JPS6015865A - Reproducing device of fm modulation signal - Google Patents

Abstract

PURPOSE:To obtain an FM modulation signal reproducing device compensating the discontinuity of an FM modulation information signal without timewise correlation in an excellent way by making noise generated due to the discontinuity of a reproduced FM modulation signal to be inconspicuous. CONSTITUTION:When dropout is detected by a dropout detecting circuit 5, a pulse signal being at a high level during the period is generated from the circuit 5 and inputted to an OR gate 11 and a monostable multivibrator 6 after being delayed by a delay circuit 13. The monostable multivibrator 6 is triggered by falling of the input and generates a pulse signal holding a high level for a time corresponding to a transient noise generating period. As a result, a pulse adding the pulse signals is obtained from the OR gate 7. A switch 12 is thrown to a terminal B when the output of the OR gate 7 is at high level and thrown to a terminal A when at low level. Since the signal is replaced with a low frequency signal via an LPF11 at the dropout period and the transient noise generating period of the reproducing audio signal, a smooth correcting signal is obtained from an output terminal 9.

Description

[Detailed Description of the Invention] Technical Field> The present invention relates to an FM modulation signal reproducing device, and particularly relates to an FM modulation signal reproducing device
The present invention relates to a device for reproducing FM modulated information signals having no correlation between each other.

<Prior art> = Generally, when a temporally correlated information signal such as a video signal is reproduced from a recording medium, even if a discontinuous portion such as a dropout occurs, this portion of the signal is reproduced from another correlated signal. This was compensated for by substituting a partial signal. However, when a discontinuous portion occurs in a reproduction information signal having no temporal correlation, such as an audio signal, it is impossible to replace the portion with another portion as described above. In particular, if a discontinuous portion occurs in the reproduced FM modulation signal, large-amplitude noise will occur in the information signal after FM demodulation, and the information will be greatly disturbed.

FIG. 1 is a diagram showing a conventional example of a dropout compensation circuit for FM modulated audio signals. In Fig. 1, l is a terminal to which a reproduced FM modulated audio signal is supplied from a head etc., 2 is a limiter, 3 is an FM demodulator, 4 is a low pass filter (LPF), 5 is 1. circuit,
6 is a mono multi-occurrer, 7 is an AND gate, 8 is a previous value hold circuit, and 9 is an output terminal for a reproduced audio signal.

FIGS. 2(a) to 2(f) are timing charts showing waveforms at each portion of FIGS. 1(a) to (f). The operation will be explained below according to the timing chart shown in FIG.

The FM modulated audio signal input from input terminal l is
The limiter 2 is manually operated to remove the phase component.

Reproduction RF signal obtained by limiter 2 (shown in Figure 2 (a))
is supplied to the FM demodulator 3 and the dropout detection circuit 5. The output signal of the FM demodulator 3 is input to an LPF 4 with a cutoff frequency of 15 KHz -20 KHz in order to remove high-frequency noise components, or to avoid the influence of the video signal in the case of audio-video mixed recording. Ru.

As mentioned above, during the dropout period, this LP
Large-amplitude noise as shown in FIG. 2(b) occurs in the output of F4, and even after the dropout period, transients occur for a while due to the influence of the time constant of LPF4. Therefore, in order to reduce the influence of this large-amplitude noise and transient noise, the audio signal level immediately before dropout occurs is held during the period in which these noises occur. Mono multi 6 is dropout detection circuit 5
Trigger at the falling edge of the output (shown in Figure 2 (C))
The output shown in figure (d) is obtained. The outputs of the monomulti 6 and the dropout detection circuit 5 are respectively supplied to the OR gate 1-7, and the OR gate 7 instructs the halt period as shown in FIG.
A signal as shown in e) is supplied to the previous value hold circuit 8.

As a result, the reproduced audio signal has a waveform as shown in FIG. 2(f).

However, if dropout compensation is performed in this way, when the hold ends and the original audio signal waveform is switched,
There is a high possibility that sudden changes will occur, resulting in a considerably distorted waveform.

In addition, the hold period becomes quite long when transient noise is included, resulting in a large difference from the original signal.Furthermore, if the dropout period is relatively long, the hold period becomes long and muting occurs. This results in a similar situation, and it becomes unpleasant to the ears.

<Objective of the Invention> The present invention was made against the background as described above, and provides an FM modulation signal reproducing device that can satisfactorily compensate for discontinuities in FM modulation information signals having no temporal correlation. The purpose is to

<Explanation of Examples> The present invention will be explained below using examples.

