JPS6014423B2 - 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 recording signal is lAm, the head gap is only 0. If there is a deviation in the amplitude, a large phase difference of 180 degrees will occur in the reproduced signal. Even if the allowable value of this phase difference is set to 90, the allowable deviation between the head gaps is only about 0.02 degrees, and such precision cannot be achieved with current machining technology. To solve this problem, we insert synchronized control pulses at predetermined time intervals into each narrow band channel during recording, and insert a time axis control circuit with a variable delay circuit in the re-output circuit. A method has been proposed in which time axis equalization for each channel is electrically performed by controlling a variable delay circuit so as to synchronize the control pulses of the channels.

Tsubakigao 49-43717 (magnetic recording and reproducing device, filed on April 17, 1948), which was previously proposed by the present applicant, is based on this idea. However, conventional time axis control circuits have the disadvantage that if abnormally high amplitude noise occurs in the signal, this noise will be mistaken for a control pulse, and correct time equalization will not be performed. Therefore, the present invention aims to improve the above-mentioned drawbacks of the prior art, and its purpose is to provide a method for performing time axis equalization without being affected by impulse noise.

A feature of the invention to achieve this objective is to divide a wideband signal into a plurality of narrowband channels, and after inserting control pulses at predetermined time intervals into each channel, a track signal equal to or less than the number of channels is In a magnetic recording/reproduction method in which the time axis of the reproduction output of each track is equalized based on the control pulse and the original wideband signal is restored, the amplitude of the control pulse inserted into each narrowband channel is The amplitude is set sufficiently higher than the amplitude of the information signal of each channel, and the control pulse in any one of the multiple channels is used as the reference control pulse, and the difference in amplitude between the control pulse and the information signal is used during equalization operation. By controlling the variable delay circuit inserted in each channel based on the phase difference between the control pulse extracted for each channel and the output pulse that is the output of the flywheel oscillator driven by the reference control pulse. The time axis of the control pulse of each channel is equalized to the time axis of the reference control pulse, and after the equalization is completed, the gate circuit provided in each channel is driven by the output pulse to extract the control pulse of each channel. The time axis control method is such that the equalization operation is continued using the control pulses generated. This will be explained below with reference to the drawings. FIG. 1 shows an example of the configuration 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 divided into a plurality of narrowband channels 1, 2, 3, and 3 by a Hadamard conversion circuit. After the signal of each channel is divided into n and a control pulse for time axis equalization is inserted at a predetermined time interval, and 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 the control pulse P is inserted. The ranking period T) is set at the center.

When waveforms 1, 2, . . 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. 0 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, they are CCDs (charge coupled devices) whose delay time is controlled by the frequency applied to the control terminal C. Or something like BBD in the evening. 2-1, 2-2
, 2-n is a gate circuit G, which is always conductive when the control terminal C is open, and when the gate signal from the flywheel oscillator 10 is applied to the control terminal C via the switch SW, when the signal is present. 0 only.

3-1, 3-2, . . . , 31n are bell detection circuits that extract the control pulse of each channel using the difference in level with the signal.

4--, 4-2,..., 4-n is the phase comparator circuit PH
・CMP, 5-1, 5-2, ......, 5-n is a low-pass filter LPF, 6-1, 6-2, ......,
6-n is a voltage controlled oscillator VC○, 7-1, 7-2,...
..., 7-n is a window comparator W.C that generates an output only when the input level is within a predetermined range.
MP, 8-1, 8-2, . . . , 8-n are switches SW, 9 is an O level detector L.DET, and 1 river is a flywheel oscillator FLY.GEN.

The flywheel oscillator approaches the input frequency with inertia, and outputs a stabilized temporal average value of the input frequency. Therefore, most of the input frequency deviations are removed by the flywheel oscillator. In this 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, a bell detector 9 extracts a control pulse P of channel n, and a flywheel oscillator 10 is controlled by the extracted control pulse. The flywheel oscillator 10 thus generates a stabilized pulse with a pulse width T and a repetition 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 applied to one input of the phase comparison circuit PH/CMP as shown in FIG. On the other hand, the signals of each channel other than channel n are
The signal is applied to the level detection circuits L and DET via the variable delay circuit DEL and the gate circuit G, where the control pulse P is extracted using the level difference between the control pulse P and the signal S. The extracted control pulse is applied to the other input of the phase comparison circuit PH/CM. Therefore, the phase comparator circuit outputs a voltage corresponding to the phase difference between the output pulse of the flywheel oscillator 10 and the control pulse of each channel, and this voltage is applied to the voltage controlled oscillator VCO via the low-pass filter LPF, and The delay time of the variable delay circuit DEL is controlled by the 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 the Hadamard inverse transform circuit H-1 (FIG. 1). On the other hand, in a steady state where the system is stable, the output of the low-pass filter LPF is at a predetermined level, so this level is set by the wind comparator W.
It is detected by CMP, and the switch SW is turned on based on its 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 installed in the control isogo of the gate circuit G.
Therefore, a region including the control pulse P is extracted with a time width T from each channel. The extracted control pulse P is applied to the phase comparison circuit PH/CMPI via the bell detection circuit L/DET, where the phase comparison with the output pulse of the flywheel oscillator 10 is performed, and according to the result, the variable delay circuit DEL is applied. adjustments are made. In addition, in the steady state, the lever detection circuit 3-1, 3
-2, . . . , 3-n are not necessarily required. As is clear from the above description, in the steady state, only the control pulse and its vicinity are extracted by the gate from the reproduced output of each channel and applied to the phase comparator circuit.

Therefore, even if a nozzle with an abnormally high amplitude occurs in the portion of 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 0. , switch SW
is turned off, and time axis equalization is performed in the same process as in the initial state described above.

After that, 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, since the time axis control is performed by gate extracting the reproduced output in a steady state, the control system is not confused by the influence of noise, and stable time axis control can be performed. I can do it.

Note that the amplitude of the control pulse must be sufficiently higher than the amplitude of the signal in order to operate the bell detection circuit 9 correctly in the n-th channel, but since the amplitude of higher-order channels is generally small in Hadamard-transformed signals, The above can be easily achieved.

[Brief explanation of the drawing]

FIG. 1 is a system diagram of a magnetic recording/reproduction disc to which the present invention is applied, FIG. 2 is a waveform diagram of a recording signal and a flywheel oscillator, and FIG. 3 is a block diagram of a time axis control circuit according to the present invention. TBC: Time 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, LP; Low-pass filter, VCO; voltage-controlled oscillator, W
・CMP: Wind controller/gulator, SW; switch,
L・DET: Level detection circuit, FLY・GEN: Flywheel oscillator. Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] 1 Divide a wideband signal into a plurality of narrowband channels, insert control pulses at predetermined time intervals into each channel, and then magnetically record on tracks equal to or less than the number of channels, and set the playback output time of each track. In a magnetic recording and reproducing method in which an original wideband signal is restored after equalizing the axis using the control pulse as a reference, the amplitude of the control pulse inserted into each narrowband channel is sufficiently higher than the amplitude of the information signal of each channel. The control pulse in any one of the plurality of channels is set as a reference control pulse, and during equalization operation, the control pulse is extracted for each channel by using the difference in amplitude between the control pulse and the information signal. The control of each channel is performed by controlling a variable delay circuit inserted in each channel based on the phase difference between the control pulse and the output pulse that is the output of a flywheel oscillator driven by the reference control pulse. The time axis of the pulse is equalized to the time axis of the reference control pulse, and after the equalization is completed, the gate circuit provided in each channel is driven by the output pulse to extract the control pulse of each channel. A time axis control method characterized by continuing equalization operation using control pulses.