Abstract:
Audio-centered information is stored on a unitary medium by using a Table-of-Contents (TOC) mechanism that specifies an actual configuration of various audio items on the medium. In particular, each one of a set of one or more Track Areas gets at least two mutually logically conforming Sub-TOCs assigned. This allows to retrieve any constituent Sub-TOC part from at least any correct copy of the Sub-TOCs. Furthermore, one or more Master-TOCs are provided for specifically pointing to each of the Sub-TOCs.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The invention relates to a method as recited in the preamble of claim 1. Storing digital audio on unitary media such as disc or tape is widespread. In case of actual sub-division of the audio into multiple sub-items, providing a Table-of-Contents (TOC) allows to access the information in an easy manner. Such TOC will specify at least what has been stored and where it has been stored. The audio may be defined according to various standardized audio formats, such as two-channel stereo, multiple (5-6) channel audio such as in surround sound applications, and possibly others. An audio provider may wish to combine various track areas having the same and/or different such formats on a single medium such as an optical disc.  
         SUMMARY TO THE INVENTION  
         [0002]    In consequence, amongst other things, it is an object of the present invention to allow an audio management system to allow a user to access various audio track areas in a fast and easy manner. Now Therefore, according to one of its aspects the invention is characterized according to the characterizing part of claim 1. A user is now able to distinguish between various track areas and to navigate among the various items of a single track area in a robust manner, and if possible, without encumbrance through data users in the TOC itself.  
           [0003]    The invention also relates to a unitary storage medium produced by the method, to a storing device arranged for practising such method, and to a reader or player device arranged for interfacing to such storage medium. A particular audio medium instance could be restricted to storing only stereo, so that the multi-channel version would effectively be a dummy. For reasons of standardizing, the multilevel TOC mechanism will then also be adopted. Further advantageous aspects of the invention are recited in dependent claims.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0004]    These and further aspects and advantages of the invention will be discussed more in detail hereinafter with reference to the disclosure of preferred embodiments, and in particular with reference to the appended Figures that show:  
         [0005]    [0005]FIGS. 1 a,    1   b  a record carrier,  
         [0006]    [0006]FIG. 2 a playback device,  
         [0007]    [0007]FIG. 3 a recording device,  
         [0008]    [0008]FIG. 4 a file system for use with the invention;  
         [0009]    [0009]FIG. 5 a storage arrangement for the invention;  
         [0010]    [0010]FIG. 6 a structure of an audio area. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0011]    [0011]FIG. 1 a  shows a disc-shaped record carrier  11  with track  19  and central hole  10 . Track  19  has a spiral pattern of turns forming substantially parallel tracks on an information layer. The carrier may be an optical disc with a recordable or prerecorded information layer. CD-R, CD-RW and DVD-RAM are recordable discs. Audio CD is a prerecorded disc. Prerecorded discs may be manufactured by first recording a master disc and then pressing consumer discs. Track  19  on a recordable record carrier may be formed by a preembossed track structure. The track may be configured as pregroove  14  to allow a read/write head to follow the track  19  during scanning. The information is recorded on the information layer by optically detectable marks along the track, e.g. pits and lands.  
         [0012]    [0012]FIG. 1 b  is a cross-section along the line b-b of a recordable record carrier  11 , wherein transparent substrate  15  caries recording layer  16  and protective layer  17 . Pregroove  14  may be implemented as an indentation, an elevation, or as a material property deviating from its surroundings.  
         [0013]    For user convenience, the audio information on the record carrier is subdivided into items, which may have a duration of a few minutes e.g. songs in an album or movements of a symphony. The carrier will also contain access information to identify the items, such as a Table Of Contents (TOC) or a file system like ISO 9660 for CD-ROM. The access information may include playing time and start address for each item, and further information like a song title.  
         [0014]    The audio information is recorded in digital representation after analog to digital (A/D) conversion. Examples of A/D conversion are PCM 16-bit per sample at 44.1 kdz known from CD audio and 1 bit Sigma Delta modulation at a high oversampling rate e.g. 64×Fs called Bitstream. The latter is a high quality encoding method, allowing either high quality decoding or low quality decoding. Reference is had to the publications ‘A digital decimating filter for analog-to-digital conversion of hi-fi audio signals’, by J. J. van der Kam, document D5 infra, and ‘A higher order topology for interpolative modulators for oversampling A/D converters’, by Kirk C. H. Chao et al, document D6. After A/D conversion, digital audio may be compressed to variable bitrate audio data for recording on the information layer. The compressed audio data is read from the carrier at such speed that after decompression substantially the original timescale will be restored when continuously reproducing the audio. Hence the compressed data must be retrieved from the record carter at a speed dependent on the varying bitrate. The data is retrieved at so-called transfer speed, i e. the speed of transferring data bytes from the record carrier to a decompressor. Providing the record carrier with constant spatial data density gives the highest data storage capacity per unit of area. The transfer speed is proportional to the relative linear speed between the medium and the read/write head. With buffer before the de-compressor, actual transfer speed is the speed before that buffer.  
