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DATFRAME(4)

  NAME

      datframe - structure of a frame of audio data on Digital Audio Tape (DAT)

  SYNOPSIS

      #include <dataudio.h>

  DESCRIPTION

      The Digital Audio Tape (DAT) recorder system is very complex.  This man
      page gives the most useful and relevant information for DAT use in
      professional systems.  It is by no means comprehensive.  Conflicts and
      questions must be resolved by reference to the definitive DAT Conference
      specification referenced below.

      Audio on Digital Audio Tapes (DAT) is blocked into frames.  A DAT
      recording has 33.33 frames every second.  One frame of data contains both
      audio and non-audio data (known as subcodes).  A program reading or
      writing a DAT in audio mode must read(2) or write(2) a minimum of one DAT
      frame.

      The dtframe structure, describing the content of a frame of DAT data, is
      defined in <dataudio.h> as follows:

            typedef struct dtframe {
               char audio[DTDA_DATASIZE];
               struct dtsubcode sc;
            } DTFRAME

      Audio samples in the audio array are linearly encoded in a 16-bit 2's
      complement format.  Encoding is carried out either without pre-emphasis
      or with a first order 50/15 Ms pre-emphasis.  Pre-emphasis is not
      recommended for professional use.  Other encodings are supported by the
      DAT format but are not permitted in professional use.  The data stream
      contains two interleaved channels, usually used as the left and right
      channels of a stereo signal.  The sample representing the left channel is
      first, followed by the sample representing the right channel.  The DAT
      Conference recommends sampling both both left and right channels
      simultaneously during recording.  The IRIS Indigo and Personal IRIS 4D/35
      audio ADC hardware samples both channels simultaneously.

      The least significant byte of each 16-bit value is first.  The bytes need
      to be swapped in order to match the native byte ordering of the IRIS
      Indigo and Personal IRIS 4D/35 and their audio hardware.  So each 4-byte
      chunk of the data array represents a pair of samples (1 left plus 1
      right) as follows.  Byte 0 is the least significant byte of the left
      channel sample; byte 1 is the most significant byte of the left channel
      sample.  Byte 2 is the least significant byte of the simultaneous right
      channel sample; byte 3 is the most significant byte of the simultaneous
      right channel sample.

      DTDA_DATASIZE is 5760 bytes.

    Subcodes
      The dtsubcode structure contains subcode information that is recorded on
      several different areas of the tape.  struct dtsubcode is defined in
      dataudio.h as follows:

            typedef struct dtsubcode {
               struct dtsubcodepack packs[7];
               struct dtsubid {
                   unchar ctrlid:4, dataid:4;
                   unchar pno1:4, numpacks:4;
                   unchar pno2:4, pno3:4;
                   unchar ipf;
               } sid;
               struct dtmainid {
                   unchar fmtid:2;
                   unchar emphasis:2;
                   unchar sampfreq:2;
                   unchar numchans:2;
                   unchar quantization:2;
                   unchar trackpitch:2;
                   unchar copy:2;
                   unchar pack:2;
               } mid;
            } DTSUBCODE;

      In referring to the DAT Conference specification, you need to know that
      the mid field contains the bits from the ID field of the main data area
      otherwise known as the Main ID bits.  The sid field contains the bits
      from the ID field of the sub data area, otherwise known as Sub ID bits.
      The packs field contains all seven data packs from the sub-data area of
      the tape.

    Main ID Bits
      The bits of the mid field have the following meanings and values:

                      value   meaning
      fmtid:            0     for audio use
                        1     reserved
                        2     reserved
                        3     reserved

                      value   meaning
      emphasis:         0     off
                        1     50/15 Msec
                        2     reserved
                        3     reserved

                      value   meaning
      sampfreq:         0     48kHz
                        1     44.1kHz
                        2     32kHz
                        3     reserved

                      value   meaning
      numchans:         0     2 channels
                        1     4 channels
                        2     reserved
                        3     reserved

                      value   meaning
      quantization:     0     16-bit linear
                        1     12-bit non-linear
                        2     reserved
                        3     reserved

                      value   meaning
      trackpitch:       0     normal track mode
                        1     wide track mode
                        2     reserved
                        3     reserved

                      value   meaning
      copy:             0     copy permitted
                        1     reserved
                        2     copy prohibited
                        3     reserved

      These bits are always present and must be recorded when making your own
      recordings.

