JPH08186838A - Magnetic recording and reproducing device - Google Patents

Abstract

PURPOSE: To suppress production of high fidelity beat in the multi-system magnetic recording and reproducing device by taking a recording characteristic up to a head into account and selecting a mixing ratio of a mixer circuit depending on the signal system of the NTSC/PAL. CONSTITUTION: The magnetic recording and reproducing device is provided with a mixer circuit 10 whose mixing ratio is varied and an NTSC/PAL discrimination circuit 11 discriminating whether a signal form of video and audio signals to be recorded is the NTSC or the PAL. A comparator circuit 14 compares levels of L, R channel audio signals subject to frequency-modulation and provides an output of a control signal which channel of the FM signals is higher by what level to the mixer circuit 10. The mixer circuit 10 uses the control signal from the comparator circuit 14 and a discrimination signal from the NTSC/PAL discrimination circuit 11 as a control signal so as to mix both the L/R channel FM signals at a mixing rate in a way that the levels of both the L/R channel FM audio signals are the same at a point of time when heads 6a, 6b are used to record the signals onto a tape while taking the recording characteristics up to the heads 6a, 6b sufficiently into account depending on the signal system.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-fidelity audio type magnetic recording / reproducing apparatus for recording an audio signal of a television signal on a magnetic tape by a rotary head, and particularly a so-called multi-system for recording a television signal of a different transmission method. Magnetic recording / reproducing apparatus.

[0002]

2. Description of the Related Art FIG. 2 is a block diagram of an audio signal recording system in a conventional magnetic recording / reproducing apparatus, showing a structure of a VHS system for recording an audio signal as a high-fidelity audio signal on a magnetic tape.

In the figure, L channel audio signal S _L
The R channel audio signal S _R and the R channel audio signal S _R are compressed by the dBX compression circuits 1L and 1R, respectively, and then the FM modulation circuits 2L and 2R.
FM modulated by R, band pass filter (BPF) 3L,
Only signals in the required band are extracted in 3R.

In this case, the FM modulation circuits 2L and 2R
The modulated audio signal is inserted between the low frequency conversion chromaticity signal band and the FM luminance signal band, and in the case of NTSC system, the carrier frequency is 1.3 MHz for the L channel and 1.7 MHz for the R channel, and the frequency deviation is The maximum transfer is ± 150 KHz.

The audio signals of both channels that have passed through the band-pass filters 3L and 3R are mixed at a constant ratio in the mixing circuit 4, amplified by the recording amplification circuit 5, and then magnetic tape is supplied by the pair of rotary heads 6a and 6b. It is recorded on the upper track (not shown).

[0006]

By the way, in such a high-fidelity VTR, a signal of 400 KHz which is a difference component of carrier frequencies of both channels is generated as a beat signal, which jumps in when a chroma signal is recorded on a magnetic tape. Then, it becomes a color noise signal as a so-called hi-fi beat. In particular, recorded FM waves (1.
3MHz, 1.7MHz) stands out most.

Therefore, in the above-mentioned conventional example, in order to improve the hi-fi beat, the FM signals of both channels are mixed at a fixed ratio at the time of mixing, and the levels of both are made uniform. However, the conventional mixing ratio does not take into consideration the recording characteristics including the head, and since it is a mixing ratio that simply aligns the levels, mixing of the FM waves of the L channel and the R channel at the time of recording on the tape is not possible. It did not reach the same level, and it was not a sufficient suppression of hi-fi beat.

When applied to a so-called multi-system magnetic recording / reproducing apparatus capable of selectively switching between an NTSC system video signal and a PAL system video signal for recording / reproducing, the carrier frequency of the NTSC system is used. (1.
3MHz ± 50KHz / 1.7MHz ± 50KHz) and PAL carrier frequency (1.4MHz ± 50KHz / 1.8M)
However, if the mixing ratio is fixed, there arises a disadvantage that the hifi beat is small in the PAL system but large in the NTSC system if the mixing ratio is fixed.

FIG. 3 is a recording frequency characteristic diagram of an audio signal in which the recording characteristics including the head are taken into consideration. The frequencies (1.3 MHz and 1.7 MHz) shown by the chain line in the figure are NTSC system and the frequencies shown by the broken line (1. 4 MHz, 1.8 MHz) is a PAL system. As is clear from this characteristic diagram, if the mixing ratio is fixed, the mixing levels will not be uniform depending on the transmission method.

An object of the present invention is to suppress the generation of hi-fi beats in a multi-system magnetic recording / reproducing apparatus capable of recording / reproducing television signals of different transmission systems.

[0011]

SUMMARY OF THE INVENTION A magnetic recording / reproducing apparatus according to the present invention comprises a modulation circuit for independently frequency-modulating each of the L channel and R channel audio signals of a television signal to be recorded, and the L channel and R channel. A first comparing circuit for detecting a no-signal portion of each audio signal, a timing pulse generating circuit for generating a pulse signal in accordance with the no-signal portion of the audio signals of both channels detected by the first comparing circuit, and a pulse A second comparison circuit that compares the levels of the audio signals of the L channel and the R channel after frequency modulation at the signal generation timing, a determination circuit that determines the transmission system of the television signal, and an L channel after the frequency modulation and And a mixing circuit for mixing the respective audio signals of the R channel, wherein the mixing circuit is a comparison result of the second comparison circuit and a discrimination circuit. The mixing ratio configured to mix a variable to both speech signals based on the determination result.

In this case, the discriminating circuit is a circuit for discriminating whether the transmission system of the television signal is the NTSC system or the PAL system.