         [0015]    [0015]FIG. 2 shows a playback apparatus according to the invention for reading a record carrier  11  of the type shown in FIG. 1. The device has drive means  21  for rotating carrier  11  and read head  22  for scanning the record track, Positioning means effect  25  coarse radial positioning of read head  22 . The read head comprises a known optical system with a radiation source for generating beam  24  that is guided through optical elements and focused to spot  23  on an information track. The read head further comprises a focusing actuator for moving the focus of the radiation  24  along the optical axis of the beam and a tracking actuator for fine positioning of spot  23  in a radial direction on the centre of the track. The tracking actuator may comprise coils for moving an optical element or may be arranged for changing the angle of a reflecting element. The radiation reflected by the information layer is detected by a known detector in the read head  22 , e.g. a four-quadrant diode, to generate a read signal and further detector signals including tracking error and focusing error signals for the tracking and focusing actuators, respectively. The read signal is processed by standard reading means  27  to retrieve the data, for example through a channel decoder and an error corrector. The retrieved data is sent to data selection means  28 , to select the compressed audio data for feeding to buffer  29 , The selection is based on data type indicators also present on the carrier, e.g. headers in a framed format. From buffer  29 , the compressed audio data go to de-compressor  31  as signal  30 . Decompressor  31  decodes the compressed audio data to reproduce the original audio information on output  32 . The de-compressor may be fitted in a stand-alone audio D/A convertor  33 , or the buffer may be positioned before the data selection. Buffer  29  may reside separately or may be combined with a buffer in the decompressor. The device furthermore has a control unit  20  for receiving control commands from a user or from a host computer not shown, that via control lines  26  is connected to drive means  21 , positioning means  25 , reading means  27  and data selection means  28 , and possibly also to buffer  29  for filling level control. To tis end, the control unit  20  may comprise digital control circuitry, for performing the procedures described below.  
         [0016]    The art of audio compression and decompression is known. Audio may be compressed after digitizing by analyzing the correlation in the signal. and producing parameters for fragments of a specified size. During de-compression the inverse process reconstructs the original signal. If the original digitized signal is reconstructed exactly, the (de-)compression is lossless. Lossy (de) -compression will not reproduce some details of the original signal which will be substantially undetectable by the human ear or eye, Most known systems for audio and video, such as or MPEG, use lossy compression, whereas lossless compression is used for computer data. Examples of audio compression and decompression are given in D2, D3 and D4 hereinafter,  
         [0017]    Data selection means  28  will retrieve from the read data certain control information, in particular indicating the transfer speed profile. The data selection means  28  will also discard any stuffing data, that had been added during recording according to the speed profile. When the control unit  20  is commanded to reproduce an audio item from the record carrier, positioning means  25  will position the reading head on the portion of the track containing the TOC. The starting address and the speed profile for that item will then be retrieved from the TOC via the data selection means  28 . Alternatively, the contents of the TOC may be read only once and stored in a memory when the disc is inserted in the apparatus. For reproducing an item, drive means  21  will rotate the record carrier at the speed indicated by the speed profile. The required rotation rate may be given as such in the speed profile for setting the drive means, Alternatively the speed profile may comprise a bitrate, and then the rotation rate can be calculated as follows. The radial position of the item can be calculated from the starting address, because the record carrier density parameters like track pitch and bit length, will be known to the playback device, usually from a standard. Subsequently the rotation rate can be derived from the bitrate and the radial position. To provide continuous reproduction without buffer underflow or overflow the transfer speed is coupled to the reproduction speed of the D/A converter, i.e. to the bit-rate after decompression. Thereto the apparatus may comprise a reference frequency source for controlling the decompressor and the rotation rate may be set in dependence on the reference frequency and the speed profile, The rotation rate may also be adjusted by the average filling level of the buffer  29 , e.g. lowering rotation rate when the buffer is more than 50% full on average.  
