Abstract:
An information reproducing apparatus which reads compressed information recorded on a recording medium by one of a plurality of different compression methods, writes the compressed information read into a memory, supplies the compressed information in the memory, to an expander in the order of writing and outputs reproduced information. The type of compression method used in compressing the information read from the recording medium is determined and the timing of starting to read the compressed information from the memory is controlled in accordance with a determination.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an information reproducing apparatus which decompresses compressed information that is recorded on a recording medium and outputs the decompressed information as reproduction information. 
   2. Description of the Related Background Art 
   An MD (Mini Disc) player, which is one type of information reproducing apparatus, has a DRAM (dynamic random access memory) in order to ensure satisfactory vibration resistance while being carried by a walking user or when used on a moving vehicle. The DRAM temporarily stores compressed information which has been read from an MD by a pickup, while the compressed information that has been stored is read and then is decompressed by a decoder, before being output as reproduction information. It is possible to reproduce by decompressing the compressed information in the DRAM while data including a misread error is read again, even when a read error is caused by vibration. Therefore, a problem of intermittent sound, so called skipping, can be prevented from occurring. 
   In playback of the MD, when compressed information is stored in the DRAM up to the storage capacity thereof, reading operation of the pickup is stopped. When the amount of compressed information stored in the DRAM decreases to a storage amount requiring replenishment, the pickup resumes the reading operation thereby storing the compressed information that has been read into the DRAM. 
   However, in the case when starting the playback of the MD, reproduced information is not immediately output from the MD player even when a command to start playback is issued. When compressed information of a predetermined storage amount required for start of reproduction is stored in the DRAM, the MD player starts outputting the reproduced information. In order to quickly output the reproduced information when the command to start playback of the MD is issued, although reducing the storage amount required for start of reproduction of the DRAM is considered, there is a possibility of impairing the vibration resistance. 
   SUMMARY OF THE INVENTION 
   An object of the present invention is to provide an information reproducing apparatus which is capable of starting the output of reproduced information quickly after starting the playback operation of a recording medium without impairing the vibration resistance. 
   The information reproducing apparatus of the present invention includes an expander for expanding compressed information recorded on a recording medium by one of a plurality of different compression methods, and outputs reproduced information based on the expanded information, the apparatus comprising: a reading device for reading compressed information recorded on the recording medium; a memory controller for writing the compressed information read by the reading device into a memory, reading the compressed information written in the memory in the order of writing and supplying the read information to the expander; and a judging device for determining which of the plurality of compression methods is used in compressing the information read by the reading device, wherein the memory controller controls the timing of starting to read the compressed information from the memory in accordance with a determination by the judging device. 
   The information reproducing apparatus of the present invention includes an expander for expanding compressed information recorded on a recording medium by one of a plurality of different compression methods, and outputs reproduced information based on the expanded information, the apparatus comprising: a reading device for reading compressed information recorded on the recording medium; a memory controller for writing the compressed information read by the reading device in a memory, reading the compressed information written in the memory in the order of writing and supplying the compressed information to the expander; a judging device for determining which of the plurality of compression methods is used in compressing the information read by the reading device; and a reading controller for controlling a reading time of the reading device in accordance with a determination of the judging device. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a block diagram showing an embodiment of the present invention. 
       FIG. 2  is a flow chart showing the operation of a player controller. 
       FIG. 3A  through  FIG. 3C  show variations in the amount of stored data RSD in playback of an MD. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   A preferred embodiment of the present invention will be described in detail below with reference to the accompanying drawings. 
   In an MD (Mini Disc) player, shown in  FIG. 1 , which is an information reproducing apparatus of one embodiment of the present invention, an MD (Mini Disc)  1  is driven to rotate by a spindle motor  2 . As the disc  1  is rotated, information recorded on the disc  1  is optically read by a pickup  3 . The pickup  3  is supported by a carriage (not shown) which is moved by a carriage motor  4  in the radial direction of the disc  1 , so that an information read point (information reading light spot) of the pickup  3  is positioned while being freely moved along the radial direction of the disc  1 . Also servo control systems are provided including a spindle servo system, a focusing servo system, a tracking servo system and a carriage servo system. 