      The pack field is optional.  It should be filled with zero when not being
      used.  The bits of the pack field are assembled with the bits of the pack
      fields from 31 other frames to build one 8-byte subcode pack.  These
      packs are duplicated in the sub data area from where they are much easier
      to recover.  All seven packs can be found in the packs array in DTFRAME.

    Sub ID Bits
      The ctrlid field is a bit field with the following meanings:

           bit name          meaning
           0   TOC ID        set if this program is stored
                             in the table of contents
           1   Shortening ID set for 33 + 3 frames at the
                             start of shortening play
           2   Start ID      set for 300 + 30 frames at
                             the start of a track
           3   Priority ID   set when the program number is
                             recorded and is well defined

      The dataid field is zero for audio use.  All other values are reserved.

      pno1, pno2 and pno3 are 3 BCD digits indicating the current program
      number.  pno1 is the most significant digit.  Program numbering starts
      with the value 001 and has to increase by increments of one.  The maximum
      program number is 799 so pno can have values from 0 - 7, and pno2 and
      pno3 can have values from 0 - 9.  The program number can also be one of
      three special values 0AA means the program number is not currently valid.
      0BB means we are in the lead-in area.  0EE means we are in the lead-out
      area.

      The program number is only required to be valid when startid is 1, i.e.
      for 300 + 30 frames.  so it is likely to disappear and be replaced by 0AA
      shortly after a track starts.

      numpacks is the number of subcode packs actually used in this frame.  It
      usually indicates that all seven packs are recorded even when they are
      all zero.

      ipf contains the interpolation flags, one for each channel as follows:

           Bit    Channel
           0x40   Left IPF
           0x20   Right IPF

      The interpolation flags indicate when uncorrectable errors have been
      detected during playback leading the DAT drive to interpolate the missing
      data.  It is usually advisable not to play the audio data from a frame
      with these flags set.

      Most of Sub ID is optional.  Only dataid is required and must be zero.
      If the bits of ctrlid are zero, the bits of the rest of Sub ID may also
      be set to zero and will be ignored.

    Subcode Packs
      Nine different pack items are currently defined and seven are reserved.
      The nine items are:

           Pack ID    Content
           0000       no information
           0001       Program Time
           0010       Absolute Time
           0011       Running Time/Pro R-Time
           0100       Table of Contents
           0101       Date
           0110       Catalog Number
           0111       International Standard Recording Code
           1000       Pro Binary

    Program Time
      Program Time indicates the time from the beginning of the program.  It is
      stored in a dttimepack structure defined in dataudio.h as follows:

            /*
             * The timecode structure looks like this:
             *
             *      struct dttimecode {
             *          unchar hhi:4, hlo:4;
             *          unchar mhi:4, mlo:4;
             *          unchar shi:4, slo:4;
             *          unchar fhi:4, flo:4;
             *      };
             *
             * This structure is identical to mtaudtimecode in sys/mtio.h so
             */
            #define dttimecode mtaudtimecode

            /* pack for ptime, atime, rtime and pro-rtime */
            struct dttimepack {
               unchar id:4, flag:1, pno1:3, pno2:4, pno3:4;
               struct dtpackedbcd {unchar dhi:4, dlo:4;} index;
               struct dttimecode tc;
               unchar parity;
            };

      The program number is stored in pno1, pno2, and pno3 as 3 BCD digits
      exactly like the Sub ID field. That information is duplicated here.
      index is the index number of the current subdivision within the program.
      The index number is expressed as 2 BCD digits.  AA indicates that the
      index number is invalid.  A program may be preceded by an index number of
      00 with the same program number.  This represents the music interval or
      pause between tracks.  Valid index numbers are 01 to 99.  Within a
      program, the first value of the index number is 01 and the value of the
      index number has to increase by one.

      The program time is represented by 2 BCD digits each for hours, minutes,
      seconds and frames.  Hours range from 00 to 99, and minutes and seconds
      from 00 to 59.  Over a three second period, frames ranges from 00 to 32,
      00 to 32, and 00 to 33.  In other words if (seconds modulo 3) is 0 or 1,
      frames ranges from 00 to 32.  If (seconds modulo 3) is 2, frames ranges
      from 00 to 33.  AA indicates the the program time is invalid.  The
      program time is set to zero at the start position of a program and
      increases within the program.  The start position of a program is the
      first position where the program number is renewed (changed) and the
      index number is not 00.

    Absolute Time
      Absolute time is stored in a struct dttimepack identical to program
      time's.  Absolute time is set to 00 at the start of the first program on
      the tape and increases throughout the tape except on the lead-in area
      (program number 0BB).  The time decreases on the lead-in area and is set
      to zero at the end point of the lead-in area.