         [0018]    [0018]FIG. 3 shows a recording device for writing information on a (re)writable record carrier  11 . During a writing operation, marks representing the information are formed on the record carrier. The marks may be in optically readable form, e.g. as areas whose reflection differs from their surroundings, by recording in materials such as dye, alloy or phase change, or in the form of areas with a direct of magnetization different from their surroundings. Writing and reading of information for recording on optical disks and usable rules for formatting, error correcting and channel coding, are well-known, e.g. from the CD system. Marks may be formed through a spot  23  generated on the recording layer via a beam  24  of electromagnetic radiation, usually from a laser diode. The recording device comprises similar basic elements as described with reference to FIG. 2, i.e. a control unit  20 , drive means  21  and positioning means  25 , but it has a distinctive write head  39 . Audio information is presented on the input of compression means  35 . Suitable compression has been described in D2, D3 and D4. The variable bitrate compressed audio on the output of compression means  35  is sent to buffer  36 . From buffer  36  the data is sent to data combination means  37  for adding stuffing data and further control data. The total data stream is sent to writing means  38  for recording. Write head  39  is coupled to the writing means  38 , which comprise for example a formatter, an error encoder and a channel modulator. The data presented to the input of writing means  38  is distributed over logical and physical sectors according to formatting and encoding rules and converted into a write signal for write head  39 . Unit  20  controls buffer  36 , data combination means  37  and writing means  38  via control lines  26  and perform the positioning procedure as described above for the reading apparatus. The recording apparatus may also have the features of a playback apparatus and a combined write/read head.  
         [0019]    [0019]FIG. 4 shows a file system for use with the invention, for which various different options are feasible. The inventors have proposed that the storage medium should be based on a UDF file system or on an ISO 9660 file system, both of which systems are standard to a skilled art person. In the alternative case, no file system should be present at all and the relevant sector spaces should be kept empty.  
         [0020]    In the file system, all audio will be stored in Audio Files located in SubDirectory SCD_AUDIO. As shown in FIG. 4, the hierarchy is based on ROOT file  50  that points to various subaltern files  52 ,  54 ,  56 . The structure of MASTER.TOC  52 , here single, will be discussed hereinafter. Further, there is a 2_CH_AUDIO file  54 , This points to TOC 2_CH_TOC  58  and also to the various stereo tracks TRACKn.2CH  60 , Furthermore, M_CH_AUDIO file  56  points to TOC M_CH_TOC  62  and in parallel therewith to the various multi-channel tracks TRACKn.MCH  64 .  
         [0021]    [0021]FIG. 5 shows a first storage arrangement for use with the invention, which by way of example has been mapped on a single serial track. Along the horizontal axis the following items are evident. Item  120  is a Lead-in area that is used for mutually synchronizing the reader and the driving of de medium. Item  122  represents the File System disclosed with reference to FIG. 4. Item  124  represents a MASTER_TOC that may be configured according to standard procedures and pertains to subsequent items Stereo AREA  126  and Multi-channel AREA  128 , and if necessary also to Extra Data AREA  130 . The lengths of these three areas need not be standardized, inasmuch as various different amounts of information may be present. With respect to the audio areas, the audio track areas proper, as well as the associated SUB 13 TOCs are included. Apart from the disclosure hereinafter, the contents of items  126 ,  128 ,  130  may be defined according to conventional standards that by themselves do not constitute part of the invention. Generally, the two audio areas may have the same structure and contain the same kinds of information, apart from distinguishing between the various channels. The audio may be plan coded or loss-less coded. All kinds of audio may be multiplexed with supplementary data, such as Compact Disc Text.  
         [0022]    Item  132  represents a Lead-Out Information. The latter item is used in particular during search operations. Its tracks do not contain information further than track numbers and addresses. The number of lead-out tracks may cover a ring of some 0.5 to 1 millimeter wide. According to the above, the stored information may either be accessed via the file system as laid down in item  122 , or via the TOC structure laid down in item  124 , and more particular, via a two- or multi-level TOC structure to be discussed hereinafter.  
         [0023]    Any of the single or plural Master TOCs  124  will begin at a respective uniformly standardized offset position from the start of the Lead-in area, such as at byte number  500  for the first Master TOC. In the embodiment a Master-TOC measures only one standard-size sector and primarily contains pointers to the various Sub-TOCs or Area-TOCs to be disclosed hereinafter. A preferred syntax of a Master-TOC is as follows:  
         [0024]    1. A 16-byte Signature identifies the Master-TOC, such as by “SACD Master TOC”, the signature containing three space characters, but the apostrophes not being part of the definition.  
         [0025]    2. A 2-byte Spec_version indicates the version number of the format used in the disc.  
         [0026]    3. A 14-byte Space has been reserved, such as for alignment staffing,  
         [0027]    4.A 4-byte integer 2CH-start_address contains the logical address of the first sector of the , stereo area.  
         [0028]    5. A 4-byte integer 2CH-end_address contains the logical address of the last sector of the stereo are&amp;  
         [0029]    6. A 4-byte integer MC-start_address contains the logical address of the first sector of the Multi channel area  
         [0030]    7. A 4-byte integer MC-end_address contains the logical address of the last sector of the Multi channel area.  
