JPH0136170B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic recording and reproducing device, in which a control track records a phase-modulated wave obtained by phase-modulating a pilot signal for reducing wow and flutter components having a frequency that is an integral multiple of the control signal. It is an object of the present invention to provide a magnetic recording and reproducing device which can suitably reduce wow and flutter components contained in an audio signal reproduced from an audio track by reproducing the same, and can reproduce the audio signal with high quality. shall be.

As is well known, a helical scan type magnetic recording/reproducing device (hereinafter referred to as "VTR") uses a capstan servo to keep the magnetic tape traveling speed constant during recording and reproduction, but in recent years the recording and reproduction time has become longer. Therefore, the running speed of the magnetic tape is slowed down, so the speed changes due to disturbances are large, and the influence of wow and flutter on the length of elongation and contraction of the magnetic tape is large. This wow and flutter is caused by the relative linear velocity between the audio track (and control track) and the audio head (and control head) along the longitudinal direction of the magnetic tape than the relative linear velocity between the video track and the rotary head, which are inclined relative to the longitudinal direction of the magnetic tape. Since the linear velocity is much smaller because the audio head (and control head) is fixed, it has a greater adverse effect on the reproduced audio signal (and the reproduced control signal).

In order to reduce this wow and flutter, it is conceivable to increase the number of pulses generated per one revolution of the capstan from the FG pulse generator in the speed control circuit of the capstan servo system, but due to manufacturing constraints, It is not possible to obtain the number of pulses necessary to reduce the wow and flutter mentioned above, and on the other hand, it is possible to reduce the wow and flutter by increasing the diameter of the flywheel that is coaxially fixed to the capstan shaft. However, it had the disadvantage of limiting the ability to make VCRs smaller and lighter.

The present invention eliminates the above-mentioned drawbacks, and an embodiment thereof will be described below with reference to the drawings.

FIG. 1 shows a block system diagram of an embodiment of the recording system of the apparatus of the present invention. In the figure, a composite video signal with a field frequency of 60 Hz to be recorded that enters input terminal 1 passes through a synchronization signal separation circuit 2, where a composite synchronization signal is separated and extracted, and then supplied to a vertical synchronization signal separation circuit 3. At this point, only the vertical synchronizing signals shown in FIGS. 2A and 3A are extracted. This vertical synchronizing signal is supplied to the frequency divider 4, where it is divided by 1/2 and the second
After being made into pulses with a repetition frequency of 30 Hz as shown in FIG.

The monomulti 5 is triggered by the rising edge of the above pulse and applies a pinched pulse having a width as shown in FIG. do. Furthermore, the flip-flop 6 generates a symmetrical square wave with a repetition frequency of 15 Hz as shown in FIGS. 2D and 3C, which is inverted in phase synchronization with the rising edge of the pulse from the frequency divider 4, and the symmetrical square wave is phase-modulated. 12 as a modulated signal. Note that FIGS. 2A to 2F and 3A to 3C are shown with different time axes.

On the other hand, the phase comparator 7 is a well-known phase locked loop (hereinafter referred to as ``PLL'') together with a voltage controlled oscillator (hereinafter referred to as ``VCO'') 8 and a frequency divider 9 consisting of a 14-bit counter.
The oscillation frequency is variably controlled by the output phase error voltage of the phase comparator 7, and the VCO 8 outputs a repetition frequency of 491.52kHz (=30×
2 ¹⁴ ) pulses are taken out and applied to the counter 10 as clock pulses.

Counter 10 is a 10 bit counter,
The monomulti 5 starts counting the clock pulses from the VCO ⁸ at the falling edge of the pulse shown in FIG. A pulse with a constant amplitude and a repetition frequency of 480 Hz as shown in FIG. supply Here, reduction filter 1
The reason why the signal waveform supplied as a carrier wave to the phase modulator 12 by 1 is a sine wave is because the band that can be transmitted in magnetic recording and reproduction is low, and if the output pulse of the counter 10 is transmitted, this pulse will have harmonics. This is because all of the frequency components cannot be transmitted through a magnetic tape that is recorded and reproduced at a slow tape running speed.

