JPH09147495A - D/a conversion unit and reproduction system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To add a vibration-proof function using a buffer memory by a D/A conversion unit connected to a reproducing device, to reduce jitters and to realize precise reproduction. SOLUTION: A reproducing unit 2 outputting the digital audio data read out from a disk is connected to a D/A conversion unit 1. The D/A conversion unit 1 writes/reads the digital audio data DT in/out a memory 14 based on a clock CK2. Then, the D/A converter 17 converts the digital audio data read out from the memory 14 to an analog signal by using the clock CK2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an A / D conversion unit or a reproduction system which operates corresponding to a digital audio data recording medium such as a CD (Compact Disc).

[0002]

2. Description of the Related Art Recording media for recording digital audio data, such as CDs and MDs (mini discs), are in widespread use, and as a player / recorder corresponding to these, stationary type, in-vehicle type, portable type, etc. have been developed. Has been done.

In some players for these disc media, a buffer memory is used to improve the vibration resistance function. In the case of the MD player, the digital audio data which is compressed and recorded in the MD is read at a high rate and is temporarily stored in the buffer memory. Then, the data is read out at a predetermined timing, the compression processing is decoded, and further D / A conversion is performed to obtain a reproduced analog audio signal.

By reproducing and outputting through the buffer memory, even if the optical head is out of focus or tracking due to disturbance, for example, and the reading is temporarily disabled, the reading operation is performed before the accumulated amount in the buffer memory becomes zero. By resuming, the reproduced sound will not be interrupted. C
It is known that the D player similarly improves the vibration resistance by reproducing and outputting the data read from the disk through the buffer memory. In particular, in the case of a portable or vehicle-mounted CD player, improving the vibration resistance in this way leads to a remarkable improvement in reproduction performance.

[0005]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention Various CDs
As a player, there are a device having a vibration resistant function improved by a buffer memory as described above, and a player having no buffer memory and having substantially the same vibration resistant performance. A CD player that does not have a buffer memory and is used in an environment with a large number of signals, especially for portable and vehicle-mounted devices,
There is a limit to the improvement of the reproduction performance, and there are many skips in reproduced voice.

Therefore, it is desirable to add an anti-vibration function by a buffer memory to such a CD player as an option later, but the anti-vibration operation by the buffer memory is closely related to the reproduction operation of the CD player. Therefore, it is difficult to realize a unit capable of performing a vibration resistant operation by connecting to a conventional CD player.

In an audio system having a digital audio device such as a CD player, an independent D / A converter device may be connected. That is, a reproduction signal is output from the CD player in the form of digital audio data and converted into an analog audio signal in the D / A converter device.
Then, the system is such that the analog audio signal from the D / A converter device is supplied to a power amplifier device or the like and output as a speaker. Such systems are often implemented in stationary or in-car player systems.

However, when such a D / A converter device is separately connected to transmit data, there is a problem in terms of jitter occurring on the data. For example, jitter that occurs during optical conversion or coaxial conversion of data during transmission, jitter due to power supply fluctuations on the CD player side, and jitter that occurs due to the difference between the clock on the transmitting side and the clock on the receiving side. There are various jitter factors such as the jitter caused by the waveform distortion. As a result, high-accuracy reproduction of the reproduced sound is hindered.

[0009]

In view of these problems, the present invention makes it possible to add a vibration resistance function using a buffer memory by a D / A conversion unit connected to a reproducing device, and The objective is to reduce jitter caused by transmission of digital data between devices and realize high-accuracy reproduction.

Therefore, as the D / A conversion unit, input means to which digital audio data is input, clock generation means, memory means, and digital audio data input from the input means based on the clock from the clock generation means Of the digital audio data stored in the memory means and reading the digital audio data stored in the memory means at a predetermined timing, and the digital audio data read from the memory control means by using a clock from the clock generation means. And a D / A conversion means for converting into an audio signal.

Then, the reproducing unit for reading and decoding the data from the recording medium and outputting the decoded digital audio data is connected to the above D / A conversion unit to transmit the digital audio data. Build a playback system. Further, the D / A conversion unit makes it possible to control the reproduction operation of the reproduction unit according to the amount of digital audio data stored in the memory means.

