JPS63193303A - Noise reducing circuit for audio signal reproducing device - Google Patents

Abstract

PURPOSE:To reduce the noise due to the variation of frequency in a reproduced FM audio signal at the time of head switching by adjusting the correction signal level in accordance with physical contraction (skew or the like) of a recording medium like a magnetic tape. CONSTITUTION:A head switching signal is delayed in a delay circuit 17 by a time corresponding to the time delay of the reproduced FM audio signal from the output terminal of a switching circuit 7, which switches reproduced FM audio signals from rotary heads 2 and 3 to obtain the continuous reproduced FM audio signal, to the input terminal of a demodulating circuit, and this delay signal is differentiated by a differentiation circuit 19 to generate a correction signal. The correction signal has the level adjusted by a level adjuster 20 and is supplied to the demodulating circuit with the phase opposite to that of the noise due to the variance of frequency of the reproduced FM audio signal at the time of head switching. The frequency variance component of the reproduced FM audio signal is supplied synchronously with the head switching signal and the time delay behind the head switching signal, and the correction signal is supplied to practically reduce the frequency variation component. Thus, the noise due to the variation of frequency of the reproduced FM audio signal is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a noise reduction circuit in a B-true signal reproducing device, and in particular, it switches an FMS voice signal sequentially reproduced from a magnetic tape by a plurality of rotary heads to continuously reproduce the FMS voice signal. Play FM
The present invention relates to a circuit for reducing M sound due to frequency fluctuation of a reproduced FM audio signal in synchronization with head switching in 11M for obtaining and demodulating an audio signal.

Conventional technology In VTRs, in order to record and reproduce audio signals with higher quality, the audio signals are frequency modulated (FM).

The obtained FM audio signal is recorded on the deep layer of the magnetic layer of the magnetic tape using, for example, two rotating heads, and the video signal is recorded on the surface layer of the magnetic layer using another rotating head. A recording system VTR or a VTR that records a frequency-division multiplexed signal obtained by frequency-division multiplexing an FM audio signal on a video signal onto a magnetic tape with a rotating head and plays it back.
has been known for a long time.

In such a VTR, two magnetic arps are scanned alternately.
After the reproduced FM audio signals obtained alternately from the two rotary heads are switched to obtain a continuous reproduced FM audio signal, the demodulation circuit performs FMIIi modulation to obtain the reproduced audio signal.

However, at the switching part (joint part) of the reproduced FM audio signals of the two rotary heads, the phases are not completely the same due to differences in tape tension, etc.
The phase of the M audio signal changes, and pulse-like noise corresponding to the changed phase is generated in the demodulated output.

For this reason, conventionally, the above-mentioned pulse-like noise has been reduced by holding the demodulated audio signal at the head switching portion at its previous value.

Problems to be Solved by the Invention However, the noise generated due to the switching of the reproduced FM audio signal between the two rotary heads is not only the pulse-like noise due to the above-mentioned phase change, but also the skew of the magnetic tape when switching the heads, etc. It also includes noise due to frequency fluctuations in the reproduced FM audio signal caused by.

When this frequency fluctuation of the reproduced FM audio signal is demodulated by the demodulation circuit, it is audible as noise, and although it is synchronized with the head switching signal, the frequency fluctuation of the reproduced FM audio signal P-wave is affected by the delay time caused by the filter circuit for the P-wave of the reproduced FM audio signal. This was delayed compared to the switching signal, and the previous value hold circuit described above could not reduce it to a certain extent.

Therefore, in the past, the tape head system was mechanically adjusted (for example, by suppressing the rotational wobbling of the rotating cylinder within a predetermined range) in order to minimize the skew of the magnetic tape during head switching. However, even with this mechanical adjustment, there is a problem in that noise due to frequency fluctuations of the reproduced FM audio signal cannot be reduced due to changes in the running system over time due to head wear and the like.

In addition, during so-called compatible playback, in which an audio signal recorded on a magnetic tape by one VTR is played back by another VTR, the frequency of the FM audio signal also fluctuates due to variations in the contact pressure of both VTRs to the magnetic tape. Since this occurs in synchronization with the head switching signal, there is a problem in that noise is generated in the m sub-audio signal output.

The present invention was created in view of the above points, and
It is an object of the present invention to provide a noise reduction circuit in an audio signal reproducing device that can reduce noise caused by frequency fluctuations of an audio signal.

