JPS60145565A - playback device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a video tape recorder (V
'T'R)

Background technology and its problems The luminance signal in the video Iba is F'M modulated on the west side, and the chroma signal is low frequency converted to frequency interleave between adjacent trunks, and Two rotary heads are used to record the tape without placing a guard punt on the tape.

Recording of °C1 audio signals in such a VTR is as follows:
Conventionally, this has been done using a fixed head on continuous tracks in the tape transport direction in a similar manner to what is called an audio tape recorder.

In the case of the above-mentioned V T'H, when the recording density is increased, the tape transport speed is made extremely low, and in so-called 8 mm video, it is reduced to about L4 cm/sec. For this reason, when recording audio signals, the relative speed between the fixed head and the tape becomes slow, making it impossible to record good audio signals.

It has been proposed that the audio signal be FM-modulated in a band between the FM-modulated luminance signal and the low-frequency converted chroma signal, and that the audio signal be combined with the video signal and recorded in a slope 1-rank. Ta.

That is, FIG. 1 shows an example of a so-called 8 mm video recording system. In the figure, the image signal from the input terminal +11 is sent to the AGC amplifier (2) and the pre-emphasis circuit (3).
, is supplied to the FM modulator (5) through the clamp circuit (4), and an FM luminance signal YFM is formed which is FM-modulated so that the sync tip is 4.2 MIIz and the white beak is 5.4 Mllz. This signal YFM
is supplied to the mixer (7) through a no pass filter (6).

In addition, the video signal from the input terminal (1) passes through the band pass filter (8) and the pre-emphasis circuit (9) and is fed to the ζ low-frequency conversion circuit aω (Jli) so that the subcarrier frequency is 743
．． A low frequency converted chroma signal CD of 44 kllz is formed. This signal CD is supplied to a mixer (7) through a low-pass filter (11).

Further, the audio signal from the input terminal (12) is supplied to a low-pass filter (14) through an AGC amplifier (13), and the band is limited to 15kllz or less. This signal is fed to a noise reduction encoder (15). This encoded signal is passed through the limiter (16) to F
For example, C1 is supplied to the M modulator (17) and has a center frequency of 1.
, 5M1lz(7) FM audio signal AFM is formed. This signal AFM is 1.5Mflz±100kll
Mixer (7) through Z bandpass filter (18)
supplied to

Further, a pulse signal synchronized with the rotation from the rotating heso-dot drum (not shown) is supplied to the ζ multiplier (20) through the terminal (19) to form a signal that goes around once in ζ4 tracks. This signal is fed to a 4-frequency pilot signal forming circuit (21), and approximately 102.
54kllz, 118.95kl12.165.2
1kllz.

14B, 6! A pilot signal varying in frequency is formed. This signal is fed to a mixer (7).

Therefore, a frequency-multiplexed recording signal is taken out from the mixer (7), as shown in FIG. 2, for example.

Note that only one pilot signal is provided for each track.

Then, this recording signal is passed through the recording amplifier (22) to the rotating heads (23a) and (2) having different azimuth angles.
3b).

In this way, the °C video signal and the back door signal are recorded.

Furthermore, in order to reproduce the signal recorded in this manner, for example, the following procedure is performed.

Zunawaji Figure 3 (, Rotating navel F (23a)
, (23b) are respectively ゛j°amp (31
a), (31b). The signals from these amplifiers (31a) (31b) are transmitted to the switch circuit (3
2), and this switch circuit (32) is supplied to the terminal (3).
3) is controlled by the head switching signal from 3). The signal from this switch circuit (32) is transmitted to the bypass filter (3
4), the l''M luminance signal YFM is taken out, and this signal is sent to the limiter (35) and the FM demodulator (36).
, the luminance signal is supplied to a de-emphasis circuit (37) and converted into tjtJ-ft1lJ. In addition, the switch circuit (32
) is supplied to a low-pass filter (38), a low-pass converted chroma signal CD is extracted, and this signal is supplied to a high-pass conversion circuit (39), a de-emphasis circuit (40), and a band-pass filter (41). Then, the C chroma signal is extracted. The luminance signal and chroma signal are mixed in a mixing circuit (42) to form a video signal, which is output to a video output terminal (43).

Further, the signal from the switch circuit IIR (32) is supplied to a bandpass filter (44) with a center frequency of 1.5M11Z, and an I''M audio signal AFM is extracted.This signal AFM is FM demodulated through a limiter circuit (45). Vessel (4
6) and the ζ audio signal is demodulated. This audio signal is supplied to a low pass filter (47).