For example, when the symmetrical square waves shown in FIGS. 2D and 3C from the flip-flop 6 are at a high level, the phase modulator 12 passes through the sine wave with a frequency of 480 Hz from the reduction filter 11 as is, and converts the symmetrical square wave shown in FIG. During the low level period, the phase of the sine wave from the reduction filter 11 is inverted and outputted, and as a result, a phase modulated wave as shown in FIG. 2F is generated and outputted. In other words, this phase modulated wave has phase change points shown in Figure 2 F every two field periods (1/30 seconds), and a 15Hz control signal produces a sine wave with a frequency of 480Hz, which is 32 times 15Hz. This is a phase-modulated signal. Furthermore, the phase change point of this phase modulated wave coincides with the zero crossing point of the sine wave from the reduction filter 11, but the waveform shown in FIG. be.

By varying the delay time of the monomulti 5, the reset timing of the counter 10 (that is, the falling point of the output pulse of the monomulti 5 shown in FIG. 2C) can be varied, and the counter 10 shown in FIG. The output pulse can be applied to the left or right direction in E of the same figure, thereby changing the phase of the phase change point of the phase modulated wave shown in F of the same figure.

The phase modulated wave generated in this way is amplified to an appropriate level by an amplifier 13, and then a mixer 14
After being superimposed with a bias signal from a bias oscillator 15, the signal is supplied to a fixed control head 16 and recorded on a control track along the longitudinal direction of a magnetic tape 17. Meanwhile, at the same time, input terminals 18a and 18b
The audio signals of the first and second channels that entered the
Mixers 20a, 20 via amplifiers 19a, 19b
b, where it is superimposed with the bias signal from the bias oscillator 15 and then applied to the fixed audio heads 21a, 21b, thereby applying it to the first and second audio tracks along the longitudinal direction of the magnetic tape 17. recorded. The composite video signal input to the input terminal 1 is recorded on a tilted video track on the magnetic tape 17 by a rotary head (not shown) through a well-known recording system (not shown).

Next, we will discuss the fourth embodiment of the regeneration system of the device of the present invention.
This will be explained with reference to FIGS. 6 to 6. FIG. 4 shows a block system diagram of essential parts of an embodiment of the regeneration system of the apparatus of the present invention. In the figure, a control head 23 reproduces the phase modulated wave recorded on the control track of the magnetic tape 17. The fifth regenerated and taken out by the control head 23
The reproduced phase modulated wave a shown in FIG. The full-wave rectified signal b shown in FIG. 5B taken out from the full-wave rectifier circuit 25 passes through the bandpass filter 27 and is converted into a sine wave c with a frequency of 960 Hz shown in FIG. Here, the waveform is shaped into a pulse d shown in FIG. This repetition frequency
The 960 Hz pulse d is output from a terminal 29 to the circuit shown in FIG. 6 as a pilot signal for reducing wow and flutter components, and is also supplied to a phase comparator 30 and a sampling hold circuit 33, respectively.

The phase comparator 30 constitutes a PLL together with the VCO 31, and the output signal of the VCO 31 and the above pulse d
generates an error voltage corresponding to the phase difference between the VCO
The output oscillation frequency of 31 is variably controlled. this
PLL is the output pulse e of VCO31 shown in Figure 5E.
The phase difference ΔT between the pulse d and the reproduced phase modulated wave a shown in FIG. The VCO3 outputs a pulse e that has a phase difference within T shown in FIG.
The response speed is designed so that it continues to occur from 1. The output pulse e of VCO31 is 1/2 frequency divider 3
The pulse f is divided by 1/2 by 2 and converted into a pulse f having a repetition frequency of 480 Hz as shown in FIG.

The multiplier 26 multiplies the reproduced phase modulated wave a by the pulse f, and as shown in FIG. During the level period, a signal g is generated by inverting the reproduced phase modulated wave a, and is supplied to the sampling and holding circuit 33. The sampling and holding circuit 33 performs an operation of holding the voltage obtained by sampling the signal g during the high level period of the pulse d during the low level period of the pulse d, and outputs a signal h as shown in FIG. 5H. This signal h is supplied to a limiter 34, where the upper and lower portions of the waveform are respectively clipped to form the signal i shown in FIG. 5I. This signal i is output to a control signal output terminal 35 and is applied to a servo circuit for ensuring that the rotating head (not shown) accurately scans over the video track.