The D / A conversion unit accumulates digital audio data, reads it at a predetermined timing, and outputs it as an analog signal, thereby improving the vibration resistance function of the reproduction system. Further, since the reading from the memory means and the D / A conversion are performed using the highly accurate clock from the clock generating means, the jitter occurring in the system up to the writing to the memory means should be canceled. become.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to FIGS. An example of this is a car-mounted CD
Playback system. FIG. 1 is a block diagram showing the configuration of a CD reproducing system. This CD playback system is DA
It is composed of a converter unit 1, a CD player unit 2, and a master unit 3. Each unit can be installed near the driver's seat of a car, so-called DI
It is formed by an N-sized housing. The power supply line 4 is connected to a car battery, and can supply a DC 12V voltage to each of the units 1, 2, and 3, for example.

The CD player unit 2 has a power supply line 4
Are connected to the regulator 31. Then, the regulator 31 converts DC 12V from the car battery into a required DC power supply voltage V _DD and supplies it to each circuit unit. A disc 90 such as a CD (compact disc) is loaded in the CD player unit 2. When the disc 90 is loaded into the CD player unit 2, the spindle motor 32 rotates the disc 90 at a constant linear velocity (CLV) during a reproducing operation. The optical head 33 causes the disk 90
The data recorded in the pit form is read.

The optical head 33 outputs a laser beam for obtaining the reflected light from the disk 90 during reproduction because of the data reading operation. Therefore, the optical head 33 is equipped with a laser diode as a laser output means, an optical system including a polarization beam splitter and an objective lens, a detector for detecting reflected light, and the like. The objective lens 33a is held by a biaxial mechanism 34 so as to be displaceable in the radial direction of the disc and the direction in which it comes in contact with and separates from the disc. The entire optical head 33 is movable in the disk radial direction by the sled mechanism 35.

The data read from the disk 90 by the optical head 33 is subjected to arithmetic processing for generating various servo error signals supplied to the RF amplifier 36 and RF signal processing as reproduction data. And RF amplifier 3
The output of 6 is supplied to the servo signal processor 37.

The servo signal processor 37 uses the focus error signal and the tracking error signal from the RF amplifier 36, the spindle error signal generated by the comparison process of the reproduction clock generated from the RF signal and the reference clock, and the like to perform the focus and tracking. ,thread,
It generates various servo drive signals for the spindle and executes the servo operation. That is, the focus, tracking, and sled servo drive signals are supplied to the focus / tracking driver 38, and the required drive power is applied from the focus / tracking driver 38 to the biaxial mechanism 34 or the sled mechanism 35. Also CLV driver 3
A spindle drive signal is supplied to 9 to execute a power application operation for driving the spindle motor 32 to rotate in CLV.

Further, in the servo signal processor 37,
Decoding processing is also performed on the reproduced RF signal obtained by the RF amplifier. That is, EFM demodulation, CIRC decoding, deinterleaving and the like are performed to decode the information read from the disk 90 into 16-bit quantization and 44.1 KHz sampling digital audio data DT.

The digital audio data DT output from the servo signal processor 37 is the D / A converter 4
3 as analog audio signal SA and terminal 4
5 is output. Also, the servo signal processor 3
The digital audio data DT output from 7 is also supplied to the terminal 46. The digital audio data DT supplied to the terminal 46 will be transmitted to the DA converter unit 1 via the cable 9.

A clock generator 44 of a crystal oscillator is used for transmission processing by the servo signal processor 37.
Clock CK1 from is used. In FIG. 1, since the clock generator 44 is connected to the D / A converter 43, the clock CK1 is used for the D / A conversion processing in the D / A converter 43, and the clock CK1 is used for the servo signal processor. The data is also supplied to 37, and transmission processing and the like are performed.

In the case of the system of this example, the D / A converter 43 and the terminal 45 indicated by the chain double-dashed line are not necessarily provided. When the D / A converter 43 is not provided, the clock generator 44 is the servo signal processor 3
7 may be connected.

The CPU 40 is a control unit for controlling the entire CD player unit 2. The CPU 40 controls the data reading operation from the disk 90 by the optical head 33 and the like via the servo signal processor 37, and also controls the various decoding processes in the servo signal processor 37 and the transmission process of the digital audio data DT to the DA converter unit 1. Will be done.

