JPH0430106B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an information reproducing apparatus, and more particularly to an information reproducing apparatus having a dropout compensation function for reproduced information from a recording medium.

In a reproducing apparatus that reproduces recorded information, a dropout compensation device that detects and compensates for so-called dropout compensation is essential in order to obtain a good reproduction signal. In the case of a video disc as a recording medium, it is common that audio information is multiplexed and recorded in addition to video information using a frequency multiplexing method, so it is necessary to perform dropout compensation for not only video information but also audio information. It is configured so that

FIG. 1 is a block diagram of an audio information reproducing circuit in a reproducing apparatus for a video disc on which information is multiplexed. The RF (high frequency) signal from the pickup is passed through a BPF (band pulse filter) 1 to the audio carrier frequency and its vicinity. Only frequency components are extracted. This extracted signal is FM detected in the detector 2 and becomes an audible band signal.
It is input to LPF (low pass filter) 3. this
The LPF 3 removes high-frequency components outside the audible band to eliminate noise. The LPF output A is dropout compensated in a dropout compensator 4, and the configuration of this compensator 4 is such that the output terminal of this switch is connected to an analog switch which is turned off by a sensor output B generated from a dropout sensor 5. and a hold capacitor provided between the reference potential point and the reference potential point. Therefore, when a dropout occurs, the level of the LPF output A immediately before the generation of the sensor output B is held and sent to the next stage circuit, thereby compensating for the dropout.

The output C of the dropout compensation 4 is applied to a de-emphasis circuit 6, which restores the pre-emphasized signal during recording to the original signal. In addition. BPF1 is input to dropout sensor 5.
The output signal of BPF is used, and sensor output B is generated by detecting a level drop in this BPF output signal.

In the case of video discs, audio information is often recorded as two-channel information; for example, the first channel is recorded at 2.3MHz, and the second
A method is used in which each channel is FM modulated and recorded on a 2.8MHz carrier. Recently, attempts have been made to multiplex record information on two other channels in addition to these first and second channels (main channels), but in this case, the information on the third and fourth channels to be added ( For example, depending on each audio signal of
The 47.2 KHz subcarrier is FM modulated, and then the FM waves of both channels are superimposed on the audio signals of the first and second channels, respectively.
After that, each superimposed signal is used as the 2.3MHz and
A method has been proposed in which a 2.8MHz carrier is modulated and recorded together with video information on a recording disk.

On the other hand, the cutoff frequency of the LPF 3 for noise reduction is selected to be higher than the audible band, for example 30 KHz, so as not to deteriorate the frequency characteristics in the audible band of the audio signal. Therefore, when the above-mentioned reproduction signal of the 4-channel audio multiplexed recording information is input to the block shown in FIG. Therefore, this subchannel carrier also appears in the output A of the LPF 3, which has a relatively high cutoff frequency, resulting in a waveform as shown in FIG. 2A. In the figure, the gentle sinusoidal waveform is the main channel audio signal, and the high frequency sinusoidal waveform is the subchannel FM wave.

Now, if a dropout occurs as shown by reference numeral a in FIG. 2A, the dropout sensor output B becomes as shown in FIG. 2B. The phase shift between the timing at which dropout occurs and the timing at which the sensor output occurs is caused by a delay time due to the time constants of the detector 2 and the LPF 3. Therefore, the dropout compensation output becomes as shown in Figure C, which has the drawback of being output as noise. That is, the dropout compensation level depends on the carrier level of the subchannel, making accurate compensation difficult.

This phenomenon also occurs when noise lower than the cutoff frequency of the LPF 3 is superimposed on the signal, and in this case, the dropout compensation level becomes dependent on the superimposed noise level, which is disadvantageous.

SUMMARY OF THE INVENTION An object of the present invention is to provide an information reproducing apparatus having a dropout compensation function that enables accurate dropout compensation and noise reduction.

The information reproducing device according to the present invention converts an audio signal in reproduced information into an audible signal and attenuates high frequency components including the high frequency range of the audible band.
The audible signal is input to the LPF, dropout compensation is performed at the LPF output, and the high frequency range of this compensation output is enhanced and corrected to compensate for the high frequency components of the audible band attenuated by the LPF. There is.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 3 is a block diagram of an embodiment of the present invention;
Components equivalent to those in FIG. 1 are designated by the same reference numerals. The RF signal is converted into an audio signal A via the BPF 1 and the detector 2, and is input to the LPF 7.
This LPF has the frequency characteristics shown in FIG. 4, and has such characteristics that it attenuates high frequency components including the high range of the audible band. Output B of this LPF7
is input to the high boost circuit 8 via the dropout compensator 4 which is a pre-hold circuit. In this high boost circuit 8, the high frequency component of the audible band attenuated by the LPF 7 is enhanced and corrected, and then becomes an input to the de-emphasis circuit 6.
Note that the dropout compensator 4 is operated by the output C of the drop sensor 5, as in the example shown in FIG.

By doing this, the carrier of the subchannel shown in the fifth head A is superimposed in the detection output of the detector 2, but when it passes through the LPF 7, the subchannel is greatly attenuated and almost disappears as shown in Figure B. do. As a result, even if a dropout occurs as shown at a in the figure, dropout compensation is performed based on the audio signal level of the main channel as shown in figure D using the sensor output in figure C. A high boost circuit 8 then converts the audible high frequency components attenuated by the LPF 7 into
We are trying to strengthen and restore it.

In this case, the input to the subchannel detection stage is
There is no problem if the output signal A of the FM detector 2 is used.

The dropout compensation level is not affected by high-frequency noise, and substantially accurate compensation is possible.

In the above example, the high boost circuit 8 and the de-emphasis circuit 6 are separated, but a single circuit having comprehensive characteristics of both circuits may be used, or the high-boost circuit may be provided after the de-emphasis circuit 6. Also good.

As described above, according to the present invention, since the dropout compensation is performed by attenuating the high-frequency components, the compensation can be performed at approximately the average level of the FM detection output, and does not depend on the level of noise or subchannel carrier. There is no advantage.

[Brief explanation of drawings]

FIG. 1 is a schematic block diagram of a conventional information reproducing device, FIG. 2 is an operational waveform diagram of each part of the block in FIG. 1, FIG. 3 is a block diagram of an embodiment of the present invention, and FIG.
This figure is a characteristic diagram of the LPF in FIG. 3, and FIG. 5 is an operation waveform diagram of each part of the block diagram in FIG. 3. Explanation of symbols of main parts, 4... Dropout compensator, 5... Dropout sensor, 7...
LPF, 8...High boost circuit.

Claims (1)

[Claims] 1. An information reproducing device for reproducing recorded information including audio information, comprising: means for converting the audio information in the reproduced information into an audible signal; and a means for converting the audio information into an audible signal, and receiving the audible signal and generating high-frequency components including the high-frequency range of the audible band. 1. An information reproducing apparatus comprising: filter means for attenuating the output of the filter means; compensating means for compensating for dropout in the output of the filter means; and means for enhancing and correcting the high frequency range of the audible band in the output of the compensating means.