JPH0463459B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a digital audio disc reproducing apparatus for reproducing analog audio signals from a disc on which digital audio signals have been recorded.

In a CD (Compact Disc) digital audio system, there are 2-channel and 4-channel discs, and in the case of a 2-channel disc, the disc is usually rotated and reproduced at a predetermined linear velocity of 1.2 to 1.4 m/s. In the case of a 4-channel disc, its linear recording density is the same as that of a 2-channel disc, and the recording signal format is also the same, and the recording linear velocity of the disc is set to twice that of a 2-channel disc, so the reproduction linear velocity and recording speed are the same. By doubling the data transfer rate
A 4-channel disc is reproduced by processing twice the amount of data as in the case of channels.
Since the 2-channel disk and the 4-channel disk have the same shape, the 4-channel disk can be attached to a 2-channel playback device, and as mentioned above, the recording signal formats are the same, so the 4-channel disk can be used for 2-channel playback. When installed in a device, the rotation system is controlled at the linear velocity for two channels, and installation and rotation are performed normally, but no sound is reproduced. Below, the operation in this case is shown in Figures 1 and 2.
This will be explained using figures. FIG. 1 is a block diagram showing a rotation control system of a conventional two-channel digital audio disk reproducing apparatus using the CD system, and FIG. 2 is a signal waveform diagram of each part thereof. In the figure, 1 is a disk, 2 is a motor for rotating this disk, 3 is a pickup that reads signals from the disk, 4 is a preamplifier, 5 is a waveform shaping circuit,
6 is a peak hold circuit that generates a voltage according to the rotational speed of the disk 1, 7 is a differential amplifier that creates an error voltage for controlling the motor rotational speed, 8 is a motor drive control circuit, and 9 is a phase lock that creates a regenerated clock pulse. Loop circuit, 10 is EFM demodulation circuit,
11 is a clock generation circuit for generating various clock signals, 12 is a phase comparator circuit, E is a reference voltage source for biasing the differential amplifier 7, and S is a changeover switch.

