JPS61122970A - Information signal regenerating device - Google Patents

Abstract

PURPOSE:To prevent the generation of noise by an excess of compensation by judging that a frequency of a generation of a drop out is high when an interval of the drop out is shorter than a predetermined period, and muting a modulation signal for a longer period than that period. CONSTITUTION:By a first transition of a drop out detecting circuit 7, a monostable multivibration (MM) MM 23 generates a pulse of a narrow width. This pulse is fed to an MM 24 and an AND gate 25, and the MM is triggered by a last transition of the pulse and the output thereof holds an H level for a predetermined period after triggering. When during this period, a next trigger pulse g is fed the H level is held for a further constant period. The pulse g generated from the MM during an output of the MM 24 being H is extracted out at the AND gate 25 and fed to an MM 26. An output of the MM 26 becomes a control input of a switching circuit 22, and the circuit 22 is connected to a terminal of the H side during an output of the MM 26, and an output of a muting circuit 21 is outputted to a terminal 14. Thereby, a generation of noises by an excess of a compensation of the dropout can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to an information signal reproducing device, and particularly to processing when dropout occurs in a reproduced information signal.

<Description of Prior Art> Various methods have been proposed for detecting dropouts in reproduced information signals and compensating for the dropouts. However, no matter what method is used, the original information will be lost, so it is impossible to restore the same signal as the original signal. In particular, when a dropout occurs in a reproduced information signal that has no temporal correlation, such as an audio signal, it cannot be replaced with another portion that is highly correlated, resulting in a signal waveform different from that of the original signal. Therefore, if the frequency of dropouts increases, the signal in the dropout compensation portion will act as noise.

FIG. 1 is a diagram showing an example of a conventional information signal reproducing device having a dropout compensation function, and FIG. 2 is a timing chart for explaining the operation of each part in FIG. In Figure 1, 1 is a magnetic tape as a recording medium, 2 is a reproduction magnetic head, 3 is a reproduction amplifier, 4 is a band pass filter (BPF), 5 is a limiter, 6 is an FM demodulator, and 7 is a dropout detection Circuit, 8 is mono multivibrator (
MM), 9 and 12 are AND gates, 10 is an inverter, 11 is a hold circuit, 13 is a mute circuit, and 14 is an output terminal.0 An FM modulated audio signal transferred from the magnetic tape 1 to the head 2 is reproduced. And this signal is sent to amplifier 3. A signal as shown in Fig. 2(a) is generated via the BPFA, and the limiter 5
and is supplied to the dropout detection circuit 7. The FM modulated signal whose amplitude has been limited by the limiter 5 is demodulated by the FM demodulator 6.

At this time, if a dropout occurs in the reproduced signal, the F
The M demodulator 6 generates large amplitude noise. Therefore, during this dropout period, the output of the demodulator 6 is held at the previous value by the hold circuit 11. If a dropout is detected by the dropout detection circuit 7, its output is the dropout detection pulse (Fig. 2(b)
(shown in Figure 2) is configured to be at a high level. Moreover, this detection pulse Φ) is triggered by the rising edge of MM8.
The pulse width of the output of this MM8 is a constant width (
1+). Detection pulse (b) and MM8 output (C)
is supplied to the AND gate 9, and the output (d) of the AND gate 9 is supplied to the hold circuit 11, and the output (d)
During the period when the demodulated signal is at a high level, the hold circuit 11 holds the demodulated signal level immediately before that. That is, if the dropout period is less than or equal to t, the dropout is compensated for by holding the previous value.

Next, the dropout period is 1. Let's consider a case where it is longer. At this time, MM during the dropout period
Since the output (C) of 8 is changed to low level, the output of inverter 10 is high level, and during the remaining dropout period, the output (d) of AND gate 9 is low level, and the output (e) of AND gate 12 is low level. Becomes a high level. The output of the AND gate 12 is supplied to the mute circuit 13 as a mute control pulse. When this mute control pulse is at a high level, the demodulated signal is muted by the mute circuit 13.

The reproduced audio signal obtained as described above is shown in Figure 2(f).
As shown in FIG.
If it is less than or equal to t1, the previous value is held, and if it is greater than or equal to t1, it is held for a period corresponding to t and then muted.

Dropouts occur in such conventional playback devices.
'#, the previous value hold part or the mute circuit would cause noise, which would enter the reproduced audio signal as a harsh noise.

<Object of the Invention> The present invention has been made in view of the above-mentioned drawbacks, and it is an object of the present invention to provide an information signal reproducing device that can obtain a reproduced information signal without noise even when the frequency of occurrence of dropouts increases. be able to.