Means for Solving the Problems The noise reduction circuit in the audio signal reproducing apparatus of the present invention switches the reproduced FM audio signals from a plurality of rotary heads to continuously reproduce the FM audio (fT signal). The above-mentioned reproduction FM from the output end to the input end of the demodulation circuit
a correction signal generation circuit that delays the head switching signal by a time corresponding to the time delay of the audio signal and generates a correction signal by differentiating the delayed head switching signal; and a correction signal generation circuit that adjusts the level of the correction signal and generates a reproduced audio signal. A level adjuster is provided for supplying a predetermined miscellaneous signal to the demodulation circuit in reverse phase.

The active head switching signal is supplied to a correction signal generation circuit, where it is converted into a correction signal. After this correction (CT number is level adjusted by a level adjuster, the playback FM when switching heads is
#li in opposite phase to noise due to frequency fluctuation of audio signal
l Tuning is supplied.

The frequency fluctuation component of the reproduced FM audio signal when switching heads is
The signal is synchronized with the head switching signal and is supplied to the demodulation circuit after being delayed by the time i delay, and is demodulated there and is perceived as noise as it is. However, in the present invention, the demodulation circuit is supplied with a correction signal that substantially reduces the frequency fluctuation component from the level adjuster, so that the demodulation circuit can hardly demodulate the frequency fluctuation component.

Embodiment FIG. 1 shows 'j!' in the audio signal reproducing apparatus according to the present invention.
! A block diagram of an embodiment of the i reduction circuit is shown. In the figure, reference numeral 1 denotes a recorded magnetic tape, on which a color video signal is recorded in a predetermined signal format and a 2-channel audio signal is recorded by separately frequency modulating two types of carrier waves, for example, by the deep recording type VTR. has been done. Reference numerals 2 and 3 designate two audio-only rotary heads that are mounted opposite to each other on the rotating surface of a rotating cylinder (not shown), and are used to record a recorded magnetic tape 1.
is alternately scanned every 12 pulse periods, and only the frequency division multiplexed signal consisting of two channels of FM audio signals recorded in the deep portion of the magnetic layer is reproduced and output.

The reproduction frequency υ1 multiplexed signals taken out separately from the rotary heads 2 and 3 are separately supplied to reproduction preamplifiers 5 and 6 via a rotary transformer 4, where they are amplified to a required level and then sent to a switching circuit. 7, respectively.

On the other hand, a head switching signal, which is a symmetrical square wave that is inverted every field period in phase synchronization with the rotation of the rotary cylinder, is generated by known means and input to the input terminal 8. This head switching signal is supplied to the switching circuit 7, which controls switching. As a result, the switching circuit 7 is switched to selectively output the reproduced frequency division multiplexed signal of the rotary head 2 or 3 which is scanning the recorded magnetic tape 1, and outputs the continuous reproduced frequency division multiplexed signal. and is supplied to bandpass filters 9 and 10, respectively.

The passband is set so that the bandpass filter 9 selects the frequency of only the FM audio signal of the first channel from the input reproduced frequency division multiplexed signal, and the bandpass filter 10 selects the frequency of only the FM audio signal of the second channel. There is. The first channel reproduced FMil voice signal that has passed through the bandpass filter 9 is supplied to a phase comparator 2S11, and the second channel reproduced FM voice signal that has passed through the bandpass filter 10 is supplied to a phase comparator 12.

The phase comparator 11 has a loop filter 13 and a voltage t/Il.
1 oscillator 14, and a first phase locked loop (PLL).Similarly, the phase comparator 12, together with a loop filter 15 and a voltage controlled oscillator 16, constitutes a first phase locked loop (PLL).
It constitutes a PLL. These first and second PLLs
operate as FM demodulation circuits. These FM11
The reproduced FM audio signal that is passed through the modulator inversion circuit contains frequency fluctuation components caused by skew of the magnetic tape and the like when switching heads.

The above frequency fluctuation component is synchronized with the head switching signal shown in FIG. 12, the demodulated output is also delayed by the rf interval τ with respect to the head switching signal.

For convenience of illustration, it is assumed that the FM audio signal is unmodulated. When the frequency fluctuation component at the time of head switching in the reproduced FM audio signal is subjected to FMI adjustment, it becomes as shown in FIG. 2 (B) or (
It is demodulated with a waveform as shown in C). That is, playing FM
The carrier frequency of the audio signal is f. Then, from the reproduced FM audio signal of one rotary head to the reproduced F of the other rotary head
When the frequency fluctuation becomes +Δf when switching to the M audio signal, it becomes a positive pulse;
When this happens, it becomes a negative polarity pulse.