   The spindle motor  2  and the carriage motor  4  are controlled by a servo control circuit  5  located in the spindle servo system and the carriage servo system. The servo control circuit  5  controls the spindle motor  2  and the carriage motor  4 , and carries out servo control such as on-off control of the servo systems as mentioned above and jump control of the information read point under the command from the player controller  16 . An RF (Radio Frequency) signal which is a read signal output from the pickup  3  is amplified by an RF amplifier  8  and then is supplied to an EFM (Eight to Fourteen Modulation) decoder  9 . The EFM decoder  9  applies error correction of the CIRC (Cross Interleave Reed-Solomon Code) scheme to data of the read signal and carries out EFM demodulation. An output of the EFM decoder  9  is connected to a memory controller  10  that controls writing and reading of a memory  11  which is a DRAM. The memory controller  10  controls writing and reading of EFM-demodulated data to and from the memory  11  when the MD  1  is played. Data read by the memory controller  10  is deleted from the memory  11 . Connected to the memory controller  10  via a selection switch  12  are two audio compression decoders  13 ,  14 . Data read by the memory controller  10  is supplied to either one of the audio compression decoders  13 ,  14  selected by the selection switch  12 . The audio compression decoder  13  demodulates a digital audio signal that has been compressed and recorded by means of audio compression technology of the ATRAC (Adaptive Transform Acoustic Coding) method. The audio compression decoder  14  demodulates digital audio signal that has been compressed and recorded by the audio compression technology of the ATRAC3 method that has a higher compression rate than the ATRAC method. The audio compression technology of the ATRAC3 method has two modes of compression rate, double compression and quadruple compression. The audio compression decoder  14  corresponds to the both modes of compression rate while switching the compression rate in accordance with a command from the player controller  16 , which operates as a judging device. The digital audio signal provided by the audio compression decoder  13  or  14  is converted into an analog audio signal by a D/A (digital to analog) converter  15 . 
   The EFM decoder  9 , the memory controller  10 , the selection switch  12  and the audio compression decoder  14  are controlled by the player controller  16 . The player controller  16  also controls the MD player under an operation command from a control portion  17 . The player controller  16  is constituted by, for example, a micro computer. 
   In the MD player having the constitution as described above, the player controller  16  starts playback operation when a playback command is issued by a user operation on the control portion  17 . 
   In the playback operation, the player controller  16  first moves the information read point of the pickup  3  into a TOC (Table of Contents) area on the MD  1  to read TOC information from the TOC area (step S 1 ) and determines TRK — MODE of a music piece to be read (step S 2 ), as shown in  FIG. 2 . The TOC information includes an item called TRK — MODE which contains information for each track (music piece) of the MD. In the case of information recorded by the ATRAC method, TRK — MODE indicates whether the audio signal recorded is stereo or monaural. In the case of information recorded by the ATRAC3 method, TRK — MODE indicates whether the recorded information is compressed by the double compression or the quadruple compression. Accordingly, by using the information of TRK — MODE, it can be determined whether the information is recorded by the ATRAC method or by the ATRAC3 method. Further in the case of information recorded by the ATRAC3 method, it can be determined whether the recorded information is compressed by the double compression or the quadruple compression. 
   When a result of the determination in step S 2  shows that the information is recorded by the ATRAC method, a storage data amount TH 1  for start of outputting a reproduced signal from the MD player is set to DS 1  (step S 3 ). When the result of the determination in step S 2  shows that the information is recorded by the ATRAC3 method with the double compression, the storage data amount TH 1  is set to DS 2  (step S 4 ). When the result of the determination in step S 2  shows that the information is recorded by the ATRAC3 method with the quadruple compression, the storage data amount TH 1  is set to DS 3  (step S 5 ). The storage data amounts DS 1 , DS 2  and DS 3  are related as DS 1 &gt;DS 2 &gt;DS 3 . A time required in the case of decoding audio signal of the amount DS 1  which is compressed by the ATRAC method, a time required in the case of decoding audio signal of the amount DS 2  which is compressed by the ATRAC3 method with the double compression, and a time required in the case of decoding audio signal of the amount DS 3  which is compressed by the ATRAC3 method with the quadruple compression are substantially the same. 
   After the storage data amount TH 1  for the start of outputting a reproduced signal from the MD player has been set as described above, data of a music piece to be played back are read from the MD  1  and a command to store the read data in the memory  11  is issued to the memory controller  10  (step S 6 ). The data of a music piece to be played back are read by the pickup  3  as an RF signal which is amplified by the RF amplifier  8  and then is supplied to the EFM decoder  9 . The RF signal is EFM-demodulated by the EFM decoder  9 , and the demodulated signal is digital data that includes audio, control and other information. The control information such as a sub code is supplied to the player controller  16 . The player controller  16  controls the servo control circuit  5  in accordance with the control information. The audio information output from the EFM decoder  9 , namely a compressed audio signal is written in the memory  11  by the memory controller  10 . 
   The player controller  16 , after the execution of step S 6 , determines whether the amount of data RSD actually stored in the memory  11  has reached the storage data amount TH 1  or not (step S 7 ). The amount of data RSD actually stored in the memory  11  is determined by a counting operation in the memory controller  10 . Specifically, the memory controller  10  up-counts by writing the data to the memory  11  and down-counts by reading the data from the memory  11 . The amount of stored data RSD which has been determined is sent from the memory controller  10  to the player controller  16 . When the amount of stored data RSD has increased and reached the storage data amount TH 1 , the player controller  16  commands a start operation to output of a reproduced signal (step S 8 ). The command is issued to the memory controller  10  and the selection switch  12 . The command is generated in response to the result of the determination in step S 2 , and controls the switching of the selection switch  12 . In the case where the result of the determination in step S 2  shows that the information is recorded by the ATRAC3 method, the player controller  16  controls the rate of decomposition by the ATRAC3 audio compression decoder  14 . 
