JPS6194478A - Reproducing device for sound signal - Google Patents

Abstract

PURPOSE:To eliminate securely a noise, which is caused by time base fluctuation in a reproduction sound signal, throughout the entire sound frequency band by synthesizing the output signal of a frequency discrimination circuit with the reproduction sound signal. CONSTITUTION:A multiple signal reproduced from the inclined track of a tape 12 is supplied to an HPF21 and BPFs 31 and 41, and a luminance signal YF, carrier chrominance signal LC and sound signal AF are introduced. Then a horizontal synchronizing signal is separated 24 from the signal Y to form 25 a burst sampling pulse,which is supplied to a demodulator circuit 34 and S/H circuit 35. A burst signal is sampled from the signal LC and its frequency is discriminated. A component during the burst period of the discriminated output is sampled and supplied to a synthesizing circuit 45 through an LPF36. After the signal AF is frequency demodulated 42, it is made a reproduction sound signal through an LPF43 and level phase adjustment circuit 44, and the output of the LPF36 is subtracted from said signal. As a result, a sound signal A can be obtained which is free from a noise caused by the time base fluctuation.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention reproduces the frequency modulated wave of an audio signal recorded on a track inclined with respect to the running direction of a magnetic tape, thereby demodulating the audio signal. , relates to an audio signal reproducing device.

Some conventional video tape recorders employ a system in which an audio signal is frequency modulated and recorded together with a video signal on a trunk that is inclined with respect to the running direction of the magnetic tape. Specifically, an audio signal is frequency-modulated in a band between a low-band-converted carrier color signal and a frequency-modulated luminance signal, and the frequency-modulated wave and luminance of the low-band-converted carrier color signal and audio signal are A signal multiplexed with a frequency modulated wave is recorded on a track inclined with respect to the running direction of the magnetic tape.

By the way, in a video tape recorder that uses a magnetic tape with a tape width of 8mm, so-called 8mm video, the subcarrier frequency of the low frequency converted carrier color signal is 743kHz.
The center frequency of the frequency modulated wave of the audio signal is 1.5 MHz,
The carrier wave frequency at the tip of the synchronization signal of the frequency modulated wave of the luminance signal is 4.2 MH2, and the carrier wave frequency at the first Eid peak is 5.4 MHz.

Since the relative speed between the magnetic tape and the rotating magnetic head is high in a video tape recorder, the audio signal is frequency-modulated and recorded along with the video signal on a trunk that is inclined with respect to the running direction of the magnetic tape. In general, it is said that audio signals are not easily affected by time axis fluctuations.

Problems to be Solved by the Invention However, in reality, vibrations of the drum motor that drives the head drum to which the rotating magnetic head is attached, eccentricity of the head drum, uneven rotation of the head drum, straight lines between the recording system and the reproducing system. differences in tape tension during recording and playback, and when using different video tape recorders for recording and playback, there may be differences in the structure of the head drum or rotating magnetic head between the two, etc. Due to the resulting time axis fluctuation, a lot of noise occurs in the reproduced audio signal demodulated from the frequency modulated wave on the playback side.The noise generated in the reproduced audio signal due to this time axis fluctuation is mainly synchronized with the rotation of the head drum. This appears as low-frequency noise due to the fundamental wave of 30H2 or 60Hz and its harmonics, and deteriorates the S/N of the reproduced audio signal.

One possible method for removing noise due to time axis fluctuations occurring in the reproduced audio signal is to use speed error information of the speed servo of the head drum. That is, for example, a change in the rotation frequency of the throat drum is detected from the output voltage of a frequency generator attached to the rotation shaft of the head drum, and the detected signal is subtracted from the reproduced audio signal. but,
Although this method removes low-frequency noise in the audio band due to time-axis fluctuations caused by changes in the rotational frequency of the head drum during playback, it also removes noise in the mid-to-high range of the audio band due to time-axis fluctuations caused by other factors. There is a disadvantage that noise is not removed.

In view of this point, the present invention is designed to reliably remove noise caused by time axis fluctuations occurring in a reproduced audio signal over the entire audio band.

Means for Solving the Problems In the video tape recorder described above, in which the audio signal is frequency-modulated and recorded together with the video signal on a track inclined with respect to the running direction of the magnetic tape, a predetermined frequency signal such as a burst signal is signals are recorded on the same track.

The signal of this predetermined frequency is subjected to the same time axis fluctuation as the frequency modulated wave of the audio signal is subjected to during recording and reproduction.

