JPS6027468B2 - Time axis control method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control method for equalizing the time axis of a reproduced signal in a multi-channel recording and reproducing system.

Since it is difficult to directly magnetically record a broadband signal such as a television signal, a method is used in which a rotating head is used or recording is performed by dividing the signal into a plurality of narrowband channels.

The latter is a method in which a wideband signal such as a television signal is divided into a plurality of narrowband channels and recorded using a circuit such as a Hadamard transform circuit. The number of tracks recorded is equal to or less than the number of divided narrowband channels. In this method, if the slit gaps of the recording/reproducing heads of each track are not arranged completely in a straight line, the phase of the reproduced output will shift, giving a large distortion to the synthesized waveform. For example, when the wavelength of the recorded signal is 1 μm, if there is a difference of only 0.5 degrees between the head gaps, a large phase difference of 180° will occur in the reproduced signal.
Even if the allowable value of this phase difference is assumed to be 90, the allowable deviation between the head gaps is only 0.025 degrees of roughness, and such precision cannot be achieved with current machining technology. to solve this problem,
During recording, synchronized control pulses at predetermined time intervals are inserted into each narrowband channel, and a time-intensive control circuit with a variable delay circuit is inserted into the playback circuit, and the variable delay circuit is used to synchronize the control pulses of each channel. A method has been proposed in which the time axis of each channel is electrically equalized by controlling the

Hakama Isho 49-43713 (magnetic recording/reproducing device, filed on April 17, 1920), which was previously proposed by the present applicant, is based on this idea. However, in the secondary time axis control circuit, the axis output of the control pulse from each reproduction channel is
Since this is performed based on the difference in level between the control pulse and the general signal, the level of the general signal must be sufficiently smaller than the level of the control pulse. If this relationship is reversed, the time base control circuit will misidentify a general signal as a control pulse, and the correct time base etc. will not be performed. The fact that the general signal level must be low in this way leads to the disadvantage that the S/N (signal-to-noise ratio) of the signal cannot be increased. Furthermore, since the control pulse has a narrow width and contains many harmonic components, ringing occurs due to the band-limited circuit, which adversely affects the signal. Furthermore, if impulsive noise with abnormally high amplitude occurs in the signal, the noise may be mistaken for a control pulse, resulting in confusion in the equalization operation. Therefore, the present invention aims to improve the above-mentioned drawbacks of the prior art, and its purpose is to
An object of the present invention is to provide a time axis control method that does not reduce the /N and is not affected by impulse noise.

In order to achieve this purpose, the present invention is characterized in that, firstly, it is performed during the vertical blanking period when no initial equalization signal exists, and secondly, after the initial equalization is completed, it is driven by the control pulse of one channel. The control pulse of each channel is centered by the output pulse of the flywheel oscillator, and the equalization operation is continued by the centered control pulse. Examples will be described below with reference to the drawings. FIG. 1 shows a configuration example of a magnetic recording/reproducing apparatus to which the present invention is applied, in which a wideband television signal applied to an input terminal IN is transmitted through a plurality of narrowband channels 1, 2, and 3 depending on the Hadamard conversion circuit. After the control pulses for time equalization are inserted into each channel signal at predetermined time intervals, the signals are divided into Recorded on magnetic tape B.

At this time, due to the nature of the Hadamard transform, higher-order channels have less influence on image quality, so recording of higher-order channels can be omitted and the number of recording tracks can be made smaller than the number of channels. Figure 2 is a waveform diagram of the recording signal of each channel into which a control pulse P has been inserted. Center it.

The amplitude of the control pulse P is set to be approximately equal to or smaller than the maximum value of the amplitude of the signal S for channels 1 to n-1, and for channel n, it is set to a value that is smaller than the maximum value of the amplitude of the signal S. is also set to a sufficiently large value. In this way, channel 1~
One of the features of the present invention is that the amplitude of the control pulse P and the amplitude of the signal S are approximately equal to each other at n-1, or that P is smaller than S, and this makes it possible to improve the signal-to-noise ratio of the signal. Note that in channel n, the amplitude of the control pulse P must be sufficiently larger than the signal amplitude S, but in the Hadamard transform, the amplitude of the signal in the higher-order channel is 4. The deterioration of the S/N of the image due to the presence of the signal can be ignored. Incidentally, the horizontal synchronizing signal is removed from the video signal input to the Hadamard transform circuit in advance, and the positions of the horizontal synchronizing signals are all set to the blanking level. When the waveform shown in FIG. 2 is recorded and reproduced on a magnetic tape, a time lag occurs between the control pulses of each channel due to misalignment of the head gap.

