JPH0115189B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to magnetic recording and playback devices, and more particularly to dropout compensation for playback video head output.

Conventionally, in a heterodyne magnetic recording/playback device, the temporary loss of a signal during playback of a frequency modulated video signal recorded from a magnetic tape is called dropout. If there is a large scratch and the magnetic head output signal is missing, the demodulated output waveform is a noise component, and during the period of the noise component, (a) the noise component level is higher than the video signal level, or (b) Under two conditions, even if the noise component level is small, the peak of the noise level is higher than the white level of the video signal, if modulated to a television signal with an RF converter, overmodulation will occur, and if this signal is received by the television, The audio output is a buzzing sound that is unpleasant.

Conventionally, a magnetic recording/reproducing apparatus has a configuration as shown in FIG. Here, 1 is a magnetic tape, 2
indicates a magnetic head, and the output signal of this magnetic head 2 is supplied via a head amplifier 3 to a dropout compensation circuit 4, a dropout detection circuit 6, and a chroma circuit 9. Dropout compensation circuit 4
is controlled by the output signal of the dropout detection circuit 6. The output signal of the dropout compensation circuit 4 is supplied to the video demodulation circuit 5, and a luminance video signal is obtained as the output signal of the video demodulation circuit 5. Further, the signal supplied from the head amplifier 3 to the chroma circuit 9 is processed by the chroma circuit 9 and then sent to the mixer circuit 10.
is supplied to the amplifier 8 from the video demodulation circuit 5.
The resulting video signal is mixed with the luminance signal passed through the clamp circuit 11 and sent to the video output circuit 1.
2, and further supplied to an RF converter 13, where it is converted into a television signal and supplied to a general television.

The flow of signal waveforms obtained with such a conventional configuration is shown in A of FIG. If the magnetic tape and the magnetic head are separated and the envelope output of the head amplifier ₃ drops out for a period of t1 as shown in _FIG . A detection signal 6a is obtained. The dropout compensation circuit 4 outputs a waveform 4a which is compensated for the period t ₂ but is not compensated for the period t ₃ and is supplied to the video demodulation circuit 5 . This demodulated output waveform becomes a noise component such as 5a only during the period _t3 , and noise having a larger amplitude than the video signal waveform is output. In the clamp circuit 11
Levels greater than the SYNC TIP will be clipped, but levels greater than the WHITE TIP will remain intact. When the output waveform 11a of this clamp circuit 11 is supplied to the RF converter 13 and converted into a television signal by the RF converter 13,
Signals larger than WHITE TIP will be overmodulated and
When the carrier component is removed and the audio is received on television, the audio output generates a buzzing sound that gives an unpleasant feeling.

The present invention has a dropout compensation circuit.
In a VTR, during a dropout period exceeding a certain setting value, the DC level of the demodulated noise signal is lowered using the dropout detection output signal, so that the peak of the noise is brought to a level below the white level of the video signal. The present invention provides a magnetic recording and reproducing device that prevents overmodulation of a converter and generates no buzz in television. The configuration of the present invention will be explained below based on the drawings showing one embodiment thereof. In FIG. 2, parts corresponding to FIG. 1 and FIG. 3A are omitted. In this example, block 7 in FIG. 2 will be explained. A low pass filter (LFP) 7 is supplied with the output of the dropout detection circuit 6, and an amplifier 8 is supplied with the output signal of the LPF 7 and the luminance video signal of the demodulated output of the video demodulation circuit 5.

The signal flow of the present invention will be explained with reference to FIG. 3B. The LPF 7 is a circuit that delays the output signal of the dropout detection circuit 6 by a period t ₂ of the dropout period t ₁ which is compensated by the dropout compensation circuit 4, and is specifically a combination of a monomarna circuit and a flip-flop circuit. It can be implemented by A signal 7b obtained by delaying the dropout detection output waveform by the dropout compensation period _t2 by the LPF 7 is supplied to the amplifier 8 during the period of the noise component 5b of the demodulated output waveform of the video demodulation circuit 5, and the DC level of the noise component decreases. . Due to the output of the amplifier 8, the noise component of the output waveform of the mixer circuit 10 becomes DC during the period _t3 as shown in the waveform 10b.
The level is changed to a lower level to become a signal smaller than the WHITE TIP, which is then supplied to the clamp circuit 11, whereby the signal larger than the SYNC TIP is clipped, and as shown in 11b, there is no noise signal larger than the video signal in the video output signal. .
Therefore, in the RF converter 13 as well, overmodulation does not occur as shown in the waveform 13b.

As described above, according to the present invention, the DC level of the noise component of the video output signal generated by dropout is lowered by using a low-pass filter signal in which the output signal from the dropout detection circuit is delayed by the dropout compensation period. The signal becomes small and will not cause overmodulation even if it is supplied to the RF converter.

[Brief explanation of drawings]

Fig. 1 is a system diagram showing a block diagram of a conventional regeneration system, Fig. 2 is a system diagram showing a block diagram of a regeneration system of the present invention, and Figs. This is a waveform chart showing the signal flow of each block diagram. 3... Head amplifier, 4... Dropout compensation circuit, 5... Video demodulation circuit, 6... Dropout detection circuit, 7... Low pass filter, (LPF), 10...
mix circuit, 11...clamp circuit, 13...RF
converter.

Claims (1)

[Claims] 1. A magnetic recording and reproducing device that modulates a reproduced video signal into a television signal using an RF converter, which includes a dropout detection circuit that detects a dropout period of a head amplifier output, and a dropout compensation circuit to which an output signal from the dropout detection circuit is added. a low-pass filter to which an output signal from the dropout detection circuit is applied and delays the output signal by a dropout compensation period;
a video demodulation circuit that demodulates the output of the head amplifier after passing through a dropout compensation circuit; an output signal from the low-pass filter that delays the output signal of the dropout detection circuit by a dropout compensation period; and a signal from the video demodulation circuit.
A magnetic recording and reproducing apparatus comprising: a circuit for reducing a DC level during a noise amplitude period to a value equal to or less than a white signal from the video demodulation circuit.