JPS62234203A - Circuit for discriminating classification of reproduced signal in magnetic tape reproducing device - Google Patents

Abstract

PURPOSE:To discriminate and output a wide-band FM video signal by extracting a signal component, which is not included in a sound signal, from an FM demodulation output signal and comparing the output level of this signal component with a preliminarily determined reference level. CONSTITUTION:An FM-modulated sound signal and an FM-modulated video signal are superposed and stored on a magnetic tape 1, and the signal reproduced by a magnetic head 2 is amplified by an amplifier 3, and only a signal in the sound signal band is extracted by a BPF 4. The sound signal is demodulated from this extracted signal by a demodulation circuit 9 and has the noise eliminated by an LPF 18 and is outputted to an output terminal 17. The envelope level of the output of the BPF 4 is detected by an envelope detector 5, and the detection output is applied to the first hysteresis comparator 6 and is compared with a comparison voltage from an input terminal 7, and the low level is outputted if there is the sound signal when the output of the detector 5 exceeds a certain value, but the high level is outputted if there is not the sound signal then. Drop-out of the output is compensated by a delay circuit 15 and an AND gate 16 to discriminate the video signal.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a discrimination circuit for discriminating the type of a reproduced signal in a video tape recorder (hereinafter referred to as "VTRJ") etc., and in particular, relates to a discrimination circuit for discriminating the type of reproduced signal in a video tape recorder (hereinafter referred to as "VTRJ") etc. The present invention relates to a discrimination circuit that discriminates whether or not a frequency modulated (hereinafter referred to as rFMJ) audio signal is included in a signal.

1 Conventional VL Technique In the following explanation, an 8 mm VTR will be used as an example.

In an 8 mm VTR, a video signal and an FM audio signal are normally recorded on the main track of a magnetic tape. FIG. 3 shows a typical recording signal spectrum in an 8 mm VTR. As shown in FIG. 3, the recording signal includes a pilot signal P, low frequency conversion color signals C and F.
In addition to the M i11 degree signal Y, an FM audio signal @A with a lower frequency band than the luminance signal Y is included, and these signals are placed on the main track of the magnetic tape! l gkL,
recorded.

By the way, in an 8 mm VTRk, in order to improve the image quality of the video signal, it is conceivable to make the spectrum of the recording signal recorded on the magnetic tape as shown in FIG. As shown in Fig. 4, the frequency band of the FMn degree signal Y is expanded to the frequency band normally used for the FMi voice signal among the recording signal bands, that is, the band of the FM luminance signal Y is moved downward. This is done so that the FM audio signal A is not recorded. In such a case, since the frequency band is expanded, it is possible to improve the quality of the luminance signal and, by extension, the image quality of the video signal, and it is possible to reproduce a good video signal.

In such a case, the audio signal is usually recorded on a linear track exclusively for audio signals on the magnetic tape, so there is no problem such as the audio signal not being able to be reproduced.

However, from the point of view of signal reproduction, there are two types of magnetic tape: 1) a magnetic tape on which signals are recorded using the normal recording method, that is, a magnetic tape on which signals are recorded using the frequency allocation shown in Figure 3; The signal with the frequency allocation shown is &l! When manufacturing an 8mm VTR that can play both recorded magnetic tape and magnetic tape, it is necessary to check the type of signal recorded on the magnetic tape to be played back, that is, whether an FM audio signal is recorded or a substitute for the FM audio signal. frequency? I! FM with expanded range! It is preferable to automatically determine whether a signal has been recorded and then switch the reproduction circuit, and such an automatic signal type determination circuit is required.

Based on the above-mentioned background, the inventor of the present invention first considered a circuit as shown in FIG. 2 as a reproduced signal type discrimination circuit. The circuit shown in FIG. 2 is based on a signal dropout detection circuit provided in a conventional VTR.

Referring to FIG. 2, 1 is a magnetic tape, 2 is a head, 3 is a preamplifier, 4 is a voice signal bandpass filter, 5 is an envelope detector, and 6 is a comparator. ,
7 is a comparison voltage (M quasi-voltage) input terminal, 15 is a delay circuit,
16 is an AND gate, 8 is a discrimination signal output terminal, and 9 is an FM
E! The voice signal demodulation circuit is a demodulated voice signal low-pass filter, and 17 is a voice signal output terminal.

