JPH0421948B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is applicable to a disc on which a PCM signal is recorded at a constant linear velocity, such as a compact disc on which an audio PCM signal is recorded.
The present invention relates to a device for reproducing PCM signals.

BACKGROUND TECHNOLOGY AND PROBLEMS In compact discs, audio PCM signals are distributed from the inner circumference to the outer circumference at a track pitch of 1.6μ.
m, recorded at constant linear velocity. During reproduction, the disk is rotated at a constant linear velocity, and while tracking control is performed from the inner circumference to the outer circumference, the recording track is scanned with a laser beam to extract the reproduced PCM signal.

The tracking control in this case is 1.6μ
Since it is carried out within the track pitch range of m,
If a defect larger than this track pitch occurs on the disk, tracking cannot be performed correctly, and a track jump occurs in which the tracking position jumps to an adjacent track or to a track further away. For this reason, the specifications of the compact disc system require that the size of disc defects be standardized and that the quality of the disc be controlled.

However, even if the disc complies with such standards, the disc may be scratched by the user, and in this case, the problem of track jump still occurs.

Furthermore, even if the disc is free of defects, track jumps also occur if large vibrations are applied to the disc during playback.

In this way, when a truck jump occurs,
This has the disadvantage that audio noise is generated and the flow of performance time is discontinuous. This discontinuity in the flow of performance time causes the time to go backwards if the direction of the track jump is toward the inner circumference, resulting in a so-called hang-up phenomenon in which the same recorded signal position is repeatedly reproduced. Furthermore, even if the direction of the track jump is toward the outer circumference, if the number of tracks that jump is large, the music will sound congested, which will cause a serious problem in terms of hearing.

OBJECTS OF THE INVENTION It is an object of the present invention to provide a device that can instantly return a playback pickup to the correct tracking position even when such a tracking jump occurs.

Summary of the Invention This invention extracts time information included in a reproduced PCM signal, for example, Q data used for performance time and address information in a subcode, from the reproduced signal, and uses this Q channel information and the device main body. It compares the time information set by a provided timer and detects the occurrence of a truck jump based on the time difference. When this tracking jump occurs, the tracking position is corrected by using the time information set by the timer as a tracking target value and adjusting the time information extracted from the reproduced signal to this target value. .

Embodiment Hereinafter, an embodiment of the present invention will be described with reference to the drawings, taking the case of a compact disc playback device as an example.

In the figure, 1 is an optical pickup, which shows the reproduced PCM signal S _P with a roughly sinusoidal waveform.
is obtained. This signal S _P is supplied to the waveform conversion circuit 3 through the amplifier 2, from which a PCM signal S _O corresponding to "1" and "0" of the recording signal is obtained, and this is supplied to a PCM signal decoder.

By the way, each data frame of a PCM signal contains one user's bit (subcode), and 98 symbols are collected, that is, 98 frames constitute one information block (subcode frame). There are 8 channels in this subcode, P, Q, ...W, and 8 bits in one symbol represent 1 channel of each channel.
It is made up of bits. Of the eight channels of subcodes, the Q data is used for displaying the song number, index, playing time, etc., and for address information.

In this example, the time information of this Q data is used, and the PCM signal S _O from the waveform conversion circuit 3 is supplied to the register 4, and the Q data is stored in this register 4. This Q data is updated every 9 data frames.

In this example, the subcode frame number is used as the time information of the Q data. This subcode frame number is such that the number increases as time passes, for example, the first subcode frame at the innermost track position of the disc is "0" and the next is "1". This can be used as time information.

Therefore, as long as the recorded track is scanned accurately, this time sequence is read out continuously.

Here, the subcode frame has a unit of 1/75 second, and since the disk rotates at a constant linear velocity, the length of this subcode frame on the track is constant, and the compact disk In the case of , it is approximately 17mm. Approximately 9 sub-coat frames and 23 sub-code frames are included in each of the innermost and outermost circumferences of the disk. Therefore, when a track jump occurs, since each innermost track contains about 9 subcode frames, there is a time difference of at least 9 subcode frames (when jumping to an adjacent track). arise. Therefore, a timer is provided to generate reference time information, and the occurrence of a truck jump can be detected by determining whether the difference between the reference time information and the time information based on the subcode frame number of the Q data is 9 subcode frames or more.

In this example, a frame synchronization signal in the reproduced signal is used as the timer clock. That is, the PCM signal from the waveform conversion circuit 3 is supplied to the frame synchronization signal detection circuit 5, which determines the frame frequency.
A 7.355kHz signal SF is obtained. When a frame synchronization signal is not detected due to dropout or the like, this signal SF is a signal in which a pulse is interpolated at the position of the missing synchronization signal. This signal SF
is supplied to the frequency dividing circuit 6 and divided into 1/98, thereby obtaining a signal SCF having a subcode frame period. This signal SCF is then supplied to the clock terminal of the counter 7 and counted.

Therefore, the count value of the counter 7 serves as reference time information, and this count value and the subcode frame number of the register 4 are compared in the comparator circuit 8.

When the time difference between the two is 9 subcode frames or less, no tracking jump occurs, and in this case, the subcode frame number data in register 4 is at the correct tracking position. Therefore, at this time, the data in the register 4 is set in the counter 7 by the signal D _N from the comparison circuit 8, and the time lag in the time information of the timer is corrected.

When the time difference between the two is 9 subcode frames or more, a detection signal D _J of the occurrence of a track jump is obtained from the comparator circuit 8, and this signal D _J is supplied to the access control circuit 9. This access control circuit 9 receives subcode/frame number data _DAS from the register 4 and a counter 7.
The tracking position of the optical pickup 1 is corrected by the signal D _J so that the data _DAS matches the count value.

In this way, even if a track jump occurs, the track jump is detected and the pickup is corrected to the correct tracking position, so that the time continuity of the audio signal is not lost.

Note that the time information is not limited to the data of the subcode frame of the Q data, for example, information on minutes and seconds may be used.Also, as a timer, it is possible to use a clock with a constant frequency that counts at the start of playback. Things can be used.

Furthermore, instead of directly changing the position of the pickup using the access control circuit 9, it is also possible to change the angle of a mirror that determines the track position of the laser beam.

Furthermore, the present invention is applicable not only to compact disc reproducing apparatuses but also to all disc reproducing apparatuses in which time information is included in the recorded PCM signal.

Effects of the Invention As described above, according to the present invention, even if a track jump occurs, the tracking position is always corrected to be correct. Gender is never lost.

Moreover, the present invention uses time information in the PCM signal, and has the advantage that the configuration for detecting track jumps is simple.

[Brief explanation of drawings]

The figure is a system diagram showing an example of the essential parts of the device of this invention. 4 is a register for storing first time information, 7 is a counter as a timer for forming second time information, and 8 is a comparison circuit.

Claims (1)

[Claims] 1 A device that reproduces PCM signals recorded on a disk that rotates at a constant linear velocity.
First time information is extracted from the signal, this first time information and second time information obtained by a timer provided in the device are compared, and the first time information is
When the difference between the first time information and the second time information exceeds a predetermined value corresponding to the time of the innermost circumference of the disk, the tracking position on the disk is such that the first time information matches the second time information. A disc playback device that is controlled as follows.