<Description based on Embodiments> Hereinafter, embodiments in which the present invention is applied to a reproducing apparatus for F'M modulated audio signals will be described with reference to the drawings.

FIG. 3 is a diagram showing an information signal reproducing apparatus as an embodiment of the present invention, and FIG. 4 is a timing chart showing the operation of the part shown in FIG. In FIG. 3, the same components as those in the apparatus shown in FIG. 1 are designated by the same reference numerals, and detailed description thereof will be omitted.

In FIG. 3, reference numeral 21 denotes a mute circuit having different muting characteristics from the mute circuit 13.

22 is a switching circuit, 23 is an MM that is triggered by the rising edge of the dropout detection pulse, and 24 is an MM that is triggered by the falling edge of the output of MM23.

25 is an AND gate, and 26 is an MM that is triggered by the rising edge of the output of the AND gate 25.

With the rise of the output of the dropout detection circuit 7, that is, the dropout detection pulse (shown in FIG. 4(b)), M
M23 generates a narrow pulse (shown in FIG. 4(b)). This pulse (g) is supplied to the retriggerable MM24 and the AND gate 25, and the MM24 receives the pulse (2).
Triggered on the falling edge of . The output of MM24 remains at a high level for a predetermined period t2 after the trigger. However, if the next trigger pulse (g) is supplied during this time, the high level is maintained for an additional period of t2.

While the output (h) of MM24 is at high level, MM23
The generated pulse (g) is extracted by the AND gate 25 (shown in FIG. 4(i)) and supplied to the MMZ 6 as a retrigger pulse. The MM 26 is a triggerable MM, and maintains a constant state for a predetermined period t after being triggered. Furthermore, if the trigger pulse (i) is manually applied again from the AND gate 25 during this period, the high level is maintained for an additional period of t.

The output (j) of the MM26 becomes the control input of the switching circuit 22, and the switching circuit 22 outputs the output (j) of the MM26.
) is connected to the H side terminal shown in the figure when the signal is at a high V level, and accordingly, the output of the mute circuit 21 is outputted to the terminal 14.

In the above configuration, the dropout interval is a predetermined period 11
If it is shorter, it is determined that dropout occurs more frequently, and the demodulated signal is muted for a period t, which is longer than that period. Accordingly, generation of noise due to overcompensation for dropout can be prevented and a good reproduced signal can be obtained.

That is, during the period when the output signal of the MM26 shown in FIG. 4(j) is at a low level, even if dropout compensation is performed using the conventional method described above, a good reproduced signal will never be obtained, and the audio signal will deteriorate. However, with the above-described configuration, such a harsh signal will not be reproduced. In addition, in Figure 3, the mute circuit 13 that performs muting when the dropout period is longer than a predetermined period, and the mute circuit 21 that performs muting when the frequency of dropouts occurs is high. Although a separate circuit is used, this is done to change the muting characteristics, and it is also possible to use the same muting characteristics and the same muting circuit.

For example, in the example shown in FIG. 3, the mute circuit 13
A similar effect can be obtained by operating .

In addition, in the above embodiment, the dropout compensation method was explained as a method of holding the previous value, but this changes depending on the type and characteristics of the reproduced signal. For example, in the case of a video signal, one horizontal scan It is common to use a method of replacing the signal with a signal from a previous period. Furthermore, even in the case of audio signals, it is possible to use a method different from the above-mentioned embodiments, such as using a low-pass filter with a low cutoff frequency or performing linear interpolation. Although the present invention has been described above, the present invention is also applicable to devices that reproduce information signals recorded using other recording methods.

As explained above, according to the present invention, it is possible to obtain an information signal reproducing device that can obtain a good reproduced information signal without generating noise even when dropouts occur frequently. can.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of a conventional information signal reproducing device, FIG. 2 is a timing chart for explaining the operation of each part of the first information signal reproducing device, and FIG. 3 is an information signal reproducing device as an embodiment of the present invention. FIG. 4 is a timing chart for explaining the operation of each part of the third embodiment. 1 is a magnetic tape as a recording medium, 2 is a reproducing magnetic head, 7 is a dropout detection circuit, 21 is a mute circuit, 22 is a switching circuit, 23, 24, and 26 are seven-way multipliers, and 25 is an AND gate. Take time off

Claims (1)

[Claims] means for reproducing information signals from a recording medium; first detecting means for detecting dropouts in the reproduced information signal obtained from the reproducing means; and detecting the frequency of dropouts using the output of the first detecting means. a second detection means for detecting the second detection means;
and means for muting the reproduced information signal according to the output of the detecting means.