[0013]

In the structure of the present invention, the signalless portions of the L channel and the R channel to be recorded are detected by the first comparison circuit, and a pulse signal is generated from the timing pulse generation circuit in accordance with the detected signalless portion. The second comparison circuit compares the levels of the frequency-modulated audio signals of both channels in accordance with the timing of the pulse signal. As a result, the levels of both modulated signals when there is no signal are known.

The mixing circuit considers the recording characteristics including the head based on the comparison result in the second comparison circuit (which signal is larger and how big) and the transmission system of the television signal determined by the determination circuit, The mixing ratio of both modulation signals is determined so that the levels of the modulation signals of both channels become the same level when the head is recorded on the tape. This suppresses the generation of high-fidelity beats in the multi-system magnetic recording / reproducing apparatus.

[0015]

1 is a block diagram showing an embodiment of a magnetic recording / reproducing apparatus according to the present invention. In the configuration shown in FIG. 2, the mixing ratio can be changed in place of the mixing circuit 4 having a fixed mixing ratio. NTS for providing the mixing circuit 10 and for discriminating whether the video and audio signals to be recorded are the NTSC system or the PAL system
A C / PAL discrimination circuit 11 is provided.

Further, the L and R channel audio signals S
First comparator circuit 1 for detecting the signalless portions of _L and S _R
2, a timing pulse generation circuit 13 for generating a pulse signal in synchronization with the timing of the no-signal portion detected by the comparison circuit 12, and an L / R that has passed through the band pass filters (BPF) 3L, 3R at the generation timing of this pulse signal. Comparison circuit 14 for comparing the levels of FM audio signals of both channels
Is provided, and the control signal from the second comparison circuit 14 and the NTSC
The mixing ratio of the mixing circuit 10 is changed based on the control signal from the / PAL discrimination circuit 11.

The control signal from the NTSC / PAL discrimination circuit 11 is FM modulation circuits 2L, 2R and BPF3.
It is supplied to L and 3R as a characteristic switching signal. The other structure is the same as the structure shown in FIG.

In the configuration of this embodiment, the L channel audio signal S _L is compressed by the dBx compression circuit 1L and then FM.
FM modulation is performed by the modulation circuit 2L, and the band pass filter (BP
F) Only the signal in the required band is extracted in 3L and the comparison circuit 1
4 and the mixing circuit 10.

The R channel audio signal S _R also has a dBx compression circuit 1R, an FM modulation circuit 2R and a band pass filter 3R.
The same processing is performed in step S3, and only the signal in the required band is supplied to the comparison circuit 14 and the mixing circuit 10.

On the other hand, the comparison circuit 12 compares the levels of the audio signals S _L and S _R of both channels with a preset reference level, and detects a portion below the reference level as a non-signal portion and outputs a detection signal. The timing pulse generation circuit 13 receives the detection signal and outputs a pulse signal to the comparison circuit 14. The comparison circuit 14 receives the pulse signal, compares the levels of the FM signals of the FM-modulated channels, and outputs to the mixing circuit 10 as a control signal the level of the FM signal of which channel.

The mixing (MIX) circuit 10 uses the control signal from the comparison circuit 14 and the discrimination signal from the NTSC / PAL discrimination circuit 11 as control signals, and has sufficient recording characteristics in accordance with the signal system and including the heads 6a and 6b. Considering this, at the time of recording on the tape with the heads 6a and 6b, the F of both channels is
The FM signals of both channels are mixed at a mixing ratio such that the M signal level becomes the same level.

The FM audio signal thus mixed by the mixing circuit 10 is amplified by the recording / amplifying circuit 5 and recorded on a track on a magnetic tape (not shown) by the pair of rotary heads 6a, 6b.

[0023]

According to the present invention, the recording characteristics including the head are taken into consideration, and the mixing ratio of the mixing circuit is switched according to the NTSC / PAL signal system. It is possible to effectively suppress the occurrence of beats.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a magnetic recording / reproducing apparatus according to the present invention.

FIG. 2 is a block diagram of a conventional magnetic recording / reproducing apparatus.

FIG. 3 is a recording frequency characteristic diagram of an audio signal.

[Explanation of symbols]

 1L, 1R dBX compression circuit 2L, 2R FM modulation circuit 3L, 3R band pass filter (BPF) 5 recording amplification circuit 6a, 6b rotary head 10 mixing circuit 11 NTSC / PAL discrimination circuit 12 first comparison circuit 13 timing pulse generation circuit 14 Second comparison circuit

Claims (2)

[Claims] 1. A modulation circuit for independently frequency-modulating each of the L channel and R channel audio signals of a television signal to be recorded, and a circuit for detecting a non-signal portion of each of the L channel and R channel audio signals. A comparison circuit of No. 1, a timing pulse generation circuit for generating a pulse signal in accordance with the non-signal portions of the audio signals of both channels detected by the first comparison circuit, and after the frequency modulation at the generation timing of the pulse signal Second comparison circuit for comparing the levels of the respective L-channel and R-channel audio signals, a discrimination circuit for discriminating the transmission system of the television signal, and the frequency-modulated L-channel and R-channel audio signals And a mixing circuit that mixes the comparison result of the second comparison circuit and the determination circuit of the determination circuit. A magnetic recording / reproducing apparatus characterized in that a mixing ratio is varied based on another result to mix the both audio signals. 2. The magnetic recording / reproducing apparatus according to claim 1, wherein the discriminating circuit is a circuit for discriminating whether the transmission system of the television signal is the NTSC system or the PAL system.