Abstract:
Audio information is stored on a unitary storage medium with a Table-of-Contents (TOC) mechanism for therein specifying an actual configuration of various audio items on the medium. In particular, one or more Sub-TOCs are each assigned to a respective different audio format. A single Master-TOC is provided for specifically pointing to each Sub-TOC.

Description:
This is a continuation of prior application Ser. No. 09/341,910 filed Jul. 20, 1999 and is incorporated by reference herein. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to digital audio storage on unitary media such as disc or tape. 
     Use of such storage is at present widespread. In case of sub-division of the audio into multiple sub-items, a Table-of-Contents (TOC) allows access to the information in a relatively fast manner. Generally, a TOC specifies at least what has been stored and where it has been stored. However, audio storage is defined according to multiple standardized audio formats, such as two-channel stereo, multiple (5-6) channel audio such as for use in surround sound applications, and possibly others. An audio provider may wish to combine various different such formats on a single medium such as an optical disc, and as a consequence, a user would want to be able to access various audio items in a fast and easy manner. 
     Those skilled in the art are directed to the following references: 
     LIST OF RELATED DOCUMENTS 
     
         
         (D1) Research Disclosure number 36411, 
         August 1994, page 412-413 
         (D2) PCT/IB97/01156 (PHN 16.452) 
         1 bit ADC and lossless compression of audio 
         (D3) PCT/IB97/01303 (PHN 16.405) 
         Audio compressor 
         (D4) EP-A 402,973 (PHN 13.241) 
         Audio compression 
         (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. 6/7, April 1986, pp. 230-8 
         (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. 
       
    
     The above references are hereby incorporated in whole by reference. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to allow the audio management system to discriminate between the various formats, and to navigate among the various items of only a single format, so that it will not be necessary to change an actual decoder strategy. 
     The invention also relates to a unitary storage medium produced by the method, and to a reader or player arranged for interfacing with such storage medium. One or more of the audio formats could effectively be a dummy, but for reasons of standardizing, the multilevel TOC arrangement also needs to be changed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       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: 
         FIGS. 1   a ,  1   b  a record carrier, 
         FIG. 2  a playback device, 
         FIG. 3  a recording device, 
         FIG. 4 , a file system for use with the invention; 
         FIG. 5 , a first storage arrangement for the invention; 
         FIG. 6 , a second storage arrangement for the invention. 
         FIG. 7  shows Table 1 which specifies a Master_TOC Syntax; 
         FIG. 8  shows Table 2 which specifies a Master_TOC_O Syntax; 
         FIG. 9  shows Table 3 which specifies a Disc_Info Syntax. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1   a  shows a disc-shaped record carrier  11  with track  19  and central hole  10 . Track  19  is arranged in a spiral pattern of turns forming substantially parallel tracks on an information layer. The carrier may be an optical disc with a recordable or a prerecorded information layer. Examples of a recordable disc are CD-R, CD-RW, and DVD-RAM, whereas audio CD is a prerecorded disc. Prerecorded discs can be manufactured by first recording a master disc and later pressing consumer discs. Track  19  on the recordable record carrier is indicated by a providing a pre-embossed track structure during manufacture of the blank record carrier. The track may be configured as a pregroove  14  to enable 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. 
       FIG. 1   b  is a cross-section along the line b-b of a recordable record carrier  11 , wherein transparent substrate  15  carries recording layer  16  and protective layer  17 . The pregroove  14  may be implemented as an indentation, an elevation, or as a material property deviating from its surroundings. 
     For user convenience, the audio information on the record carrier has been subdivided into items, which usually have a duration of a few minutes e.g. songs on an album or movements of a symphony. Usually the record carrier also contains access information for identifying the items, such as in a so-called Table Of Contents (TOC), or included in a file system like ISO 9660 for CD-ROM. The access information may include playing time and start address for each item, and also further information like a song title. 