   In the case of information recorded by the ATRAC method, the compressed audio signal which has been read from the memory  11  is sent from the memory controller  10  through the selection switch  12  to the ATRAC audio compression decoder  13  which demodulates the digital audio signal that is compressed and recorded by the ATRAC method. Then, the demodulated digital audio signal is converted into an analog reproduced audio signal by the D/A converter  15 . 
   In the case of information compressed by the double compression or the quadruple compression and recorded by the ATRAC3 method, the compressed audio signal which has been read from the memory  11  is sent from the memory controller  10  through the selection switch  12  to the ATRAC3 audio compression decoder  14  which demodulates the digital audio signal that is compressed by the double compression or the quadruple compression of the ATRAC3 method. Then, the demodulated digital audio signal is converted into analog reproduced audio signal by the D/A converter  15 . 
   The player controller  16 , after starting the output of the reproduced signal, determines whether the amount of data RSD actually stored in the memory  11  has reached a full storage data amount THfull or not (step S 9 ). The full storage data amount THfull is the maximum amount of data which can be stored in the memory  11 . When the amount of stored data RSD has reached the full storage data amount THfull, the player controller  16  commands the memory controller  10  to stop writing of data (step S 10 ), and commands the servo control circuit  5  to enter a pause state and to turn off the servo systems (step S 11 ). Accordingly, writing of data to the memory  11  is stopped, driving of the pickup  3  by the servo control circuit  5  is stopped, and operations of the focusing servo system, the tracking servo system and the carriage servo system are stopped. 
   The player controller  16 , after the execution of step S 11 , determines TRK — MODE of the music piece of which data has been stored in the memory  11  (step S 12 ). This is similar to the determination in step S 2 . 
   When a result of the determination in step S 12  shows that the information is recorded by the ATRAC method, the storage data amount TH 2  for resumption of storing data into the memory  11  is set to DR 1  (step S 13 ). When the result of the determination in step S 12  shows that the information is recorded by the ATRAC3 method with the double compression, the storage data amount TH 2  is set to DR 2  (step S 14 ). When the result of the determination in step S 12  shows that the information is recorded by the ATRAC3 method with the quadruple compression, the storage data amount TH 2  is set to DR 3  (step S 15 ). 
   After setting the storage data amount TH 2  for the resumption of storing data into the memory  11  as described above, it is determined whether the amount of stored data RSD in the memory  11  has reached the storage data amount TH 2  for the resumption of storage (step S 16 ). When the amount of stored data RSD that is stored has decreased to the storage data amount TH 2 , the player controller  16  commands the servo control circuit  5  to cancel the pause state and to turn on the servo systems (step S 17 ), and commands the memory controller  10  to restart writing of data (step S 18 ). Accordingly driving of the pickup  3  is resumed by the servo control circuit  5 , and operations of the focusing servo system, the tracking servo system and the carriage servo system are resumed. Thus similarly to the case of step S 6 , data of the music piece to be played back is read from the pickup  3  as the RF signal, and the RF signal is sent through the RF amplifier  8  and the EFM decoder  9  to the memory controller  10  as compressed audio signal, while writing of the compressed audio signal in the memory  11  by the memory controller  10  is restarted. 
   After the execution of step S 18 , the control returns to step S 9 , so that the operations described above are repeated. 
     FIG. 3A  through  FIG. 3C  show variations in the amount of stored data RSD during playback of the MD  1  in the MD player described above.  FIG. 3A  shows the case where the compressed audio signal of the music piece to be played back is recorded by the ATRAC method,  FIG. 3B  shows the case where the compressed audio signal of the music piece to be played back is recorded by the ATRAC3 method with the double compression, and  FIG. 3C  shows the case where the compressed audio signal of the music piece to be played back is recorded by the ATRAC3 method with the quadruple compression. 