The CPU 40 can communicate with the CPU 12 of the DA converter unit 1 by the asynchronous communication line 8 connected between the terminal 47 and the terminal 20 of the DA converter unit 1. Further, the CPU 40 can communicate with the CPU 52 via the bus interface 53 of the master unit 3 by the bus line 6 connected between the terminal 42 and the terminal 54 of the master unit 3 via the bus interface 41.

In the DA converter unit 1, the power supply line 4 is connected to the regulator 11. Then, the regulator 11 converts DC 12V from the car battery into a required DC power supply voltage V _DD and supplies it to each circuit unit. In the DA converter unit 1, the digital audio data DT transmitted from the CD player unit 1 is fed to the terminal 2
1 to the digital audio interface 15.

Digital audio interface 15
The digital audio data DT received at is supplied to the memory controller 13 and written in the D-RAM 14. The digital audio interface 15 extracts subcode information (sub Q data) such as an address from the input digital audio data DT and supplies it to the CPU 12.

The memory controller 13 is a D-RAM 14
The digital audio data DT stored in is read at a predetermined timing and supplied to the digital filter 16. The digital audio data DT processed by the digital filter 16 is converted into an analog audio signal SA by the D / A converter 17, band-limited by the low-pass filter 18, and then output from the terminal 22. Terminal 22
Is connected to a terminal 60 of the master unit 1 by an audio cable 5.

D-RAM by the memory controller 13
The write / read operation for 14 is performed based on the timing signal TM from CPU 12. As a clock for the write / read operation, a clock generator 19 using a crystal oscillator used for processing in the D / A converter 17 is used.
The clock CK2 from is supplied.

The D-RAM 14 is used as a buffer memory for improving the vibration resistance function, that is, D-RAM.
By outputting a reproduction sound signal from the terminal 22 via the RAM 14, the optical head 33 in the CD player unit 2 is out of tracking due to disturbance or the like, and the data reading from the disk 90 is temporarily interrupted. However, while the data is still stored in the D-RAM 14 (that is, while the reading from the D-RAM 14 is continued and the output of the analog audio signal via the D / A converter 17 is continued). On the side of the CD player unit 2, for example, by accessing the correct tracking position and restarting the data reading, the operation can be continued without affecting the reproduction output.

Data output from the D-RAM 14 for audio output is continuously performed at regular intervals.
Therefore, in order to constantly store a certain amount of data in the D-RAM 14, it is necessary to perform data writing at a higher rate than data reading from the D-RAM 14. Therefore, the CPU 12 can instruct the CPU 40 to execute the read operation from the disk 90 in a high speed mode such as double speed or quadruple speed. The data storage amount of the D-RAM 14 can be constantly maintained at a certain level or more by performing the read operation in the high speed mode such as the double speed or the quadruple speed intermittently. It goes without saying that the greater the amount of data stored in the D-RAM 14, the higher the vibration resistance.

When the CD player unit 2 is read at a normal speed, it is difficult to improve the anti-vibration function by the operation of the D-RAM 14, but the D-RAM 14 has not only the anti-vibration function but also the jitter reduction as will be described later. Since it also has a function, the jitter reducing function can be improved regardless of the reproduction speed of the CD player unit 2.

In the master unit 3, the power supply line 4 is connected to the regulator 51. And regulator 5
Reference numeral 1 converts 12V DC from the car battery into a required DC power supply voltage V _DD and supplies it to each circuit section. The master unit 3 has a terminal 6 to which an audio cable 5 is connected.
Analog audio signal S from 0 to CD playback sound
A is supplied. In this example, the analog audio signal SA is supplied from the terminal 22 of the DA converter unit 1. In the case of a system configuration in which the DA converter unit 1 is not connected, the analog audio signal SA is supplied from the terminal 45 of the CD player unit 2 as shown by the broken line in the figure.

