JPS63106959A - Rotary head signal reproducing device - Google Patents

Abstract

PURPOSE:To reduce switch noise, by providing a second switch which selects and outputs the output signal of a delay unit or that of a level holding unit, and shortening a level holding interval. CONSTITUTION:After the higher FM carrier component of an FM demodulation voice signal is eliminated by a low-pass filter 53, the just before value at a point where the switch noise is generated is inputted to the level holding unit 54, and is held at that level, and the FM demodulation voice signal is delayed, and is matched with temporal timing at a position where the switch noise is generated of the output signal of the low-pass filter, and the switch noise interval of a delayed FM demodulation voice signal is held at the level held at the level holding unit 54. Since the delayed FM demodulation voice signal does not pass a filter, a very short interval to hold the switch noise is enough, and furthermore, since the impulsive switch noise has been already removed, the interval to hold the noise is not extended further even when it passes the filter for eliminating an FM carrier component hereafter. Consequently, it is possible to shorten the interval to hold the noise, and to reduce the switch noise.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention provides a signal reproducing device for a rotary head that reduces noise generated at the joint between signals that are alternately reproduced by a pair of rotary heads (hereinafter referred to as switch noise). It is related to.

(Prior Art) In recent years, a technology for recording audio with a rotating head in a video tape recorder has been established, and a dramatic improvement in sound quality has been achieved compared to the audio recorded in a video tape recorder that conventionally recorded with a fixed head. However, the problem with the rotating head is that the FM modulated wave of the audio (hereinafter referred to as FM audio signal) is discontinuous at the part where the alternate reproduction outputs of the two heads are switched and connected, so noise (switch noise) occurs during demodulation. ) occurs. Those aiming for high-fidelity must minimize this switch noise.

An example of conventional signal reproduction for a rotary head will be described below with reference to the drawings.

FIG. 3 shows the main parts of the FM audio signal block of a conventional signal reproducing device for a rotary head, and FIG. 4 shows the waveforms of each part.

In Fig. 3, La, lb are rotating heads, 2a, 2
b is an amplifier, 3 is a switch, 4 is a bandpass filter, 5
6 is a low-pass filter, 7 is a level holding circuit, 8 is an output terminal, and 9 is a pulse generator.

The operation of the rotary head signal reproducing device configured as described above will be described below.

First, an FM audio signal recorded on a magnetic tape is alternately reproduced every half cycle of one rotation by a pair of rotary heads 1a and 1b, and amplified by amplifiers 2a and 2b, respectively. Obtain the FM audio playback signal.

At the same time, the fourth rotary head synchronized with the rotation of the rotating heads la and lb
A pulse shown in FIG. 4 (hereinafter referred to as a head switching pulse) is output from the pulse generator 9, and at this timing, the switch 3 switches between the FM audio reproduction signals shown in FIGS. 4A and A' and outputs an output C.

Next, the output C of the switch 3 is band-limited by a bandpass filter 4 and demodulated by an FM demodulator 5.

The output C of switch 3 is at the switching point of the rotary head, i.e.
Since the phase is discontinuous at the joint portion, when this is demodulated, the FM demodulated audio signal generates switch noise at the switching point of the rotary head, as shown in the fourth diagram.

In the conventional rotary head signal reproducing device, in order to reduce the switch noise, first, the FM demodulated audio signal is passed through a low-pass filter 6 so that the level holder 7 can accurately maintain the audio signal level. After the high frequency FM carrier component is removed (FIG. 4E), the signal is input to the level holder 7. The level holder 7 receives the head switching pulse B at the same time, uses the edge of the head switching pulse B as a trigger, and holds the level of the signal E immediately before the head switching pulse B is input for one hour t.

When time t has passed, level retention is released and the input signal E
is output as is. The starting point of the switch noise generation is synchronized with the edge of the head switching pulse B, so if 1 time t is set to a length that covers the period in which the switch noise occurs, the period in which the switch noise occurs is always as follows. Interpolation is performed using the immediately previous signal level, and a signal waveform F is output from the level holder 7.

