JP2002367295A - Reproducing device for compressed audio data - Google Patents

Abstract

PROBLEM TO BE SOLVED: To dissolve generation of needless radiation in a compressed audio data reproducing device reproducing both of compressed audio data and normal CD data audio. SOLUTION: A digital signal processing section 13 is provided with a reference clock generator 131, an EFM signal decoder 132 demodulating an EFM signal inputted from a RF amplifier 12, switching circuits 133a, 133b, and a D/A converter 134. When an output from the EFM signal decoder 132 is CD audio data, the switching circuits directly output it to a D/A converter 134, in the case of compressed audio data, the switching circuits output it to the D/A converter 134 through a MP3 decoder 14. A bit clock passing through the switching circuit 133a is branched and inputted to a multiplier circuit 144 through a clock input section 143 of the MP3 decoder 14. This multiplier circuit 144 converts a bit clock to a decoder reference clock.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a compressed audio data reproducing apparatus which serves both as an audio CD player and an MP3 player, and more particularly to a CD-R on which compressed audio information known as an MP3 format or the like is recorded.
(CD recordable disc), CD-RW (CD rewritable disc), mini disc, and other recording media (hereinafter, referred to as discs) in which decoders necessary for reproducing compressed information are improved. .

[0002]

2. Description of the Related Art Conventionally, an MP3 format (MPEG-1 Audio Layer-3) for compressing audio data has been known. When audio data is compressed based on the MP3 format, the original sound quality can be compressed to a file size of about 1/10 (up to 1/12) without deteriorating the audibility. For this reason, if this kind of technology is applied to an audio player, it is possible to record more than ten times the number of songs on a single disc than a normal audio CD.

[0003] In particular, since a large amount of data can be handled by one disc, a plurality of CDs are required.
The CD changer that stores the CD is unnecessary, and the current C
Since it is possible to provide a CD changer containing ten or more songs as many as the D changer, it has attracted attention as an in-vehicle audio player for which there is a strong demand for a smaller player.

[0004]

By the way, a general in-vehicle audio player is widely used as a medium for audio recording in addition to the reproduction of a disk which has been compressed based on the MP3 format. Normal audio CD playback is also required. In particular, when reproducing both a disk on which such MP3 data is recorded and a normal audio CD, a disk shape, a disk drive control and data reading mechanism, a reproducing mechanism such as an amplifier and a speaker, an operation and display device Such,
Because of the large number of functionally common parts, attempts have been made to play both discs with one player.

[0005] By the way, C recorded on an audio CD is
When reproducing D audio data (CD_DA data), EFM modulation (Eight-to-Fourteen Modulation), which is a modulation method suitable for recording and reproducing on a disk, is performed from an optical pickup that reads information recorded on the disk. The applied RF signal is output and demodulated into a reproduction signal by a digital / analog converter (D / A converter). To expand and reproduce the MP3 compressed data as described above, a dedicated decoder is used. There is a need to.

At present, a DSP (digital signal processing unit) for demodulating CD audio data and servo control of an optical pickup as described above, and circuit blocks constituting an MP3 decoder are becoming LSIs. Each circuit block is often realized by a one-chip LSI.

In this case, conventionally, a reference clock generator for obtaining an audio sampling frequency required for demodulation processing and a synchronization frequency required for servo control is provided for each LSI constituting each circuit block.
However, the frequency of the reference clock is a relatively high frequency of several tens of MHz, and there is a problem that unnecessary radiation is likely to occur due to this harmonic component.

In particular, in the conventional apparatus, the MP3 decoder is always driven, and when the audio CD is reproduced, the CD is reproduced.
The audio data is bypassed or passed through the MP3 decoder, and is supplied to the D / A converter at the subsequent stage. However, if the MP3 decoder is constantly driven as described above, a shielding structure is required to prevent noise caused by the unnecessary radiation as described above, and this causes a problem that the device becomes complicated and large.

In an apparatus capable of reproducing both such CD audio data and compressed data such as MP3, at the time of switching between the two data, data recorded on a disk is read, and this is read by an MP3 decoder. A minute time lag may occur between the expansion and the conversion to the analog signal by the D / A converter, which may cause noise.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and is intended to provide an audio CD reproducing apparatus having a decoder for expanding audio data compressed in an MP3 format or the like.
It is an object of the present invention to provide a compressed audio data reproducing apparatus capable of eliminating unnecessary radiation caused by the decoder when reproducing audio data.

It is another object of the present invention to provide a compressed audio data reproducing apparatus capable of preventing generation of noise when switching between CD audio data and compressed data such as MP3.

