JPS609931Y2 - magnetic recording and playback device - Google Patents

Description

[Detailed description of the invention] The invention uses a rotating head to sequentially record a video signal as a recording trajectory inclined with respect to the longitudinal direction of a magnetic tape.
A magnetic recording and reproducing device that sequentially records an audio signal and a control signal synchronized with the rotational phase of the rotary head (synchronized with the vertical synchronization signal of the video signal to be recorded) as the locus extending in the longitudinal direction of the magnetic tape using a fixed head. The purpose is to reduce and eliminate wow and flutter in a reproduced audio signal in a VTR.

Recently, the recording density of VTRs has been increasing, and VH3 type cassette VTRs with a tape speed of 1.6C711/sec have already been put into practical use.

However, as tapes run at lower speeds, wow and flutter in audio signals has become a serious problem.

Assuming the same machine precision, if the tape speed is halved, the wow and flutter will approximately double.1. (At a tape speed of 5 cm/s, there is a possibility that wow and flutter will be about twice as high as the approximately 2.4C71/s for an audio microcassette.

Therefore, conventional measures have been taken to reduce wow and flutter during low-speed tape running, such as increasing the precision of the machine or installing an impedance roller, but these measures are still well within the allowable range. This is difficult and requires high machining precision, resulting in high costs.

The present invention electrically corrects the wow and flutter of audio signals in VTRs, and eliminates wow and flutter during low-speed tape running without requiring much mechanical precision.
The object of the present invention is to provide a new device that can bring the values within a sufficiently permissible range.

FIG. 1 shows a schematic diagram for explaining the state of recording signals on a tape in a simple ITR.

In FIG. 1, on the magnetic tape 6 are an audio track a1 recorded by an audio signal recording and reproducing head H□, a video signal recording band opening recorded by a rotating video head (not shown), and a control head. Control track C recorded by ratio
exists.

The control track receives a 30H2 rectangular wave signal as shown in Figure 2A input from terminal 1 (this is a signal locked to the vertical synchronization signal of the input television signal (synchronized to the rotational phase of the rotary head). The signal) is recorded through the switch SW, and during playback, it is reproduced as a differential waveform as shown in Figure 2. This positive direction component is amplified by the pulse amplifier 2, and the signal and phase of the reference oscillator 4 are A capstan control method is generally adopted in which the phase is compared in the comparator 3 and the rotation speed of the capstan motor 5 that drives the tape is controlled using the error signal so that the tape speed is controlled to be the same constant speed as during recording. It is often done.

Sometimes the capstan motor is a synchronous motor that is synchronized to the power supply frequency, but in this case the tape is driven at a constant speed that depends on the number of revolutions of the capstan motor.

In either case, wow and flutter may occur in the audio playback signal due to slippage and tape expansion/contraction due to fluctuations in the roundness and eccentricity of the capstan shaft or tape tension, or changes in tape speed due to tape vibration. This causes the occurrence of

In the case of a capstan servo, the servo is always applied to keep the playback tape speed constant, but its response range is only for very low frequency components (usually below IHz).
It cannot respond to high frequency fluctuations.

This is because the inertia of the tape drive system is large.

Generally, when the tape speed becomes low, such as several cm/sec or less, the largest factors for wow and flutter are components such as the roundness and eccentricity of the capstan shaft, and the roundness of the capstan pulley. , the frequency of this component is 1
Usually around 0Hz.

Of course, this harmonic component is also generated.

The next largest component is a component due to uneven rotation of the reel and variation in tape tension, and is usually a component of about IHz or less.

Next, what cannot be ignored is that in the case of a VTR, unlike an audio tape recorder, the rotating video head contacts the tape at a frequency of 60 Hz, so there is a flutter component due to vibrations including 60 H2 and its high frequency subharmonics of 30 Hz. be.

This component can be significantly reduced by providing impedance rollers in the tape running system before and after the rotating cylinder.

