JPH0732480B2 - Playback device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reproducing apparatus suitable for application to a video tape recorder (VTR) which reproduces a signal in which an audio signal is FM-modulated and recorded together with a video signal.

2. Background Art and its Problems The luminance signal in the video signal is FM-modulated on the high frequency side, and the chroma signal is converted to low frequency so as to frequency interleave between adjacent tracks, and two rotary heads with different azimuth angles are used. It is used to record without placing a guard band on an inclined track on the tape.

In such a VTR, recording of an audio signal has conventionally been performed on a continuous track in the tape transfer direction using a fixed head by a method similar to what is called an audio tape recorder.

However, in the above-mentioned VTR, when the recording density is increased, the tape transfer speed is made extremely low, and is currently set to, for example, 1.33 cm / sec. For this reason, in recording an audio signal, the relative speed between the fixed head and the tape becomes slow, and good audio signal recording cannot be performed.

Therefore, it has been proposed that the audio signal is FM-modulated in the band between the FM-modulated luminance signal and the low-frequency converted chroma signal, and is superimposed on the image signal and recorded on the inclined track.

That is, in FIG. 1, (1) is a tuner,
The video signal from this tuner (1) is AGC amplifier (2), emphasis circuit (3), clamp circuit (4)
Is supplied to the FM modulator (5) to form an FM luminance signal Y _{FM which} is FM-modulated so that the sync tip has a frequency of 4.0 MHz and the white peak has a frequency of 5.2 MHz. Also, the video signal from the tuner (1) is a bandpass filter (6), AC
C circuit (7), is supplied to a low-pass filter (9) sub-carrier frequency through the frequency converter (8) down-conversion chroma signal C _D of 688kHz is formed.

Further, the first audio signal (left signal for stereo, main signal for dual audio) A _L and the second audio signal (right signal for stereo, sub signal for dual audio) A _R from the tuner (1) are respectively supplied. AGC amplifier (10L), (10R), noise canceller (11
L), (11R), pre-emphasis circuit (12L), (12R)
Are supplied to the FM modulators (14L) and (14R) through, and are FM-modulated so that the carrier frequency is 1.325MHz and 1.625MHz, respectively, and the frequency variation width is constant 150kHz.
In addition, these signals are converted to the frequency converter (21L), (21L
R) and also from the oscillator (22) eg 150kHz
Is supplied to these converters (21L) and (21R) to be signals having carrier frequencies of 1.475 MHz and 1.775 MHz, respectively. The levels of these signals are adjusted, and the FM audio signals A _LF1 , A _LF2 , A _RF3 , which are adjusted so that the levels are A _LF1 <A _LF2 <A _RF3 <A _RF4 , as shown in FIG.
A _RF4 is formed. The FM audio signals A _LF1 and A _RF3 among them are supplied to the mixing amplifier (16 ₀ ) through the band pass filters (15 ₁ ) and (15 ₃ ), respectively, and the FM audio signals A _LF2 and A _RF3 are also supplied.
_RF4 is supplied to the mixing amplifier (16e) through the bandpass filters (15 ₂ ) and (15 ₄ ), respectively. The mixture amplifier (16 _0), signals each heating circuit from (16e) (17
₀ ), (17e). The adder circuit (17 _0), (1
The above-mentioned FM luminance signal Y _FM and low frequency conversion chroma signal C _D are commonly supplied to 7e). The added signals are respectively recording amplifier (18 _0), the rotary head (19 ₀₎ of different azimuth angles to each other through (18e), is supplied to the (19e).

In this device, the spectrum of the recording signal is as shown in FIG. And of these, FM audio signals A _LF2 and A _RF4 are removed to the head (19o), and FM to the head (19e).
A signal excluding A _LF1 and A _RF3 of the audio signal is supplied.

And with this head (19o), (19e), the tape T
As shown in FIG. 4, tilted tracks to and te having different recording azimuths are alternately formed on the upper side, and the signals [Y _FM + C _D + A _LF1 + A _RL3 ] or the signal [Y _FM + C _D + A _LF2 +
A _RL4 ] is recorded. A control signal CTL from a servo system (not shown) is recorded on the continuous track t _C.

In this way, the video signal and the audio signal are recorded.

Then, for example, the following is performed to reproduce the signal thus recorded.