In addition, if one of the two rotating heads 2 and 3 has a large contact pressure at the start of tape sliding contact with the recording y% magnetic tape 1 for each frame, the contact pressure at the time when the other rotating head starts tape sliding contact with the recording y% magnetic tape 1 is large. Since the contact pressure at is small, the above frequency fluctuation is 1
Each field shows a change that alternately increases or decreases with respect to the carrier frequency fo. However, which rotary head has the greater contact pressure at the start of tape sliding contact differs depending on the VTR, so the phase of the demodulated output of the frequency fluctuation with respect to the head switching signal is It will be one of the two types shown in C).

In FIG. 1, the head switching signal entering the input terminal 8 is supplied to the delay circuit 17, where the bandpass filter 9
．． The signals are delayed by a time equal to the time delay τ caused by 10, and the phases are made in-phase or anti-phase by manual operation of the phase switch 18 before being supplied to the differentiating circuit 19. This results in
From the differentiating circuit 19, a differential pulse as shown in FIG. 3(B) is taken out when the head switching signal shown in FIG. 3(A) is in phase, and a differentiated pulse as shown in FIG. is taken out. This differential pulse is output as a correction signal.

This correction signal (differential pulse) is level-adjusted by a level adjuster 20 and then applied to the voltage controlled oscillators 14 and 16 as a control voltage. Therefore, the voltage controlled oscillator 14
a first FM demodulation circuit that includes a voltage controlled oscillator 16 and demodulates and outputs the reproduced eight-tone signal of the first channel from the phase comparator 11 to the output end 'F22 via the low-pass filter 21; The second FMtl tone circuit outputs the reproduced audio signal of the second channel in m tone to the output terminal 24 via the low-pass filter 23, and has a waveform in which a correction signal is added to the reproduced audio signal.

Therefore, the noise can be reduced by operating the phase switch 18 and the level adjuster 20 so that the reproduced sound is listened to and the noise is minimized. In other words, the noise due to frequency fluctuation components in the reproduced FM audio signal when switching heads is
When the head switching signal is output with a phase as shown in FIG. 2(B), the phase switch 18 causes the correction signal to have a phase opposite to that of the noise as shown in FIG. 3(8). Furthermore, if noise is output with a phase as shown in FIG. 2(C), the phase of the correction signal is set to be opposite to the noise as shown in FIG. 3(C), and level adjustment p! By adjusting the level of the correction signal at 20, the above noise can be reduced.

Effects of the Invention As described above, according to the present invention, by adjusting the correction signal level according to the physical contraction (skew, etc.) of a recording medium such as a magnetic tape, the frequency in the reproduced FM audio signal when switching heads is adjusted. It is possible to reduce noise caused by fluctuations to a minimum, and also eliminate the noise caused by variations in the contact pressure between the playback device and the recording medium during compatible playback, or changes in contact pressure due to aging of the same playback device, changes over time, etc. Similarly, noise can be reduced to a minimum value by phase switching and level adjustment.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the circuit of the present invention;
FIG. 2 is a waveform diagram for explaining the noise reduced in the present invention, and FIG. 3 is a waveform diagram for explaining the operation of the circuit shown in FIG. 1. 1... Recorded magnetic tape, 2.3... Rotating head,
8... Head switching signal input terminal, 9.10... Bandpass filter, 17... Delay circuit, 18... Phase switcher, 19... Fine powder circuit, 20... Level adjuster, 22
゜24...Playback audio signal output terminal. Patent applicant: Victor Japan Co., Ltd. Figure 1

Claims (1)

[Claims] Reproducing FM audio signals sequentially taken out from a plurality of rotary heads that cyclically scan a recorded recording medium are supplied to a switching circuit, and are switched based on a head switching signal to reproduce one continuous reproduction. In an audio signal reproducing device which obtains an FM audio signal and then demodulates the FM using a demodulation circuit to obtain a reproduced audio signal, the first reproduced FM audio from the output end of the switching circuit to the input end of the demodulation circuit is provided. a correction signal generation circuit that delays the head switching signal by a time corresponding to the time delay of the signal and generates a correction signal by differentiating the delayed head switching signal; and a demodulation circuit that adjusts the level of the correction signal. and a level adjuster for supplying the level-adjusted correction signal to the demodulation circuit in a phase opposite to the noise caused by the frequency fluctuation of the reproduced FM audio signal at the time of head switching in the reproduced audio signal extracted from the head. A noise reduction circuit in an audio signal reproducing device, characterized in that: