JP2945253B2 - Audio switching device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an audio switching device,
More specifically, Hi-Fi video cassette recorder (Hi
In a Fi Video Cassette Recorder (VCR), an audio switching device for automatically switching Hi-Fi audio to fixed-head linear audio when there is a large amount of noise during playback of a Hi-Fi audio non-recording tape or playback of a Hi-Fi audio recorded tape. About.

[0002]

2. Description of the Related Art In a conventional HiFi VCR, even when reproducing a recording tape using only linear audio or a tape on which HiFi audio is recorded, the reproduction FM wave is small when the reproduction FM wave is small and the noise level is large. HiFi) level (envelope) is detected, the level is determined (when the level is low), and the HiFi playback audio is automatically switched to the linear playback audio.

FIG. 2 is a block diagram of a conventional voice switching device.
In the figure, 41 and 42 are low-pass filters (LPF), 43
46 to an amplifier; 47, a head switching pulse generator;
Is a bandpass filter (BPF), 49 is a demodulator, 50
Is a delay unit, 51 is a dropout detection circuit, 52 is a sample hold circuit, 53 is a low-pass filter (20 KH
z), 54 are noise reduction circuits, 55 is a bandpass filter (150 KHz ± 50 KHz), 56 is MI
X circuit, 57 is a noise detection comparator, 58 is an amplifier, 59
Is a band pass filter, 60 is a demodulator, 61 is a dropout detection circuit, 62 is a delay unit, 63 is a sample and hold circuit, 64 is a band pass filter (150 kHz ± 5).
0 KHz), 65 is a low-pass filter (20 KHz),
66 is a noise reduction circuit, and 67 is an amplifier.

[0004] The reproduced FM wave passes through a band-pass filter 48, a demodulator 49, a delay unit 50, a sample-and-hold circuit 52, and a drop-out detection circuit 51 to reduce HiFi switching noise. Is input to the low-pass filter 53 of 20 kHz. 150KHz for noise component pickup before input
Input to the ± 50 KHz band-pass filter 55, Lch /
After each Rch noise is mixed by the MIX circuit 56, the noise level is detected and compared with a preset reference level by the noise detection comparator 57. If the noise level exceeds the reference level, the HiFi sound is converted to a linear sound. The switching control signal is output to the switch circuit for switching. That is,
150 of the signal after returning the HiFiFM wave to normal sound
Looking at the noise level in the KHz ± 50 KHz band,
It is determined whether the iFi sound is recorded (REC) or not and switched.

[0005]

As described above, in the conventional audio switching device, the audio signal after the HiFiFM wave demodulation determines the noise level in a 150 KHz ± 50 KHz band to convert the HiFi audio into the fixed head linear audio. Has been determined to be switched to
Even when playing back a tape with no sound recording or playing back a tape with HiFi sound recorded, the discrimination can be switched only when playing back a tape with a small FM frequency and a large dropout. HiFi audio band (2
(0 Hz to 20 KHz), there is a problem in that the switching cannot be performed smoothly in the case of a tape with a jumbled sound.

[0006] The present invention has been made in view of such circumstances, and when the noise is large when reproducing a high fidelity audio non-recording tape or reproducing a high fidelity recorded tape,
It is an object of the present invention to provide an audio switching device that automatically switches high-fidelity audio to fixed-head linear audio.

[0007]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention automatically converts a fixed head linear sound to a fixed head linear sound when reproducing a large amount of noise when reproducing a non-recorded tape or reproducing a recorded tape. A first noise detection comparator for generating a control signal by performing noise detection of a reproduced FM wave in a high-fidelity video cassette recorder to be switched; a first level adjustment circuit for adjusting a level of a signal after demodulation of high-fidelity audio; A second level adjusting circuit for adjusting the level of the reproduced sound, an inverter for inverting the output signal of the second level adjusting circuit, and a level adjusted and inverted by the second level adjusting circuit and the inverter M to mix the signals
An IX circuit, a second noise detection comparator for detecting noise of an output signal from the MIX circuit, and an OR for outputting a control signal from the first noise detection comparator and the second noise detection comparator And a switch circuit for switching high-fidelity sound to linear sound by a control signal from the OR circuit.

[0008]

The level of the demodulated signal of the HiFi audio FM wave is adjusted through a level adjustment circuit, and the level of the head linear audio signal is adjusted by the level adjustment circuit and inverted at the same time. The component is picked up and compared with the reference level by the noise detection comparator. If the noise level is high, the switch switching control signal is sent to the OR circuit together with the output control signal of the other noise detection comparator to switch the switch circuit. , HiF
The i sound is switched to the linear sound.

[0009]

Embodiments will be described below with reference to the drawings. FIG. 1 is a configuration diagram for explaining an embodiment of a voice switching device according to the present invention. In the drawing, reference numerals 1 and 2 denote low-pass filters (LPFs), 3 to 6 denote amplifiers, 7 denotes a head switching pulse generator, 8 is a band pass filter (BPF), 9 is a demodulator, 10 is a delay unit, 11 is a dropout detection circuit,
12 is a sample and hold circuit, 13 is a low-pass filter (20 KHz), 14 is a noise reduction circuit, 15
Is a band pass filter (150KHz ± 50KHz),
16 is a MIX circuit, 17 is a noise detection comparator, 18 is an amplifier, 19 is an OR circuit, 20 is a level adjustment circuit, 21 is an inverter, 22 is a MIX circuit, 23 is a level adjustment circuit,
4 is a noise detection comparator, 25 is a bandpass filter (B
PF), 26 is a demodulator, 27 is a dropout detection circuit, 28 is a delay unit, 29 is a sample and hold circuit, 30
Is a band pass filter (150KHz ± 50KHz),
31 is a low-pass filter (20 KHz), 32 is a noise reduction circuit, 33 is an amplifier, and 34 is a level adjustment circuit.

The HiFi reproduced audio FM wave passes through a band pass filter 8, a demodulator 9, a delay circuit 10, a sample and hold circuit 12, and a dropout detection circuit 11, and
After the iFi switching noise is reduced, the signal passes through a 20 KHz low-pass filter 13 for removing noise components and a noise reduction circuit 14, is input to a level adjustment circuit 23, and after being level-adjusted, a MIX circuit 22.
Is input to On the other hand, the linear reproduction audio signal is supplied to the switch circuit and is simultaneously input to the level adjustment circuit 20, where the level is adjusted to match the level with the HiFi audio signal, and after being inverted by the inverter 21, the MIX circuit 22 Supplied to

Here, since the signal is mixed with the HiFi audio signal but the phase is inverted, only the noise component in the HiFi audio signal band (20 Hz to 20 KHz) remains and is picked up. This is input to the noise detection comparator 24 and compared with a preset reference level. When it is determined that the noise level is high, a switching control signal of the switch circuit is output to the OR circuit 19. In the OR circuit 19, the noise detection comparator 17 and the noise detection comparator 24 perform an OR operation with the switching control signal of the switch circuit.
After that, a control signal is output to a switch circuit for switching the HiFi sound to the linear sound and the switching is performed.

[0012]

As is apparent from the above description, the present invention has the following effects. That is, HiF
i. A level adjustment circuit for adjusting the level of the demodulated signal, a level adjustment circuit for adjusting the linear audio, an inversion circuit for inverting the signal, and an M for mixing the inverted signal.
An OR circuit for ORing control signals from both the IX circuit, a noise detection comparator for performing noise detection therefrom and performing comparative detection, and a noise detection comparator and another noise detection comparator, and outputting a control signal; Circuit and a switch circuit for switching the HiFi audio to the linear audio. In the conventional method, the tape is recorded on a soft tape or a recorded tape that has not been switched smoothly and in which the deviation of the recording FM wave is recorded with a deviation. At the time of reproduction, the HiFi audio band (20H
Even if a jumbled sound generated within the frequency range (z.about.20 KHz) is generated, it is possible to smoothly switch to the linearly reproduced sound by comparing the HiFi reproduced sound with the linear reproduced sound and performing noise level detection.

[Brief description of the drawings]

FIG. 1 is a configuration diagram for explaining an embodiment of a voice switching device according to the present invention.

FIG. 2 is a configuration diagram of a conventional voice switching device.

[Explanation of symbols]

1, 2 ... low-pass filter (LPF), 3-6: amplifier, 7: head switching pulse generator, 8: band-pass filter (BPF), 9: demodulator, 10: delay unit, 11: dropout detection circuit, 12 ... Sample hold circuit
13: low-pass filter (20 KHz), 14: noise reduction circuit, 15: band-pass filter (150
KHz ± 50 KHz), 16: MIX circuit, 17: Noise detection comparator, 18: Amplifier, 19: OR circuit, 20:
Level adjustment circuit, 21: inverter, 22: MIX circuit, 2
3 ... level adjustment circuit, 24 ... noise detection comparator, 25 ...
Bandpass filter (BPF), 26 ... demodulator, 27 ...
Dropout detection circuit, 28 delay unit, 29 sample hold circuit, 30 bandpass filter (150K
Hz ± 50KHz), 31 ... Low-pass filter (20K
Hz), 32: noise reduction circuit, 33: amplifier, 34: level adjustment circuit.

Continued on the front page (58) Fields surveyed (Int.Cl. ⁶ , DB name) G11B 20/02 G11B 20/06 H04N 5/91

Claims (1)

(57) [Claims] 1. A high-fidelity video cassette recorder that automatically switches to a fixed head linear audio when there is a large amount of reproduction noise during reproduction of a non-audio recording tape or reproduction of an audio-recorded tape. A first noise detection comparator for generating a control signal, a first level adjustment circuit for adjusting the level of the signal after the Hi-Fi audio demodulation, a second level adjustment circuit for adjusting the level of the linear reproduced audio, An inverter for inverting the output signal of the second level adjustment circuit; and M for mixing the signal whose level has been adjusted and inverted by the second level adjustment circuit and the inverter.
An IX circuit, a second noise detection comparator for detecting noise of an output signal from the MIX circuit, and an OR for outputting a control signal from the first noise detection comparator and the second noise detection comparator An audio switching device, comprising: a circuit; and a switch circuit for switching high-fidelity audio to linear audio according to a control signal from the OR circuit.