JPS5939802B2 - Time axis equalizer control method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control method for a video recording system recorded by channel division using orthogonal transformation, and particularly to a control method for a time axis equalizer used in the system.

The present applicant proposed a system using a Walsh-Hadamard transform circuit as a video recording system based on channel division, and disclosed the technology in Japanese Patent Application No. 49-96302 and others.

The gist of this technique is to divide a video signal into a plurality of channels using a Walsh-Hadamard conversion circuit, narrow the frequency band of each divided channel, and record it on a magnetic tape using a plurality of magnetic heads. To reproduce recorded information, signals are read from the magnetic tape using a plurality of magnetic heads, the time axes of the signals of each channel are equalized, and then a time-series video signal is obtained using a Walsh-Hadamard inverse transform circuit. The time axis equalization described above is necessary to absorb jitter caused by the operation of the mechanical system of the video tape recorder, and a control signal for time axis equalization is inserted in advance into each channel before recording. Now, a drawback of the conventional control method for the time axis equalizer is that the above-mentioned control signal includes a DC component, which causes noise on the reproduced television screen. Therefore, the present invention aims to improve the above-mentioned drawbacks of the conventional technology, and its purpose is to provide a control method for a time axis equalizer that does not generate noise on the playback screen. The purpose is to use a bipolar pulse signal as the signal.

This will be explained in detail below. Note that it is assumed that the transformations referred to in this specification are orthogonal transformations. The present inventors have discovered that in a channel division recording method using the Walsh-Hadamard transform, if a DC component is included in the control signal inserted into each channel, the same DC component will overlap in each divided channel, resulting in a reverse It has been noticed that during conversion, the DC component is converted into large spike-like noise, which greatly impairs the quality of the screen.

For example, in the inverse transformation of the fourth-order Walsh-Hadamard transform, X' = H-1 ・Y and Y (Yl, y2, y3, y4), but if each channel contains a DC component of Δe, then Y-
(y1+ΔE, y2+ΔE, y3+ΔE, y4+Δe)
Therefore, Jτ − ′
＼ ′ becomes.

However, X is a reproduced signal that does not contain noise. As shown in the above equation, a spike-like noise of 4Δe is generated for the signal X,
Moreover, the amplitude is expanded to four times that of the original DC current, greatly degrading the image quality. Therefore, in the present invention, a bipolar pulse that does not include a direct current component is used as a control signal. FIG. 1 is a program diagram of a video recorder according to the present invention, in which a video signal is input from an input terminal 1N, sampled by clock signals CL1 to CL4 for each channel, and each sample value is input to a Hadamard transform circuit H.
It is Hadamard transformed by Control signal Cl is applied to the conversion output.
, C2, C3, and C4 are added, and the signals of each channel are recorded on the magnetic tape T by a magnetic head. The control signal at this time is a bipolar pulse with a waveform as shown in FIG. 2B. FIG. 2A shows the waveform of a conventional control signal and is shown for comparison. A signal recorded on the magnetic tape T is read out by a magnetic head and applied to a time base equalizer TBC. The time base equalizer TBC absorbs jitter in the signals of each channel due to irregularities in the mechanical operation of the video tape recorder, and a PLL (phase lock group) including a variable delay element is provided for each channel. The PLL
By applying a single reference signal to the channels, the time axis of each channel is equalized. The time base equalizer TBC is operated by the aforementioned control signal (FIG. 2B). Time base equalizer TBC
The output is inversely transformed by the Hadamard inverse transform circuit H-1, and a time-series video signal is obtained at the output terminal 0UT. Note that it is also possible to modulate the signals of each divided channel by AM or FM and record them on a magnetic tape, in which case a modulator MOD and a demodulator DEM are inserted as shown by the dotted lines in the figure.

When the signal is modulated, the frequency spectrum becomes as shown in A in Figure 3, and as shown in the figure, a blank B is created in the low frequency region, so it is possible to insert a control signal in the form of an AM or FM wave into this part. It is possible. As described above in detail, in the present invention, since the control signal does not include a DC component, noise does not occur in the inverse conversion output, and therefore, a video output with a high quality screen can be obtained.

[Brief explanation of drawings]

FIG. 1 is a program diagram of a video tape recorder according to the present invention, FIG. 2A is a waveform of a conventional control signal, and FIG.
FIG. B shows a waveform of a control signal according to the present invention, and FIG. 3 shows a frequency vector according to a modification of the present invention. H: Hadamard transform circuit, H-1: Hadamard inverse transform circuit, TBC: time base equalizer, C1 to C4: control signal.

Claims (1)

[Claims] 1. A video signal is divided into a plurality of channels by orthogonal transformation, a control signal is added to each channel, magnetically recorded, and the recording is reproduced to perform time axis equalization between channels using the control signal. A video recording system for converting originally equalized signals of multiple channels into a single time-series video signal, characterized in that the control signal is a bipolar pulse signal. Control method for time axis equalizer.