JP4672913B2 - Compressed audio data playback device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a compressed audio data playback apparatus that also serves as an audio CD player and an MP3 player. In particular, the present invention relates to a CD-R (CD recordable disc) or CD-RW on which compressed audio information known as an MP3 format or the like is recorded. This is an improvement in the decoder portion necessary for reproducing compressed information from a recording medium (hereinafter referred to as a disc) such as a (CD rewritable disc) or a mini disc.
[0002]
[Prior art]
Conventionally, an MP3 format (MPEG-1 Audio Layer-3) for compressing audio data is known. When audio data is compressed based on this MP3 format, the original sound quality can be compressed to a file size of about 1/10 (maximum 1/12) without degrading the original sound quality. For this reason, if this type of technology is applied to an audio player, the number of songs more than ten times that of a normal audio CD can be recorded on a single disc.
[0003]
In particular, as a result of being able to handle a large amount of data with a single disc, a CD changer that accommodates multiple CDs becomes unnecessary, or a CD that contains more than 10 times the number of songs of the current CD changer. Since a changer can be provided, it is attracting attention as an in-vehicle audio player that is strongly demanded to downsize the player.
[0004]
[Problems to be solved by the invention]
By the way, a general in-vehicle audio player is required to reproduce a normal audio CD widely used as an audio recording medium, in addition to the reproduction of a disk compressed based on the MP3 format. ing. In particular, when reproducing both a disc on which such MP3 data is recorded and a normal audio CD, the disc shape, the disc drive control and data reading mechanism, the reproduction mechanism such as an amplifier and speaker, the operation and display device Since there are many functionally common parts, an attempt has been proposed in which one player plays both discs.
[0005]
By the way, when reproducing CD audio data (CD_DA data) recorded on an audio CD, EFM modulation (a modulation method suitable for recording / reproducing on a disk) is used from an optical pickup that reads information recorded on the disk. An RF signal subjected to Eight-to-Fourteen Modulation is output, and this is demodulated into a reproduction signal by a digital analog converter (D / A converter). In order to decompress and reproduce the MP3 compressed data as described above It is necessary to use a dedicated decoder.
[0006]
At present, circuit blocks constituting DSPs (digital signal processing units) and MP3 decoders for demodulating CD audio data as described above, and servo control of optical pickups, and LSIs are progressing. Is often realized by a one-chip LSI.
[0007]
In this case, conventionally, a reference clock generator for obtaining an audio sampling frequency necessary for demodulation processing and a synchronization frequency necessary 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 due to this harmonic component is likely to occur.
[0008]
In particular, in the conventional apparatus, the MP3 decoder is always driven, and when reproducing an audio CD, the CD audio data is supplied to the D / A converter in the subsequent stage by bypassing or through the MP3 decoder. However, when the MP3 decoder is always driven as described above, a shielding structure is required for countermeasures against noise due to the above-described unnecessary radiation, which causes a problem that the apparatus becomes complicated and large.
[0009]
Further, in an apparatus capable of reproducing both CD audio data and compressed data such as MP3, the data recorded on the disk is read at the time of switching between the two data, and is decompressed by the MP3 decoder. Furthermore, a slight time lag occurs before conversion to an analog signal by the D / A converter, which may cause noise.
[0010]
The present invention has been made in view of the above-described problems of the prior art, and in an audio CD playback apparatus having a decoder for decompressing audio data compressed by the MP3 format or the like, playback of CD audio data is performed. 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 at the time.
[0011]
Another object of the present invention is to provide a compressed audio data reproducing apparatus capable of preventing noise from being generated during switching processing between CD audio data and compressed data such as MP3.
[0012]
[Means for Solving the Problems]
In order to achieve the above-mentioned object, the invention of claim 1 processes the input compressed audio data and CD audio data and outputs an analog audio signal; and the digital signal processor And a decoder for expanding the compressed audio data and a reference clock output from the digital signal processing unit are input to the decoder of the compressed audio data, and a clock for the decoder operation is generated based on the reference clock. It is characterized by generating.