The circuit of FIG. 2 operates as follows. The signal reproduced from the magnetic tape 1 by the magnetic head 2 is 1lfJ
Of the amplified signals that are amplified by the stationary amplifier 3,
Only the signals in the FM audio signal band are extracted by the bandpass filter 4. FM1 extracted by bandpass filter 4
1f voice signal is t! ! The signal is tuned to tI by the modulation circuit 9, and the low-pass filter 18 removes g, etc., and output from the output terminal 17.

On the other hand, the output of the bandpass filter 4 is transmitted to the envelope detector 5.
It is also given to The envelope detector 5 detects the envelope level of the output signal, and its detection output is sent to the comparator 6.
It is compared with the comparison voltage from the input terminal 7. In this circuit, when the output of the envelope m-detector 5 is higher than the comparison voltage, the output of the comparator 6 is low level, and when the output of the envelope m-detector 5 is lower than the comparison voltage, the output of the comparator 6 is high level. becomes. That is, when the output of the envelope detector 5 is a sound signal whose level is higher than a certain value, the output of the comparator 6 becomes low level, and conversely, when the sound signal does not exist, the output of the comparator 6 becomes low level. Output becomes high level.

By the way, if the output of the comparator 6 is directly derived as the discrimination output, signal dropout compensation is not performed, and even if there is a scratch on the magnetic tape 1 and there is a signal dropout, discrimination cannot be performed. There is a problem that the output cannot be switched. Therefore, a delay circuit 15 and an AND gate 16 are used to compensate for signal dropout. As a result, the output signal level of comparator 6 is
and.

The output signal level ■ of the delay circuit 15 and the AND gate 16
The relationship with the output No. 12 level ■ is as shown in FIG. In other words, even if an instantaneous high-level pulse appears during the output of the comparator 6 as shown in the circle ``■'' in Figure 5 due to signal dropout, the output ``■'' of the AND gate 16 will be delayed from the output ``■'' of the comparator 6. Since this is a logical product with the delayed output (2) delayed by the circuit 15, signal dropout compensation has been achieved.

[Problems to be Solved by the Invention] By the way, with the frequency allocation as shown in Fig. 3, magnetic tape or FMS voice signals recorded by superimposing video signals and FM audio signals should not be recorded (pilot signals and normal When playing a magnetic tape (with only video signals), the discrimination circuit shown in Figure 2 is effective! 11, and if an audio signal is recorded, the output of the output terminal 8 will be low level, and if no audio signal is recorded, the output of the output terminal 8 will be high level. Therefore, the reproducing circuit can be switched as appropriate based on the signal appearing at the output terminal 8.

However, when playing back a magnetic tape on which signals are recorded with the frequency allocation shown in Figure 4, the second
According to the discriminating circuit shown in the figure, depending on the modulation degree and modulation frequency of the FMI 11 degree signal, the lower sideband of the FM degree signal passes through the band pass filter 42. The above voltage is derived, and the output of the comparator 6 is always at a low level. Therefore, even though the output terminal 8 is playing back a magnetic tape on which no FM audio signal is recorded, a determination output indicating that an FM audio signal is recorded, that is, a low level signal is derived. There is a problem with storing it away.

In this way, instead of the magnetic tape and audio signal on which the FM8 voice signal and the video equalization signal are recorded in a superimposed manner, a wideband video signal whose band has been expanded and modulated to include the frequency band of the audio signal is used instead of the audio signal. As a reproduction signal type discrimination circuit for a VTR that can reproduce both recorded magnetic tapes, it is insufficient to simply use a conventional signal dropout detection circuit by modifying the design. The disadvantage was that the objective could not be achieved.

Therefore, it is an object of the present invention to provide a circuit for determining the type of reproduced signal in a magnetic tape reproducing apparatus, which can fully achieve the objective.

[Means for Solving the Problems] A reproduced signal type discrimination circuit in a magnetic tape reproducing apparatus according to the present invention includes a first filter means for extracting a signal in a frequency-modulated audio signal band; a first comparison means for comparing the output level of the means with a predetermined first MnP level; a second filter means for extracting a No. 3 component that is not included in the original audio signal from the demodulated signal; a second filter which predetermines the output level of the second filter means;
and a discriminating means for deriving a discrimination output based on the output of the first comparing means and the output of the second comparing means.

