JPS593710A - Fm modulation magnetic recording and reproducing device for multichannel sound signal - Google Patents

Abstract

PURPOSE:To reproduce a sound free of waveform distortion by providing demodulation circuits corresponding to heads individually, and switching sound signals demodulated during an overlap period in which both resproducing heads scan on a magnetic tape at the same time. CONSTITUTION:Sound signals of two channels are recorded together with a video signal in such a way that a sound of one channel is FM-demodulated and frequency-multiplexed in the upper band of the sound band of the other sound and then they are FM-modulated at a time. Both FM sound signals are separated from the outputs of preamplifiers 24 and 25 individually through BPFs 51 and 52, and demodulated by demodulators 53 and 54. The 1st sound signal reproduced by reproducing heads 22 and 23 are sent from LPFs 55 and 56. The 2nd FM-modulated sound signal is reproduced by BPFs 57 and 58 and demodulated by demodulators 59 and 60. Changeover switches 63 and 64 are operated in the overlap period in which the signals are reproduced by reproducing heads 22 and 23 at the same time.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for frequency multiplexing recording of an audio signal on a video signal recording track in a magnetic recording surface reproducing device.
In particular, the present invention relates to an audio signal recording method suitable for recording and reproducing multi-channel audio signals.

In a magnetic tape recording/reproducing device (hereinafter simply abbreviated as VTR), the luminance signal is subjected to frequency modulation (FM), and the chromaticity signal is frequency-converted and added to the lower side of the FM luminance signal, and the azimuth angle is Recording is performed sequentially on a magnetic chip using a plurality of different rotating heads. Furthermore, the audio signal is recorded on a recording track in the longitudinal direction of the magnetic tape by a fixed head. However, the improvement in recording density in recent years has been remarkable, achieving a recording density 17 times higher than that of VTRs of about 10 years ago.

Therefore, the running speed of the magnetic tape is extremely slow, about i 0 m/S. Therefore, the conventional method of recording audio signals on the longitudinal recording track of a magnetic tape using a fixed head cannot achieve sufficient sound quality in terms of the audio signal reproduction signal band, wow/fluff characteristics, reproduction level fluctuations, etc. It is becoming difficult to obtain.

As an example of a method to improve this drawback, frequency modulation (F
A known method is to frequency-multiplex a (M-modulated) audio signal with the FM-modulated video signal and sequentially record and reproduce it on a magnetic tape using a rotating head (hereinafter abbreviated as audio FM multiplexing method).

The features of the audio FM multiplexing system are as follows: (1) The playback signal band does not depend on the tape running speed and is wideband.

(2) Good wow and flutter characteristics because it is less susceptible to time axis fluctuations due to uneven tape running speed.

(3) There is no playback signal level fluctuation.

(4) Low distortion rate and high S/N.

etc., and high quality playback audio can be obtained.

Although this method of FM modulating the audio signal and frequency multiplexing it with the video signal has many advantages, there is a problem that frequency multiplexing inevitably narrows the video signal recording band. In particular, when recording 2-channel audio signals by modulating and multiplexing each channel with 17cFM, a recording band that is approximately twice as large as that for 1-channel is required, which significantly narrows the video recording band. This makes it difficult to put it into practical use. As a means of transmitting two channels of audio signals without using many bands, the audio of one channel is FM modulated, frequency multiplexed onto the upper band of the other audio band, and then FM modulated all at once. FM-F
M multiplexing methods are possible.

FIG. 1 shows an example of a recording circuit configuration using a two-channel audio signal multiplex recording system based on the FM-FM system. The video signal input from input terminal 1 is passed through low pass filter (LPF) 2.
The signal is then separated into a luminance signal component and a chromaticity signal component by a bandpass filter 3. The luminance signal component separated by the LPF 2 is high frequency emphasized by the emphasis circuit 4 and then input to the 1M modulator 5. The output signal of the 1M modulator 5 is applied to an adder 7 after unnecessary low-frequency signal components are removed by a high-pass filter 6 . Further, the chromaticity signal component separated by BpF 3 is converted to a low frequency component by a frequency converter 8, and unnecessary high frequency components are removed by an LPF 9.
It is added to adder 7.

On the other hand, the first audio signal and the second audio signal are inputted from input terminal 10 and input terminal 11, respectively, and are high-frequency emphasized by emphasis circuits 12 and 13. The second audio signal with high frequency emphasis in the emphasis circuit 13 is FM.
In the modulator 14, for example, the carrier wave center frequency 2fH (fB
: horizontal scanning frequency) and added to the adder 15. Further, the first audio signal, which has been high-frequency emphasized by the emphasis circuit 12, is directly applied to the adder 15. Therefore, the output signal Sve2trum of the adder 15 becomes as shown in FIG. Part A in the figure is the first directly added
The part B in the figure is the occupied band of the FM-modulated second audio signal. The output signal of the adder 15 is applied to the FM modulator 16 and subjected to FM modulation.
Unnecessary high-frequency components are removed by the PF 17 and added to the adder 7.