[0012]

According to one aspect of the present invention, there is provided a digital signal processor for processing input compressed audio data and CD audio data and outputting an analog audio signal. Unit, a decoder connected to the digital signal processing unit for expanding the compressed audio data, and a reference clock output from the digital signal processing unit are input to a decoder for the compressed audio data. A clock for the decoder operation is generated based on the clock signal. According to the first aspect of the present invention having such a configuration, a dedicated clock generator is not required for a decoder for expanding compressed audio data, and it is necessary to operate a decoder for expanding data as in the reproduction of CD audio data. In the case where there is no unnecessary radiation, unnecessary radiation from the decoder part is eliminated.

According to a second aspect of the present invention, the reference clock is:
A bit clock which is a synchronous clock of the audio signal generated in the digital signal processing unit, and the decoder is provided with a multiplier circuit for converting the bit clock into a clock for decoder operation. And Claim 2 having such a configuration.
According to the invention, when compressed audio data is output to a decoder, the bit clock output from the digital signal processing unit is directly used and converted into a clock for decoder operation, so that the digital signal processing unit and the like use a dedicated clock for the decoder. Does not need to be generated, and the configuration of the entire apparatus is simplified.

According to a third aspect of the present invention, the digital signal processing section includes a switching circuit for switching between compressed audio data and CD audio data, and a D / A converter for converting the processed digital audio signal into an analog signal. When the data to be processed is CD audio data, the data is directly output to a D / A converter, and when the data to be processed is compressed audio data, the data is output to the D / A converter via the decoder. It is characterized by being. The invention of claim 3 having such a configuration is:
Compressed audio data that needs to be expanded can be sent to the D / A converter via the decoder only by controlling the switching circuit in the digital signal processing unit. Can be shared by the compressed audio data and the CD audio data.

According to a fourth aspect of the present invention, a mute circuit for cutting off the output of the analog audio signal when the decoder of the compressed audio data rises is provided on the output side of the analog audio signal of the digital signal processing section. And According to the invention of claim 4 having such a configuration, it is possible to cut noise generated at the time of starting the expansion processing of the compressed audio data.

[0016]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of a compressed audio data reproducing apparatus according to an embodiment of the present invention.

(1. Configuration of the First Embodiment) The compressed audio data reproducing apparatus of the present embodiment includes an operating device 1 including an operating panel and control buttons for a user to operate the device from outside, Formed by, for example, an LCD (Liquid Crystal Display) to display the status of the device (for example, the type and presence or absence of a disc, the content of the song being played or the artist name, the volume of the playback sound, the order of the song being played, etc.) Display device 2 provided. Further, an amplifier 3 and a speaker 4 for amplifying an audio signal obtained from CD audio data and MP3 compressed data are provided.

The compressed audio data reproducing apparatus includes:
A disk drive unit 5 and a pickup unit 6 are provided. The disk drive unit 5 includes a position detection mechanism 51 for detecting the presence / absence and a fixed position of the disk, a disk mounting completion detection mechanism 52, a disk loading motor 5
3. Each mechanism includes a detection mechanism 54 for detecting the innermost peripheral position of the pickup, a spindle motor 55 for moving the pickup, and a spindle motor 56 for rotating the disk. The pickup unit 6 includes a mechanism for reading data recorded on a disk, such as a focus coil 61, a tracking coil 62, a laser diode 63, and a photodetector (photodetector) 64.

In order to control the disk drive unit 5 and the pickup unit 6 as described above, and to convert the CD audio data and the MP3 compressed data obtained from the pickup unit 6 into audio signals that can be output from the speaker 4, this compressed audio The data reproducing apparatus includes a main control unit 10, a mechanism control unit 11, an RF signal processing unit 12, a digital signal processing unit (D
SP) 13, an MP3 decoder 14 having a function of decoding CD-ROM data (compressed audio data) supplied from the digital signal processing unit 13, a buffer memory 15, and a mute circuit 16 are provided.

The main control unit 10 is constituted by a so-called microcomputer, and includes the operation device 1, the display device 2, the disk drive unit 5, and the pickup unit 6.
And are connected to and control the control units and the processing units.

The main control unit 10 is provided with a reproduction control unit 101 for controlling the drive stop of the reproducing apparatus. The reproduction control unit 101 detects the presence or absence of a disk and the position of the disk drive unit 5 such as a fixed position. The mechanism 51 is connected to a disk mounting completion detecting mechanism 52.

The main controller 10 obtains TOC (Table Of Contents) from the digital signal processor 13 as management information recorded in the lead-in of each disk read from the pickup unit. A disc discrimination unit 102 is provided for discriminating whether a disc inserted into the apparatus is an audio CD or a CD-ROM on which MP3 compressed data is recorded.