Therefore, if the reproduction side supplies this predetermined frequency signal to the frequency discrimination circuit and detects the frequency change due to time axis fluctuation of this predetermined frequency signal, the detected signal is the time that occurs in the reproduced audio signal. You can get the same thing as noise due to axis fluctuation.

In the present invention, focusing on this point, a frequency discrimination circuit is provided to detect a change in frequency due to time axis fluctuation of a signal of a predetermined frequency reproduced from a track inclined with respect to the running direction of the magnetic tape. By synthesizing the output signal of the circuit with the reproduced audio signal, noise caused by time axis fluctuations occurring in the reproduced audio signal is removed.・Embodiment FIG. 1 is an example of an audio signal reproducing device according to the present invention, in which a multiplexed signal of a low frequency-converted carrier color signal, a frequency modulated wave of an audio signal, and a frequency modulated wave of a luminance signal is transmitted to a magnetic tape running on a magnetic tape. This is the case with a playback system of a video tape recorder that records on tracks inclined with respect to the direction.

The rotary magnetic head 11 reproduces the multiplexed signal recorded on the track inclined with respect to the running direction of the magnetic tape 12, and the reproduced multiplexed signal passes through the reproducing amplifier circuit 13 to the bypass filter 21. The frequency modulated wave YF of the luminance signal is supplied to the band pass filter 31 and the band pass filter 41, the frequency modulated wave YF of the luminance signal is supplied to the band pass filter 21, the carrier color signal LC that has been low-pass converted is supplied to the band pass filter 31, and the audio signal is supplied to the band pass filter 41. The frequency modulated waves AF are separately extracted.

The frequency modulated wave YF of the luminance signal obtained from the bypass filter 21 is supplied to the luminance signal reproduction processing circuit 22, and the demodulated reproduced luminance signal Y is introduced into the luminance signal output terminal 23. The low frequency converted carrier color signal LC obtained from the band pass filter 31 is supplied to the carrier color signal regeneration processing circuit 32, and the reproduced carrier color signal C converted to the original frequency is output to the carrier color signal output terminal 33. be introduced. Frequency modulation wave AF of the audio signal obtained from the bandpass filter 41
is supplied to a frequency demodulation circuit 42 to demodulate the audio signal, and the demodulated audio signal output from the frequency demodulation circuit 42 is supplied to a low-pass filter 43 where components of, for example, 15 kHz or higher are removed, and the output of the low-pass filter 43 is O~
A reproduced audio signal limited to the 15 kHz audio band is obtained. The reproduced audio signal output from the low-pass filter 43 includes noise due to time axis fluctuations during recording and reproduction, as described above.

The low-pass converted carrier color signal LC output from the bandpass filter 31 is supplied to a frequency demodulation circuit 34 different from the frequency demodulation circuit 42 . Further, the reproduced luminance signal Y obtained at the luminance signal output terminal 23 is supplied to the horizontal synchronization signal separation circuit 24,
The extracted horizontal synchronizing signal is supplied to the pulse forming circuit 25 to obtain a burst extraction pulse.
The scraped pulses are supplied to frequency demodulation circuits 3 and 4. Then, in the frequency demodulation circuit 34, a burst signal is extracted from the low-pass converted carrier color signal C of the output of the bandpass filter 31 using a burst extraction pulse, and the frequency of the extracted burst signal is discriminated. . The output signal of the frequency demodulation circuit 34 is supplied to a sample and hold circuit 35, and the burst extraction pulse obtained from the pulse forming circuit 25 is supplied to the sample and hold circuit 35, where the burst extraction pulse generates a frequency A portion of the signal output from the demodulation circuit 34 during the burst signal period is extracted and held for one line period. The output signal of the sample and hold circuit 35 is supplied to a low-pass filter 36 to remove components of, for example, 15 kHz or higher.

The output signal of this low-pass filter 36 has a polarity.

Level b Yo'O' Apart from the phase, this noise is the same as the noise due to time axis fluctuations contained in the reproduced audio signal output from the low-pass filter 43.

- The reproduced audio signal output from the low-pass filter 43 is supplied to the synthesis circuit 45 through the level and phase adjustment circuit 44, and the signal output from the low-pass filter 36 is supplied to the synthesis circuit 45.
5, and the output signal of the low-pass filter 36 is subtracted from the reproduced audio signal passed through the level and phase adjustment circuit 44, for example.

Therefore, noise caused by time axis fluctuations occurring in the reproduced audio signal is removed, and a reproduced audio signal A free of noise due to time axis fluctuations is obtained at the audio signal output terminal 46.