When the 4-channel disc 1 is attached to the 2-channel playback device, the changeover switch S is connected to the A side, the motor 2 starts rotating, and the servos turn in the order of the focus servo and the tracking servo, and the disc 1 of the pick-up 3 is turned on. Signal reading starts. In the CD method, the digital signal is EFM
(Eight to Fourteen Modulation) Modulated and recorded on disk. What is EFM modulation?
As is well known, an 8-bit digital signal is converted to 14 bits using a conversion table, then 3 bits are added to make 17 bits, and the inversion interval (bit content is 1)
The number of bits from 1 to the next 1 is always modulated so that the minimum is 3 bits and the maximum is 11 bits. The digital signal thus modulated (FIG. 2a) is recorded on the disk 1 in the form of bit 13, with the inversion position at the time when the bit becomes 1, as shown in FIG. 2b. This is read by a pickup 3, amplified by a preamplifier 4, and a waveform shaping circuit 5.
The EFM signal 1 shown in Figure 2c is waveform-shaped by
4 is obtained, and an EFM pulse signal 15 (FIG. 2d) corresponding to the inversion of this signal 14 is output from the waveform shaping circuit 5. The EFM pulse signal 15 is applied to a peak hold circuit 6 to produce a sawtooth wave voltage 16 (Fig. 2e) corresponding to the pulse interval of the EFM pulse signal 15 (the inversion interval of the EFM signal 14), thereby increasing its maximum value, i.e. Peak hold signal 1 that holds the voltage value corresponding to the maximum interval of pulses 15
7 is obtained at the output of the peak hold circuit 6.
The maximum inversion interval of the EFM signal 14 is 1 as described above.
1T (T is time per bit), the voltage value of the peak hold signal 17 is always constant as long as the rotation linear speed of the disk 1 is constant. Since both the 2-channel disk and the 4-channel disk are recorded in the same signal format and at the same density, the voltage value of the peak hold signal 17 will also vary if the rotational speed is the same. Therefore, the voltage value of this signal 17 is independent of the disk mounted, and is proportional to the rotational linear velocity of the disk; if the linear velocity is slower than a predetermined value, the peak hold signal 17 is large, and if it is faster than a predetermined value, it is small. This peak hold signal 17 is applied to the differential amplifier 7,
Here, it is compared with the motor rotation reference voltage E of the two channels, and the error voltage is applied to the motor drive control circuit 8 through the contact A of the changeover switch S, and the speed of the motor 1 is controlled.
Frequency Control) Loop operation is performed.
By the operation of this AFC loop, the rotational speed of the disk 1 is controlled so that the maximum inversion interval 11T of the EFM signal 14 becomes a predetermined time, and the linear velocity becomes constant. Here, the 4-channel disk 1 is installed, but as mentioned above, it has the same recording signal format and signal density as the 2-channel disk, so it is set at the same speed as the 2-channel disk, that is, at the same voltage E. The linear velocity is controlled to a predetermined linear velocity. When the AFC loop operates in this manner, the frequency of the EFM pulse signal 15 output from the waveform shaping circuit 5 after passing through the pickup 3 and preamplifier 4 becomes the same as the frequency for two channels. The EFM pulse signal 15 is also input to the phase lock loop circuit 9, and this circuit generates a 4.3218MHz regenerated clock signal 18 (second
Figure g) is obtained. This regenerated clock signal 18 and
The EFM pulse signal 15 is applied to the EFM demodulation circuit 10 and demodulated, but as mentioned above, the signal from the 4-channel disk is reproduced with its frequency reduced to 1/2, so the 2-channel signal is
It is demodulated as if the EFM pulse signal was added. The EFM demodulation circuit 10 demodulates the EFM signal into a digital audio signal, and simultaneously decodes a control signal (subcode) recorded in each frame period together with the digital audio signal and detects a frame synchronization signal. The frequency of the synchronization signal is 7.35kHz, the same as for 2 channels (4
The channel frame frequency is 14.7kHz). This reproduction frame synchronization signal is applied to the phase comparator circuit 12. On the other hand, the clock generation circuit 11 supplies the phase comparison circuit 12 with a stable reference frame synchronization signal of 7.35 kHz, which is a reference signal for an APC (Automatic Phasc Control) loop. This reference frame synchronization signal and the reproduced frame synchronization signal from the EFM demodulation circuit 10 are compared in phase by a phase comparison circuit 12, and a phase error voltage is output. When the phase lock loop circuit 9 is phase synchronized, the switch S is switched to the B contact side by a command from a sequence circuit (not shown) to form an APC loop, so that the phase error voltage is reduced to the motor drive control circuit 8.
is applied to control the rotational phase of the disk 1. In this way, when a 4-channel disk is attached to a 2-channel playback device, the rotational linear velocity of the disk becomes the rotational linear velocity of 2 channels, and even the rotational phase of the disk is controlled, so the rotation of the disk is 2-channel. It's no different than if a disk was installed. However, since a 4-channel disk is installed, the data transfer rate demodulated by the EFM demodulation circuit 10 should be twice the data transfer rate when using 2 channels, but it becomes the data transfer rate when using 2 channels. ing. Therefore, when a 4-channel disk is attached to a 2-channel playback device, audio signals cannot be played back and only the disk rotates at the same speed as when the 2-channel playback device is used. As a result, it is difficult for the user to notice that the 4-channel disk has been installed incorrectly, and the incorrect state can continue.

This invention was made to eliminate the above-mentioned drawbacks, and detects a channel number display signal in a control signal (subcode) recorded in advance as a digital audio signal on a disk. A digital audio disk playback device that can automatically release a state in which a wrongly installed disk continues to rotate without being able to play back, by determining whether the disk is in the correct position and stopping the rotation of the disk if not. It provides:

Hereinafter, one embodiment of the present invention will be described with reference to FIG. FIG. 3 is a block diagram showing one embodiment of the present invention.
indicates the same or equivalent parts as the same reference numerals in Fig. 1,
19 is a sequence circuit that controls each part of the playback device; 20 is a channel display circuit; 21 is an attachment/detachment mechanism for attaching and detaching a disk according to a command from the sequence; 22a, 22b, and 22c are a channel display circuit 20 and a motor drive from the sequence circuit 19, respectively; This is a control command signal to the control circuit 8 and the disk attachment/detachment mechanism 21.