The main control unit 10 includes the digital signal processing unit 1
The control unit 103 of the mute circuit 16 provided downstream of the third D / A converter 134 is provided. That is, the mute circuit 16 outputs the CD audio data and the MP audio data.
The mute circuit control unit 103 mutes the serial data for a certain period of time to switch to a silent state when switching to an audio signal based on the MP3 compressed data from the 3 decoder 14. , The mute circuit 16 is operated to cut off the output from the D / A converter 14 of the digital signal processing unit 13.

The mechanism control unit 11 includes the disk drive unit 5
The operation of the disc loading motor 53, the pickup moving spindle motor 55 and the disc rotating spindle motor 56, and the focus coil 61 and the tracking coil 62 provided in the pickup section 6 are controlled.

The laser diode 63 and the photodetector (photodetector) 64 of the pickup section 6
It is connected to the signal processing unit 12. That is, this RF
In response to a command from the signal processing unit 12, a laser beam emitted from a laser diode 63 is applied to the data recording surface of the disk, and the reflected light is read by a photodetector (photodetector) 64, and the read data is converted to an RF signal. The RF signal processed by the processing unit 12 and subjected to the EFM modulation, and a tracking error signal and a focus error signal are obtained.

Each signal obtained in this way is input to the digital signal processing unit 13, of which a tracking error signal and a focus error signal are sent to the mechanism control unit 11, and based on these signals, The mechanism control unit 11 controls operations of the focus coil 61 and the tracking coil 62 provided in the pickup unit 6. On the other hand, after determining whether the RF signal is CD audio data or MP3 compressed data, the RF signal is converted into an audio signal.

The digital signal processing unit 13 has a built-in reference clock generator 131 for generating a clock signal of a predetermined frequency (L / R clock and bit clock of an arbitrary frequency). The generated reference clock is transmitted to the mechanism control unit 11, the CD audio data demodulation unit, and the compressed audio decoder 1
4 for synchronizing the signals. Note that the reference clock generator 131 may be provided outside the digital signal processing unit 13.

The digital signal processing unit 13 demodulates the EFM signal input from the RF signal processing unit 12
An M signal decoder 132, switching circuits 133a and 133b, and a D / A converter 134 are provided.

The EFM signal decoder 132 has a CD_DA
The decoder decodes data, that is, CD audio data, and converts it into a digitized audio signal composed of three signals of an L / R clock, a bit clock, and serial data. The L / R clock indicates whether the current audio sampling data transferred as serial data is L channel data or R channel data,
It has a frequency corresponding to the time division cycle of the L channel data and the R channel data. The bit clock is a synchronous clock of each sampled data transferred as serial data.

Further, the EFM signal decoder 132
The compressed audio data is sent to the MP3 decoder 14 by L / R
Output with the clock and bit clock.
These signals are input to the compressed data processing unit 141 of the MP3 decoder 14.

The switching circuits 133a and 133b are connected to the EF.
If the output from the M signal decoder 132 is CD audio data, it is directly output to the D / A converter 134 and
When the output from the M signal decoder 132 is compressed audio data, the compressed audio data is output to the D / A converter 134 via the MP3 decoder 14.
The circuit is switched according to the disk type determined as 0.

The D / A converter 134 converts the CD audio data from the EFM signal decoder 132 or the digital audio signal restored by the expansion processing in the MP3 decoder 14 into an analog signal and outputs the analog signal. The D / A converter 134 is connected to the audio amplifier 3 that amplifies the analog audio signal with a predetermined gain and supplies the amplified audio signal to the speaker 4.

The MP3 decoder 14 receives the L / R clock from the switching circuit 133a of the digital signal processing unit 13,
Input bit clock and compressed audio data,
A compressed data processing unit 141 that outputs the compressed audio data to the buffer memory 15 for storing the compressed audio data and a data expansion processing unit 142 that reads out compressed audio data from the buffer memory 15 and performs expansion processing. This data decompression processing unit 142
Is the switching circuit 1 of the digital signal processing unit 13.
33b.

The MP3 decoder 14 has a decoder operation clock input section 143 for branching and inputting a bit clock from among the signals input to the compressed data processing section 141 for decoder operation, and an input from the input section 143. Decoder reference clock (about 60 MHz) necessary to read compressed audio data from the buffer memory 15 and expand the extracted bit clock (for example, 2.8 MHz).
And a multiplying circuit 144 for converting the data into

(2. Operation of Embodiment) The operation of this embodiment will be described below with reference to the flowchart shown in FIG. When an audio CD or a CD-ROM on which compressed audio data is recorded is inserted into the reproducing apparatus of the present embodiment having the above-described configuration, the main control unit 10 detects this, and the disk drive unit 5 Then, the pickup unit 6 is operated to start the rotation of the disk and the reading of the recorded data (S01).