That is, in FIG. 5, the rotary heads (19o), (19e)
Playback signals are taken out through amplifiers (40o) and (40e), respectively. The signal from this amplifier (40o) is supplied to the bandpass filters (41 ₁ ) and (41 ₃ ) whose center frequencies are 1.325MHz and 1.625MHz, and the signal from the amplifier (40e) is centered at 1.475MHz. And 1.775 MHz band pass filters (41 ₂ ) and (41 ₄ ). Furthermore, these band-pass filters (41 _2), (41 ₄₎ signal from the frequency converter (23 _2), (23 ₄₎ is supplied to and oscillator converts signals from (22) the converters (23 ₂ ) (fed to 23 _4), each carrier frequency 1.
The signals are 325MHz and 1.625MHz. The signals from the bandpass filter (41 ₁ ) and the frequency converter (23 ₂ ) are supplied to the switch circuit (45 L), and the signals from the bandpass filter (41 ₃ ) and the frequency converter (23 ₄ ) are supplied to the switch circuit. (45R) will be supplied. The switch circuits (45L) and (45R) are controlled by a head switching signal supplied to a terminal (46) from a pulse generator provided in association with the rotary drum, for example. This switch circuit (45
Signals from L) and (45R) are output from the limiter circuit (42
L) and (42R) are supplied to FM demodulators (43L) and (43R) to demodulate audio signals A _L and A _R , respectively. These audio signals A _L and A _R are low pass filters (44 L) to
(44R) is supplied. This low pass filter (44L),
The signals from (44R) are sample hold circuits (47L), (47R), low-pass filters (48L), (48R), de-emphasis circuit (49L) for dropout compensation.
It is supplied to audio output terminals (52L) and (52R) through (49R), output amplifiers (51L) and (51R).

As for the sample signals supplied to the sample hold circuits (47L) and (47R), for example, the signal from the switch circuit (45L) is supplied to the envelope detection circuit (24), and this detection output is supplied to the Schmitt circuit (25). The detection signal is supplied to the monostable multivibrator (26), and the output signal of the multivibrator (26) and the signal from the Schmitt circuit (25) are connected to the OR circuit ( It is synthesized and formed in 27). That is, as shown in FIG. 6A, the playback signal is dropped out (DO).
6B, an envelope output as shown in FIG. 6B and a Schmitt output as shown in FIG. 6C are formed.
A hold signal as shown in FIG. 6E is formed from the multivibrator output as shown in FIG. 6D and the Schmitt output described above.

Further, signals from the amplifiers (40o) and (40e) are supplied to the switch circuit (60), and the switch circuit (60) is controlled by the signal from the terminal (46). The signal from the switch circuit (60) is supplied to the high-pass filter (61) to extract the FM luminance signal Y _FM , and this signal is supplied to the limiter (62), FM demodulator (63), and emphasis circuit (64). Then, the luminance signal Y is demodulated. Further, the signal from the switch circuit (60) is supplied to the low pass filter (65) to extract the low frequency conversion chroma signal C _D , and this signal is supplied to the high frequency conversion circuit (66) and the band pass filter (67). And the chroma signal C is taken out. The luminance signal Y and the chroma signal C are mixed in the mixing circuit (68) to form a video signal, which is supplied to the video output terminal (69).

In this way, the video signal and the audio signal are reproduced.

In this case, since the audio signal is FM-modulated and recorded and reproduced by the rotary head together with the video signal, the audio signal is not deteriorated even if the tape transfer speed is reduced.

Also, in the recorded FM audio signal, crosstalk from adjacent tracks is reduced due to azimuth loss, and the carrier frequency is different between adjacent tracks by 150 kHz, so the frequency of the beat signal is outside the audible band, and there is interference. Not good playback can be done.

By the way, in this device, FM demodulator (43L), (43R)
If the demodulation output of the signal is as shown in FIG. 6F due to the influence of dropout (DO), the signal obtained by passing this signal through the low-pass filters (44L) and (44R) is the sixth signal. As shown in FIG. G, there is a slight delay and a signal in which vibration continues after the pulse due to dropout.
Therefore, in order to compensate the dropout, it is necessary to sample and hold even this oscillating portion, and the multivibrator (26) is provided as described above, and the hold is performed as shown in FIG. 6H.