In particular, harmonic components of 60 Hz can be attenuated sufficiently for practical purposes.

As mentioned above, there are various causes of wow and flutter in audio signals in VTRs, and in order to alleviate this, conventional means for improving mechanical accuracy and various suppressing means have been devised.

However, there is a contradiction between mass production and mechanical precision, and this becomes extremely difficult especially when the tape speed becomes 2 cm/sec or less.

Therefore, it is an object of the present invention to attempt to correct such problems in terms of electrical circuits.

A charge transfer device (BBD or CCD) is a well-known method for electrically varying the signal delay time.
).

In order to control the signal delay time using a charge transfer element, it is necessary to detect the amount of wow and flutter, and change the transfer lock frequency depending on the detected amount, but this is not the case with ordinary audio tapes. Recorders typically do not include means for detecting wow and flutter.

However, even with such an audio tape recorder, it is possible to electrically compensate for wow and flutter by adding a method of recording a reference frequency signal on a separate track during recording and detecting wow and flutter from the reproduced signal during playback.

This invention solves the problem of wow and flutter in VTR audio signals.
It relates to a means for removing wow and flutter from an audio signal, and in particular, it detects wow and flutter using a control track without creating a separate track for wow and flutter detection, and electrically eliminates wow and flutter from an audio signal. This provides a means of compensating the situation.

As mentioned above, the signal recorded on the control track of the VTR is a 30H2 square wave (PAL) in the case of the NTSC system.
Normally, only a 30Hz unidirectional pulse like the one in Figure 2 is used for control during playback, but if the playback signal like the one in Figure 2 is double-wave rectified, it can be reduced to 60Hz. pulses are obtained.

However, in reality, in the current standards for VH3VTRs, etc., the rectangular wave pulse shown in Figure 2 A is not recorded as a pulse with a duty of 50-50, but is recorded as a duty of about 40-60, and the rising and falling edges of the pulse are recorded. Since it is designed to be clearly distinguishable, the falling pulse cannot be used and becomes a 30 Hz repetitive component.

Therefore, if Fig. 2A is recorded as a pulse with a duty of -50-50, a pulse of 60 Hz can be obtained.

According to the sampling theorem, the frequency component of wow and flutter that can be detected from pulses with a repetition period of 60 Hz (~30 Hz) is below 30 Hz (15 Hz), but in actual circuit configurations it is about one-third of the repetition period. 10Hz (Hz) is the limit.

Therefore, the wow/flutter, which can be identified using the control signal, and the 1/1 generated from the capstan.
This is part of the flutter around 0Hz.

However, since the amount of wow and flutter that can be detected is the largest around 4H2, the above control signal can be used to detect wow and flutter.
Even if flutter is reduced, a considerable reduction effect can be obtained.

FIG. 3 shows an example of a specific circuit configuration for correcting wow and flutter using the control signal.

In FIG. 3, parts similar to those in FIG. 1 are designated by the same numbers.

A rectangular wave with a duty of 50-50 is recorded as a control signal from terminal 1, and during playback, the signal that has passed through SW1 is passed through a double-wave rectifier circuit 7 and a pulse amplifier circuit 8, and is output to the reference oscillator 4 by a phase comparator 9. Compare the output and phase.

In that case, the output of the pulse amplifier 2 is as shown in Figure 4, and the output of the pulse amplifier 8 is as shown in Figure 4. Therefore, if the signal of the reference oscillator 4 is set as Sampling is performed every second, and the phase comparator 9 performs sampling at twice the period.

The output signal of the phase comparator 9 is passed through a hold circuit 10,
Controls a variable frequency oscillator (VCO) 11 for clock generation.

On the other hand, the audio signal is reproduced from the head H, passes through the amplifier 12, and is guided to the charge transfer element 13.

A signal is transferred to the charge transfer element 13 by the clock from the charge transfer element 11, and a reproduced audio signal with wow and flutter reduced is obtained at a terminal 14.

