JPH0746469B2 - Information signal reproducing device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an information signal reproducing apparatus, and more particularly to processing when a dropout occurs in a reproduced information signal.

<Description of Prior Art> Various methods have been proposed for detecting dropouts in a reproduced information signal and compensating for the dropouts. However, no matter what method is used, the original information is lost, and therefore the same signal as the original signal cannot be restored. In particular, when a dropout occurs in a reproduction information signal having no temporal correlation, such as an audio signal, it cannot be replaced with another portion having a high correlation, resulting in a signal waveform different from the original signal. Therefore, if the dropout occurrence frequency increases, the signal of the dropout compensation portion acts as noise.

FIG. 1 is a diagram showing an example of a conventional information signal reproducing apparatus having a dropout compensation function, and FIG. 2 is a timing chart for explaining the operation of each unit in FIG. In FIG. 1, 1 is a magnetic tape as a recording medium, 2 is a reproducing magnetic head, 3 is a reproducing amplifier, 4 is a bandpass filter (BPF), 5 is a limiter, 6 is an FM demodulator, and 7 is a dropout detection circuit. , 8 are mono-multi vibrators (M
M), 9 and 12 are AND gates, 10 is an inverter, 11 is a hold circuit, 13 is a miute circuit, and 14 is an output terminal.

When the FM-modulated audio signal is reproduced from the magnetic tape 1 by the head 2, this signal becomes a signal as shown in FIG. 2 (a) via the amplifier 3 and BPF 4, and is supplied to the limiter 5 and the dropout detection circuit 7. It The FM-modulated signal whose amplitude is limited by the limiter 5 is demodulated by the FM demodulator 6.

At this time, if dropout occurs in the reproduced signal, FM
Large-amplitude noise is generated from the demodulator 6. Therefore, during this dropout period, the output of the demodulator 6 is held at the previous value by the hold circuit 11. When the dropout detection circuit 7 detects the dropout, the output of the dropout detection pulse (shown in FIG. 2 (b)) becomes high level. The detection pulse (b) is supplied to MM8 to trigger at the rising pulse width of the output of the MM8 is constant width (t _1). The detection pulse (b) and the output (c) of the MM8 are supplied to the AND gate 9, the output (d) of the AND gate 9 is supplied to the hold circuit 11, and immediately before that during the period when the output (d) is at the high level. The demodulation signal level of is held by the hold circuit 11. That is, when the dropout period is t ₁ or less, the dropout is compensated by the previous value hold.

Next, consider the case where the dropout period is longer than t ₁ . At this time, since the output (c) of the MM8 shifts to the low level during the dropout period, the output of the inverter 10 becomes the high level, and the output (d) of the AND gate 9 is the low level and the output of the AND gate 12 during the remaining dropout period. (E) becomes high level. And gate 12
Is supplied to the miute circuit 13 as a miute control pulse. When the miute control pulse is at high level, the demodulated signal is muted by the miute circuit 13.

The reproduced audio signal obtained as described above is shown in FIG.
As shown in the figure, if the dropout period is a predetermined length t ₁ or less, the previous value is held, and if t ₁ or more, then t ₁
Is held after holding for the corresponding period.

When dropouts for a short period frequently occur in such a conventional reproducing apparatus, the previous value hold portion or the mute portion becomes noise, and it enters into the reproduced audio signal as annoying noise.

<Objects of the Invention> The present invention has been made in view of the above-mentioned drawbacks, and even when a dropout of a period longer than a predetermined period occurs or a dropout frequency of a short period becomes high. An object of the present invention is to obtain an information signal reproducing device that can obtain a reproduced information signal without extra noise.

<Description of Embodiments> Embodiments in which the present invention is applied to an FM-modulated audio signal reproducing apparatus will be described below with reference to the drawings.

FIG. 3 is a diagram showing an information signal reproducing apparatus as one embodiment of the present invention, and FIG. 4 is a timing chart showing the operation of each part in FIG. Incidentally, in FIG. 3, the same components as those of 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 is a miute circuit having a different miuteing characteristic from that of the miute circuit 13, 22 is a switching circuit,
23 triggers on the rising edge of the dropout detection pulse M
M and 24 are MMs that trigger on the falling edge of the output of the MM 23, 25 is an AND gate, and 26 is an MM that triggers on the rising edge of the output of the AND gate 25.