[For f'\'] The second filter means in the present invention is a frequency modulated video signal, and when the lower side wave component whose band has expanded to within the frequency modulated & voice signal band is demodulated. A signal component not included in the audio signal of the water flux, for example, a pulse noise band component including a high frequency component, which occurs in the water flux is extracted. The level of the signal extracted by the second filter means is compared by the second comparison means, and together with the output of the first comparison means is applied to the discrimination means. therefore,
Since the discriminating means performs a discriminating operation based on the output of the first comparing means and the output of the second comparing means, the second comparing means is able to detect points that are insufficient based on the output of the first comparing means. Since it can be compensated for by the output, accurate discrimination operation can be performed.

[Embodiments of the invention] An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention. In FIG. 1, 1 is a magnetic tape, 2 is a magnetic head,
3 is a preamplifier L1iS device, 4 is a bandpass filter for passing FM audio signals (first filter hand FU), 5 is an envelope detector, 6 is a first hysteresis comparator (first comparison means), 7 is the first comparison voltage input terminal, 8 is the output terminal for outputting the discrimination signal, 9 is the FM demodulator, 10 is the second band pass filter (the second filter hand f1.11 is the level detector, 12 is the 2 hysteresis comparator (second
13 is a second comparison voltage input terminal, 14 is an OR gate, 15 is a delay circuit, and 16 is an AND gate.

Referring to FIG. 1, the signals recorded on the magnetic tape 1 are
FMF5 voice signal band signal <FMg voice signal or FM
Since no signal is rejected by the first bandpass filter 4, the output level of the envelope detector 5 is small and the first hysteresis comparator 6 The output becomes high level. As a result, a high level signal indicating that no FMg voice signal is recorded on the magnetic tape 1 is derived from the output terminal 8. Conversely, if an FMg voice signal is recorded on the a-air tape 1, the output of the bisteresis comparator 6 will be at a low level, which will appear at the output terminal 8.

Therefore, when a signal is recorded with a frequency allocation as shown in FIG.

It is possible to accurately determine whether or not the F~1 loud voice signal A is recorded based on the output of the first hysteresis comparator 6.

Next, a description will be given of the discrimination operation of reproduction No. 11 (() when a signal is recorded with the frequency allocation as shown in FIG. 4.

When the lower side wave of the FMI 11 degree signal spreads in the FM & voice signal band, the lower side wave component is handled by the first band pass filter 4, and the output of the envelope detector 5 becomes a predetermined level or higher. . Therefore, the output of the first hysteresis comparator 6 becomes low level. On the other hand, the child signal component of the FMlfi degree signal is output by the FM demodulator 9. ! ! 31, pulse noise becomes noticeable in the output voltage, as shown in FIG. 6, for example. Such pulse-like 21 noise contains quite a lot of high-frequency components that are not included in a normal audio signal. The second bandpass filter 10 extracts pulsed noise band components including high frequency components that are not included in the original audio signal. The signal extracted by the second band pass filter 10 is sent to the level detector 1
1 and is applied to the second hysteresis comparator 12. The M2 hysteresis comparator 12 compares the second comparison voltage with the output of the level detector 11, and derives a high level output when the output of the level detector 311 exceeds the second comparison voltage. That is, when the demodulated signal of the FMtl modulation circuit 9 contains a pulse noise band component that is not included in a normal FM demodulated audio signal and exceeds a predetermined value, the second hysteresis comparator 1
2 derives the high level.

Therefore, the output of the two-man OR gate 14 which inputs the output of the first hysteresis comparator 6 and the output of the second hysteresis comparator 12 is (if both side waves are absent) and ■FMFMg voice signal is not recorded and instead FMI! Is the frequency signal range of the i1 degree signal an FMS voice signal? ! A high level signal is derived in both cases when recording is extended to the rI region.

The output of the OR gate 14 is directly given to the AND gate 16 and is also passed through the delay circuit 15 to the AND gate 16.
6, signal dropout compensation is performed. Therefore, the output of the AND gate 16 is delivered to the output terminal 8 as an output for determining the type of reproduced signal.

In this embodiment, both the first comparator 6 and the second comparator 12 are hysteresis comparators. In this way, when using a hysteresis comparator, fluctuations in the input signal level do not immediately appear as fluctuations in the output signal level, and a certain amount of redundancy is maintained, so the output signal level does not reverse frequently and is relatively stable. It has the advantage of becoming a thing. However, the first
And the second comparison means 6 and 12 do not have to be hysteresis comparators.