However, as described above, if the control signal is used as it is, the 60 Hz frequency characteristic of VTRs cannot be removed.

As a means to improve this, it is possible to record harmonic components of the control signal in a superimposed manner on the control track, and to remove flutter of high frequency components based on the high frequency components.

However, in this case, care must be taken to ensure that the superimposed recorded components do not interfere with the detection of the control signal.

FIG. 5 shows an example of its specific configuration, and FIG. 6 shows waveforms for explanation.

In FIG. 5, parts that operate in the same way as in FIGS. 1 and 3 are labeled with the same numbers.

In FIG. 5, 15 is an input terminal for a video signal to be recorded, and a vertical synchronizing signal separating circuit 16 separates the vertical synchronizing signal separating circuit.

One of the outputs of 16 is led to a flip/flop circuit 17 to obtain a 30 Hz rectangular waveform, and this waveform is differentiated by a differentiating circuit 18 and passed through a diode 19 to obtain a waveform.

On the other hand, in order to obtain an oscillation signal synchronized with the vertical synchronization signal (output of 16), a phase locked loop (PLL) consisting of a variable oscillator 21, a frequency divider 22, and a phase comparator 23 is configured.

This PLL circuit is, for example, 5 times the vertical synchronization signal (300
In order to obtain signal 2 synchronized with H2), the frequency division of the divider 22 is set to 115.

The output of the PLL is differentiated by a differentiating circuit 24, and a signal E corresponding to a falling edge is obtained through a diode 25. Eight and E are added together in an adder circuit 20, and a signal such as is obtained at the output, which is passed through SWl. Recorded by control head tag.

A positive direction pulse is used as a control signal, and a negative direction pulse is used as a wow/flutter detection pulse.

In this case, the reference oscillator 4-2 is selected to be five times the vertical synchronization frequency, and the frequency divider circuit 4-1 is set to 1110, so that the fifth
With the circuit connection shown in the figure, wow and flutter can occur as in the case of Figure 3.
can be removed.

Furthermore, in this case, the sampling period for detecting wow and flutter is 300 Hz, and wow and flutter components up to approximately 100 Hz can be removed and reduced.

In order to remove even higher components, the frequency of the component to be superimposed on the control signal should be made even higher.

Considering the case where the tape speed is 1 cm/Sec, the recording wavelength of the harmonic 600H2, which is twice the vertical synchronization signal, is approximately 16μ.
m, and at the recording wavelength, it is possible to record and reproduce up to about 1110, and it is possible to reproduce up to the 10th harmonic of 600H2, and the waveform shown in Figure 6 will be reproduced as a waveform that is very similar to the recording waveform. .

Therefore, harmonic components of about 600H2 can be recorded and reproduced, and wow and flutter can be removed and reduced to components of about 300H2.

Next, consider the relationship between the magnitude of wow and flutter and the number of bits of the charge transfer element.

The relationship between the magnitude W%pp of wow and flutter, its frequency doctrinal numerator, and the amount of time axis variation T is as follows: As the frequency component becomes lower, the amount of time variation (ie, the amount of correction) increases.

Now, if f = lOH2, W = 1%pp, then 1 τ=2a×10x100=”’奥/S80.

If the reference delay time DE0 of the charge transfer element is 1 m5ec, the above-mentioned flutter can be corrected by a variable amount of 16%.

Furthermore, if the reference clock frequency is 50 KHz, then the charge transfer element will only need to have 50 bits.

In reality, it has wow and flutter of various frequency components, and if you consider the case of about 0.5% γms, it will be 100%.
You will need something on the order of bits.

Note that in the case of capstan servo, the low frequency wow component is extremely small, but in the case of capstan drive using a power-synchronized motor as described above, deviation from the reproduction average clock frequency is detected and detected. All you have to do is remove it.

This method is well known as a method using a flywheel oscillator.