Note that since the reproduction control signal i rises at the next phase change point of the reproduced phase modulated wave a, it becomes a pulse with a repetition frequency of 15 Hz. However, when used in a conventional two-head VTR, the control signal frequency is 30Hz, so in this case, the rising and falling edges of signal i are detected and repeated in phase synchronization with them. Frequency 30Hz
It is sufficient to generate a pulse and use it as a reproduction control signal.

By the way, a phase shift shown by Ts in FIG. 5I occurs between the reproduction control signal i and the phase change point of the reproduced phase-modulated wave a, that is, the time of reproducing the vertical synchronizing signal. However, when recording, flip-flop 6
The output pulse of the output pulse and the sine wave (pilot signal) c from the low-pass filter 11 are controlled to have a constant phase, and the phase shift Ts is determined by the time constant of the full-wave rectifier circuit 25, the time constant of the bandpass filter 26, and zero-cross detection. Since it is determined by the zero level setting of the device 28, it is possible to manage it to a constant value, and it is possible to perform tracking with the same accuracy as before. Although there is some drift in the sine wave c, since its frequency is higher than that of the required control signal i, the drift of the reproduction control signal i is extremely small and is practically acceptable. In addition, in the present invention, since the phase modulated wave is recorded on the control track and is played back, the playback level fluctuates much more than when recording and playing back the amplitude modulated wave whose amplitude is modulated by the control signal. Not affected by Furthermore, if one attempts to record and reproduce frequency-modulated waves, the recording frequency modulator requires two signal frequency generators, a low-pass filter, and a switch circuit that switches both frequencies in phase synchronization with the control signal. On the other hand, the circuit configuration of the present invention, in which the phase modulator 12 is composed of a phase inversion circuit and a switch circuit, is simpler.

Next, the operation of reducing the wow and flutter components of the reproduced audio signal by the apparatus of the present invention will be explained with reference to the block diagram shown in FIG. In the figure, a pulse d having a repetition frequency of 960 Hz shown in FIG. 5D, which has entered the terminal 29 as a pilot signal, is applied to the PLL 36 and the terminal A of the changeover switch SW, respectively. The pulse d is a signal reproduced from the control track of the magnetic tape 17, and has the same time axis fluctuation component due to wow and flutter as the audio signal reproduced from the audio track formed along the longitudinal direction of the tape. (This is called a "wow/flatter component"). The PLL 36 is designed to follow the frequency fluctuations of the input pulse d, and even when the input pulse d has many dropouts, the PLL 36 continues to oscillate within the variable range of the VCO inside the PLL 36 to generate pulses that are phase-synchronized with the input pulse d. can be used to prevent malfunctions of subsequent circuits.

However, since PLL36 cannot completely follow the frequency fluctuation of input pulse d, PLL3
The effect of reducing wow and flutter components is slightly inferior to the case where 6 is not passed. Therefore, the changeover switch SW connects terminals A and C only when there is a lot of dropout in the input pulse d, and extracts the pulse d that has passed through the PLL 36, and when there is no dropout in the input pulse d (actually, there is no dropout). Terminals A and C are connected to prevent the PLL 36 from passing through. The pulse d taken out from the terminal C of the changeover switch SW is supplied to a frequency divider 37 and a bucket brigade device (BBD) 38 constituting a variable delay circuit, respectively.

The repetition frequency of input pulse d is 960Hz,
Since it is difficult to directly detect wow and flutter components lower than this, the frequency divider 37 divides the pulse d from the changeover switch SW by 1/13, for example, to 74Hz.
After that, it is supplied to the PLL 39, where wow and flutter components of 1 Hz or more are detected and extracted as voltage changes. The output voltage of this PLL39 is VCO40
is applied as the oscillation control voltage. The VCO 40 is an oscillator for generating clock pulses for the BBDs 38, 51a and 51b that constitute the variable delay circuit.
The output oscillation frequency is controlled by the clock drive circuit 41.
and 42, respectively, where it is shaped into a BBD clock pulse. In addition, BBD38,51a
and 51b have the same number of stages, and the wah/wah sound above 1Hz.
A large number of stages is used because it is necessary to widen the variable range of delay time in order to improve the flutter component. Further, the clock drive circuits 41 and 42 may be used in common as long as they can simultaneously drive the three BBDs 38, 51a and 51b.