The main control section 10 has a disk discriminating section 102
Thus, TOC (TaC) as management information recorded in the lead-in of each disk read from the pickup unit 6
bleOf Contents) (S02), the disc inserted into the apparatus is an audio CD or a CD-RO.
M is determined (S03).

If the disc is an audio CD, (S
03 (NO), the switching circuits 133a and 133b provided in the digital signal processing unit 13 are switched to the D / A converter 134 side. At the same time, the RF
The EFM signal input to the EFM signal decoder 132 via the signal processing unit 12 is demodulated and converted into a digitized audio signal composed of three signals of an L / R clock, a bit clock, and serial data (S0
4).

The converted digital audio signal is output to the D / A converter 134 via the switching circuits 133a and 133b, and the D / A converter 134 converts the digital audio signal into an analog signal (S0).
5) This is output from the speaker 4 via the mute circuit 16 and the amplifier 3 (S06).

On the other hand, the inserted disc is a CD-ROM
In the case of (YES in S03), the TOC information is transmitted from the digital signal processing unit 13 to the main control unit 10, where the TOC information is determined to be a CD-ROM. In this case, the main control unit 10
, The switching circuits 133a and 133b provided in the digital signal processing unit 13 are switched to the MP3 decoder 14 side. At the same time, the RF
The EFM signal input to the EFM signal decoder 132 via the signal processing unit 12 is demodulated and converted into a digital signal composed of three signals of an L / R clock, a bit clock, and compressed audio data. The switching circuit 133a controls the M signal outside the digital signal processing unit 13.
The data is output to the P3 decoder 14 (S07).

Of the three signals of the L / R clock, bit clock, and compressed audio data that have passed through the switching circuit 133a, only the bit clock is branched,
Decoder operation clock input unit 1 of MP3 decoder 14
The signal is input to the multiplication circuit 144 via 43. The multiplying circuit 144 converts the bit clock input from the input section 143 into a decoder reference clock necessary for expanding the compressed audio data (S08).

As described above, when the decoder reference clock is supplied, the MP3 decoder 14 becomes operable. A reset signal is sent from the main control unit 10 to the MP3 decoder 14 which has detected the operation, and the MP3 decoder 14 Is initialized (S09).

When the MP3 decoder 14 is initialized, the digitized compressed audio data obtained by the digital signal processing unit 13 is input to the compressed data processing unit 141 of the MP3 decoder 14 and furthermore, the buffer memory 15 Is accumulated in

After obtaining the reference clock for data expansion as described above, the MP3 decoder 14 sequentially reads out the compressed audio data stored in the buffer memory 15, expands the compressed audio data, and converts it into a digital audio signal. The converted digital audio signal is returned to the digital signal processing unit 13 again together with the L / R clock and the bit clock, and is supplied to the D / A converter 134 via the switching circuit 133b.
Sent to

That is, the MP3 decoder 14 reads and analyzes the data stored in the buffer memory 15 (S10), and this data is used as the compressed audio data (M
(Compressed data in P3 format) (S1
1 (YES), decompress this to D / A converter 134
(S12). If the analyzed data is data of another format (NO in S), the process is terminated, and an error display or the like is performed from the main control unit 10 on the display device 2 (S13). The data analysis method is not limited to the above, and an appropriate method can be used.

In the D / A converter 134, the decompressed compressed audio data is analog-converted in the same manner as in the processing of the digitized audio signal from the audio CD (S05), and is passed through the mute circuit 16 and the amplifier 3. Output from the speaker 4 (S06).

Incidentally, the MP3 decoder 1 as described above
When the processing by step 4 starts, an audio signal is output from the speaker when the apparatus is started or switched to initialize the MP3 decoder 14, accumulate data in the buffer memory 15, or expand compressed audio data. There may be a slight time lag between the two.
Therefore, in the present embodiment, the mute circuit control unit 103 of the main control unit 10 controls the mute circuit 1 for a certain period of time.
6 is operated to cut off the audio output from the speaker. As a result, it is possible to prevent the occurrence of noise that occurs when switching the reproduction output.

