JPH0724089B2 - Magnetic recording / reproducing device - Google Patents

Description

The present invention relates to a magnetic recording / reproducing apparatus, and more particularly to a magnetic recording / reproducing apparatus used for audio signals.

[Conventional technology]

Generally, in a method of recording an audio signal on a video tape used in a magnetic recording / reproducing apparatus, as shown in FIG. 2, a fixed head similar to a normal tape recorder is used to record on an audio track 13 of a video tape. However, since the sound quality is not good, recently, a high quality video tape recorder which stores a FM audio signal on the video track 14 using a rotary head has been developed.

In that case, as shown in FIG. 3, the FM audio signal 17 is inserted in the intermediate band of the occupied frequency band of the low frequency conversion color signal 16 and the FM modulated luminance signal 18.

By the way, when this FM audio signal 17 is reproduced by using the rotary head, noise on the pulse is generated when the rotary head is switched. This is because the phase of the reproduced FM audio signal does not completely match due to the difference in the tension of the tape at the joint where the two rotary heads are switched. This is because a phase change corresponding to the phase difference between the two FM voice signals appears, and pulsed noise corresponding to the changed phase is generated in the demodulated AM voice signal.

In the case of reproducing a video signal, the rotary head for video is switched during the vertical blanking period, so that there is no practical problem, but in the case of an audio signal, it is a major obstacle.

In order to solve this problem, in the conventional magnetic recording / reproducing apparatus, the sample and hold circuit shown in FIG. 4 is provided as a countermeasure. However, FIG. 4 is a block diagram of a first example of a conventional magnetic recording / reproducing apparatus.

In FIG. 4, the FM audio signal 17A from the rotary head 1 and the FM audio signal 17B from the rotary head 2 are the switching circuit 6
And is supplied to a sample and hold circuit 9 through a bandpass filter (hereinafter referred to as BPF) 7 and a demodulator 8.

Since the head switching signal c from the control head 3 is synchronized with the rotary head for video, it is delayed by the delay circuit 10 so as to be synchronized with the rotary heads 1 and 2, and is further FM-modulated. The control pulse generated at the phase conversion point is generated. The switch circuit 6 is switched by this control pulse.

The control pulse is a monostable multivibrator (hereinafter referred to as MMV
12) is converted into a hold pulse having a predetermined pulse width.

The sample and hold circuit 9 outputs the input signal level immediately before the hold pulse is generated as the output level while the hold pulse is continuing, and outputs the input signal level immediately after the hold pulse as the output level when the hold pulse disappears. Output a signal.

FIG. 6 is a waveform diagram of each part for explaining the operation of the magnetic recording / reproducing apparatus shown in FIG.

As shown in FIG. 6, the output signal of the switch circuit 6 has a phase difference between the FM audio signals 17A and 17B at the portion h. Also, BP
I in the output signal of F7 indicates the delay time due to the band-pass filter, and j in the output signal of the demodulator 8 indicates the noise pulse generated by the above-mentioned phase difference.

Therefore, in order to remove the noise pulse j, a hold pulse having a pulse width obtained by adding the delay time i and the time of the noise pulse j is required.

Next, FIG. 5 is a block diagram of a second example of the conventional magnetic recording / reproducing apparatus.

The second example shown in FIG. 5 is the BP in the first example described above.
In order to eliminate the effect of delay due to F7, FM audio signals 17A and 1
7B switching is done after BPF.

[Problems to be solved by the invention]

In the above-mentioned conventional magnetic recording / reproducing apparatus, in the first example, it is necessary to lengthen the pulse time width of the hold pulse in order to completely remove the noise pulse. For example, when the hold pulse is set to about 20 μs, Is difficult to hear.

Also, in the second example, the number of BPFs needs to be doubled.
In the case of the HS method, 4 types of 2 types of 1.3 MHz band and 1.7 MHz band are required, which causes a problem that the price increases due to an increase in the number of constituent parts.

An object of the present invention is to provide a magnetic recording / reproducing apparatus in which the hold pulse has a short time width and the bandpass filter does not increase.

[Means for solving problems]

A magnetic recording / reproducing apparatus of the present invention includes first and second rotary heads for reproducing first and second FM audio signals, respectively, and the first and second FM audio signals in response to supply of a head switching pulse. A switch circuit which outputs a selection FM audio signal for switching a signal; a control head which supplies a control signal corresponding to the head switching pulse; and a control circuit which delays the control signal by a predetermined first delay time to generate the head switching pulse. 1 delay circuit,
A bandpass filter that passes the selected FM audio signal with a second delay time and outputs a third FM audio signal from which unnecessary frequency components have been removed, and demodulates the third FM audio signal to generate an FM audio signal. A demodulator, a hold pulse generation circuit that generates a hold pulse having a predetermined time width in response to the supply of the trigger pulse, and a sample output of the AM audio signal in response to the supply of the hold pulse to output an audio output signal. In a magnetic recording / reproducing apparatus including a sample and hold circuit for generating, a second delay for generating the trigger pulse by delaying the head switching pulse by a third delay time that is substantially equal to and does not exceed the second delay time. The circuit is further provided.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of the present invention.

