JPS5838849B2 - Magnetic recording and reproducing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic recording and reproducing force type in which a signal is converted into a modulated signal by frequency modulation, is recorded on a magnetic tape, and is also reproduced and demodulated.

2. Description of the Related Art As a magnetic recording and reproducing method for audio signals and the like, a so-called alternating current bias method is generally used in which a high frequency bias is superimposed on the signal and recorded.

However, this method still has problems that need to be improved, such as wow and flutter, distortion, and noise.

For the purpose of improving these various electrical characteristics, a recording method using frequency modulation, that is, converting the signal into a modulated signal by frequency modulation and recording it, can be considered, but this method improves many electrical characteristics. The problem is that it is greatly affected by wow and flutter, and the signal-to-noise ratio deteriorates.

This invention was made in view of the above circumstances, and involves converting a signal into a modulated signal by frequency modulation, recording it on a magnetic tape, and demodulating the modulated signal reproduced by the magnetic tape using a frequency detector. In the magnetic recording and reproducing system, a control channel for recording and reproducing a control signal is provided together with a signal channel for recording and reproducing an input signal, and the reproduced signal from the signal channel is frequency demodulated by a phase-locked loop frequency detector. The reproduced signal from the control channel is frequency demodulated, and the center frequency of the voltage controlled oscillator in the phase-locked loop frequency detector is controlled by the demodulated output, thereby eliminating the effects of wow and flutter. This makes it possible to improve electrical characteristics.

Embodiments of the present invention will be described below with reference to the drawings.

In FIG. 1, a recording section 1 and a reproducing section 2 each have a signal channel and a control channel.

The signal channel 3 of the recording section 1 includes a voltage controlled oscillator 4 and a head 5, and the control channel 6 includes an oscillator 7.
and a head 8.

The voltage controlled oscillator 4 of the signal channel 3 functions as a frequency modulator, and normally oscillates at a specific oscillation frequency. When an input signal is applied to the input terminal a, the oscillation frequency is changed by this signal, and the input It converts the signal into a modulated signal.

The output end of the oscillator 7 of the control channel 6 is connected to the head 8, and is also connected to a phase comparator 15 of the control channel 13 in the reproduction section 2, which will be described later.

The signal channel 9 of the reproducing section 2 is connected to the head 10 and the limiter 1.
1 and a phase locked loop 12.
The control channel 13 also includes a head 14 and a phase comparator 15.
and a low-pass filter 16.

The phase-locked loop 12 of the signal channel 9 functions as a frequency detector and is composed of a phase comparator 17, a low-pass filter 18, and a voltage-controlled oscillator 19.

This phase locked loop 12 includes a phase comparator 1
7, the phase of the modulated signal, which is the input signal, is compared with the oscillation output of the voltage controlled oscillator 19, and the comparison output obtained here is filtered by a low-pass filter 18 and taken out from the output terminal.

The phase comparator 15 of the control channel 13 compares the phase of the signal given from the head 14 and the oscillation output of the oscillator 7. The low-pass filter 16 that filters is
It is provided for frequency demodulating the signal obtained from the head 14.

The center frequency (free-running frequency) of the voltage controlled oscillator 19 is controlled by the output of the low-pass filter 16.

Next, the operation of this embodiment will be explained.

In the signal channel 3 of the recording section, when an audio signal S is applied to the input terminal a, the oscillation frequency of the voltage controlled oscillator 4 is changed by this audio signal S to generate the modulated signal SM.
get.

That is, the audio signal S is obtained by frequency modulating the oscillation output M of the voltage controlled oscillator 4 to obtain the modulated signal SM.

This modulated signal SM is applied to the head 5.

Further, in the control channel 6, a control signal C, which is the oscillation output of the oscillator 7, is applied to the head 8.

By performing recording in this manner, the control signal C is recorded on the magnetic tape (not shown) together with the modulated signal SM.

In this case, the modulated signal SM, control signal, and C are recorded on separate tracks.

The modulated signal SM and control signal C recorded as described above are reproduced by the reproducing section 2.

