JPS62188006A - Magnetic recording and reproducing device - Google Patents

Abstract

PURPOSE:To improve hearing sense by controlling a switch circuit and a holding circuit by using two delay circuits in a reproducing device which switches the outputs of two rotary heads by a switch circuit and outputs them from a sample holding circuit. CONSTITUTION:An FM audio signal 17A from a rotary head 1 is applied to the switch circuit 6 through a preamplifier 4 and an FM audio signal from a rotary head 2 is also applied to the switch circuit 6 through a preamplifier 5. Then, the switched signal is sent to the sample holding circuit 9 through a BPF 7 and a demodulator 8 and a playback output is sent out of the sample holding circuit 9. In this constitution a head switch signal (c) from a control head 3 is applied to the changeover switch 6 and also applied to the holding circuit 9 through a monostable multivibrator 12 to reduce noise pulses. In this case, the noises are removed completely by providing a delay circuit 11 additionally and newly in front of the vibrator 12 and shortening hold pulse time width, thereby improving hearing sense.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magnetic recording and reproducing device, and particularly to a magnetic recording and reproducing device used for reproducing audio signals.

[Conventional technology]

Generally, when used in a magnetic recording/reproducing device, audio signals are recorded on audio tape using a fixed head similar to that of a normal tape recorder, as shown in Figure 2, on audio track 13 of the audio tape. However, the sound quality is not good, and recently a rotating head is used to record video track 1.
High quality video tape recorders have been developed which record FM audio signals on 4-hi.

In that case, the FM audio signal 17 is as shown in FIG.
It is inserted into the intermediate frequency band between the frequency band occupied by the low-pass converted color signal 16 and the FM-modulated luminance signal 18.

By the way, when this FM audio signal 17 is reproduced using a rotary head, pulse noise is generated when the rotary head is switched. This is due to the difference in tape tension at the joint where the two rotating heads switch.
The phases of the M audio signals do not completely match, and therefore, a phase change corresponding to the phase difference between the two FM audio signals at the time of switching appears in the FM audio signal after switching, and the changed phase of the demodulated AM audio signal appears. This is because a pulse-like noise commensurate with that is generated.

In the case of video signal reproduction, switching of the video rotary head is performed during the vertical retrace period, so there is no practical problem, but in the case of audio signals, it becomes a major problem.

In order to solve this problem, conventional magnetic recording and reproducing devices
This problem is solved by providing a sample and hold circuit shown in FIG. However, FIG. 4 is a block diagram of a first example of a conventional magnetic recording/reproducing apparatus.

In FIG. 4, an FM audio signal 17 from the rotating head 1
A and the FM audio signal 17P from the rotary head 2 are switched by a switch circuit 6 and passed through a bandpass filter (hereinafter referred to as BP).
F) 7, which passes through a demodulator 8 and is supplied to a sample and hold circuit 9.

Since the head switching signal C from the control head 3 is synchronized with the video rotating head, it is delayed by the delay circuit 10 so as to be synchronized with the rotating heads 1 and 2.
A control pulse is created that occurs at the phase change point of the modulated head switching signal C. The switch circuit 6 is switched by this control pulse.

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

The sample and hold circuit 9 uses the input signal level immediately before the hold pulse is generated as the output level while the hold pulse continues, and when the hold pulse disappears, the output level is the input signal level immediately after that. Outputs the audio output signal as .

FIG. 6 is a waveform diagram of each part for explaining the operation of the magnetic recording/reproducing apparatus shown in FIG. 4.

As shown in FIG. 6, in the output signal of the switch circuit 6, a phase difference occurs between the FM audio signals 17A and 17B at a portion h. Further, i in the output signal of the BPF 7 indicates a delay time due to the bandpass filter, and j in the output signal of the demodulator 8 indicates a noise pulse generated due to the above-described phase difference.

Therefore, in order to remove the noise pulse j, a hold pulse having a pulse width equal to 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 a conventional magnetic recording/reproducing apparatus.

The second example shown in FIG.
In order to eliminate the influence of the delay caused by the PF 7, switching between the FM audio signals 17A and 17B is performed after the BPF.

[Problem that the invention seeks to solve]

In the above-mentioned conventional magnetic recording/reproducing device, in order to completely remove noise pulses in the first example, it is necessary to increase the pulse time width of the hold pulse. For example, when the hold pulse is set to about 20 μs, the audio There is a problem that it becomes difficult to space between the two.