In addition, in the above-mentioned practical example, the input signal frequency component is FMM
Considering the case where the noise leaks into the output signal of the modulator 9, and in order to avoid malfunction due to this leaked component, the explanation will be made assuming that the second bandpass filter 1o is set to extract only pulse noise. did. however,
FMt! ! If the leakage of the input signal frequency component in the output signal component of the Wi-Fi device 9 is sufficiently small, the second band-pass filter 10 can be replaced with a high-pass filter having a pass band higher than the audio signal band. You may.

In addition, in the detailed explanation of the invention, a discrimination circuit applied to an 8 mm VTR was taken as an example, but the present invention is applicable to a normal VT
It goes without saying that the present invention is particularly applicable to so-called high-fidelity VTRs and other magnetic tape playback devices in general.

[Effects of the Invention] As described above, according to the present invention, a second filter means for extracting signal components that are not included in the original audio signal is provided at the subsequent stage of the FM converter, and the size of the second filter means is When F exceeds a predetermined comparison level, F
FM IPl with expanded band instead of M audio signal
! Since it is determined that the magnetic tape is recorded, it is possible to provide a determination circuit that can accurately determine the type of signal recorded on the magnetic tape to be reproduced.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a groove bottom of an example of the present invention. FIG. 2 is a block diagram showing an example of the circuit filling that forms the background of the present invention. FIG. 3 is a diagram showing frequency allocation of recording signals of an 8 mm VTR. Figure 4 shows an 8mm VTR that does not record FM audio signals.
FIG. 7 is a diagram showing frequency allocation when the band of the F tvl A11 signal is expanded to that band. Figure 5 shows
FIG. 3 is a timing chart showing signal levels at each point (■), (2), and (2) in FIG. 2; FIG. 6 shows that when a magnetic tape on which an FMM degree signal whose band has been expanded to the FMΔ voice signal band is recorded instead of the FM tone signal is demodulated, FMt! ! FIG. 3 is a diagram showing an example of pulse noise appearing in the output of a regulator. In the figure, 1 is a magnetic tape, 4 is a first bandpass filter, 6 is a first hysteresis comparator, 10 is a second bandpass filter, and 12 is a second hysteresis comparator. In addition, in the figures, the same reference numerals indicate the same or corresponding parts. Agent Daikichi Masu Recommendation 1 Figure 1 2 -1 move, Tape 4: Passed through i1 filter 6: 4 I 2; Shimabi 1 town; Ko 2 Satoshi yio: Fishi 7/2
:: 62t + p hit ξ (shihaku 2 figure! Tou j figure

Claims (4)

[Claims] (1) A magnetic tape on which a frequency-modulated audio signal and a frequency-modulated video signal are recorded in a superimposed manner, and a video signal whose band is expanded to the frequency band of the audio signal and is modulated is the audio signal. A reproduction signal type discrimination circuit in a magnetic tape reproducing apparatus capable of reproducing both a magnetic tape on which a wideband frequency modulated video signal recorded instead of a wideband frequency modulated video signal is recorded, the circuit comprising: a signal in the frequency modulated audio signal band; The first thing to extract
a first filter means for predetermining an output level of the first filter means;
a first comparing means for comparing with a reference level of the first filtering means; a demodulating means for demodulating the output of the first filtering means; and a signal component not included in the original audio signal is extracted from the output signal of the demodulating means. a second filter means for predetermining an output level of the second filter means;
a reproduction signal type in a magnetic tape reproduction apparatus, the magnetic tape reproduction apparatus comprising: a second comparison means for comparing with a reference level; and a discrimination means for deriving a discrimination output based on the output of the first comparison means and the output of the second comparison means. discrimination circuit. (2) The magnetic tape according to claim 1, wherein the second filter means extracts pulse noise band components including high frequency components that are not included in the original audio signal. A reproduction signal type discrimination circuit in a reproduction device. (3) A reproduced signal type discrimination circuit in a magnetic tape reproducing apparatus according to claim 1 or 2, wherein the first and second comparison means are both comparison means having hysteresis characteristics. (4) The discrimination means derives a discrimination output based on the logical sum of a directly input signal and a signal obtained by passing the input signal through a predetermined delay circuit, in order to compensate for signal dropout. Claim 1, which is
A reproduction signal type discrimination circuit in a magnetic tape reproduction apparatus according to item 2 or 3.