FIG. 3 shows a playback F of a playback device as an embodiment of the present invention.
FIG. 3 is a diagram showing a drop error I/compensation circuit for an M-modulated audio signal. Components in FIG. 3 that are similar to those in FIG. 1 are designated by the same numbers. In FIG. 3, 10 is a delay circuit, 11 is an LPF with a cutoff frequency sufficiently lower than LPF 4, 12 is a changeover switch, 13 is a delay circuit, and both delay circuits 10 and 13 are cut-off circuits of LPF II. It has a delay time depending on the frequency, and functions to compensate in advance for the time delay caused by the signal passing through the LPFII.

FIG. 4 is a timing chart showing waveforms of each part in FIGS. 3(a) to (i), and the operation will be explained below using FIG. 4. The reproduced FM modulated audio signal input from the input terminal l is passed through the mink 2, and the amplitude change is removed (
(shown in FIG. 4(a)). This signal is input to the FM demodulator 3 and dropout detection circuit. If a dropout occurs in this FM modulated audio signal, large amplitude noise and transient noise as shown in FIG. It is input to circuit lO and LPFI l. The respective output waveforms are shown in FIGS. 4(d) and (e). This LPF
ll has a cutoff frequency lower than LPF4, which can almost eliminate the large amplitude noise and transient noise mentioned above, and the delay circuit IO is connected to this LPFI.
The time delay due to I has a delay time equal to 1. The output of the delay circuit IO is supplied to the illustrated A side terminal of the changeover switch 12, and the output of LPFII is similarly supplied to the B side terminal.

On the other hand, when a dropout is detected by the dropout detection circuit 5, the circuit 5 generates a pulse signal that is at the /\i level for that period (as shown in FIG. 4(C)). The circuit 5
The output of the delay circuit 13 having the delay time of the above-mentioned
(as shown in section 414(f)). This delayed dropout detection pulse is input to the OR gate 11 and the monomulti 6. The monomulti 6 is triggered by the fall of the input, and generates a pulse signal that maintains a high level for only 2 times during a period corresponding to the period during which the transient noise occurs (as shown in FIG. 4(g)). As a result, the OR gate 7 obtains a pulse (shown in FIG. 4(h)) which is the sum of these pulse signals.

The switch 12 is connected to the illustrated B side terminal when the output of the OR gate 7 is at a high level, and is connected to the illustrated A side terminal when the output is at a low level. Therefore, during the dropout period of the reproduced audio signal shown in FIG.
A smooth correction signal as shown in Figure (i) can be obtained.

- According to the playback device configured as described above, when a dropout occurs in the playback FM modulated audio signal, large amplitude noise and transient noise contained in the output of the FM demodulator 3 are removed from the large amplitude noise and transient noise that are not included in the output of the FM demodulator 3. By replacing it with a low-frequency reproduced audio signal, a smoother trompe-au I/correction signal can be obtained compared to the conventional Holt method described above.

FIG. 5 is a diagram showing a reproducing device as another embodiment of the present invention. The example shown in Fig. 5 is a magnetic recording and reproducing device that sequentially records a mixed signal of a color video signal and an audio signal on a magnetic tape by two rotating heads while forming adjacent tracks, and then reproduces the mixed signal. (hereinafter simply VT
The present invention is applied to a regeneration system (referred to as R).

The 14th method is a well-known method in which the luminance signal of a color video signal is FM-modulated in a relatively high band, the chromaticity signal is frequency-converted to a lower band, and the audio signal is FM-modulated in an intermediate band. shall be taken as a thing. 3 in Figure 5
Components similar to those in the figure are designated by the same numbers.

20 and 21 are rotating heads, which are arranged in a cylinder (not shown) with a 180° phase difference. 22.2
3 is a preamplifier, 24 is a head selector switch, 25
26 is a bypass filter (HPF) for luminance signal separation, 27 is a bandpass filter (BPF) for audio signal separation, 28 is a chrominance signal processing system circuit, 29 is a luminance signal processing system circuit, 30 31 is a mixer, 31 is a reproduction amplifier, 32 is a color video signal output circuit, and 33 is a terminal to which a signal related to the rotational phase of the rotary head described above is input. The signal inputted to the terminal 33 is a 30 Hz rectangular wave that repeats high and low levels every 1/60th of a second, assuming that the video signal described above is an NTSC signal. 34 is a head switching signal forming circuit, 35 is a differentiation circuit,
36 is a one-shot multi, 37 is an OR gate, 38 is an audio signal reproducing amplifier, and 39 is an output terminal for the reproduced audio signal.

The operation will be explained below. Reproduction signals obtained from the heads 20 and 21 are supplied to the vent changeover switch 24 via amplifiers 22 and 23, respectively. The head switching switch 24 is controlled by a head switching pulse generated by a head switching signal forming circuit 34 based on a 30 Hz rectangular wave signal supplied to a terminal 33. The reproduced mixed signal converted into a continuous signal by the head switch 24 is passed through the LPF 25, BPF 26 . B.P.
Supplied to F27. The low frequency conversion chromaticity signal is separated by the LPF 25, and is subjected to well-known processing in the color signal processing system circuit 28 to restore the original band (3.58 MHz for NTSC signals).
) and then supplied to the mixer 30.

