JPS6034141Y2 - Low frequency signal regenerator - Google Patents

Description

[Detailed description of the invention] In a conventional magnetic recording and reproducing device (VTR), a low frequency signal (hereinafter referred to as an audio signal) is recorded or reproduced by a fixed head on a magnetic track separate from the video signal. It is done like this.

Incidentally, in general household VTRs, in order to enable long-time recording, the magnetic tape speed has recently tended to increase or decrease, and some current tape speeds are 2 cm/sec.

However, if the tape speed becomes even slower than this, bias recording and reproduction of audio signals using a conventional fixed head becomes nearly impossible.

Therefore, a device has been proposed that uses a rotating magnetic head (hereinafter referred to as a rotary head) for recording a video signal to record an audio signal in a superimposed manner on the recording track of the video signal, or to reproduce it from this. Due to the high relative speed of the head for recording audio signals with respect to the magnetic tape, the above-mentioned disadvantages are avoided.

An example of this recording apparatus will be described with reference to FIG. 1. Reference numeral 1 denotes an input terminal for a video signal to be recorded, and 2 denotes an input terminal for an audio signal to be recorded.

The video signal supplied to terminal 1 is sent to horizontal synchronization signal separation circuit 3
The horizontal synchronizing signal SH (see FIG. 2A) is taken out, which is supplied to the delay circuit 4, and from its output side,
A delayed signal SD (FIG. 2B) which is delayed in time from the horizontal synchronizing signal SH and has a time width W is obtained, and the switching circuit 5 is driven by this signal.

That is, by this signal So, the switching circuit 5 is always in the state shown by the solid line, and during the period when the signal SD is obtained, the switching circuit 5 is switched to the state shown by the dotted line.

On the other hand, the signal supplied to the terminal 1 is supplied to a clamp circuit 6, in which, for example, the level of the video signal is clamped.

This clamped signal is supplied to the switching circuit 5.

Furthermore, the audio signal supplied to the terminal 2 is supplied to a sample and hold circuit 8 through a low-pass filter 7, where it is sampled and held using a horizontal synchronizing signal SH.

Figure 2C shows the input signal S to the sampling hold circuit 8.
A1 indicates the output signal Ss from the same circuit 8.

This signal Ss is supplied by the switching circuit 5 to the frequency modulator 9, frequency modulated, and sent to the rotary head 10, where it is recorded on the magnetic tape 11.

The above-mentioned temporal position of the signal SD with respect to the video signal is selected so as to be located at its back porch or flotate porch within the horizontal blanking period, and the time width W is, for example, 2.
It is possible to choose about microseconds.

In this way, the frequency modulator 9 includes the switching circuit 5.
The video signal and the audio signal switched at are supplied, and FIG. 2E shows the signal Se supplied from the sample-and-hold circuit 8 to the frequency modulator 9.

Therefore, in this example, the audio signal is recorded as a burst signal within the horizontal blanking period of the video signal.

As the delay circuit 4, it is possible to use two monostable circuits connected in series.

The low-pass filter 7 is for extracting signals with a sampling frequency (in this case, the repetition frequency tH of the horizontal synchronization signal) of 1n or less.

A circuit for reproducing signals and extracting audio signals from the magnetic tape 11 on which video signals and audio signals have been recorded in this manner will be explained with reference to FIG.

That is, the video signal recorded on the magnetic tape 11 is reproduced by the rotary head 10 and transmitted to the picture tube 13 of the monitor television 12.
It is normal to see what is shown on the screen.

14 and 15 are an FM demodulator and a horizontal synchronization signal separation circuit in the monitor television 12, and the horizontal synchronization signal separation circuit 15
The output of is shown as signal S1 in FIG. 4A.

This signal S1 is supplied to a delay circuit 16, and a delayed signal S2 as shown in FIG. 4B is obtained at its output side.

The delay time T and time width W in this case are chosen similarly to those in FIG.

On the other hand, the signal obtained from the demodulator 14 is clamped to the level of the video signal by a clamp circuit 17, and is supplied to a sampling hold circuit 18.

Therefore, the signal reproduced by the rotary head 10 is sampled by the sampling signal S2 in the sampling hold circuit 18.

Since this sampling time coincides with the time when the audio signal was recorded in FIG. 2, a signal related only to the audio signal is obtained from the sampling and hold circuit 18.

FIG. 4C shows this output signal S3.

Since such an output signal S3 is supplied to the low-pass filter 19, an audio signal shown in the fourth diagram is obtained at the output terminal 20.

In this manner, the rotary head 10 reproduces the audio signal.