The delay time of the BBD 38 is varied by the clock pulse from the clock drive circuit 41 according to the wow and flutter components of the input pulse d of 1 Hz or more. After removing the clock component through the zero cross detector 4
3, where it is shaped into a pulse with steep rises and falls. Similarly, BBD51a,5
The delay time 1b is varied by the clock pulse from the clock drive circuit 42 in accordance with the wow and flutter components of 1 Hz or more of the input pulse d, so that the reproduced audio signal in which the low frequency wah component has been reduced is passed through the reduction filter described later. Output to 52a and 52b. Here, since the BBDs 38, 51a, and 51b have a long delay time in order to reduce the wah component with a particularly low frequency, the phase lag due to the delay occurs in the input pulse d of these and the high frequency flutter component of the reproduced audio signal. It becomes large and cannot be reduced. This flutter component that cannot be reduced is BBD3
8, 51a and 51b.

After the pulse containing the flutter component that cannot be reduced, which is extracted from the zero-cross detector 43, is divided by 1/3 by the frequency divider 44 to 320Hz.
The signal is supplied to the PLL 45, where a flutter component of 10 Hz or more is detected, and then supplied to the VCO 46, where the output oscillation frequency is variably controlled in accordance with the detected flutter component. The output oscillation frequency of the VCO 46 is waveform-shaped into a BBD clock pulse by a clock drive circuit 47, and then supplied to BBDs 53a and 53b, which constitute a variable delay circuit, respectively.
The delay time is variably controlled. Since the BBDs 53a and 53b only need to reduce flutter components of 10 Hz or more, the variable range of the delay time can be narrow, and therefore the delay time can be shortened, and even high frequency flutter components can be reduced.

On the other hand, the audio signals of the first and second channels, which are respectively reproduced by the two audio heads from the first and second audio tracks of the magnetic tape 17 that have entered the input terminals 48a and 48b, are used for input sensitivity adjustment. It is supplied to the reduction filters 50a, 50b via the variable resistors 49a, 49b, where the high-frequency components that cannot be transferred by the BBDs 51a, 51b that perform sampling operations are removed, and then the BBDs 51a, 5
1b. As mentioned above, BBD51a,
The reproduced audio signals of the first and second channels whose wah components have been reduced by the reduction filter 52
After the clock component is removed by a, 52b
It is supplied to BBD53a, 53b, and here BBD5
1a and 51b, the flutter components of 10 Hz or higher, which could not be completely reduced, are reduced.

As a result, BBD53a and 53b produce wah sounds.
The reproduced audio signals of the first and second channels with reduced flutter components are taken out, and after the clock components are removed by reduction filters 54a and 54b, the reproduced audio signals are amplified to an appropriate level by amplifiers 55a and 55b. , further via output voltage adjusting variable resistors 56a, 56b to output terminals 57a,
It is output from 57b.

In the embodiment shown in FIG. 6, a BBD is used as the variable delay circuit, but it is of course possible to use a charge transfer device such as a CCD or the like.