(Problem to be solved by the invention) However, in the conventional configuration, the period of impulse-like switch noise after FM demodulation is expanded by the response delay of the low-pass filter for removing the FM carrier component, so the level is maintained. The period of switch noise that requires the level to be maintained by the device is getting longer. Since this level holding section is constant and does not depend on the frequency of the audio signal, the higher the frequency of the audio signal, the larger the ratio of the level holding section to the wavelength.
The audio signal waveform cannot be reproduced faithfully. That is, there is a problem in that the influence of switch noise increases.

In view of the above problems, the present invention provides a signal reproducing device for a rotary head that reduces the influence of a low-pass filter for removing FM carrier components, shortens the level holding period, reduces switch noise, and has high fidelity. It is characterized by this.

(Means for Solving the Problems) In order to solve the above problems, a signal reproducing device for a rotary head according to the present invention includes at least a pair of rotary heads for reproducing FM modulated waves of audio recorded on a magnetic tape. a first and second amplifier that amplifies the output signal of each of the pair of rotating heads; a first pulse generator that generates a pulse synchronized with the rotation of the pair of rotating heads; and the first pulse generator. The output pulse of the generator is input to the first or second
a first switch that selects and outputs the output signal of the amplifier; a bandpass filter that receives the output of the first switch as an input; and an FM that receives the output of the bandpass filter as an input.
a demodulator, a first low-pass filter and a delay device each receiving the output of the FM demodulator, and adjusting the output pulses of the first pulse generator to the temporal timing of the switch noise generation position. A second pulse generator generates a pulse with a constant time width corresponding to the switching noise section in synchronization with the rising and falling edges, and the output of the first low-pass filter is inputted, and the output of the first low-pass filter is input. Level holding for holding the output value of the first low-pass filter immediately before the output pulse of the second pulse generator is input for the certain time width each time the output pulse of the pulse generator is input. a second switch to which the output pulse of the second pulse generator is input and selects and outputs the output signal of the delay device or the output signal of the level holder; and a second low-pass filter as an input.

(Function) Therefore, according to the configuration of the present invention, after the high-frequency FM carrier component is removed from the FM demodulated audio signal by the low-pass filter, the value immediately before the point where switch noise occurs is determined by the level holder. is entered and held at that level. At the same time, the FM demodulated audio signal is delayed so that the output signal of the low-pass filter and the switch noise generation position are time-aligned, and the switch noise section of the delayed FM demodulated audio signal maintains the level. It is held at the level held in the container.

Therefore, since the delayed FM demodulated audio signal has not passed through the filter, the switch noise retention interval is very short, and since the impulse-like switch noise has already been removed, after this, Even if the signal is passed through a filter for removing FM carrier components, the retention period is not extended. Therefore, the holding interval can be made shorter than before,
Switch noise can be reduced.

(Example) An example of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of signal processing after FM demodulation of a signal reproducing device for a rotary head according to an embodiment of the present invention, and FIG. 2 shows waveforms of various parts.

The blocks and operations up to FM demodulation are the same as in the conventional example, so drawings and explanations will be omitted.

In FIG. 1, 50 and 52 are input terminals, 51 is a second
a pulse generator, 53 is a first low-pass filter, 54
55 is a level holder, 55 is a delay device, 56 is a second switch, 57 is a second low-pass filter, and 58 is an output terminal.

These components are configured as shown in FIG. 1 to form a signal reproducing device for a rotary head according to the present invention.

Hereinafter, the operation of the signal reproducing device for a rotary head according to the present invention will be explained with reference to the drawings.

First, an FM audio signal recorded on a magnetic tape is reproduced by a pair of rotary heads, FM demodulated is performed, and an FM demodulated audio signal a is input to the input terminal 52.