The purpose of the clamp circuit 17 in this case is to prevent harmonic components of 60 Hz from being mixed into the audio signal if the vertical synchronization signal level fluctuates.

In this way, the recording and playback of audio signals to video signals can be done with a simple circuit, and when playing back audio, the horizontal synchronization signal is always used as a reference, and since the playback circuit has a sampling and hold circuit 1B, rotation If the head 10 operates stably even with speed deviations, and the audio signal insertion time is 2 μs, then the speed deviation of 2 μs (2/63.5
) is stable against

However, even with such a reproducing device, in a helical scan VTR, a pair of heads (two heads) alternately scan the magnetic tape 11, that is, a pair of heads 1
Jumping occurs in the horizontal period due to skew due to zero switching.

For this reason, a skew also occurs in the sampling pulse, and a harmonic signal of the frequency at which the skew occurs (constant periodic sound of N times 60H2) is mixed into the output terminal of the audio signal, causing deterioration of the SN.

This invention takes into consideration a reproducing circuit in order to avoid such drawbacks, and this will be explained with reference to FIG. 5 and subsequent figures.

The video signal including the audio signal reproduced by the rotary head 10 is supplied to an input terminal 21, passed through a clamp circuit 22, and further supplied to a low-pass filter 25 via first and second sampling and hold circuits 23 and 24. , the output thereof is supplied to the output terminal 26.

On the other hand, a part of the signal supplied to the input terminal 21 is supplied to the horizontal synchronizing signal separation circuit 27 to separate the horizontal synchronizing signal Sa shown in FIG. 6A, which is supplied to the switching pulse forming circuit 28.

This switching pulse forming circuit 28 is composed of a delay circuit 29 and a bistable circuit 30 called a D-type flip-flop, and the above-mentioned horizontal synchronizing signal Sa is supplied to this delay circuit 29. A delayed signal sb having a delay time T1 shown in FIG.

This delay time τ1 is preferably selected to be approximately < 1/2 of one horizontal opening period 1H.

This delayed signal sb is supplied to the clock input terminal C of the above-mentioned bistable circuit 30, and the signal SC supplied to the input terminal 31 is supplied to the terminal of the bistable circuit 30, respectively.

This signal Sc is generally called PG and is obtained based on the rotation of a rotating head (rotating drum).
Generally, the rotation speed of the rotating drum is 3 (2) revolutions per second, so it is obtained as a signal of 30H2, and conventionally the 6th
In Figure C, the low level period of the signal SC is the period when the first head (head A) of a pair of rotating heads plays the signal from the tape, and the high level period is the period when the signal is played back from the tape by the second head (head B). It is used as a so-called head switching signal during the signal reproduction period.

As a result, the signal Sd shown in FIG. 6 is obtained from the terminal Q of the bistable circuit 30 at the first delayed signal sb after the signal SC becomes high level.

Although not shown in FIG. 6, the bistable circuit 3 is activated by the first delayed signal sb after the signal Sc becomes low level.
The signal Sd from the output terminal Q of 0 is also set to low level.

In this invention, the output signal Sd from the bistable circuit 30 is used as a switching signal for the pair of rotating heads.

Furthermore, in this invention, the repetition period of the horizontal synchronization signal Sa is
, an oscillator 33 having an oscillation frequency of nf, 4 (where n is a positive integer) is provided, and the output signal Sf shown in FIG. ) is supplied to a step-down circuit (in this case, a quaternary counter) 34 which steps down the frequency by l/n, and the signal sh shown in FIG. 6H is obtained at its output side.

Further, the output signal Sd from the switching pulse forming circuit 28, that is, the output signal Sd from the bistable circuit 30, and the horizontal synchronization signal Sa from the horizontal synchronization signal separation circuit 27 are supplied to the AND circuit 32, and when the signal Sd is at a low level, for example, Only then, as shown in FIG.
4, thereby resetting the counter 34.

Therefore, the signal Sf supplied to this counter 34 is the signal S
During the low level period d, it is reset every four pulses.

Although such a reset is not performed during the high level period of the signal Sd, it goes without saying that a signal is obtained every four pulses.

Furthermore, in this invention, the horizontal synchronizing signal Sa is supplied to the first delay circuit 35 to obtain the first delayed signal Se shown in FIG. 6E, and the output signal sh from the counter 34 mentioned above is is supplied to the second delay circuit 36 to obtain the second delay signal Si shown in FIG. 6I.

In this case, the delay time T1 of the first delayed signal Se with respect to the horizontal synchronizing signal Sa is selected to be equal to the time period explained at the time of recording in FIG.

The delay time D2 of the second delay signal Si can be selected at any time within one period sampled during recording.