     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 kHz known from CD audio and 1 bit Sigma Delta modulation at a high oversampling rate e.g. 64×Fs called bitstream. The latter method represents a high quality encoding method, with a choice between high quality decoding and low quality decoding, the latter allowing a simpler decoding circuit. Reference is made in this respect to documents D5 and D6 infra. After A/D conversion, digital audio is compressed to variable bitrate audio data for recording on the information layer. The compressed audio data is read from the record carrier at such a speed, that after decompression substantially the original timescale will be restored when reproducing the audio information continuously. Hence the compressed data must be retrieved from the record carrier at a speed dependent on the varying bitrate. The data is retrieved from the record carrier at so-called transfer speed, i.e. the speed of transferring data bytes from the record carrier to a de-compressor. The record carrier may have uniform spatial data density, which gives the highest data storage capacity per unit of area. In such system the transfer speed is proportional to the relative linear speed between the medium and the read/write head. If before the de-compressor a buffer has been provided, actual transfer speed is the speed before that buffer. 
       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 record carrier  11  and a read head  22  for scanning the record carrier 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 a beam  24  that is guided through optical elements and focused to spot  23  on an information layer 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 a tracking error and focusing error signals for the tracking and focusing actuators, respectively. The read signal is processed by a reading means  27  to retrieve the data, which reading means are of a usual type for example comprising a channel decoder and an error corrector. The retrieved data is passed to a data selection means  28 , to select the compressed audio data for passing on to buffer  29 . The selection is based on data type indicators also recorded on the record carrier, e.g. headers in a framed format. From buffer  29 , the compressed audio data are passed on to de-compressor  31  as signal  30 . This signal may also be outputted to an external de-compressor. De-compressor  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 high quality audio D/A convertor  33 . Alternatively, the buffer may be positioned before the data selections means. The buffer  29  may be positioned in a separate housing 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  such as a system bus is connected to drive means  21 , positioning means  25 , reading means  27  and data selection means  28 , and possibly also to buffer  29  for buffer filling level control. To this end, the control unit  20  may comprise control circuitry, such as a microprocessor, a program memory and control gates, for performing the procedures described below. Control unit  20  may be implemented as a logic circuit state machine. 
     The art of audio compression and de-compression 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, whereas lossy (de)-compression will not reproduce certain details of the original signal which however are substantially undetectable by the human ear or eye. Most known systems for audio and video, such as DCC or MPEG, use lossy compression, whereas lossless compression is used for storing computer data. Examples of audio compression and decompression can be found in D2, D3 and D4 hereinafter, of which in particular the lossless compression from D2 is suitable for high quality audio. 
     According to the invention, data selection means  28  are arranged to retrieve from the read data certain control information. The data selection means  28  are also arranged to discard any stuffing data, that had been added during recording. When the control unit  20  is commanded to reproduce an item of audio from the record carrier, the positioning means  25  are controlled to position the reading head on the portion of the track containing the TOC. The starting address 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 the item the drive means  21  are controlled to rotate the record carrier at an appropriate rotary velocity, to be derived from timing indications stored with the audio. The radial position of the item can be calculated as based on the starting address, because the record carrier density parameters like track pitch and bit length, are predetermined and 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 bitrate after decompression. To this end 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. Alternatively or additionally the rotation rate may be adjusted using the average filling level of buffer  29 , e.g. decreasing the rotation rate when the buffer is more than 50% full on average. 
       FIG. 3  shows a recording device according to the invention 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 any optically readable form, e.g. in the form of areas whose reflection coefficient differs from their surroundings, by recording in materials such as dye, alloy or phase change, or in the form of areas with a direction of magnetization different from their surroundings when recording in magneto-optical material. 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 , which may be placed in a separate housing. Suitable compression has been described in D2, D3 and D4. The variable bitrate compressed audio on the output of the compression means  35  is passed to buffer  36 . From buffer  36  the data is passed to data combination means  37  for adding stuffing data and further control data. The total data stream is passed 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 encoder. 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 the write head  39 . Unit  20  is arranged for controlling buffer  36 , data combination means  37  and writing means  38  via control lines  26  and for performing the positioning procedure as described above for the reading apparatus. Alternatively the recording apparatus may be arranged for reading having the features of the playback apparatus and a combined write/read head. 
       FIG. 4  shows a file system for use with the invention, for which various different options are feasible. As main choices the inventors have proposed that the storage medium should be based on either the UDF file system or the ISO 9660 file system, or both, which systems are standard to the skilled art person. In the alternative case, no file system would be present at all and the relevant sector spaces should be kept empty. 