One of the input signals passes through a low-pass filter 53,
The high-frequency FM carrier component is removed to form a signal, which is input to the level holder 54. The other input signal is synchronized with the position of the start point of the switch noise in the delay device 55, so that only the time t1 is the input FM signal.
The demodulated audio signal a is delayed to obtain a signal f.

The second pulse generator 51 receives a pulse (head switching signal C) synchronized with the rotation of the rotary head from a first pulse generating circuit (not shown), and receives this head switching signal C.
The rising and falling edges of the head switching signal, which are delayed by t2 to match the switch noise, are used as triggers to generate a pulse b whose timing is t, from just before the switch noise start point of the signal. Here, t is
This is the switch noise section of the signal f.

The level holder 54 operates according to the timing of the pulse d.
The value AI (A2
．． A3) is held for a time t3 and a signal e is output.

Next, the second switch 56 receives the pulse d at the same time as the level holder 54, and at the timing of the pulse d, the second switch 56 receives the signal e.
Alternatively, the signal f is switched and the signal g is output. That is, in the period of pulse t, the level of the level holding period of signal e is output, and in the other periods, signal f is output, so that the switch noise period of signal f is changed immediately before the switch noise occurs. The level Al of the audio signal e (A2. A
3) can be interpolated. The signal g thus obtained
The FM carrier component is attenuated by the second low-pass filter 57, resulting in a signal. As shown in the signals a and s, since the level of the switch noise of the signal a input to the first low-pass filter 53 is large, the transient response is prolonged and the switch noise section of the signal d is extended. Conventionally, only this section was held, so the holding section was long and had a large effect on the audio signal. Since the signal g retains the switch noise section of the signal f, it is not affected by the low-pass filter and requires a very short retention period, and the signal retention level is the audio signal level At after removing the FM carrier component. (A2. A3), so the nozzle level will not be held.

In the manner described above, the switch noise retention interval can be shortened, and the audio signal with very little switch noise can be changed.

(Effects of the Invention) According to the present invention, as is clear from the above examples, F
The impulse-like switch noise with a high level after M demodulation does not pass through a low-pass filter, and the retention period of the switch noise can be made very short compared to that which passes through a conventional low-pass filter. can.

In addition, in the present invention, since impulse-like switch noise is removed, even if the FM carrier component of the FM demodulated signal is removed by the second low-pass filter, the retention interval is not extended, and the fidelity is maintained. A highly accurate FM audio signal can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a signal processing block after FM demodulation of a signal reproducing device for a rotary head according to an embodiment of the present invention, FIG. 2 is a diagram showing signal waveforms of each part of the first embodiment, and FIG. , a block diagram of a conventional signal reproducing device for a rotary head, and FIG. 4 is a diagram showing signal waveforms in the numbered part in the third figure. 50, 52... Input terminal, 51... Second pulse generator, 53... First low pass filter, 54...
Level holder, 55... Delay device, 56... Second switch, 57... Second low pass filter, 58...
・Output terminal.

Claims (1)

[Claims] at least one pair of rotary heads for reproducing FM modulated waves of audio recorded on a magnetic tape; first and second amplifiers for amplifying output signals of each of the pair of rotary heads; a first pulse generator that generates pulses synchronized with rotation; and a first switch that receives the output pulse of the first pulse generator and selects and outputs the output signal of the first or second amplifier. , a bandpass filter whose input is the output of the first switch, an FM demodulator whose input is the output of the bandpass filter, and a first low-pass filter whose respective inputs are the outputs of the FM demodulator. A filter, a delay device, and the output pulse of the first pulse generator are synchronized with the temporal timing of the switch noise generation position, and are synchronized with the rise and fall of the pulse to generate a pulse with a constant time width corresponding to the switch noise section. A second pulse generator that generates a level holder that holds the output value of the first low-pass filter immediately before the output pulse is input for the certain time width;
a second switch to which the output pulse of the second pulse generator is input and selects and outputs the output signal of the delay device or the output signal of the level holder; and the output of the second switch is input. A signal reproducing device for a rotary head, comprising: a second low-pass filter.