Therefore, the output of the adder 7 is a signal obtained by adding the FM modulated luminance signal, the low frequency conversion chromaticity signal, and the FM-FM audio signal, and its spectrum is K as shown in FIG.

The output signal of the adder 7 thus obtained is amplified by the recording amplifier 18 and then recorded on the magnetic tape 21 by the recording heads 19 and 20.

Figure i4 shows an example of a reproduction circuit configuration using a two-channel audio signal multiplex recording method based on the FM-FM method. The signal read out from the magnetic tape 21 by the playback head 22.23 is amplified by the preamplifier 24.25, and then sent to the input terminal 26.
A series of signals are generated by a switching circuit 27 controlled by a reproduction track switching signal inputted from the switching circuit 27.

The output signals of the switching circuit 27 are EPF2B, LPF3
2.

The signal is supplied to the BPF 37 and separated into an FM modulated luminance signal, a low frequency conversion chromaticity signal, and an FM modulated audio signal. HP
The FM modulated luminance signal separated by F 28 is demodulated by a demodulator 29, and unnecessary high frequency components are removed by an LPF 30.
De-emphasized by the de-emphasis circuit 31,
be fed to adder 35.

Furthermore, the low frequency converted chromaticity signal separated by the LPF 32 is converted to a high frequency signal by the frequency conversion circuit 6, and then sent to the BPF 3.
4, unnecessary frequency components are removed, and the resultant signal is supplied to an adder 65. Therefore, a video signal including luminance and chromaticity signals is obtained as the output signal of the adder 65, and is output from the output terminal 36.

On the other hand, the FM modulated audio signal extracted by the BPF 37 is demodulated by the demodulator 38, and then passed through the LPF 39, Bp
At F40, the signal is separated into a first audio signal and an FM-modulated second audio signal. The separated FM modulated second sound is demodulated by a demodulator 41, and unnecessary high frequency components are removed by an LpF 42.

The first and second audio signals demodulated in this manner contain impulsive noise caused by phase discontinuity of the reproduced FM audio signal that occurs when switching between reproduction tracks. Previous value holding circuits 43 and 44 are used to remove impulsive noise generated when switching reproduction tracks.

The previous value holding circuits 45 and 44 are controlled by an output signal of a holding pulse generator 45 that generates holding pulses based on a reproduction track switching signal inputted from an input terminal 26. 5th pressure Figure 4 shows signal waveforms at various parts. (a) is the reproduced FM audio signal, (b) is the reproduction track switching pulse, (c) is the holding pulse generator output signal, (b) is the reproduced audio signal obtained from LPF39 or 421, (e) is the previous value retained This is the output signal of circuit 46 or 44. The reproduced audio signal from which noise has been removed passes through de-emphasis circuits 46 and 47 and is output from output terminals 48 and 49.

By holding the previous value in this manner, extremely large intrusive noise at the time of switching reproduction tracks can be removed, but waveform distortion is newly generated due to holding the previous value.

The waveform distortion caused by holding the previous value is proportional to the error area of the waveform from the original waveform, so it is approximately 2 times the product of the holding time and the signal frequency.
It will be proportional to the power of Therefore, the waveform distortion increases rapidly as the holding time becomes longer and as the tone becomes higher.

When recording and reproducing only the first audio signal, the band can usually be widened sufficiently, so the retention time is 10 to 20 minutes.
It is about μS and does not pose a problem.

However, in the FM-FM system, since the frequency-multiplexed signal is further FM modulated, the first
An LPF 59 and a BPF 40 are required to separate the audio signal from the FM-modulated second audio signal, and both filters can only widen the band by about fH at most. Therefore, the time width of impulsive noise when switching playback tracks is about 60 to 100 μ5, so simply holding the previous value will cause extremely large waveform distortion.
This poses a serious problem in practice.

One object of the present invention is to provide a circuit that eliminates the waveform distortion caused by holding the previous value, which is a problem with the above-mentioned FM-FM method.

Therefore, in the present invention, a separate demodulation circuit is provided for each playback head, and the demodulated sounds are switched during the period when both playback heads simultaneously scan the piezomagnetic tape (the so-called overlap period). , prevents the generation of impulsive noise itself that inevitably occurs when switching in the FM band, and therefore eliminates the need to hold the previous value,
This enables high-quality audio recording and playback without noise or waveform distortion.

The present invention will be explained below with reference to Examples. FIG. 6 shows the circuit configuration of an embodiment of the FM-FM type reproducing circuit according to the present invention. - Since the recording side is the same as that in FIG. 1, the description thereof will be omitted. Further, circuits with the same functions as those in FIG. 4 are given the same numbers. Signals read out from the magnetic tape 21 by the reproducing heads 22.25 are each amplified by preamplifiers 24.2'5. The video signal reproducing circuit (not shown) is connected to the video signal reproducing circuit (not shown) in the same way as in FIG.
The signal is output from the output terminal 50 through a switching circuit 27 which is switched by a reproduction track switching signal inputted from the input terminal 26.

