency converter, 25...Crystal oscillator, 26...Band pass filter, 27...Burst gate circuit, 28...
...Phase comparator, 29...Frequency converter, 30...
...Variable frequency oscillator, 31...Band pass filter, 33...Gate circuit.・Eagle/Eagle 2 figure rji* Fin 4 broadside

Claims (1)

[Claims] 1 Separate a color television signal to be recorded into a luminance signal and a carrier chrominance signal, angle-modulate the luminance signal, frequency convert the carrier chrominance signal to a low frequency band, and convert the angle-modulated luminance signal into the angularly modulated luminance signal. The above-mentioned low frequency conversion carrier color signal is superimposed on the low frequency side and recorded on a magnetic recording medium, and during reproduction, the reproduced angle modulated luminance signal is angularly demodulated to obtain a reproduced luminance signal, and the reproduced low frequency A first signal obtained by converting the frequency of a converted carrier color signal using the output of a fixed oscillator having a subcarrier frequency of a standard television signal and a second signal obtained by converting the frequency of the output of a variable oscillator using the output of the fixed oscillator are compared in phase. , the frequency of the variable oscillator is controlled by a signal corresponding to the phase difference, and the frequency of the reproduced low-frequency conversion carrier signal is converted by the second signal, thereby producing a carrier color signal of the original frequency without time axis fluctuation. After obtaining the subcarrier frequency, the fixed oscillator output of the subcarrier frequency is gated to create a new burst signal, and the burst signal of the carrier color signal, which has become the original frequency, is replaced with this new burst signal. Magnetic recording and reproducing method.