Further, the signal Sf from the oscillator 33 is supplied to the drum motor 38 through the frequency down-conversion circuit 37, and the motor 38, that is, the rotary head is rotated in synchronization with the signal Sf.

In this case, the frequency down-down ratio of the frequency down-down circuit 37 is nX
262.5, which causes the drum to move at a speed of 3 (2
) rotates at a rotational speed of

According to such a configuration, the head drum, that is, the rotary head rotates in synchronization with the signal Sf from the oscillator 33, and therefore the synchronization signal Sa from the synchronization signal separation circuit 27 is synchronized with this.
will also be obtained.

As described above, since the head switching signal forming circuit 28 is provided, the switching between the A head and the B head is performed at the intermediate position of the horizontal synchronizing signal Sa, as explained in Figure 6. (within the vertical blanking period). Conventionally, the switching position of this switching signal Sc was not determined, which disturbed the horizontal synchronization signal and thereby the audio signal to be reproduced. In this case, since the head is switched while avoiding the horizontal synchronization signal position, the horizontal synchronization signal is not disturbed, and therefore the audio signal is reliably reproduced.

Furthermore, the output from the clamp circuit 22 is sampled by the signal Se shown in FIG. be done.

FIG. 7C shows the state of this signal Sj. In this figure, parts corresponding to those in FIG. 6 are designated by the same reference numerals.

The signal Sj held in this manner is further sampled and held in the second sampling and holding circuit 24 using the delayed signal Si from the second delay circuit 36.

FIG. 7E shows the state of this signal Sk, which is obtained at the output terminal 26 through the low-pass filter 25, so that the audio signal is reproduced.

In FIG. 6 and FIG. 7, the generation points of some of the horizontal synchronization signals are marked with t, t2t, t, and t4, respectively, and the time between t2 and t2 is shown as the other time t□ and t4. ,
The time is shorter than between t4 and t4.

In other words, this indicates a state in which skew has occurred.

Therefore, as is clear from FIG. 7C, the output signal Sj sampled and held by the first sampling and holding circuit 23 is also obtained in a shorter period of time than at other times between 12 and 13.

However, according to this invention, since the above-mentioned signal Sj is further sampled in the second sampling and hold circuit 24 using the signal Si having a constant period, the output signal Sk is Each sampling and hold period is constant, so that it is possible to avoid mixing of harmonic signals due to the skew mentioned at the beginning, and it is therefore possible to prevent the SN from deteriorating.

In FIG. 5, the video signal reproduction system is omitted.

Further, in the embodiment shown in FIG. 5, the AND circuit 3 is activated only during the low level period of the signal Sd, that is, during the reproduction period by the A head.
Since the counter 34 is reset by the signal Sg obtained from 2, that is, every 4 pulses, a specific signal (pulse) of the signal Sf supplied to the counter 34, ie, the example of FIG. Then horizontal synchronization signal S
The first pulse after a (1st pulse) is taken out,
Based on this, the second sampling circuit 24 is sampled, so that the sampling instant is always determined.

Although such an operation is not performed during the playback period by the B head, by making the above-described determination during the playback period by the A head, it is almost possible to avoid disturbance of the sampling point within the playback period by the B head. Even if a disturbance occurs during the reproduction period by the B head, this disturbance will be corrected again in the next reproduction period by the A head.

According to the invention described above, by providing the two sampling and holding circuits 23 and 24, it is possible to reliably avoid mixing of harmonics during reproduction.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an example of a recording device to explain the playback device according to this invention, FIG. 2 is a waveform diagram to explain its operation, and FIG. 3 is a block diagram showing a normal playback device. FIG. 4 is a waveform diagram for explaining the same, FIG. 5 is a block diagram showing an example of a reproducing apparatus according to this invention, and FIGS. 6 and 7 are waveform diagrams for explaining the respective operations. 10 is a rotating magnetic head, 23 and 24 are first and second sampling and holding circuits, 27 is a horizontal synchronizing signal separation circuit, 33 is a reference signal oscillator, and 38 is a drum motor.

Claims (1)

[Scope of utility model registration request] A plurality of reproducing signals from a magnetic tape on which a video signal and a low frequency signal sampled with a sampling signal related to a synchronization signal and inserted within a horizontal blanking period of the video signal are recorded on each magnetic track. a rotating magnetic head; a first sampling and hold circuit for extracting a low frequency signal from the reproduced video signal by sampling the signal reproduced by the rotating magnetic head with reference to a horizontal synchronizing signal in the signal; A low frequency signal reproducing device comprising a second sampling and holding circuit that samples the output from the first sampling and holding circuit using a sampling signal having a constant repetition period synchronized with the rotation of the rotating magnetic head.