This time difference is equalized by the time base equalization circuit TBC shown in FIG.

The equalized signals are integrated by Hadamard inverse transform circuit H-1 (FIG. 1) to obtain the original wideband video signal. After Hadamard inversion, a new synchronized horizontal synchronization signal is constructed from the output of the flywheel oscillator of the TBC and the regenerated and inversely converted vertical synchronization signal, and this horizontal synchronization signal is applied to the output of Hadamard inversion circuit H-1. Insert a signal.
Next, the time base equalization circuit according to the present invention will be explained with reference to FIG.

Reference numbers 1-1, 1-2, . . . , 1-n are variable delay elements DEL, and in the embodiment, CCDs (charge-coupled devices) whose delay time is controlled by the frequency applied to the control terminal C. Or something like BBD. 2-1, 2-2,
..., 2-n is a gate circuit G which is always conductive when the control terminal C is open, and when a gate signal is given from the flywheel oscillator 10 to the control terminal C via the switch SW, the signal is present. It shall be applicable only to

4-1, 4-2, . . . , 4-n are phase comparison circuits PH/CPM, 5-1, 5-2, . . . , 5-n are reduction filters LPF, 6-1 ,6-2,.・・・．・・６−
n is a voltage controlled oscillator VC0, 7-1, 7-2,...
. . , 7-n is a window comparator W. 7-n which generates an output only when the input level is within a predetermined range. CM circle, 8-1, 8-2, ..., 8-n are switches SW, 9 is a bell detector LVL, 10 is a flywheel oscillator FL
Y・GEN, 1 1-1, 11-2, ......, 11-
This is the M-bell detection circuit L/DET.

The flywheel oscillator approaches the input frequency with inertia and outputs a stabilized temporal average value of the input frequency. Therefore, input frequency jitter is almost eliminated by the flywheel oscillator. In the embodiment, it is assumed that the flywheel oscillator 10 generates a pulse having a pulse width equal to the control pulse insertion interval T at a repetition frequency equal to the input frequency, and an example of its waveform is shown by FW in FIG. In FIG. 3, it is assumed that the switch SW is open in the initial state, and therefore the gate G is always conductive.

In channel n, the bell detector 9 centers the control pulse P of channel n, and the flywheel oscillator 10 is controlled by the centered control pulse. The flywheel oscillator 10' thus generates a stabilized pulse with a pulse width T and a return period equal to that of the control pulse. It is assumed that the pulse width T is approximately equal to the horizontal scanning blanking period during which the control pulse P is inserted. The output of the flywheel oscillator 10 is sent to the phase comparator circuit PH/CM as shown in FIG.
applied to one input of P. On the other hand, the signals of each channel including channel n are applied to the other input of the phase comparison circuit PH/CMP via the variable delay circuit DEL, the gate circuit G, and the level detection circuit L/DET. In addition, as described above, in the current state, the number of gates G is a constant.
In this state, when the vertical blanking period (vertical female line erasing period) begins, only the control pulse P appears and the signal S does not appear, as shown in FIG.

In this period TL, there are at least 2q horizontal line sections due to the principle of the television system, and therefore the same number of control pulses P exist. Therefore, during this period, the output pulse of the flywheel oscillator serving as a reference and the control pulse of each channel are input to the broad phase comparison circuit, and a voltage corresponding to the phase difference between the two is output from the phase comparison circuit PH/CPM. be done. This voltage is applied to the voltage controlled oscillator VCO via the low-pass filter LFF, and the delay time of the variable delay circuit DEL is controlled by its output frequency. Since the phase comparator circuit, low-pass filter, voltage controlled oscillator, and variable delay element form a closed control loop, the system has a predetermined phase relationship between the two inputs of the phase comparator circuit, and its output becomes 0. completely controlled. In a steady state in which the control system is stable, the time axes of control pulses at the outputs of the variable delay elements in each channel are completely equalized with respect to the output of the flywheel oscillator 10. Therefore, the equalized output OUT of each channel is extracted from the output of the variable delay element and applied to Hadamard inverse transform circuit H-1 (FIG. 1). On the other hand, when the system is stable, the output of the reduction filter LPF is at a predetermined level, so this level is detected by the window comparator W/CM Misaki, and the switch SW is turned on based on the output.