Note that in the specific configuration examples shown in Figures 3 and 5, the clock oscillator frequency that drives the charge transfer element is controlled in an open loop, but closed loop control as shown in Figure 7 provides even more stability. Accurate wah and
Flutter can be suppressed.

That is, in FIG. 7, two charge transfer elements 13 and 26 are used, an audio signal is passed through 13, a reference signal reproduced from a control signal is passed through 26, and 2
The phase of the reproduction reference signal which is the output of 6 and the reference oscillator 4-2
By comparing the phases of the signals in the phase comparator 9 and controlling the variable frequency oscillator 11 for clock oscillation through the hold circuit 10, the reproduced reference signal appearing at the output of 26 can be synchronized with the reference oscillator phase.

Therefore, wow and flutter can be accurately and stably removed from the reproduced audio signal appearing at the terminal 14.

Although it is preferable that the bit release of the charge transfer element 26 be the same as the bit number 01 of 13, the number of bits may be reduced.

Although the case where the signal shown in FIG. 6 is recorded as the signal to be recorded on the control track has been described, as another recording waveform, the waveform shown in FIG. 8A may be recorded.

Figure 7A is a vertical synchronization signal, and if a signal synchronized with this signal is recorded, a signal like . can.

Therefore, it is possible to control the speed of the VTR using the vertical synchronization signal of the signal train recorded in this way, and the above-mentioned wow and flutter control can be performed using the high-frequency pulse train that is reproduced with the opposite polarity to the synchronization signal. It becomes possible.

As described above, by using the means of the present invention, it is possible to electrically suppress wow and flutter in the audio signal of a VTR during low-speed tape running without creating a new recording track, and to compare the mechanical accuracy. It is possible to realize a device that does not require

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the recording pattern on the magnetic tape of a VTR and an outline of the tape drive system, Fig. 2 is a waveform diagram of the same operation, Fig. 3 is a block diagram showing an embodiment of the present invention, and Fig. 4 is a diagram showing an outline of the tape drive system. FIG. 5 is a block diagram showing another embodiment of the present invention; FIG. 6 is a waveform diagram of the same operation; FIG. 7 is a block diagram showing essential parts of another embodiment of the present invention; FIG. 8 is an operational waveform diagram in another embodiment of the present invention. 1... Control signal input terminal, 2. Death...
...Amplifier, 3,9...Phase comparator, 4...
...Reference oscillator, 5...Capstan motor, 7...Double wave 'I[E circuit, 10...
-Hold circuit, 11...variable oscillator, 13...charge transfer element (variable delay circuit).

Claims (1)

[Scope of utility model registration request] A video signal is recorded at the center of the magnetic tape by a rotating magnetic head that rotates in phase synchronization with a vertical synchronization signal of the video signal to be recorded, and an audio signal is recorded by a fixed magnetic head at one edge of the magnetic tape. , in a magnetic recording and reproducing apparatus in which a fixed magnetic head records a signal synchronized with the rotational phase of the rotating magnetic head on the other side edge of the magnetic tape as a control signal for tracking control of the rotating magnetic head during reproduction, A signal having a frequency higher than the vertical synchronization signal frequency synchronized with the vertical synchronization signal of the video signal to be recorded is recorded as the control signal, and a signal having a frequency higher than the vertical synchronization signal frequency synchronized with the vertical synchronization signal of the video signal to be recorded is recorded, and the reproduction tracking of the rotating magnetic head is controlled from the control signal reproduced during reproduction. At the same time as obtaining the first control signal, a second control signal having a higher frequency than the vertical synchronizing signal is obtained, and from this second control signal, time axis fluctuations accompanying wow and flutter of tape running are detected. 1. A magnetic recording and reproducing apparatus characterized in that a variable delay circuit provided in a reproduced audio signal processing circuit is controlled in accordance with a detection signal to suppress wow and flutter in a reproduced audio signal.