The output of the dropout detection circuit 7, that is, the rising edge of the dropout detection pulse (shown in FIG. 4 (b)) causes the MM
23 generates a narrow pulse (shown in FIG. 4 (g)). This pulse (g) is supplied to the retriggerable MM 24 and the AND gate 25, and the MM 24 is triggered by the trailing edge of the pulse (g). The output of the MM24 holds the high level for a predetermined period t ₂ after the trigger. However, when the next trigger pulse (g) is supplied during this period, the high level is maintained for the period of t ₂ .

The pulse (g) generated from the MM23 while the output (h) of the MM24 is at the high level is extracted by the AND gate 25 (fourth).
(Shown in Fig. (I)), the MM26 is supplied as a trigger pulse. MM26 is a retriggerable MM and has a predetermined period after the trigger.
t ₃ Holds high level. Further, if the trigger pulse (i) is input again from the AND gate 25 during this period, the high level is maintained for the period of t ₃ .

The output (j) of the MM26 becomes the control input of the switching circuit 22, and when the output (j) of the MM26 is at a high level, the switching circuit 22 is connected to the H side terminal shown in the figure. It will be output to 14.

In the above configuration, if the dropout interval is shorter than the predetermined period t ₂ , it is determined that the dropout occurrence frequency is high, and the demodulated signal for a period t ₃ longer than that period is muted. Along with this, noise can be prevented from occurring due to excessive dropout compensation, and a good reproduction signal can be obtained. That is, while the output signal of the MM26 shown in FIG. 4 (j) is at a high level, even if dropout compensation is performed by the method of the prior art, a good reproduced signal is never obtained.
In the case of the audio signal, it is rather audible, but according to the above configuration, such an audible signal is not reproduced.

Incidentally, in FIG. 3, a miute circuit 13 for performing a muteing when the dropout period is longer than a predetermined period,
Although it is a separate circuit from the muting circuit 21 that performs muting when the frequency of dropouts is high, this is done to change the characteristics of muting. Is also possible. For example, in the example of FIG. 3, the same effect can be obtained by operating the miute circuit 13 by the logical sum of the output of the AND gate 12 and the output of the monomulti 26.

Further, in the above embodiment, the dropout compensation method has been described as a method of holding the previous value. However, this method changes depending on the type and characteristics of the reproduced signal. It is common to use a method of replacing the signal before the scanning period. Further, even in the case of an audio signal, it is possible to use a method different from the above-described embodiment, such as using a low-pass filter having a low cutoff frequency or performing linear interpolation.

Further, in the above-mentioned embodiment, the reproducing apparatus for the FM modulated signal has been described, but the present invention can be applied to an apparatus for reproducing the information signal recorded by using another recording method.

<Explanation of Effect> As described above, according to the present invention, even when a dropout for a period longer than a predetermined period occurs or a dropout for a short period is high in frequency, excellent noise is eliminated. It is possible to obtain an information signal reproducing device which can obtain various reproduced information signals.

[Brief description of drawings]

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 FIG. 1, 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 in FIG. Reference numeral 1 is a magnetic tape as a recording medium, 2 is a reproducing magnetic head, 7 is a dropout detection circuit, 21 is a miute circuit, 22 is a switching circuit, 23, 24 and 26 are monomultis, and 25 is an AND gate.

Claims (1)

[Claims] 1. A reproducing means for reproducing a signal recorded on a recording medium from the recording medium and outputting it as a reproducing information signal, and whether or not a dropout occurs in the reproducing information signal outputted from the reproducing means. And a dropout detecting unit that generates a dropout pulse indicating a period during which dropout is occurring, and a period during which the dropout indicated by the dropout pulse generated by the dropout detecting unit is occurring. If it is longer than the predetermined period, the first indicating the first period
First pulse signal generating means for generating a pulse signal, and second pulse signal generating means for generating a second pulse signal indicating a second period in synchronization with the generation of the dropout pulse in the dropout detecting means. Third pulse signal generating means for generating a third pulse signal indicating a third period longer than the second period each time the second pulse signal generating means generates the second pulse signal, A second pulse signal generated by the second pulse signal generating means and a third pulse signal generated by the third pulse signal generating means
Fourth pulse signal generating means for generating a fourth pulse signal according to the output state of the pulse signal, and a first pulse signal generated by the first pulse signal generating means or generated by the fourth pulse signal generating means. Information signal reproducing apparatus, which mutes the reproduction information signal output from the reproducing means according to any one of the fourth pulse signals.