As mentioned above, the magnetic recording and reproducing device of the present invention has the following features:
A phase modulation means for phase modulating a carrier wave having a constant frequency that is an integral multiple of the control signal with a control signal having a constant frequency for causing a rotating head to perform tracking scanning on a track inclined with respect to the longitudinal direction of the magnetic tape; a recording means for recording the phase modulated wave obtained by the means on a control track along the longitudinal direction of the magnetic tape and recording an audio signal on an audio track along the longitudinal direction of the magnetic tape; A control head that reproduces the phase modulated wave; and a pilot signal generating means that performs zero cross detection after full-wave rectification of the phase modulated wave reproduced from the control head to generate a pilot signal having a frequency approximately twice that of the carrier wave. and a pulse generating means that is supplied with a pilot signal and generates a pulse having the same frequency and phase synchronization as the carrier wave of the reproduced phase modulated wave from the control head; and phase change point detection means for sampling and holding the output signal of the multiplier with the pilot signal to detect the phase change point of the reproduced phase modulated wave. By using it as a delay time control signal for a variable delay circuit provided in the transmission path of the reproduced audio signal of an audio track, it is possible to reduce the wow and flutter components contained in the reproduced audio signal, and also to Since the playback control signal is generated and output to the servo circuit, the wow and flutter components of the playback audio signal can be electrically reduced without increasing the diameter of the flywheel that is coaxially fixed to the capstan shaft. Since the amplitude of the phase modulated wave is constant, the control signal and the pilot signal for reducing wow and flutter components can be reproduced without being affected by level fluctuations, compared to when recording and reproducing amplitude modulated waves. Furthermore, the configuration of the recording system modulator is simpler than when recording and reproducing a frequency-modulated wave, and the frequency-modulated wave in this case has a time difference between the first frequency and the second frequency. Although it is a sequential composite signal, the transmission characteristics of a VTR differ depending on the frequency, and when the tape running speed is slow, the transmission characteristics of both frequencies are different and cause wow and flutter. Since the transmission frequency is constant when recording and reproducing waves, it has the advantage that it is particularly suitable for recording and reproducing pilot signals for reducing wow and flutter components.

[Brief explanation of drawings]

FIG. 1 is a block system diagram showing one embodiment of the recording system of the apparatus of the present invention, FIGS. 2 A to F, and FIGS. 3 A to C.
1 is a signal waveform diagram for explaining the operation, FIG. 4 is a block system diagram showing an embodiment of the main part of the reproduction system of the apparatus of the present invention, and FIGS. 5A to 5I are respectively for explaining the operation of FIG. 4. FIG. 6 is a block system diagram showing an embodiment of another essential part of the reproduction system of the apparatus of the present invention. 1...Input terminal, 6...Flip-flop,
7, 30...phase comparator, 12...phase modulator,
16, 23... Control head, 17... Magnetic tape, 18a, 18b... Audio signal input terminal, 21a, 21b... Audio head, 25
... Full wave rectifier circuit, 26 ... Multiplier, 28, 43
... Zero cross detector, 29 ... Reproduction pilot signal output terminal, 33 ... Sampling hold circuit, 34 ... Limiter, 35 ... Reproduction control signal output terminal, 38, 51a, 51b, 53
a, 53b...bucket brigade device (BBD), 48a, 48b...playback audio signal input terminal, 57a, 57b...playback audio signal output terminal.

Claims (1)

[Claims] 1. Phase modulation of a carrier wave with a constant frequency that is an integral multiple of the control signal using a control signal of a constant frequency for causing a rotating head to perform tracking scanning on a track inclined with respect to the longitudinal direction of the magnetic tape. a phase modulating means for recording a phase modulated wave obtained by the phase modulating means on a control track along the longitudinal direction of the magnetic tape, and a recording means for recording an audio signal on an audio track along the longitudinal direction of the magnetic tape. a control head that reproduces the phase modulated wave from the control track on the magnetic tape; and a control head that performs zero cross detection after full-wave rectification of the phase modulated wave reproduced from the control head, and a pilot signal generating means for generating a pilot signal of twice the frequency; and a pulse generator for generating a pulse having the same frequency and phase synchronization as the carrier wave of the reproduced phase modulated wave from the control head, to which the pilot signal is supplied. a multiplier for multiplying the pulse by the reproduced phase modulated wave from the control head; sampling and holding the output signal of the multiplier with the pilot signal to obtain a phase change point of the reproduced phase modulated wave; phase change point detection means for detecting the phase change point included in the reproduced audio signal by using the pilot signal as a delay time control signal of a variable delay circuit provided in the transmission path of the reproduced audio signal of the audio track. A magnetic recording/reproducing device characterized in that it reduces wow and flutter components, and generates a reproduction control signal from the detection signal of the phase change point and outputs it to a servo circuit.