The invention of claim 1 having such a configuration eliminates the need for a dedicated clock generator in the decoder for decompressing the compressed audio data, and it is necessary to operate the data decompression decoder as in the reproduction of CD audio data. When there is no error, unnecessary radiation from the decoder portion is eliminated.
[0013]
  The present invention also provides:The reference clock is a bit clock that is a synchronization 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 operating the decoder. It is characterized by being. Having such a configurationThe present inventionWhen outputting compressed audio data to the decoder, it is necessary to use the bit clock output from the digital signal processing unit as it is and convert it to a clock for decoder operation, thereby generating a dedicated clock for the digital signal processing unit etc. The configuration of the entire apparatus is simplified.
[0014]
  In particular, the present inventionThe digital signal processing unit includes a switching circuit between compressed audio data and CD audio data, and a D / A converter that performs analog conversion on the processed digital audio signal, and the switching circuit is configured to process data of CD audio data. In this case, this is directly output to the D / A converter. When the data to be processed is compressed audio data, it is sent to the D / A converter via the decoder.In addition to outputting, the bit clock in the compressed audio data is input to the multiplication circuit.It is characterized by that. Having such a configurationThe present inventionCompressed audio data that requires data expansion can be sent to the D / A converter via the decoder side only by controlling the switching circuit in the digital signal processing unit. This circuit can be shared between compressed audio data and CD audio data.In addition, when the data to be processed is CD audio data, the switching circuit directly outputs the data to the D / A converter, so that the bit clock is not output to the multiplication circuit. Generation of unnecessary radiation due to the decoder during data reproduction can be eliminated.
[0015]
  Claim 2The present invention is characterized in that a mute circuit is provided on the analog audio signal output side of the digital signal processor to cut off the output of the analog audio signal when the decoder of the compressed audio data rises. Having such a configurationClaim 2According to the present invention, it is possible to cut noise generated at the start of the decompression process of compressed audio data.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the compressed audio data reproducing apparatus of the present invention will be specifically described below with reference to the drawings.
[0017]
(1. Configuration of the first embodiment)
The compressed audio data reproducing apparatus according to the present embodiment includes an operating apparatus 1 including an operation panel and control buttons for a user to operate the apparatus from the outside, and the state of the apparatus (for example, the type, presence / absence of a disc, playback) A display device 2 formed of, for example, an LCD (Liquid Crystal Display) is provided to display the content of the title of the song and the name of the artist, the volume of the playback sound, the order of the song being played, and the like. Further, an amplifier 3 for amplifying an audio signal obtained from CD audio data and MP3 compressed data and a speaker 4 are provided.
[0018]
The compressed audio data reproducing apparatus is provided with a disk drive unit 5 and a pickup unit 6. Among them, the disk drive unit 5 includes a position detection mechanism 51 such as the presence / absence of a disk and a fixed position, a disk mounting completion detection mechanism 52, a disk loading motor 53, a detection mechanism 54 for the innermost peripheral position of the pickup, and a pickup movement. For example, a spindle motor 55 for rotating the disk and a spindle motor 56 for rotating the disk. The pickup unit 6 includes a reading mechanism for data recorded on the disk, such as a focus coil 61, a tracking coil 62, a laser diode 63, and a photodetector (photodetector) 64.
[0019]
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 MP3 compressed data obtained from the pickup unit 6 into audio signals that can be output from the speaker 4, this compressed audio data reproducing apparatus 1 includes a main control unit 10, a mechanism control unit 11, an RF signal processing unit 12, a digital signal processing unit (DSP) 13, and a decoding function for CD-ROM data (compressed audio data) supplied from the digital signal processing unit 13. Are provided with an MP3 decoder 14, a buffer memory 15 and a mute circuit 16.
[0020]
The main control unit 10 is constituted by a so-called microcomputer and is connected to and controls the operation device 1, the display device 2, the disk drive unit 5, the pickup unit 6, and the control units and processing units. Is.
[0021]
The main control unit 10 is provided with a reproduction control unit 101 that controls driving stop of the reproduction apparatus. It is connected to a disk installation completion detection mechanism 52.