The analog audio signal SA input to the terminal 60 is supplied to the T _CD terminal of the selection section 58. The master unit 3 also has a function as a radio tuner and a tape player, and can output an audio signal received and demodulated by the tuner / tape player unit 57 and an audio signal reproduced from a cassette tape. . These audio signals are supplied to the T _TU terminal of the selection unit 58. The selection unit 58 is switched under the control of the CPU 52. The analog audio signal selected by the selection unit 58 is supplied to the power amplifier 59, amplified, and output as sound from the speaker 70.

The operation section 56 is provided with operation keys for the user to perform various operations on this system. For example, CD playback key, track access key, stop key, radio tuning key, tape playback key, stop key,
Fast forward / rewind keys, volume keys, etc. are formed. The display unit 55 is formed of, for example, a liquid crystal display, and displays the operation mode, the track number during CD reproduction, the reproduction progress time, the operation state, the tuning frequency during radio reception, etc. under the control of the CPU 52. .

The CPU 52 controls the entire system according to the operation information from the operation section 52 and the control program stored in the internal ROM. For example, when CD reproduction is instructed, the CPU 40 is connected via the bus line 6.
To the CD player unit 2
The playback operation in is executed. At this time, the selection unit 58 is connected to the T _CD terminal. As a result, the digital audio data DT read from the disc 90 by the CD player unit 2 is D / A converted via the D-RAM 14 in the DA converter unit 1 and supplied to the master unit 3 as an analog audio signal SA. Then, this analog audio signal SA is supplied to the selection unit 5
8 is sent to the power amplifier 59, amplified, and output from the speaker 70.

When the disc 90 is reproduced, the servo signal processor 37 disc 9
The subcode information such as the track number and the address (time information) is read from 0, but the CPU 40 transmits these subcode information to the CPU via the bus line 6.
52. The CPU 52 executes the track number display, the reproduction progress time display and the like on the display unit 55 according to the transmitted subcode information.

Further, for example, when the user instructs the radio reception or the reproduction of the cassette tape from the operation unit 56, the CPU 52 controls the tuner / tape player unit 57 to execute the required operation and the selection unit 5
8 is connected to the T _TU terminal. As a result, the analog audio signal SA output from the tuner / tape player unit 57 is sent to the power amplifier 59 via the selection unit 58, amplified, and output from the speaker 70.

In this example, especially the DA converter unit 1
By the processing described in (1), it is possible to improve the vibration resistance in the disc reproducing operation and simultaneously prevent the deterioration of the sound quality due to the jitter. Hereinafter, this point will be described.

The CD player unit 1 reproduces the disc 90 and the servo signal processor 37 decodes the digital audio data DT.
Is supplied to the DA converter unit 1 according to the accuracy of the clock CK1. In the DA converter unit 1, the memory controller 13 performs writing / reading with the accuracy of the clock CK2, sends the digital audio data DT to the D / A converter 17 via the D-RAM 14, and the D / A converter 17
In the A converter 17, conversion into an analog signal is performed based on the clock CK2.

The processing of the CPU 12 for obtaining the anti-vibration function by the D-RAM 14 is shown in FIGS. As the control of the memory controller 13 of the CPU 12, the data storage process of FIG. 2 and the access process of FIG. 3 are performed.
As step F101 in FIG. 2, the CPU 12 monitors the accumulated amount of digital audio data in the D-RAM 14 via the memory controller 13. D-RAM1
The case where the accumulated amount of 4 becomes zero means that the reproduced audio output is interrupted. In this case, the process proceeds from step F102 to error processing.

If the amount of data stored in the D-RAM 14 is full, the writing to the D-RAM 14 needs to be temporarily interrupted, and the process proceeds from step F103 to the access process shown in FIG. If the storage amount of the D-RAM 14 is not full, the data storage process of FIG. 2 is continued.

In this case, the digital audio data DT supplied to the digital audio interface 15
Is written from the memory controller 13 to the D-RAM 14, the CPU 12 reads the address in the subcode data of the supplied digital audio data DT. As an address in the CD system format, an absolute address on the disc is indicated by a value of minutes / seconds / frames according to the reproduction progress time.