     If a the system is present however, all audio will be stored in Audio Files, that are 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 ,  66  as shown. The structure of MASTER.TOC  52  will be discussed hereinafter. Furthermore, there is a 2C_AUDIO file  54 . This points to TOC 2C_AREA.TOC  58  and in parallel therewith to the various stereo tracks TRACKn.2CH  60 . Furthermore, there is MC_AUDIO file  56 . This points to TOC MC_AREA.TOC  62  and in parallel therewith to the various stereo tracks TRACKn.MCH  64 . For reasons of safety, the MASTER.TOC has been provided in three contiguously positioned copies MASTER1.3.TOC 52 . Likewise for reasons of safety, the subaltern TOCs have been provided in two copies 2C_AREA1,2.TOC  58  and MC_AREA1,2.TOC. 62 , respectively. These two copies are positioned before and behind, respectively, the associated audio. As a further feature, the audio formats have an additional overall the each, 2C_TAREA.2CH  59  and MC_TAREA.MCH that contain the file information of all associated track files, respectively. Finally, a picture file  66  has been provided that may be related to a similar organization as has been provided for the audio. 
       FIG. 5  shows a first storage arrangement for use with the invention, which for 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 the medium. Item  122  represents the File System that has been disclosed with reference to  FIG. 4 . Item  124  represents a TOC that may be configured according to standard procedures and pertains to subsequent items Stereo Audio Item  126  and Multi-channel Audio Item  128 , and if necessary also to Extra Data Item  130 . The length of item  124  need not be standardized, inasmuch as various different amounts of information may be present. Item  126  represents Stereo Audio Information, that may be defined according to a conventional standard and by itself does not constitute part of the invention. Item  128  represents Multi Channel Audio Information, that may be defined according to a conventional standard and by itself does 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 the distinguishing definitions of the various channels. The audio may be plain coded or lossless coded. All kinds of audio may be multiplexed with supplementary data such as Compact Disc Text. 
     Item  130  represents Extra Data Information that may be defined in a conventional standard and by itself does not form part of the invention. Item  132  represents a Lead-Out Information. The latter item is used in particular during search operations. The number of lead-out tracks may be large enough to 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. 
       FIG. 6  shows a second storage arrangement for use with the invention, pertaining to a two-level TOC structure. Along the horizontal axis the following items are evident, next to items that have already been shown in  FIG. 5  and carry the same reference numerals. For clarity, items  120  and  132  have been suppressed. 
     Master TOC  134  begins at a uniformly standardized offset position with respect to the start of the Lead-in area at byte number  510 . According to the embodiment, the Master-TOC measures only one standard-size sector and primarily contains pointers to the various Sub-TOCs or Area-TOCs. A preferred syntax of the Master-TOC has a header with a Signature that identifies the Master-TOC, such as by “SACD Master TOC”. Referring to  FIGS. 7 and 8 , Tables 1 and 2 specify the precise syntax of the MASTER_TOC. The syntax has been given in elementary computer notation, together with the associated lengths and formats. Master_TOC_Signature is an 8 byte string identifying the Master TOC. The value of Master_TOC_Signature must be “SACDMTOC” ($53 $41 $43 $44 $4D $54 $4F $43). 
     Referring to  FIG. 9 , Table 3 specifies the disc info syntax in the same manner. In particular: 
     2CH_TOC — 1_Address is a 5 byte integer containing the logical sector number (LSN) of the first sector of Area TOC-1 in the 2 Channel Stereo Area. If the 2-Channel Stereo Area is not present, the value of 2CH_TOC — 1_Address must be zero. 
     2CH-TOC — 2_Address is a 4 byte integer containing the LSN of the first sector of Area TOC-2 in the 2 Channel Stereo Area. if the 2-Channel Stereo Area is not present, the value of 2CH_TOC — 2_Address must be zero. 
     MC_TOC — 1_Address is a 4 byte integer containing the LSN of the first sector of Area TOC-1 in the Multi Channel Stereo Area. If the Multi Channel Area is not present, the value of MC_TOC — 1_Address must be zero. 
     MC_TOC — 2_Address is a 4 byte integer containing the LSN of the first sector of Area TOC-2 in the Multi Channel Stereo Area. If the Multi Channel Area is not present, the value of MC_TOC — 2_Address must be zero. 
     The format of Disc_Flags must be as follows: a hybrid bit and seven reserved bits. 
     The Hybr bit must be set to one on a Hybrid Disc. The Hybr bit must be set to zero on a not-Hybrid Disc.