[0022]
The main control unit 10 obtains TOC (Table Of Contents) as management information recorded in the lead-in of each disk read from the pickup unit from the digital signal processing unit 13, so that it is stored in the apparatus. A disc discrimination unit 102 is provided for discriminating whether the inserted disc is an audio CD or a CD-ROM on which MP3 compressed data is recorded.
[0023]
The main control unit 10 is provided with a control unit 103 of a mute circuit 16 provided at a subsequent stage of the D / A converter 134 of the digital signal processing unit 13. That is, the mute circuit 16 is for muting the serial data for a certain period to switch to the silent state when switching between the CD audio data and the audio signal based on the MP3 compressed data from the MP3 decoder 14. 103 controls the mute circuit 16 to operate and cut the output from the D / A converter 14 of the digital signal processing unit 13 until the MP3 decoder 14 starts up.
[0024]
The mechanism control unit 11 includes a disk loading motor 53, a pickup moving spindle motor 55 and a disk rotating spindle motor 56, a focus coil 61 and a tracking coil 62 provided in the pickup unit 6. To control the operation.
[0025]
The laser diode 63 and the photodetector (photodetector) 64 of the pickup unit 6 are connected to the RF signal processing unit 12. That is, in accordance with a command from the RF signal processing unit 12, the laser light emitted from the laser diode 63 is applied to the data recording surface of the disk, and the reflected light is read and read by the photodetector (photodetector) 64. Data is processed in the RF signal processing unit 12, and an RF signal subjected to EFM modulation, a tracking error signal, and a focus error signal are obtained.
[0026]
Each signal obtained in this way is input to the digital signal processing unit 13, and among these, the tracking error signal and the focus error signal are sent to the mechanism control unit 11, and the mechanism control is performed based on these signals. The unit 11 controls the operation of the focus coil 61 and the tracking coil 62 provided in the pickup unit 6. On the other hand, after the RF signal is discriminated whether it is CD audio data or MP3 compressed data, each is converted into an audio signal.
[0027]
The digital signal processing unit 13 has a built-in reference clock generator 131 that generates a clock signal having a predetermined frequency (an L / R clock and a bit clock having an arbitrary frequency), and is generated by the reference clock generator 131. The reference clock is supplied to the mechanism control unit 11, the CD audio data demodulating unit, and the compressed audio decoder 14 to synchronize signals. The reference clock generator 131 may be provided outside the digital signal processing unit 13.
[0028]
The digital signal processing unit 13 includes an EFM signal decoder 132 that demodulates the EFM signal input from the RF signal processing unit 12, switching circuits 133 a and 133 b, and a D / A converter 134.
[0029]
The EFM signal decoder 132 decodes CD_DA data, that is, CD audio data, and converts it into a digitized audio signal composed of three signals of L / R clock, 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, and the frequency corresponding to the time division cycle of the L channel data and the R channel data. Have The bit clock is a synchronous clock for each sampling data transferred as serial data.
[0030]
The EFM signal decoder 132 outputs the compressed audio data to the MP3 decoder 14 together with the L / R clock and the bit clock, and these signals are input to the compressed data processing unit 141 of the MP3 decoder 14.
[0031]
The switching circuits 133a and 133b directly output to the D / A converter 134 when the output from the EFM signal decoder 132 is CD audio data, and the MP3 decoder when the output from the FM signal decoder 132 is compressed audio data. 14 to the D / A converter 134, and switches the circuit according to the disc type determined by the main control unit 10.
[0032]
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.
[0033]
The MP3 decoder 14 receives the L / R clock, the bit clock and the compressed audio data from the switching circuit 133a of the digital signal processing unit 13 and outputs the compressed data to the buffer memory 15 for storing them, A data expansion processing unit 142 that reads compressed audio data from the buffer memory 15 and performs expansion processing. The output side of the data expansion processing unit 142 is connected to the switching circuit 133 b of the digital signal processing unit 13.
[0034]
The MP3 decoder 14 includes a decoder operation clock input unit 143 for branching and inputting a bit clock from among the signals input to the compressed data processing unit 141 for decoder operation, and a bit clock input from the input unit 143. A multiplication circuit 144 is provided which converts (for example, 2.8 MHz) into a decoder reference clock (about 60 MHz) necessary for reading out and decompressing the compressed audio data from the buffer memory 15.