   As shown in  FIG. 3A  through  FIG. 3C , when a playback command is produced at the control portion  17 , data of the music piece to be played back is read from the MD  1 , and the data which has been read is stored in the memory  11 . After the playback command is issued, the amount of stored data RSD in the memory  11  gradually increases. When the amount of stored data RSD in the memory  11  reaches the storage data amount TH 1  for the start of outputting a reproduced signal, the compressed audio signal is read from the memory  11  in step S 8  and is sent through the audio compression decoder  13  or  14  and the D/A converter  15  so that an analog reproduced audio signal is output. The storage data amount TH 1  is set to one of DS 1  through DS 3  of which amounts are related as DS 1 &gt;DS 2 &gt;DS 3 . In the case the compressed audio signal of the music piece to be played back is recorded by the ATRAC method, the amount of data RSD that is stored in the memory  11  reaches the amount DS 1 , the largest among DS 1  through DS 3 , as shown in  FIG. 3A . In the case where the compressed audio signal of the music piece to be played back is recorded by the ATRAC3 method with the double compression, the amount of stored data RSD in the memory  11  reaches the amount DS 2  which is the intermediate level among DS 1  through DS 3  as shown in  FIG. 3B . In the case where the compressed audio signal of the music piece to be played back is recorded by the ATRAC3 method with the quadruple compression, the amount of stored data RSD in the memory  11  reaches the amount DS 3 , the lowest level among DS 1  through DS 3 , as shown in  FIG. 3C . Thus, the analog reproduced audio signal is early output in the order of information recorded by the ATRAC3 method with the quadruple compression, information recorded by the ATRAC3 method with the double compression and information recorded by the ATRAC method. 
   After that, when the amount of stored data RSD in the memory  11  has increased further to reach the full storage data amount THfull, the writing into the memory  11  is stopped and the reading from the MD  1  becomes in a pause state. Accordingly, the amount of stored data RSD gradually decreases after reaching the full storage data amount THfull. 
   When the amount of stored data RSD in the memory  11  has decreased to the storage data amount TH 2  for the resumption of storage, the pause state is canceled to resume reading of the data of music piece to be played back from the MD  1 , and the data that has been read is stored in the memory  11 . The storage data amount TH 2  for the resumption of storage is set to one of DR 1  through DR 3  of which amounts are related as DR 1 &gt;DR 2 &gt;DR 3 . In the case where the compressed audio signal of the music piece to be played back is recorded by the ATRAC method, the amount of stored data RSD in the memory  11  reaches the amount DR 1 , the largest among DR 1  through DR 3 , as shown in  FIG. 3A . In the case where the compressed audio signal of the music piece to be played back is recorded by the ATRAC3 method with the double compression, the amount of stored data RSD in the memory  11  reaches the amount DR 2 , the intermediate level among DR 1  through DR 3 , as shown in  FIG. 3B . In the case where the compressed audio signal of the music piece to be played back is recorded by the ATRAC3 method with the quadruple compression, the amount of stored data RSD in the memory  11  reaches the amount DR 3 , the lowest level among DR 1  through DR 3 , as shown in  FIG. 3C . Thus, the operation to store the read data in the memory  11  is early restarted in the order of the information recorded by the ATRAC method, the information recorded by the ATRAC3 method with the double compression, and the information recorded by the ATRAC3 method with the quadruple compression. In other words, an interrupt period of storing data in the memory  11  is the longest with the information recorded by the ATRAC3 method with the quadruple compression, followed by the information recorded by the ATRAC3 method with the double compression, then the information recorded by the ATRAC method. 
   During the subsequent playback of the MD  1 , the storage of data to the memory  11  and the interruption of the storage are repeated as described above. 
   Since the reading operation by the pickup  3  can be put in a longer pause in the case of recorded information that has been compressed by a higher compression rate, as described above, energy consumption can be reduced. The pickup  3  can also be used in reading the information recorded on other part of the MD  1  during the pause of the reading operation of the pickup  3 , namely during the pause of storing data in the memory  11 . 
   The embodiment described above is an example of using the MD as a recording medium, although the present invention is not limited to the above constitution and can be applied to any reproducing apparatus that plays back a recording medium having compressed information recorded thereon. 
   In the embodiment described above, compressed information of all music pieces is recorded by the same compression method on an MD. However, the present invention can also be applied to the case where the compressed information of all music pieces is recorded on the MD not by the same compression method but using a plurality of compression methods. For example, in the case where the first music piece is recorded by the ATRAC method, the second music piece is recorded by the ATRAC3 method with the quadruple compression and the third music piece is recorded by the ATRAC method, the storage data amounts TH 1  and TH 2  are set as TH 1 =DS 1  and TH 2 =DR 1  for the first piece, TH 1 =DS 3  and TH 2 =DR 3  for the second piece and TH 1 =DS 1  and TH 2 =DR 1  for the third piece. While TH 1  and TH 2  are determined in accordance with the compression method for each music piece with the setting, TH 1  and TH 2  may also be determined in accordance with the compression method employed for the preceding and subsequent pieces. That is, when the duration of the second piece is shorter than the first and third pieces in the example described above, setting of TH 1 =DS 1  and TH 2 =DR 1  may be employed not only for the first and third pieces but also for the second piece. 
   The information reproducing apparatus of the present invention is, as described above, capable of starting the output of reproduced information quickly after starting the playback of a recording medium without impairing the vibration resistance.