The signal from this low-pass filter (47) passes through a pre-hold circuit (48) for dropout compensation, a low-pass filter (49), a de-emphasis circuit (50), and an output amplifier (51) to output audio ( 52).

Further, the sample signal supplied to the bold circuit 1f8 (48) is, for example, a signal from a switch circuit (32) supplied to an envelope detection circuit (53), and this detection output is supplied to a Schmitt circuit (54). A period below the level of is detected, and this detection signal is supplied to the monostable multi-by break (55), which
55) and the signal from the Schmitt circuit (54) are combined in the OR circuit (56) to form "ζ".In other words, as shown in FIG. 4A, there is a dropout (
DO), an envelope output as shown in Fig. 4B and a Schmitt output as shown in Fig. 4C are formed, and a multi-high break output as shown in Fig. 4 and the above-mentioned Schmitt output are formed. From this, a bold signal as shown in FIG. 4E is formed.

Furthermore, the signal from the switch circuit (32) is supplied to the pilot signal detection circuit (57), and a four-frequency pilot signal is detected. This detection signal is supplied to the tracking control signal formation circuit (58), A trussogging control signal is formed according to the level of each pilot signal.

This control signal is transmitted through the terminal (59) to the servo rotation I/8 (
The signal is supplied to the figure 'fl').

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 together with the video signal by the rotary head, the audio signal will not deteriorate even if the tape transport speed is reduced.

By the way, in this device, the demodulated output of the FM demodulator (46) is affected by the drop error (Do), for example, the fourth
If the signal is as shown in Figure F, the signal obtained when this signal passes through the low-pass filter (47) is as shown in Figure 4G.
As shown in , the signal is delayed somewhat and the oscillation continues after the pulse due to dropout. Therefore, to compensate for dropout, it is necessary to bold up to this vibration part, and as mentioned above, multi-pie break (5
5) is provided, and a hold is performed as shown in FIG. 4H.

However, when held for a long time like this,
The signal waveform was distorted, the signal deteriorated, and the sound became extremely harsh, especially when many dropouts occurred.

On the other hand, it was considered to perform bolding on the signal before passing through the low-pass filter (47), but in this case, there would be some time delay in detecting dropout, and the fourth
If a hold is performed with a time-delayed signal as shown in Figure I, bolding may occur in the middle of the pulse due to dropout, as shown in Figure 4J, which may generate a large level of noise. Ta.

Therefore, the present applicant previously proposed a device that solved this problem. Zunawaji In Figure 5, the FM demodulator (
The demodulated output of 46) is supplied to a hold circuit (48) through a low-pass filter (47), and this hold output and the demodulated output from the FMtfL modulator (46) are supplied to a switch (60). Also, Schmitt circuit (54
) is directly supplied to the bold circuit (48) to perform bolding, and this signal also causes the switch (
60) is switched, the demodulated signal is taken out from 1lr1, and the hold output is taken out when dropout is detected. The signal from this switch (60) is supplied to a low pass filter (49).

Although the audio signal path has been omitted in the above description, the rest of the configuration is the same as that shown in FIG. 3.

In this device, if a repeating signal has a dropout (Do) as shown in Fig. 6A, and this demodulated output is as shown in Fig. 6B, this signal is passed through a low-pass filter. 1 drop as shown in Fig.
A signal similar to BoJ can be obtained. By switching this signal to FM demodulation, a signal as shown in FIG. 6E is obtained. That is, the bolded signal is close to the original signal level, and the dropout is compensated for by using the signal for which the holding period is short.

Note that a spike-like signal appears in the delay time of dropout detection, but this is extreme! ,, short period, and much different from the switching noise of the switch (60) (, low-pass filter (
49) as shown in FIG. 6F.

Compensation for ζ dropout is performed in this way, and according to this device, there is little risk that the bold period will become long or large-level noise will occur, and good compensation can be performed.

However, in this device °ζ, the low-pass filter is (
47), (49) 2 (161) is required.In this case, if you try to obtain steep characteristics in the voice band, a large-scale circuit of 6th to 7th order is required for the filter, and In this case, the capacitor needs to have a large capacity and is externally connected to tC.