[0035]
(2. Action of the embodiment)
Hereinafter, the operation of the present embodiment will be described with reference to the flowchart shown in FIG.
When a CD-ROM in which an audio CD or compressed audio data is recorded is inserted into the playback 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).
[0036]
The main control unit 10 is inserted into the apparatus by the disc discriminating unit 102 in accordance with TOC (Table Of Contents) as management information recorded in the lead-in of each disc read from the pickup unit 6 (S02). It is determined whether the disc is an audio CD or a CD-ROM (S03).
[0037]
When the disc is an audio CD (NO in S03), 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 EFM signal input from the pickup unit 6 to the EFM signal decoder 132 via the RF signal processing unit 12 is demodulated and digitized into three signals of L / R clock, bit clock, and serial data. (S04).
[0038]
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 (S05), which is converted into a mute circuit 16. And it outputs from the speaker 4 via the amplifier 3 (S06).
[0039]
On the other hand, when the inserted disc is a CD-ROM (YES in S03), the TOC information is transmitted from the digital signal processing unit 13 to the main control unit 10, and is determined to be a CD-ROM here. In this case, the switching circuits 133a and 133b provided in the digital signal processing unit 13 are switched to the MP3 decoder 14 side according to a command from the main control unit 10. At the same time, the EFM signal input from the pickup unit 6 to the EFM signal decoder 132 via the RF signal processing unit 12 is demodulated, and is converted into a digital signal composed of three signals of L / R clock, bit clock, and compressed audio data. The digital signal is output to the MP3 decoder 14 outside the digital signal processing unit 13 by the switching circuit 133a (S07).
[0040]
In this way, only the bit clock is branched out of the three signals of the L / R clock, the bit clock, and the compressed audio data that have passed through the switching circuit 133a, and the decoder operation clock input unit 143 of the MP3 decoder 14 is branched. This is input to the multiplier circuit 144. In the multiplication circuit 144, the bit clock input from the input unit 143 is converted into a decoder reference clock necessary for decompressing the compressed audio data (S08).
[0041]
In this way, when the decoder reference clock is given, the MP3 decoder 14 becomes operable, so that the reset signal is sent from the main control unit 10 that has detected this to the MP3 decoder 14, and the MP3 decoder 14 is initialized. Is made (S09).
[0042]
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 further stored in the buffer memory 15. The
[0043]
After obtaining the reference clock for data decompression as described above, the MP3 decoder 14 sequentially reads the compressed audio data stored in the buffer memory 15 and decompresses it to convert it into a digital audio signal. The converted digital audio signal is returned to the digital signal processing unit 13 together with the L / R clock and the bit clock, and sent to the D / A converter 134 via the switching circuit 133b.
[0044]
That is, the MP3 decoder 14 reads and analyzes the data stored in the buffer memory 15 (S10), and when this data is compressed audio data (MP3 format compressed data) (YES in S11), this Is output to the D / A converter 134 (S12). If the analyzed data is data in another format (NO in S), the process is terminated and error display and the like are performed from the main control unit 10 to the display device 2 (S13). The data analysis method is not limited to the above, and an appropriate method can be used.
[0045]
In the D / A converter 134, the decompressed compressed audio data is converted into an analog signal in the same way as the processing of the digitized audio signal from the audio CD (S05), and is output from the speaker 4 via the mute circuit 16 and the amplifier 3. Is output (S06).
[0046]
By the way, when the processing by the MP3 decoder 14 as described above is started, at the time of starting up or switching the device in order to initialize the MP3 decoder 14, accumulate data in the buffer memory 15, or decompress compressed audio data, There is a possibility that a slight time lag may occur before the audio signal is output from the speaker. Therefore, in the present embodiment, the mute circuit control unit 103 of the main control unit 10 activates the mute circuit 16 for a certain period of time to cut the sound output from the speaker. As a result, it is possible to prevent the occurrence of noise that occurs when switching the reproduction output.