In addition, in the second example, the number of BPFs is doubled; for example, in the case of VH3 system, 1.3MHz band and 1.7MHz band are required.
There is a problem that 4 pieces of 2 types of Z band are required, which leads to an increase in price due to an increase in the number of component parts.

SUMMARY OF THE INVENTION An object of the present invention is to provide a magnetic recording and reproducing apparatus in which the time width of a hold pulse is short and the number of bandpass filters does not increase.

[Means for solving problems]

The magnetic recording and reproducing apparatus of the present invention includes first and second rotary heads for reproducing FM audio signals, a control head for outputting a head switching signal for switching between the first and second rotary heads, and a control head for outputting a head switching signal for switching between the first and second rotary heads; a first delay circuit that delays the head switching signal by a first predetermined time to synchronize the signal and the video signal and generates a control pulse based on the head switching signal; Second
a switch circuit for switching the FM audio signal from the rotating head; a bandpass filter for removing unnecessary frequency components from the FM audio signal output from the switch circuit; and a bandpass filter for demodulating the output from the bandpass filter to generate an AM audio signal. a second delay circuit that delays the control pulse for a second predetermined time within the group propagation time in the demodulation circuit; The device includes a monostable multivibrator that outputs a hold pulse having a time, and a sample and hold circuit that samples and holds the AM audio signal using the hold pulse and outputs an audio output signal.

〔Example〕

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

FIG. 1 is a block diagram of one 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. 4 described above.

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

Here, the switch circuit 6 transmits the FM-modulated head switching signal C from the control head 3 to a delay circuit 10 serving as a first delay circuit, so as to synchronize the FM audio signals 17A and 17B with the video signal. It operates when a control pulse delayed by a predetermined time of 1 and generated at a phase change point of the head switching signal C is supplied.

The control pulse is transmitted to B by the delay circuit 11 as a second delay circuit.
M is delayed by a second predetermined time shorter than the group propagation time of PF7.
MV12 is supplied.

MMV12 responds to the pulse from delay circuit 11, BP
A hold pulse having a pulse width corresponding to a third predetermined time obtained by adding the noise pulse time to the difference time between the group propagation time of F7 and the second predetermined time is generated and supplied to the sample and hold circuit 9. Therefore, the pulse time width of the hold pulse can be shortened compared to the conventional example.

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

The sandal and hold circuit 9 uses the input signal level immediately before the hold pulse is generated as the output level while the hold pulse continues, and outputs audio as the input signal level immediately after the hold pulse disappears. Output a signal.

FIG. 7 is a waveform diagram of each part for explaining the operation of the embodiment shown in FIG. 1.

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

[Effect of the Invention'1 As explained above, the magnetic recording/reproducing device of the present invention can shorten the time width of the hold pulse by adding the second delay circuit, so that the audibility is improved and the bandpass filter is This has the effect of preventing a rise in prices without increasing the amount of money.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a plan view for explaining signal recording positions on a videotape, and FIG.
The figure is a characteristic diagram showing the correlation between the 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 a conventional magnetic recording/reproducing device, respectively, and FIG. FIG. 4 is a waveform diagram 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. 1.2... Rotating head, 3... Control head, 4.5
...Preamplifier, 6...Switch circuit, 7...B
PF, 8... Demodulator, 9... Sample and hold circuit, 10.11... Delay circuit, 12... MMV,
13...Audio track, 14...Video track,
16...Low frequency conversion color signal, 17A, 17B...FM
Audio signal, 18... Luminance signal. ! , 2 rotations 4・y)'' 3 Shin Kōji 8 1 Do Otsu Atsu + times tS 11! 1 Kaya 2 times Kaya 3 Mani 5"

Claims (1)

[Claims] first and second rotating heads for reproducing FM audio signals;
a control head that outputs a head switching signal to switch between the first and second rotating heads; a control head that delays the head switching signal by a first predetermined time to synchronize the FM audio signal and the video signal; a first delay circuit that generates a control pulse based on the signal; a switch circuit that switches the FM audio signals from the first and second rotary heads when the control pulse is input; and an FM output from the switch circuit. A bandpass filter that removes unnecessary frequency components from the audio signal, and demodulation of the output from the bandpass filter.
a demodulator that outputs an M audio signal; a second delay circuit that delays the control pulse by a second predetermined time within the group propagation time in the bandpass filter; Magnetic recording characterized in that it includes a monostable multivibrator that outputs a hold pulse having a third predetermined time, and a sample and hold circuit that samples and holds the AM audio signal using the hold pulse and outputs an audio output signal. playback device.