The embodiment shown in FIG. 1 is obtained by adding a delay circuit 11 as a second delay circuit to the first example of the conventional magnetic recording / reproducing apparatus shown in FIG.

In FIG. 1, the FM audio signal 17A from the rotary head 1 and the FM audio signal 17B from the rotary head 2 are supplied to the BPF 7 switched by the switch circuit 6 after passing through the preamplifiers 4 and 5, respectively.

Here, the switch circuit 6 uses the delay circuit 10 as the first delay circuit for the FM-modulated head switching signal c from the control head 3 so as to synchronize the FM audio signals 17A and 17B with the video signal. When the control pulse generated at the position conversion point of the head switching signal c is supplied after being delayed by a predetermined time of 1,
Operate.

The control pulse is sent to the BPF7 by the delay circuit 11 as the second delay circuit.
Is delayed for a second predetermined time shorter than the group propagation time of MMV12
Is supplied to.

The MMV12 generates a hold pulse having a pulse width corresponding to the third predetermined time obtained by adding the noise pulse time to the difference time between the group propagation time of the BPF7 and the second predetermined time in response to the pulse from the delay circuit 11. And supplies it to the sample and hold circuit 9. Therefore, the pulse time width of the hold pulse can be shortened as compared with the conventional example.

On the other hand, the FM voice signal from the BPF 7 is demodulated into an AM voice signal by the demodulator 8 and supplied to the sample and hold circuit 9.

The sample and hold circuit 9 outputs the input signal level immediately before the hold pulse is generated as the output level while the hold pulse is continuing, and outputs the input signal level immediately after the hold pulse as the output level when the hold pulse disappears. Output a signal.

FIG. 7 is a waveform chart of each part for explaining the operation of the embodiment shown in FIG.

In FIG. 7, k is the time from when the rotary head is switched to when the hold pulse is generated (that is, the second predetermined time), and k <i is set.

〔The invention's effect〕

As described above, in the magnetic recording / reproducing apparatus of the present invention, the time width of the hold pulse can be shortened by adding the second delay circuit. This has the effect of preventing a rise.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a plan view for explaining a signal recording position of a video tape, and FIG.
FIG. 4 is a characteristic diagram showing the correlation of occupied frequency bands of a video signal and an audio signal, FIGS. 4 and 5 are block diagrams of the first and second examples of the conventional magnetic recording / reproducing apparatus, and FIG. FIG. 4 is a waveform chart of each part for explaining the operation of the magnetic recording / reproducing apparatus shown in FIG. 4, and FIG. 7 is a waveform diagram of each part for explaining the operation of the embodiment shown in FIG. 1,2 ... Rotating head, 3 ... Control head, 4,5 ... Preamplifier, 6 ... Switch circuit, 7 ... BPF, 8 ... Demodulator, 9 ... Sample and hold circuit, 10, 11 …… Delay circuit, 12 …… MMV, 13 …… Voice track, 14 …… Video track, 16 …… Low frequency conversion color signal, 17A, 17B …… FM voice signal, 18 …… Luminance signal.

Claims (1)

[Claims] 1. A first and a second rotary head for respectively reproducing a first and a second FM audio signal, and switching selection of the first and second FM audio signals in response to supply of a head switching pulse.
A switch circuit for outputting an FM voice signal, a control head for supplying a control signal corresponding to the head switching pulse, and a first delay circuit for delaying the control signal by a predetermined first delay time to generate the head switching pulse. And a bandpass filter which outputs the third FM voice signal from which the unnecessary frequency component is removed by passing the selected FM voice signal for a second delay time,
A demodulator that demodulates the FM audio signal to generate an AM audio signal, and a hold pulse generation circuit that generates a hold pulse having a predetermined time width in response to the supply of the trigger pulse,
In a magnetic recording / reproducing apparatus including a sample and hold circuit which samples and holds the AM audio signal and generates an audio output signal in response to the supply of the hold pulse, the head switching pulse is substantially equal to the second delay time. A magnetic recording / reproducing apparatus further comprising a second delay circuit for delaying a third delay time which does not exceed this and generating the trigger pulse.