         [0031]    8. A 4-byte integer Extra_data_start_address contains the logical address of the first sector of the Extra Data area.  
         [0032]    9. A 4-byte integer Extra_data_end_address contains the logical address of te last sector of the Extra Data area.  
         [0033]    The total information pertaining to the above is  56  bytes. Further features may be added to a Master-TOC. If a certain area, such as the stereo area, the Multi channel area, or the Extra Data area is not present, both start and end addresses of the area in question have value zero.  
         [0034]    Next, items  126  and  128  will contain Sub-TOCS or Area-Tocs for the Stereo and Multi-Channel Audio intervals, respectively, formatted as will be disclosed hereinafter with respect to FIG. 6. A preferred syntax of a Sub-TOC is as follows:  
         [0035]    1. A 16-byte Signature identifies the Sub-TOC in question such as by “SACD stereo TOC” for a stereo audio area and “SACD MC TOC” for a Multi Channel audio area, the number of bytes being attained by adding trailing space characters  
         [0036]    2. A 2-byte Spec_version indicates the version number of the format used in the disc.  
         [0037]    3. A 4-byte Sub_TOC_length indicates the number of bytes present in the actual TOC.  
         [0038]    4. A 10-byte Space has been reserved, such as for alignment stuffing.  
         [0039]    5. A variable size set of /* Disc Parameters */ may be present, such as a Name of an Album( ) and a Name of a Catalogue( ).  
         [0040]    6. A 4-byte disc_play_time indicates the total linear playing time of the disc expressed as a time code.  
         [0041]    7. A 4-byte disc_name_pointer indicates the offset in bytes from the start of the Sub_TOC in question to the start of the disc_name( ) field. If the value in question is 0, this indicates that the disc_name( ) field is absent.  
         [0042]    8. A 4-byte disc_date_pointer indicates the offset in bytes from the start of the Sub_TOC in question to the start of the disc_date( ) field. If the value in question is 0, this indicates that the disc_date( ) field is absent.  
         [0043]    9. A 4-byte disc_copyright_pointer indicates the offset in bytes from the start of the Sub_TOC in question to the start of the disc_copyright( ) field. If the value in question is 0, this indicates that the disc-copyright( ) field is absent.  
         [0044]    10. A 4-byte disc_publisher_pointer indicates the offset in bytes from the start of the Sub_TOC in question to the start of the disc_publisher( ) field. If the value in question is 0, this indicates that the disc_publisher( ) field is absent.  
         [0045]    11. A variable size Track_List( ) may be present for each one of a plurality of audio tracks to contain an offset information with reference to the start of the TOC in question, plus various further items, such as the name of track and any of a great multiplicity of items that are presumably interesting to a listener of the recording in question.  
         [0046]    [0046]FIG. 6 shows an exemplary structure of an audio area  126 ,  128  in FIG. 5. Here, the track area is preceded by Area or Sub-TOC- 1  and succeeded by Area TOC- 2 . These are two identical copies. Another manner of logical conformance may be produced by bit-wise inversion. Anyway, each copy taken separately must contain all information contained in the two TOCs. The locations thereof are for each separate Area TOC given in a higher level Master TOC. A gap between the Track Area and succeeding Area TOC- 2  is not allowed, On the other hand, a gap between preceding Area TOC- 1  and the Track Area is allowed, symbolized by area G, Such gap will generally not contain significant information, in particular, no other TOC or track. Therefore, logically the tack area will abut at both ends to the TOCS. Due to the doubling of the Area TOCs and their mutual distance, any interference therewith through environmental or other influences will usually not be doubled for the two copies. In consequence, the probability for correct storage of all parts of the Area TOO in at least one of the two versions thereof will be practically guaranteed, even without the providing of internal redundancy. Error correcting through such redundancy would often cost an unjustified delay. In fact, if the preceding TOC is correct, the starting of a track may be effected virtually immediately.  
         [0047]    List of related documents:  
         [0048]    (D1) Research Disclosure number 36411, August 1994, p. 412-413  
         [0049]    (D2) PCT/IB97/01156 (PHN 16.452) 1 bit ADC and lossless compression of audio.  
         [0050]    (D3) PCT/IB97/01303 (PHN 16.405), Audio compressor.  
         [0051]    (D4) EP-A 402,973 (PHN 13.241), Audio compression.  
         [0052]    (D5) ‘A digital decimating filter for analog-to-digital conversion of hi-fi audio signals’ by J. J. van der Kam in Philips Techn. Rev. 42, no, 67, April 1986, pp. 230-8.  
         [0053]    (D6) ‘A higher order topology for interpolative modulators for oversampling A/D converters’, by Kirk C. H. Chao et al in IEEE Trans. on Circuits and Systems, Vol 37, no. 3, March 1990, pp. 309-18.