On the other hand, the FM audio signals are separated from the outputs of the preamplifiers 24 and 25 by BPFs 51 and 52, respectively, and demodulated separately by demodulators 53 and 54. Below, LPF5
5, 56 are shown in Figure 1 LPF59, BpF 57, 5B
to the BPF 40, demodulators 59 and 60 to the demodulator 41,
LPF 61.

62 is a circuit corresponding to LPF 42, and LPF 5
The LpF 56 outputs the first audio signal reproduced by the reproduction head 22, and the LpF 56 outputs the first audio signal reproduced from the reproduction head 26. Further, from the LPF 61, the second audio signal reproduced by the reproduction head 22 is transmitted to the LPF 61.
The second audio signal reproduced by the reproduction head 23 is output from the PF 62.

FIG. 7 shows the signal waveform of the section shown in FIG. (α) is the output signal waveform of the preamplifier 24, (b) is the output signal waveform of the preamplifier 25, and (C) is the playback track switching signal (,Z) is the first or second signal demodulated from the output signal of the preamplifier 24. The audio signal waveform (=) is the first or second audio signal waveform demodulated from the output signal of the preamplifier 25. As is clear from the waveforms (α) and (b), there is a period in which signals are simultaneously reproduced from both the reproduction heads 22 and 24, a so-called overlap period.
In the demodulated signal waveforms of (d) and (ri), those parts have the same waveform. Therefore, when extracting the first audio signal reproduced from two tracks as a continuous signal, simply send the reproduction track switching signal. using LpF55
If the output of -L 56 is switched and outputted by the switching circuit 63, a continuous signal as shown in FIG. 7(a) can be obtained. Similarly, the output switching circuit 64 of LPF61 and 62
By switching at , the second audio signal can be extracted as a continuous signal. The first and second audio signals obtained in this manner are sent to the de-emphasis circuit 65.
, 66, and then output from output terminals 67 and 68, respectively.

By providing two systems of demodulation circuits in this way and switching after demodulation to extract continuous audio signals, it is possible to eliminate the large waveform distortion caused by holding the previous value at the time of switching playback tracks, which was a major problem in FM-FM demodulation circuits. be able to.

In this embodiment, a 2-head VTR has been described, but VTRs with 3 or more heads can also be used by switching between two systems of reproduction and demodulation circuits, thereby continuously switching the reproduction signal from each track in the audio signal band. It can be obtained as an audio signal.

As described above, according to the present invention, it is possible to remove impulsive noise and waveform distortion at the time of switching playback tracks, which are problems when recording FM-FM audio signals with a rotating head, resulting in a significant improvement in sound quality. There is.

[Brief explanation of drawings]

Figure 1 is a circuit diagram of an FM-FM audio signal recording device, Figure 2 is an FM-FM audio signal spectrum diagram, Figure 3 is a recording signal spectrum, and Figure 4 is an FM-FM audio signal spectrum diagram.
A circuit configuration diagram of the M system audio signal reproducing device, FIG. 5 is a signal waveform diagram of the fourth joint section, FIG. 6 is a circuit diagram showing an embodiment of the present invention, and FIG. 7 is a diagram of the fourth joint section. It is a signal waveform diagram. 51, 52, 57.58... BPF 53.54, 59.60... FM demodulator 55,! M,
61.62...LpF 63.64......Switching circuit 口壬嶌4 Diagram! 5 Figure

Claims (1)

[Claims] 1. A frequency-modulated multi-channel audio signal obtained by frequency-modulating a signal obtained by mixing a first audio signal and a frequency-modulated second audio signal is frequency-multiplexed with a frequency-modulated video signal to generate a plurality of frequency-modulated audio signals. In a video/audio magnetic recording and reproducing apparatus that sequentially records data with a head and reproduces it by sequentially switching a plurality of heads, the frequency-modulated multi-channel audio signal reproduced by a first set of heads is demodulated, and the frequency modulated multi-channel audio signal is demodulated. a first demodulation circuit that obtains a second audio signal; and a second demodulation circuit that demodulates the frequency modulated multi-channel audio signal reproduced from a second set of heads to obtain the first and second audio signals. and a first successive demodulation circuit that receives as input the first audio signal obtained from the first demodulation circuit and the first audio signal obtained from the second demodulation circuit. a second signal switching circuit that receives the second audio signal obtained from the second demodulation circuit and the second audio signal obtained from the second demodulation circuit and outputs a continuous second audio signal. Channel audio signal frequency modulation magnetic recording and reproducing device. 2. The first and second demodulation circuits extract the reproduced frequency modulated multi-channel audio signal. a first bandpass filter; a first demodulator for demodulating the frequency modulated multi-channel audio signal; and a low-pass filter for extracting the first audio signal from the output signal of the first demodulator. a second bandpass filter for extracting the frequency-modulated second audio signal from the output signal of the first demodulator; and an output signal of the second bandpass filter. 2. The multi-channel audio signal frequency modulation magnetic recording and reproducing apparatus according to claim 1, further comprising a second demodulator for demodulating. 2. The multi-channel audio signal frequency modulation magnetic recording and reproducing apparatus according to claim 1, wherein said first and second signal switching circuits are switched based on both signals.