In the signal channel 9 of the reproducing section 2, the modulated signal SM captured by the head 10 is sent to the phase comparator 17 of the phase locked loop 12 via the limiter 11.

In the phase-locked loop 12, a phase comparator 17 compares the phase of the modulated signal SM with the oscillation output M' of the voltage controlled oscillator 19, and sends the resulting phase difference voltage to the low-pass filter 18.

The low-pass filter 18 filters high-frequency components contained in the phase difference voltage.

The filtered phase difference voltage of the high frequency component is the amount by which the modulated signal SM is displaced with respect to the center frequency of the voltage controlled oscillator 19, and is the audio signal S.

This audio signal S contains wow and black components when extracted only by the demodulation process described above.

That is, the modulated signal SM is frequency modulated by wow and flutter while being recorded and reproduced via a magnetic tape, and the audio signal S, which is the demodulated output, naturally has a frequency modulation caused by the wow and flutter. Contains noise components.

Thus, in the control channel 13, the control signal C captured by the head 14 is applied to a phase comparator 15.

The control signal C at this time is frequency modulated by wow and flutter while being recorded and reproduced via the magnetic tape.

This wow and flutter is the same as that experienced by the modulated signal SM.

The phase comparator 15 compares the phase of the control signal C frequency-modulated by the wow and flutter with the oscillation output of the oscillator 7, and generates a phase comparison voltage on the output side.

The high frequency components of this phase comparison voltage are filtered out by a low-pass filter 16, and an element for varying the free running frequency of the voltage controlled oscillator 19 is applied to a variable capacitance diode.

The phase comparison voltage obtained at the output of the low-pass filter 16 is a voltage proportional to the frequency excursion due to wow and flutter experienced by the control signal C.

Therefore, the center frequency of the oscillation output from the voltage controlled oscillator 19 is controlled according to wow and flutter.

FIG. 2 shows changes in frequency detection characteristics in this case.

In this figure, the detection characteristic line A changes to a position B or C as the center frequency of the voltage controlled oscillator 19 is controlled by the wow/black component.

Therefore, the frequency modulation component received by the modulated signal SM of the signal channel due to wow and flutter is
Since the center frequency of the voltage controlled oscillator 19 of the locked loop 12 is corrected by the same wow and flutter, it is not included in the detection output.

As a result, even if the modulated signal SM to be reproduced is frequency modulated by wow and flutter, the voltage controlled oscillator 19
The center frequency of the demodulated output changes according to the wow and flutter, and the noise caused by the wow and flutter in the demodulated output is removed.

In this way, an audio signal S (output signal) from which noise caused by wow and flutter has been removed can be obtained from the output terminal.

As is clear from the above description, the present invention solves the problem of noise caused by wow and flutter, which is considered inevitable in magnetic recording and reproducing systems based on frequency modulation, by using a simple method using a phaeo-locked loop as a frequency demodulator. This configuration can almost completely solve the problem and has the effect of significantly improving the electrical characteristics in recording and reproducing audio signals and the like.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a magnetic recording apparatus according to the present invention, and FIG. 2 is a graph showing the behavior of frequency detection characteristics in the reproduction section of the apparatus. 3...Signal channel of recording section, 6...
・Same control channel, 9... Signal channel of the reproduction section, 12... Phase locked loop (phase locked loop type frequency detector), 13
...Player control channel, 15...
・Phase comparator, 16...Low pass filter, 19・
...Voltage controlled oscillator (voltage controlled oscillator).

Claims (1)

[Claims] 1. A modulated signal frequency-modulated by a human input signal is recorded on a signal channel on a magnetic tape, and at the same time a control signal is recorded on a control channel on the magnetic tape, and a reproduced signal from the signal channel is phase-locked.
At the same time, the loop type frequency detector performs frequency demodulation to extract an output signal corresponding to the input signal, and at the same time, the reproduced signal from the control channel is frequency demodulated, and this demodulated output is used to perform frequency demodulation in the phase locked loop type frequency detector. A magnetic recording and reproducing method characterized by controlling the center frequency of a voltage-controlled oscillator.