JPH0719332B2 - Magnetic recording / reproducing device - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a magnetic recording / reproducing apparatus for recording / reproducing a video signal and an audio signal using a magnetic tape (hereinafter abbreviated as VTR, particularly suitable for improving reproduced sound quality). About the method.

[Background of the Invention]

With recent improvements in magnetic heads and magnetic tapes, magnetic recording / reproducing characteristics of video signals have improved. Therefore, the desired S / N
The amount of tape required to obtain the tape has been reduced, and the tape speed has been reduced to improve the recording density. However, the audio signal has a drawback in that the band of the reproduced audio output is narrowed by the tape speed being slowed because the audio head is fixed and the S / N is deteriorated. In addition, wah and flutter performance was difficult due to the instability of the tape running system.

Therefore, in order to reduce or eliminate the drawbacks of the above technique, the following technique of recording also as a video track is known. As a first method, as disclosed in Japanese Patent Application Laid-Open No. 51-135519,
FM modulated according to the audio signal The FM modulated signal is recorded on the recording track for the video signal, and then the FM is modulated according to the luminance signal.
The modulated luminance modulation signal and the low-frequency converted chroma low-frequency signal are overwritten and recorded on the same track on which the FM voice modulation signal is recorded. First, the FM audio modulation signal is recorded, and then the video modulation signal is overwritten,
The FM voice modulation signal is recorded deep inside the magnetic layer of the magnetic tape, and then the brightness modulation signal having a higher frequency than the FM voice modulation signal is recorded on the surface of the magnetic layer without being erased.

However, since the FM-modulated FM voice-modulated signal is recorded together with the video signal, there is a drawback that noise occurs in the voice signal during reproduction. The conventional audio reproducing circuit shown in FIG. 1 will be described below with reference to the waveform chart of FIG.

In FIG. 1, 12 is a magnetic tape, 1 and 2 are first and second audio heads, and 3 and 4 are first and second preamplifiers for amplifying the output signals of the first and second audio heads 1 and 2. Reference numeral 5 is a switch circuit for alternately switching and selecting the output signals of the preamplifiers 3 and 4, 6 is a demodulation circuit for demodulating the FM voice signal selected by the switch circuit 5, 7 is a switch for holding the previous value, and 8 is the front. A value holding capacitor, 10 is a mono-multi, 11 is a 30 Hz pulse source for driving the switch circuit 5 and the mono-multi 10, and 9 is an output terminal.

The first and second voice heads 1 and 2 are arranged on the rotary cylinder at intervals of 180 degrees and alternately sweep the magnetic tape 12.
Then, the pulse source 11 generates a pulse signal synchronized with the sweep of the voice heads 1 and 2, and controls the switch circuit 5. The FM audio signals reproduced by the audio heads 1 and 2 are amplified by the preamplifiers 3 and 4 and supplied to the switch circuit 5. Waveforms 14 and 15 in FIG. 2 are output signal waveforms of the preamplifiers 3 and 4, respectively. The waveform 11 in FIG. 2 is the output signal waveform of the pulse source 11. The output signals of the preamplifiers 3 and 4 are switched by the switch circuit 5 and become a continuous signal as shown by the waveform 16 in FIG. However, when the switch circuit 5 switches, that is, at the rising and falling portions of the output pulse of the pulse source 11,
The phase of the FM audio signal is disturbed and the sign 2 of the waveform 16 in Fig. 2 is changed.
The phase becomes discontinuous at the switching portions indicated by 2,23,24. When such an FM voice signal is demodulated by the demodulator 6, spike noises 25, 26 and 27 are generated in the demodulated output at the phase discontinuity portion of the FM voice signal as shown by the waveform 17 in FIG.

Therefore, when the switch circuit 5 is switched by the output of the mono-multi 10 triggered by the output pulse of the pulse source 11, the switch 7 is turned off, the voltage immediately before the switch circuit 5 is switched is held by the capacitor 8, and spike noise is output. I try not to be. The output waveform is shown as waveform 18 in FIG. Sign
The part indicated by 28, 29, 30 is the place where the previous price was held. However, this previous value holding portion is different from the original signal, and this newly becomes switch noise.

[Object of the Invention]

It is an object of the present invention to provide a noise reduction circuit that eliminates the drawbacks of the above techniques and reduces switching noise.

[Outline of Invention]

To achieve the above object, the present invention is characterized in that a switching noise generation period is replaced with an audio signal obtained by demodulating an FM signal in which no phase discontinuity occurs in a switch circuit.

The noise reduction circuit of the present invention will be described below with reference to an embodiment shown in FIG. In FIG. 3, reference numeral 31 is a second FM demodulator, the input terminal of which is connected to the output terminal of the second preamplifier 4 and the output terminal of which is connected to the other input terminal of the second switch circuit 32. ing. The second switch circuit 32 is controlled by the output of the monomulti 10, and selects the demodulation output of the first FM demodulator 6 and the demodulation output of the second demodulator 31. Then, the selected demodulation output is supplied to the output terminal 9.