MP by the mute circuit control unit 103
The detection of the rising edge of the 3 decoder 14, in other words, the determination that the audio signal has started to be input to the D / A converter 14 of the digital signal processing unit 13 is performed as follows. In other words, the main control unit 10 can recognize that the digital signal processing unit 13 and the MP3 decoder 14 have started up normally through the interface with the digital signal processing unit 13 and the MP3 decoder 14.
The main control unit 10 controls mute of the output from the digital signal processing unit 13 based on the recognition result. as a result,
Until the communication interface with the MP3 decoder ends normally, the main control unit 10 can mute the digital signal processing unit 13.

Note that the mute circuit 16 is configured so that mute control is performed for a predetermined time from a predetermined timing (for example, when it is confirmed that an MP3 file exists or a CD-ROM is detected). You can also.

As described above, in the present embodiment, the bit clock obtained by the reference clock generator 131 provided in the digital signal processing unit 13 can be obtained without providing the MP3 decoder 14 with a dedicated clock generator. , From the compressed audio signal input to the MP3 decoder 14, and used as a reference clock for expansion. As a result, a clock generator dedicated to the MP3 decoder 14 becomes unnecessary, and generation of unnecessary radiation is suppressed.

(3. Other Embodiments) The present invention is not limited to the above embodiment, and each control unit and processing unit is constituted by a dedicated LSI. However, this circuit constitution is not necessarily required. It is not limited to the illustrated one. It is possible to mount each unit collectively on one integrated LSI. Also, the compressed data recorded on the disc has been described as being compressed based on the currently mainstream MP3 format, but may be compressed based on another compression format. Also, as a recording medium for compressed audio data,
An optical disk, a magneto-optical disk, a magnetic disk, a memory such as a ROM or a RAM may be used, or a single medium may contain files other than compressed audio data.

[0051]

As described above, according to the present invention, it is possible to obtain a compressed audio data reproducing apparatus in which the generation of unnecessary radiation is suppressed and the accompanying apparatus can be reduced in size and simplified. Further, when the mute circuit is provided, it is possible to prevent noise from occurring at the time of rising of the decoder of the compressed audio data.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a first embodiment of a compressed audio data reproducing apparatus according to the present invention.

FIG. 2 is an enlarged view of a digital signal processing unit and an MP3 decoder in the compressed audio data reproducing device of FIG. 1;

FIG. 3 is a flowchart showing the operation of the first embodiment of the compressed audio data reproducing apparatus according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Operation device 2 ... Display device 3 ... Amplification amplifier 4 ... Speaker 5 ... Disk drive unit 6 ... Pickup unit 10 ... Main control unit 11 ... Mechanism control unit 12 ... RF signal processing unit 13 ... Digital signal processing unit 14 ... Compression Audio decoder 15 ... Buffer memory 16 ... Mute circuit 51 ... Position detection mechanism 52 ... Mounting completion detection mechanism 53 ... Loading motor 54 ... Detection mechanism 55 ... Spindle motor 56 ... Spindle motor 61 ... Focus coil 62 ... Tracking coil 63 ... Laser diode 64 Photodetector 101 Reproduction control unit 102 Disc discrimination unit 103 Mute circuit control unit 131 Reference clock generator 132 RF signal decoder 133a, 133b Switching circuit 134 D / A converter 141 Compression data processing unit 142 De Data decompression processing unit 143 Decoder operation clock input unit 144 Multiplier circuit

Claims (4)

[Claims] 1. Compressed audio data and CD input
A digital signal processing unit that processes audio data and outputs an analog audio signal; a decoder connected to the digital signal processing unit for expanding the compressed audio data; and a decoder output from the digital signal processing unit A compressed audio data reproducing apparatus, comprising: inputting a reference clock to a decoder of the compressed audio data; and generating a clock for operating the decoder based on the reference clock. 2. The method according to claim 1, wherein the reference clock is a bit clock that is a synchronization clock of an audio signal generated in the digital signal processing unit, and the decoder converts the bit clock into a clock for decoder operation. 2. The compressed audio data reproducing apparatus according to claim 1, further comprising a multiplying circuit of 3. The digital signal processing section includes a switching circuit for switching between compressed audio data and CD audio data, and a D / A converter for converting the processed digital audio signal into an analog signal.
A / A converter, wherein the switching circuit directly outputs the CD audio data to the D / A converter when the data to be processed is CD audio data, and outputs the D / A converter via the decoder when the data to be processed is compressed audio data. 3. The compressed audio data reproducing apparatus according to claim 1, wherein the compressed audio data is outputted to a / A converter. 4. A mute circuit for cutting the output of the analog audio signal when the decoder of the compressed audio data rises is provided on the output side of the analog audio signal of the digital signal processing unit. The compressed audio data reproducing device according to claim 2 or claim 3.