The minimum unit of data on a CD is one frame composed of 588 bits. In each frame, the first 24 bits are synchronization data, and the subsequent 14 bits are a subcode data area. After that, data and parity are allocated. One frame is composed of 98 frames in this structure, and the subcode data extracted from 98 frames is collected to form one block of subcode data. That is, the address is recorded in units of 98 frames. 98 frames to which one address is given are called one sub-coding frame (sub-frame).
Minute / second / frame values are given as absolute addresses. That is, the frame on the address corresponds to the number of "subframe" in the unit of "second", and one second includes 75 frames.

When the address (subcode Q data) about the currently supplied digital audio data is fetched in step F104, the D-RAM 14 is read in step F105.
The continuity of the data is confirmed by comparing with the address of the last data in the digital audio data stored in. That is, the address of the data written in the D-RAM 14 immediately before is compared. The address is stored in the variable SUBLAS by the CPU 12 in step F107 of the previous routine.
Holds as T.

That is, in step F105, the address of the digital audio data supplied this time (subcode Q data) and the address of the digital audio data supplied last time (SUBLAST) are subtracted, and the address difference is 5
Check whether it is within the subframe. Originally, the address difference between the previous data and the current data should be one subframe. However, the read data from the disk 90 may be lost for some reason, and in such a case, the data continuity cannot be maintained. However, if there is a data loss of about 5 subframes, it will not have a great effect when viewed as reproduced audio, and since the user cannot recognize the data loss, it should be considered that continuity is maintained. There is.

If it is determined in step F105 that the continuity is maintained, the process proceeds to step F106, and the CPU 12 causes the data input this time to be written in the D-RAM 14. Then, in step F107, the step relating to the next input data
The address of this data is set to the variable SU in preparation for the processing of F105.
Keep as BLAST. Then, the process returns to step F101.

While the storage amount in the D-RAM 14 is not full, the above processing is repeated to store the digital audio data supplied from the CD player unit 2 in the D-RAM 4. On the other hand, D-RAM
The reading process from 14 is always performed at a predetermined timing, and thus the reproduced voice is continuously output.

If it is determined in step F105 that data has been lost, and if it is determined in step F103 that the amount of data stored in the D-RAM 14 has become full, the process proceeds to the access process shown in FIG. That is, when data loss occurs,
This is because it is necessary to reread the data of the missing portion from the disk 90, and when the accumulated amount becomes full, it is necessary to temporarily wait for the reading of the subsequent data from the disk 90. Because there is.

After proceeding to the access processing of FIG. 3, step
The CPU 12 as the F201 is the disk 9 with respect to the CPU 40.
An instruction is given to execute a track jump so that the read position from 0 is returned by one track. In response to this, the CPU 40 causes the servo signal processor 37 to execute the track jump of the optical head 33.

In step F202, the CPU 12 causes the D-RAM
The accumulated amount of 14 is monitored, and if the accumulated amount becomes zero, the process proceeds from step F203 to error processing. Until the accumulated amount becomes zero, the address (sub-Q data) of the digital audio data supplied after the track jump of the optical head 33 is confirmed (F
204), the value is the address SU of the last data of the digital audio data stored in the D-RAM 14.
Check whether it is the next address of BLAST (F
205).

If it is not the address next to the address SUBLAST, it is confirmed whether or not the address of the data input in step F206 is a value larger than the address SUBLAST. 90 read data is still D-RA
Returning to step F202, it is determined that the last data of the digital audio data stored in M14 has not been reached.

On the other hand, when the address of the input data is larger than the address SUBLAST, the step
In F207, if the address difference is within 5 subframes,
That is, it is confirmed whether or not the data to be continuously written in the D-RAM 14 is maintained. Here, the case where it is determined that the continuity cannot be maintained may be the case where the return amount is too small in the track jump executed in step F201, for example. Therefore, the process returns to step F201 and the read position is moved backward by the track jump again.

The case where a positive result is obtained in step F205 or F207 is a case where the data inputted this time is judged to be the proper continuous data accumulated in the D-RAM 14 at that time, and When the data is D
-Write to RAM (F208), set the address of this data as the variable SUBLAST (F209), and return to step F101 in the data storage process of FIG.