This state will be called a steady state. In a steady state, the delay time of the variable delay element is controlled so that time axis equalization is almost achieved, and its output is provided to the output terminal OUT and also applied to the gate circuit G.

A flywheel oscillator 10 is connected to the control terminal of the gate circuit G.
Therefore, the region including the control pulse P is extracted from each channel with a time width T. The output control pulse P is applied to the &phase comparator circuit PH/CM via the bell detection circuit L/DET, where the phase is compared with the output pulse of the flywheel oscillator 10, and the control pulse is varied according to the result. Adjustment of the delay circuit DEL is performed. As is clear from the above description, in the steady state, only the control pulse and its vicinity out of the reproduced output of each channel are centered by the gate and applied to the phase comparator circuit.

Therefore, even if abnormally high amplitude noise occurs in the general signal S, the noise is blocked by the gate circuit and does not disrupt the operation of the control system. It is assumed that the center frequency of the voltage controlled oscillator is selected such that the delay time of the variable delay element is an integral multiple of the period of the control pulse.

In a steady state, if for some reason the synchronization of the time axis is greatly lost and the control pulse goes outside the pulse width T of the flywheel oscillator, the output of the window comparator W・CMP of the channel becomes 01. , switch S
W is turned off and time axis equalization is performed in the same process as in the initial state described above.

Thereafter, when synchronization is achieved again, the switch SW is turned on and the steady state is restored. As explained in detail above, according to the present invention, initial equalization is performed during the vertical planking period when no signal is present, and during other periods, the reproduction output is gated out to perform time axis control, so that the control system Since there is no confusion with noise and there is no need to make the amplitude of the control pulse larger than the amplitude of the signal,
/N can be increased.

[Brief explanation of drawings]

FIG. 1 is a system diagram of a magnetic coin picture reproducing device to which the present invention is applied, and FIG. 2 is a waveform diagram of recording signals and a flywheel oscillator.
FIG. 3 is a block diagram of a time axis control circuit according to the present invention, and FIG. 4 is a waveform of a reproduced signal during a vertical blanking period. TBC: Time axis control circuit, H-1: Hadamard (inverse) conversion circuit, P: Control pulse, S: Signal, G: Gate circuit, DEL: Variable delay element, PH/CMP; Phase comparison circuit, LPF; Low-pass filter, VCO; voltage controlled oscillator,
W・CMO: window controller/regulator, SW: switch, L・DET: level detection circuit, FL1・GEN: flywheel oscillator. Figure 1 Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] 1 After dividing the video signal into a plurality of channels and inserting control pulses of a predetermined time width and magnitude within the horizontal and vertical blanking periods expressed in a constant period in each channel, the number of channels is equal to or greater than the number of channels. In a magnetic recording/reproduction method in which the original video signal is restored after magnetically recording on a small number of tracks and equalizing the time axis of the reproduction output of each track with reference to the control pulse, the amplitude of the control pulse of one channel of the video signal is is larger than the control pulse of other channels, and using this control pulse as a reference control pulse, first, so that the position of the control pulse of the other channel on the time axis coincides with the position of the reference control pulse on the time axis. By controlling the delay time of a variable delay circuit inserted into each channel within the vertical blanking period based on the phase difference between the output pulse of the flywheel oscillator driven by the reference control pulse and the control pulse of each channel. Time axis equalization is performed, and after the equalization is completed, the control pulses of each channel are centered via the gate circuit using the output pulses of the flywheel oscillator, and the centered control pulses are combined with the output pulses of the flywheel oscillator. A time axis control method characterized in that equalization operation is continued by controlling the delay time of the delay circuit based on the phase difference.