However, when such a long-term hold is performed,
When the signal waveform is distorted and the signal is deteriorated and a large number of dropouts are generated, it is extremely offensive to the ears.

On the other hand, it was possible to sample and hold the signal before passing through the low-pass filters (44L) and (44R), but in this case there is some time delay in the detection of dropout. When holding is performed with a signal having a time delay as shown in I, there is a possibility that holding is performed in the middle of the pulse due to dropout and a large level of noise is generated as shown in FIG. 6J.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and it is an object of the present invention to provide good dropout compensation with a simple structure.

SUMMARY OF THE INVENTION The present invention detects a dropout in a reproduced signal when reproducing a signal in which a voice signal is FM-modulated and recorded,
A signal obtained by FM demodulating the reproduced signal and a signal obtained by supplying the demodulated signal to a first low-pass filter to remove noise and then sample-holding with the dropout detection signal are the dropout detection signal. Reproduction by outputting the sampled and held signal during the dropout period, extracting the demodulated signal during the other period, and outputting the extracted signal through the second low-pass filter. This is a device, which enables good dropout compensation with a simple configuration.

Embodiment In FIG. 7, the demodulation output of the FM demodulator (43L) is supplied to a sample hold circuit (47L) through a low pass filter (44L) having a delay time almost the same as the delay time of the dropout detection output, and this hold The output and the demodulated output from the FM demodulator (43L) are supplied to the switch (28). In addition, the output signal of the Schmitt circuit (25) is directly supplied to the sample hold circuit (47L) to perform sample hold, and the switch (28) is switched by this signal, and normally the demodulated signal is taken out and dropped out. When is detected, the sample hold output is taken out. The signal from this switch (28) is a low-pass filter (48L).
Is supplied to.

Although only the path of the audio signal A _L is shown above, the audio signal A _R
The path of is similarly configured. Others are the same as those in FIG.

In this device, for a reproduction signal having a dropout (DO) as shown in FIG. 8A, when the demodulated output is as shown in FIG. 8B, the signal obtained by passing this signal through a low-pass filter is When the sample is held with the dropout detection signal as shown in FIG. 8C, a signal as shown in FIG. 8D is obtained. Then, by switching this signal to the FM demodulation output, a signal as shown in FIG. 8E is obtained. That is, the sampled and held signal is close to the original signal level, and the dropout is compensated for by the signal whose holding period is short.

A spike-shaped signal appears during the delay time of dropout detection, but this is an extremely short period of time, and the switch (28)
The switching noise is almost the same as the switching noise of No. 1 and is removed by the low-pass filter (48L) as shown in FIG. 8F.

In this way, dropout compensation is performed, but with this device, the configuration is simple only by providing the switch (28), and the hold period may become long and a large level of noise may occur. Fewer and better compensation can be done.

This device can also be applied to a VTR that FM-modulates an audio signal and records it in the deep magnetic layer of the tape using a head with a wide gap width.

EFFECTS OF THE INVENTION According to the present invention, good dropout compensation can be performed with a simple configuration.

[Brief description of drawings]

1 to 6 are diagrams for explaining a conventional apparatus, FIG. 7 is a system diagram of an example of the present invention, and FIG. 8 is a waveform diagram for the explanation. (43L), (43R) are FM demodulators, (44L), (44R), (48
L) and (48R) are low-pass filters, (47L) is a sample and hold circuit, (25) is a Schmidt circuit for detecting dropout, and (28) is a switch.

Claims (1)

[Claims] 1. A device for reproducing a signal in which a voice signal is FM-modulated and recorded, and means for detecting dropout by detecting a period during which a reproduced FM voice signal from a reproducing head is below a predetermined level. A means for demodulating the reproduced FM audio signal and a delay time of the detection output from the dropout detection means, while removing the component corresponding to the noise of the output signal limited to the audio frequency band from the demodulation means. A first low-pass filter having a delay time, and an output signal from the dropout detection means,
Of the output signals of the first low-pass filter, a sample hold circuit that holds the waveform value immediately before the dropout, and an output signal from the dropout detection means,
A switch circuit that selectively outputs the output signal of the sample hold circuit during the dropout period and the output signal from the demodulation unit during the period other than the dropout period, and an output signal from the switch circuit. And a second low-pass filter for removing a component corresponding to the noise and a component corresponding to the noise generated by switching the switch.