Further, the FM modulated luminance signal separated by the BPF 26 is subjected to well-known processing such as AGC, FM demodulation, clipping, and clamping in a luminance signal processing system circuit 29, and is then supplied to a mixer 30. The reproduced color video signal obtained by the mixer 30 is outputted from a terminal 32 via a reproduction amplifier 31.

The FM modulated audio signal separated by the single filter filter 27 is demodulated by the FM demodulator 3 via the limiter 2. The demodulated audio signal is supplied to the A-side terminal of the switch 12 via the LPF4 and the delay circuit 1O, and to the B-side terminal of the switch 12 via the LPFII, and is dropped out as in the embodiment shown in FIG. The generation period and the transient noise generation period are LPFI with a low cutoff frequency.
The one via I is obtained from switch 12.

By the way, although the mixed signal is made into a continuous signal by the head switch 24, a slight time lag inevitably occurs at the joint portion.

In the case of video signals, even if discontinuity occurs due to this shift,
You can push it to a part that does not appear on the playback screen. However, in the case of an audio signal, if a discontinuity occurs due to head switching within 1/60 seconds, it will be reproduced as noise. In particular, in the case of an audio signal recorded with FM modulation, the reproduced FM modulation signal will be discontinuous, so when the FM modulation signal including the discontinuous portion is demodulated, the demodulated audio signal will contain large amplitude noise and transient noise. will occur. This noise occurs during head switching and thereafter during the follow-up period of the phase locked loop (PLL) included in the FM demodulator 3.

Therefore, when reproducing an FM modulated audio signal, the same processing as when a dropout occurs must be performed when switching heads.

In FIG. 5, the head switching signal forming circuit 34 appropriately changes the phase of the aforementioned 30 Hz rectangular wave signal to generate a head switching signal and supplies it to the head switching switch 24. On the other hand, this head switching signal is also supplied to the differentiating circuit 35, and the differentiating circuit 35 generates a sink-like pulse in the positive direction or negative direction at the head switching timing. This whisker-like pulse triggers the one-shot multivibrator 36, and the vibrator 36 generates a signal that momentarily becomes high level at the head switching timing. This signal is logically summed with the dropout detection signal from the dropout detection circuit 5 at the OR gate 37, and thereafter noise removal processing is performed at the time of head switching as well as at the time of occurrence of dropout. That is, the demodulated audio signal is outputted from the switch 12 through the LPF II having a low cutoff frequency even when the head is switched and during the corresponding transient noise generation period. The audio signal output from the switch 12 is output from a terminal 39 via a reproduction amplifier 38.

If the VTR has the above-mentioned playback system, large-amplitude noise and transients caused by the discontinuity will occur when a dropout occurs, or during a discontinuous part of the specially reproduced FM modulated audio signal when the head is switched, and during the transient noise generation period immediately thereafter. By replacing the noise with a low-frequency reproduced audio signal that does not contain these noises, a good reproduced audio signal is obtained.

In the above two embodiments, an example is explained in which the present invention is applied to a reproduction system of an audio signal recorded with FM modulation. It would be very effective if applied to a device that reproduces things.

<Description of Effects> As described above in detail using the embodiments, according to the present invention, when reproducing an FM modulated information signal having no temporal correlation, the reproduced FM modulated signal The present invention provides an FM modulation signal reproducing device that can satisfactorily compensate for noise caused by discontinuities in the noise by making it inconspicuous.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an example of a conventional dropout compensation circuit for FM modulated audio signals, Fig. 2 is a timing chart showing waveforms of various parts in Fig. 1, and Fig. 3 is a playback device as an embodiment of the present invention. FIG. 4 is a timing chart showing the waveform of the numbered part in FIG. 3, and FIG. 5 is a diagram showing a playback device as another embodiment of the present invention. be. 3 is an FM demodulator, 4 is an LPF, 5 is a dropout detection circuit, 11 is an LPF with a low cutoff frequency, 12 is a changeover switch, 34 is a head switching signal forming circuit, 35 is a differentiation circuit, and 36 is a one-shot multivibrator. It is. Applicant Canon Co., Ltd.

Claims (1)

[Claims] 1) A device for reproducing an information signal recorded in FM modulation from a recording medium, comprising an FM demodulating means, a means for receiving the output of the FM demodulating means and removing high-frequency components thereof, and discontinuity of the reproduced information signal. An FM modulated signal reproducing device comprising: means for detecting a signal; and means for changing a band to be removed by the removing means in accordance with the detection.