[0047]
The detection of the rise of the MP3 decoder 14 by the mute circuit control unit 103, 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. That is, the main control unit 10 can recognize that the digital signal processing unit 13 and the MP3 decoder 14 have started up normally at the interface with the digital signal processing unit 13 and the MP3 decoder 14, and based on the recognition result. The main control unit 10 controls the mute of the output from the digital signal processing unit 13. As a result, the main control unit 10 can mute the digital signal processing unit 13 until the communication interface with the MP3 decoder ends normally.
[0048]
The mute circuit 16 may be configured to be muted for a predetermined time from a predetermined timing (for example, when it is confirmed that an MP3 file exists or is a CD-ROM). it can.
[0049]
As described above, in this embodiment, a bit clock obtained by the reference clock generator 131 provided in the digital signal processing unit 13 is not provided in the MP3 decoder 14 without providing a dedicated clock generator in the MP3 decoder 14. 14 is branched from the compressed audio signal input to 14 and used as a reference clock for expansion. As a result, a dedicated clock generator for the MP3 decoder 14 becomes unnecessary, and generation of unnecessary radiation is suppressed.
[0050]
(3. Other embodiments)
The present invention is not limited to the above-described embodiment, and each control unit and processing unit is configured by a dedicated LSI. However, the circuit configuration is not necessarily limited to that illustrated. It is possible to mount each unit together in one integrated LSI. Further, 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. The compressed audio data recording medium may be an optical disk, a magneto-optical disk, a magnetic disk, a memory such as ROM or RAM, or the like, and a file other than compressed audio data is mixed in one medium. May be.
[0051]
【The invention's effect】
As described above, according to the present invention, it is possible to obtain a compressed audio data reproducing apparatus in which the occurrence of unnecessary radiation is suppressed, and the accompanying apparatus can be downsized and simplified.
In addition, when the mute circuit is provided, it is possible to prevent the generation of noise at the start 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.
2 is an enlarged view of a digital signal processing unit and an MP3 decoder part in the compressed audio data reproduction 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]
1 ... Operating device
2 ... Display device
3 ... Amplification amplifier
4 ... Speaker
5. Disk drive unit
6 ... Pickup part
10 ... Main control section
11 ... Mechanism control unit
12 ... RF signal processor
13. Digital signal processing unit
14: Compressed audio decoder
15 ... Buffer memory
16 ... Mute circuit
51. Position detection mechanism
52. Installation completion detection mechanism
53 ... Motor for loading
54. Detection mechanism
55 ... Spindle motor
56 ... Spindle motor
61 ... Focus coil
62 ... Tracking coil
63 ... Laser diode
64 ... Photo detector
101 ... Reproduction control unit
102: Disc discriminator
103. Mute circuit control unit
131: Reference clock generator
132 ... RF signal decoder
133a, 133b ... switching circuit
134 ... D / A converter
141: Compressed data processing unit
142: Data decompression processing unit
143 ... Decoder operation clock input section
144: Multiplier circuit

Claims (2)

A digital signal processing unit that processes the input compressed audio data and CD audio data and outputs an analog audio signal; a decoder connected to the digital signal processing unit for decompressing the compressed audio data; In the compressed audio data reproducing apparatus , the reference clock output from the digital signal processing unit is input to the decoder of the compressed audio data, and the clock for the decoder operation is generated based on the reference clock .
The reference clock is a bit clock that is a synchronization 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 operating the decoder. And
The digital signal processing unit includes a switching circuit between compressed audio data and CD audio data, and a D / A converter that performs analog conversion of the processed digital audio signal,
When the data to be processed is CD audio data, the switching circuit directly outputs the data to the D / A converter. When the data to be processed is compressed audio data, the switching circuit outputs the data to the D / A converter via the decoder. In addition, a compressed audio data reproducing apparatus , wherein a bit clock in the compressed audio data is input to a multiplication circuit . 2. The compressed audio according to claim 1, wherein a mute circuit is provided on the analog audio signal output side of the digital signal processing unit to cut off the output of the analog audio signal when the decoder of the compressed audio data rises. Data playback device.

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