In so-called 8mm video, unmodulated carrier waves with different frequencies between adjacent tracks are recorded as pilot signals for tracking control during playback on tracks that are inclined with respect to the running direction of the magnetic tape. A method is adopted. Specifically, the pilot signal is transmitted between four adjacent trunks, with fl for the first trunk and f2 for the second trunk. On the third track, f3. In the fourth track, the frequency is changed to f.

FIG. 2 shows another example of the audio signal reproducing device according to the present invention.
°A multiplexed signal of the frequency modulated wave of the carrier color signal, the frequency modulated wave of the audio signal, the frequency modulated wave of the luminance signal, and the pilot signal described above is recorded on a track inclined with respect to the running direction of the magnetic tape. This is the case of a playback system of a video tape recorder based on the above-mentioned method, and a change in frequency due to a time axis fluctuation that a frequency modulated wave of an audio signal undergoes during recording and playback is detected from the pilot signal.

The rotary magnetic head 11 reproduces a multiplexed signal including the pilot signal recorded on the track that is inclined with respect to the running direction of the magnetic tape 12, and the reproduced multiplexed signal is transmitted through the reproduction amplification circuit 13. taken out. The luminance signal system and the carrier color signal system are the same as in the example of FIG.

Further, as in the example of FIG. 1, a reproduced audio signal containing noise due to time axis fluctuations during recording and reproduction is extracted from the output of the low-pass filter 43.

The multiplexed signal passed through the regenerative amplification circuit 13 is also supplied to bandpass filters 51, 52, 53.54, and from the bandpass filters 51.52, 53.54, f, .
f2. f3. The pilot signal of frequency f is separated and extracted. As mentioned above, this pilot signal was recorded as an unmodulated carrier wave, but due to time axis fluctuations during recording and playback, the frequency changes to f, .
It changes around f2+f'3+'4. The pilot signals output from the bandpass filters 51, 52, 53, 54 are supplied to a switching selection circuit 55, where they are sequentially switched and extracted field by field according to the track to be reproduced, and the extracted four fields are A pilot signal whose center frequency changes every field as one cycle is supplied to a frequency demodulation circuit 56, and its frequency is discriminated. The output signal of the frequency demodulation circuit 56 is supplied to the DC level correction circuit 57, and the change in the DC level due to the change in the center frequency □ of the pilot signal output from the switching selection circuit 55 is corrected, and the DC level is The constant signal is supplied to a low-pass filter 58 to remove components of, for example, 15 kHz or higher. The signal output from the low-pass filter 58 is the same as the noise due to time axis fluctuations contained in the reproduced audio signal output from the low-pass filter 43, except for the polarity, level, and phase.

The reproduced audio signal output from the low-pass filter 43 is then supplied to the synthesis circuit 45 through the level adjustment circuit 47.
The output signal of the low-pass filter 58 is transmitted to the phase adjustment circuit 59.
For example, the signal passed through the phase adjustment circuit 59 is subtracted from the reproduced audio signal passed through the level adjustment circuit 47. Therefore, noise caused by time axis fluctuations occurring in the reproduced audio signal is removed, and a reproduced audio signal Δ free of noise caused by time axis fluctuations is obtained at the audio signal output terminal 46.

Note that a horizontal synchronization signal can also be used as a signal of a predetermined frequency for detecting a change in frequency due to time axis fluctuations that the frequency modulated wave of the audio signal receives.

Effects of the Invention According to the present invention, by using a signal of a predetermined frequency recorded on a track inclined with respect to the running direction of a magnetic tape together with a frequency modulated wave of the audio signal, time axis fluctuations occurring in a reproduced audio signal can be suppressed. noise can be reliably removed across the entire audio band.

[Brief explanation of the drawing]

1 and 2 are connection diagrams each showing an example of an audio signal reproducing apparatus according to the present invention.

Claims (1)

[Claims] From a track that is inclined with respect to the running direction of the magnetic tape,
a rotating magnetic head that reproduces a multiplexed signal of a frequency modulated wave of the audio signal recorded on the recording head and a signal of a predetermined frequency; a circuit that separates and extracts the frequency modulated wave of the audio signal from the reproduced multiplexed signal; a frequency demodulation circuit that demodulates the audio signal from the extracted frequency modulated wave; a circuit that separates and extracts the signal of the predetermined frequency from the reproduced multiplexed signal; and a frequency demodulation circuit that demodulates the audio signal from the extracted frequency modulated wave. A frequency discrimination circuit detects a change in frequency, and a demodulated playback audio signal output from the frequency demodulation circuit is combined with a signal output from the frequency discrimination circuit to eliminate noise due to time axis fluctuations occurring in the playback audio signal. An audio signal reproducing device comprising a synthesis circuit for removing.