Next, its operation will be explained. If a 4-channel disc is attached to a 2-channel playback device, it will operate in exactly the same manner as previously described.
The 4-channel disk has a linear velocity of 2 channels, and the EFM demodulation circuit 10 demodulates data at the data transfer rate of 2 channels. At the same time, the data transfer rate control signal for two channels, that is, the Q channel of the subcode is decoded, and this Q channel signal is applied to the sequence circuit 19. In the CD system, 8 bits are recorded in the subcoat for each frame period, and 8 channels of P, Q, ..., W are assigned to each bit, and each of the 98 bits extracted every 98 frames is controlled and controlled. It is used for display. This channel signal is shown in FIG. The Q channel includes a channel number display that distinguishes channels 2 and 4, and other information such as synchronization signal, presence or absence of emphasis, track number, index for subdivision of one track, and playing time of each track. recorded. Channel display is performed by indicating that if the first bit of the control signal is 0, there are two channels, and if it is 1, there are four channels. In the sequence circuit 19, it is determined how many channels the disk has based on the Q channel control signal, and if it is determined that there are 4 channels, each control command signal 22a, 22b, 22
c is set to high level, and if it is determined that there are 2 channels, set to low level. When the control command signal 22a goes high, the channel display circuit 20 displays the 4-channel disc, informing the user that a 4-channel disk has been installed by mistake, and when the control command signal 22b goes high, the motor The drive control circuit 8 applies a reverse voltage to the motor 2 to stop the motor 2, and when the control command signal 22c becomes high, after the motor 2 is stopped, the drive control circuit 8 operates the disk attachment/detachment mechanism 21 to remove the disk from the 4-channel disk. be taken out automatically.

When the 2-channel disk is installed, it operates normally, the control command signals 22a, 22b, and 22c from the sequence circuit 19 are all low level, and the channel display circuit 20 correctly displays that the 2-channel disk is installed. , motor drive control circuit 8, and disk attachment/detachment mechanism 21 are kept as they are, and two-channel disk playback is performed.

In the above embodiment, an example was shown in which a 4-channel disk was attached to a 2-channel disk playback device, but the present invention can of course be applied to a case where a 2-channel disk is attached to a 4-channel playback device. be.

Since this invention is configured as described above,
Even if a disc with the wrong number of channels is installed by mistake, the disc will not continue to rotate without being played, but will automatically stop rotating immediately and allow the user to install the disc in a timely manner. This has the effect of quickly making you realize that something is wrong.

[Brief explanation of drawings]

Figure 1 is a block diagram showing the rotation control system of a conventional digital audio playback device.
3 is a block diagram showing one embodiment of the present invention, and FIG. 4 is a diagram showing the signal of the Q channel of the subcode recorded on the disk. In the figure, 1 is a disk, 2 is a motor, 3 is a pickup, 5 is a waveform shaping circuit, 6 is a peak hold circuit, 7 is a differential amplifier, 8 is a motor drive control circuit, 9 is a phase lock loop circuit, and 10 is a
EFM demodulation circuit, 11 is a clock generation circuit, 12
1 is a phase comparison circuit, 19 is a sequence circuit, 20 is a channel display circuit, 21 is a disk attachment/detachment mechanism,
S is a changeover switch, and E is a reference voltage source. The same reference numerals in the drawings indicate the same or equivalent parts.

Claims (1)

[Scope of Claims] 1. A digital audio disk reproducing device for reproducing audio signals of a predetermined number of channels from a disk on which digital audio signals of a predetermined number of channels and a control signal including an indication of the predetermined number of channels are recorded, a pickup for reading out recorded signals from the disk; rotation drive control means for rotating the disk at a predetermined speed corresponding to the predetermined number of channels from the signals read from the pickup; and means for demodulating the signal read from the pickup. , and means for detecting a channel number display signal recorded on the disk from the demodulated signal, determining whether this is the predetermined number of channels, and if not, applying a disk rotation stop signal to the rotation drive control means. Digital audio disc playback device. 2. The digital device according to claim 1, further comprising means for automatically removing the disk by using a disk attachment/detachment mechanism to remove the disk after the disk is stopped by applying a disk rotation stop signal. Audio disc playback device. 3. The digital audio disc reproducing apparatus according to claim 1, further comprising means for detecting a channel number display signal and displaying the number of channels on the disc.