By performing the above processing, the CD
The digital audio data reproduced by the player unit 2 is sequentially read out in the D-AM 14 of the DA converter unit 1 with a certain amount of storage being always maintained, D / A converted, and sent to the master unit 3. It will be. That is, even if the read operation by the optical head 33 is temporarily interrupted due to disturbance or the like, the sound output from the speaker 70 can be continued without interruption, and the vibration resistance is significantly improved. Since such an improvement in vibration resistance is obtained by using the DA converter unit 1, even if the CD player unit 2 is a device that does not have the vibration resistance function of the buffer memory, the DA converter unit 1 is By connecting it, vibration resistance can be improved.

Further, the digital audio data DT decoded by the CD player unit 2 is to be transmitted to the DA converter unit 1, and a jitter component may be superimposed here. For example, there is jitter caused by waveform distortion in the cable 9 and jitter caused by a difference in processing clocks between the digital audio interface unit 15 and the servo signal processor 37. There is also jitter due to fluctuations in the power supply voltage due to driving by the optical head 33 and the spindle motor 32.

In the case of the present example, the digital audio data is input in the DA converter unit 1 in such a state as to contain the jitter, but the data accumulated in the D-RAM 14 in the DA converter unit 1 is the clock C.
Since it is read out with the crystal precision as K2 and is D / A converted, it is possible to obtain a reproduced audio signal with effectively reduced jitter. Further, since the DA converter unit 1 and the CD player unit 1 have separate regulators (11, 31) for obtaining the power supply voltage V _DD , respectively, D- in the DA converter unit 1
The influence of the power supply voltage fluctuation due to the driving of the optical head 33 and the spindle motor 32 on the writing / reading operation to the RAM 14 and the operation of the D / A converter 17 is almost eliminated, and in this respect also, the high sound quality reproduction by the jitter reduction is realized. To be done.

[0056]

As described above, according to the present invention, in the D / A conversion unit, the digital audio data is stored in the memory means, and the digital audio data stored in the memory means is read at a predetermined timing to perform D / A conversion.
A conversion is performed, and these processes are executed using the clock from the clock generating means in the D / A conversion unit. Therefore, the so-called anti-vibration function is improved in the D / A conversion unit, and a sound reproduction system with anti-vibration performance can be easily constructed simply by connecting to a device such as a CD player having no anti-vibration property. effective.

Further, since the reading from the memory means and the D / A conversion are performed by using the highly accurate clock from the clock generating means, the system up to the reproducing apparatus such as a CD player and the writing to the memory means. The jitter that occurs at 2 can be significantly reduced, and there is an effect that high-accuracy reproduction is possible.

[Brief description of the drawings]

FIG. 1 is a block diagram of a playback system according to an embodiment of the present invention.

FIG. 2 is a flowchart of a data storage process according to the embodiment.

FIG. 3 is a flowchart of access processing according to the embodiment.

[Explanation of symbols]

 1 DA converter unit 2 CD player unit 3 Master unit 11, 31, 51 Regulator 12, 40, 52 CPU 13 Memory controller 14 D-RAM 15 Digital audio interface 17 D / A converter 19, 44 Clock generator 37 Servo signal processor

Claims (4)

[Claims] 1. Input means for inputting digital audio data, clock generating means, memory means, and digital memory data input from the input means based on a clock from the clock generating means. Memory control means for reading the digital audio data stored in the memory means at a predetermined timing and for reading the digital audio data stored in the memory means, and using the clock from the clock generation means for the digital audio data read from the memory control means. A D / A conversion unit comprising: a D / A conversion means for converting into an analog audio signal. 2. Instructing an external digital audio data reproducing apparatus which supplies digital audio data to the input means, in accordance with a storage amount of the digital audio data in the memory means, concerning a reproducing operation. The D / A conversion unit according to claim 1, further comprising a control means capable of performing the operation. 3. A reproducing unit that reads and decodes data from a recording medium and outputs decoded digital audio data, and digital audio data supplied from the reproducing unit is stored in a memory unit based on an internal clock. Then, the D / A conversion unit capable of reading the digital audio data accumulated in the memory unit at a predetermined timing, converting the read digital audio data into an analog audio signal using the internal clock, and outputting the analog audio signal. And a playback system characterized by being composed of. 4. The D / A conversion unit can control the reproduction operation of the reproduction unit in accordance with the amount of digital audio data stored in the memory unit. Playback system described.