Therefore, such a low-pass filter is S/+1111
This required a circuit configuration that required an extremely large number of people, which was disadvantageous in terms of design, and required a large number of external components and connection pins, which was a problem that required a lot of practical personnel.

OBJECTS OF THE INVENTION In view of these points, the present invention is designed to provide good dropout compensation with a simple configuration.

Summary of the Invention The present invention provides an audio signal that can be converted to FM! When reproducing the recorded signal, the Do1:J sozoout in the reproduced signal is detected, and the FMili-circulated signal from the reproduced signal is passed through a switch circuit to a low-pass filter and a pre-hold circuit. or a series circuit in which these are arranged in reverse, and outputs the signal from this series circuit, and also outputs the signal from the dropout detection signal by setting the pre-hold circuit in bold state and outputting the above. This is a reproducing device in which a signal is fed back to about 10 series circuits via the switch circuit described above, and according to this, good dropout compensation can be performed with a simple configuration.

In FIG. 7 of the embodiment, the fjL output of the FMifi adjuster (46) is passed through the switch (60) to the ゛ζ low-pass filter (
47), the output of the hold circuit (48) is supplied to the de-emphasis circuit (50), and the output of the bold circuit 1+'&(48) is fed back to the switch (60). Then, the signal from the Schmitt circuit (54) is driven to the hold circuit (48), and the switch (60) is switched to the feedback loop side by 9J.

Note that although only the audio signal path has been omitted in the description, the rest is constructed in the same manner as in FIG.

In this device, if the demodulated output is -2 as shown in Fig. 8-13 for a reproduced signal having a dropout (DO) as shown in Fig. 8A, this signal is converted into Fig. 8C. The dropout detection signal causes the switch (
When the switch (60) is switched, a signal like the one shown in the eighth figure is taken out from the switch (60). When this signal is supplied to the low-pass filter (47), a somewhat delayed signal is obtained as shown in FIG. 8E. Each time this delayed signal is held in the hold circuit (48),
A signal such as J< is taken out from the hold circuit (48) as shown in FIG. 8F.

Then °ζThis bolded signal is also the switch (6
0), a spike-like signal remains at the input of the low-pass filter (47) (D in Figure 8) at the beginning of dropout, but thereafter a constant signal is supplied, and the low-pass filter (47) (47) output (Fig. 8E
) will cause some vibration, but it will soon stop and a stable signal will be obtained when bold is released.

Koushi °C dropout? However, with this device, there is little risk of the bold period becoming long or large-level noise occurring, and only one low-pass filter is required, resulting in an extremely simple configuration. Compensation can be made.

According to this device, only one low-pass filter is required, so the circuit can be miniaturized, it can be easily integrated into an IC, and costs can be reduced.

Note that the above-described device can also be used to remove noise when switching the rotary head.

The circuit configuration is shown in Figure 9 as a bold circuit (4
8) and the low-pass filter (47) are connected in reverse, and the effect is the same. In this case the short delay circuit (61) is connected to the Schmitt circuit (54) to ensure that the switching occurs after the switching of the switch (60).
! 8 (48) Control C may be provided between the control a11 terminal and the tonneau.

Note that this device 6' can also be applied to a VTR that performs FM modulation on the audio signal and records it deep in the magnetic layer of the tape using a head with a wide gap width.

Effects of the Invention According to the present invention, it has become possible to perform good dropout compensation with a simple configuration.

[Brief explanation of the drawing]

1 to 4 are diagrams for explaining a conventional device, FIGS. 5 and 6 are diagrams for explaining a device previously proposed by the applicant, and FIG. 7 is an example of the present invention. FIG. 8 is a waveform diagram for explaining the system diagram, and FIG. 9 is a system diagram of another example. (46) is an FM restorer, (47) is a low-pass filter,
(48) is a front bold circuit, (54) is a Schmitt circuit for dropout detection, and (60) is a switch. Ma Hidemori Matsukuma Figure 7 Figure 9 54 61

Claims (1)

[Claims] When reproducing a signal recorded by FM modulating an audio signal, a dropout in the reproduced signal is detected, and the FM decoded & Ifd signal from the reproduced signal is passed through a switch circuit to a low-pass filter and a pre-hold circuit. series circuit,
Or, supply these to a series circuit arranged in reverse, output the signal from this series circuit, and output the above-mentioned drop °7.
A reproducing device wherein the pre-bold circuit is put into a hold state by the detection signal 1-, and the output signal 2 is fed back to the series circuit via the switch circuit.