In such a circuit, the second FM demodulator 31 demodulates the output signal of the second preamplifier 4 and supplies it to the second switch circuit 32. By the way, the magnetic tape 12 wound around the outer circumference of the cylinder is wound around the outer circumference of the cylinder by 180 degrees or more. Therefore, as shown by the waveforms 14 and 15 in FIG.
The FM audio signals reproduced from the second audio heads 1 and 2 are reproduced during the switching period of the switch circuit 5. Therefore, when the output signal of the second preamplifier 4 (waveform 15 in FIG. 2) is demodulated by the second demodulator 31, the demodulation output becomes a demodulation output that does not include spike noise, as shown in the waveform 19 in FIG. . The second switch circuit 32 selects the output signal of the second demodulator 31 from the output of the first demodulator 6 at the time when the first switch circuit 5 switches, and the first demodulator again after a lapse of a predetermined time. 6 output signal is selected. Then, the switching timing of the second switch circuit 32 is set to the first and second demodulators 6, 31.
By making the phases of the output signals of 1 to coincide with each other, a noise-free audio signal is output to the output terminal 9 as shown by the waveform 20 in FIG. It is the mol-multi circuit 10 that controls the switching of the second switch circuit. The switch circuit 32 selects the output of the first FM demodulator 6 when the output of the mono-multi circuit 10 is at high level, Sometimes the output of the second FM demodulator 31 is selected. The waveform 21 in FIG. 2 is the output signal waveform of the mono-multi circuit 10.

FIG. 4 is a circuit diagram of the switch circuit 32. Terminals 33 and 34 are connected to FM demodulators 6 and 31, respectively, and their DC potentials are V ₁ and V ₂ , 35 and 36 are switches and 3
7 is a capacity, and the capacity value is C. 38 is a resistance whose value is R. The operation of this circuit will be described with reference to the waveform chart of FIG. The switches 35 and 36 are controlled by the pulses 21 and 40 so as to be turned on when the pulse is high and turned off when the pulse is low level. First, the FM voice signal of the second preamplifier 4 is input to the FM demodulator 31, and normal demodulation is performed. After the voice signal 19 is output, the pulse 40 turns on the switch 36. At this time the terminal
The potential difference between 33 and 34 V ₁ -V _2, and the output impedance of the FM demodulator 6 and the switch 35
If the impedance of is much smaller than the series impedance of C and R of the capacitor 37 and resistor 38, V ₁ −V ₂ is
All are applied to the capacitor 37 and the resistor 38.
6 No noise is generated by turning on. If the time t from when the switch 36 is turned on to when the switch 35 is turned off is sufficiently larger than the product of the capacitor 37 and the resistor 38, that is, the time constant CR, the capacitor 37 is charged and the potential difference between V _{1 and} V ₂ is reached. have. In this state,
Even if the switch 35 is turned off, the DC potential of the terminal 9 remains at V ₁ , and therefore the buffer output is from the first demodulator 6 to the second demodulator 6.
The FM demodulator voice signal of the demodulator 31 is smoothly replaced, and when the switch 35 is turned on, the demodulator output of the first demodulator 6 is returned to again, and the switch 36 is turned off.

Therefore, according to the present invention, spike noise can be smoothly compensated with a normal signal. Since the compensated voice signal is output as a voice signal only during the spike noise generation period, it has an advantage that it can be tolerated even if the S / N and distortion are somewhat bad.

〔The invention's effect〕

As described above, according to the present invention, it is possible to suppress spike / noise generation due to switching of the preamplifier output by compensating with the FM demodulation signal of another system.

[Brief description of drawings]

FIG. 1 is a block diagram of a conventional FM demodulation circuit, FIG. 2 is a waveform diagram of each part of FIGS. 1 and 3, FIG. 3 is a block diagram of a noise reduction circuit of the present invention, and FIG. FIG. 5 is a circuit diagram of the switch circuit of the invention, and FIG. 5 is a waveform diagram for explaining the operation of FIG. 5 …… Head signal changeover switch 6,31 …… FM demodulator, 32 …… Switch 35,36 …… Switch, 37 …… Capacitance C 38 …… Resistance R, 39 …… Buffer 21 …… Switch 32 and switch 35 Drive pulse 40 …… Switch 36 Drive pulse 11 …… SW30 Head output signal switching pulse

 ─────────────────────────────────────────────────── ─── Continued front page (72) Hiroshi Toeda Hiroshi Toeda 1410 Inada, Katsuta City, Ibaraki Prefecture Inside the Tokai Plant, Hitachi, Ltd. (72) Masaaki Hirano 1410 Inada, Katsuta City, Ibaraki Hitachi Tokai Plant, Ltd. (56) Reference JP-A-59-63013 (JP, A)

Claims (1)

[Claims] 1. A first method using a frequency conversion voice carrier.
In a helicopter scan type magnetic recording / reproducing apparatus for recording an audio signal on a video recording track by a second audio head, a first preamplifier for amplifying an output signal of the first head during reproduction, and a second preamplifier during reproduction. A second preamplifier that amplifies the output signal of the head and the outputs of the first and second preamplifiers are alternately switched,
A first switch for outputting and a first switch for performing FM demodulation on an output signal of the first switch
Demodulator, a second demodulator that constantly performs FM demodulation on the output signal of the second preamplifier, and is turned off for a certain period from the time when the first switch is switched, and during an on period other than that period. A second switch for outputting an output signal of the first demodulator, and a second switch which is turned on before a certain period of time when the second switch is turned off,
The on period continues until at least the second switch is turned on again, and during the on period, the third switch that outputs the output signal of the second demodulator, the output end of the second switch, and the A magnetic recording / reproducing apparatus, wherein a resistor and a capacitor connected in series with the output end of the third switch are provided, and the signal from the output end of the second switch is used as an audio output signal.