      When the first program cannot begin after the time is set to zero, the
      time should be zero continuously until the first program begins.  The
      program number of this area should be 0BB and this area should be less
      than 33 frames.

    Running Time
      Running time is stored in a pack with ID 3, and the flag bit zero.  The
      pack is a time pack identical to program and absolute times'.  The
      running time is a continuously increasing time code beginning from some
      value at the start point of each recording.  The time increases within
      one recording.

    Pro R Time
      Pro R time is a variation on the running time pack for professional use.
      Pro R time is indicated when the flag bit is one.  Pro R time is stored
      in a dtprotimepack defined in dataudio.h as follows:

            /* pack for pro-rtime */
            struct dtprotimepack {
               unchar id:4, flag:1, fill:1, sid:2;
               unchar freq:2, xrate:3, msb:3;
               unchar lsb;
               struct dttimecode tc;
               unchar parity;
            };

      Pro R time stores a running time in the tc field just like running time.
      The other fields give addition information about the stored time value.

      The sid field indicates the type of time code recorded as follows:

           value   meaning
           00      IEC (SMPTE) timecode (IEC 461)
           01      local sample address code of Pro DIO time code.
           10      time-of-day code of Pro DIO time code (IEC 958)
           11      reserved

      The freq field indicates the sampling frequency used for the time
      conversion to Pro R time as follows:

           value   meaning
           00      48kHz
           01      44.1kHz
           10      32kHz
           11      reserved

      When the sid field indicates IEC (SMPTE) time code, the xrate field
      indicates the transmission rate of the time code as follows:

           value   meaning
           000     30Hz
           001     29.97Hz, non-drop frame
           010     29.97Hz, drop frame
           011     25Hz
           100     24Hz
           101     reserved
           110     reserved
           111     reserved

      For any other value of sid, this field must have the value 000.

      The msb, and lsb fields provide 11 bits of binary data.  When sid
      indicates IEC (SMPTE) time code these bits record a Time code Marker (TC
      Marker). TC Marker is the time difference between the IEC time code frame
      and the DAT frame.

      When sid indicates one of the Pro DIO time codes, the binary data records
      the 32-bit binary code corresponding to the first sample of a DAT frame
      converted into hour, minute, seconds, frame and sample (called the sample
      number).

      The range of value indicated by these 11 bits is different for each value
      of freq as shown in the following table:

           frequency   range
           48kHz       0 - 1439
           44.1kHz     0 - 1322
           32kHz       0 - 959.

    Table of Contents
      The TOC pack contains one entry from the table of contents.  The TOC is
      stored in a struct dttocpack defined in dataudio.h as follows:

            /* pack for table of contents */
            struct dttocpack {
               unchar id:4, flag:1, pno1:3, pno2:4, pno3:4;
               struct dtpackedbcd point;
               struct dttimecode atime;
               unchar parity;
            };

      The table of contents may be recorded repeatedly over the entire length
      of the tape or only at the beginning of the tape.  In the first case it
      is called repeated TOC (R-TOC). In the latter case it is called user's
      TOC (U-TOC).

      The standard table of contents entry has a program number in pno1, pno2
      and pno3, and an index number in point. The starting position of that
      program, index pair is given in atime. Several special values of pno and
      index with specific meanings are also used.  The following table shows
      these values.

           Point   Program Number        Atime
           AA      0BB                   all "0"
           BB      PNO of TOC area       all "0"
           B0      No. of TOC entries    all "0"
           A0      No. of 1st program    start of 1st program
           A1      No. of last program   start of last program
           C0      No. of a skip area    start of skip area
           C1      No. of a skip area    end of skip area
           CC      0BB                   all "0"
           EE      PNO of TOC area       all "0"

      Point BB is the beginning of the table of contents.  Point CC is a
      continuation of the table of contents.  Point EE is the end of the table
      of contents.

      A location in absolute time is found by scanning the tape at 150X play
      speed.  Since it is possible to do exactly the same kind of search for a
      program number, the table of contents is not terribly useful.

    Date
      The date pack is a time stamp giving the time and date of recording.  It
      is stored in a struct dtdatepack which is defined in dataudio.h as
      follows:

            /* pack for date */
            struct dtdatepack {
               unchar id:4, dayow:4;
               struct dtpackedbcd year;
               struct dtpackedbcd month;
               struct dtpackedbcd day;
               struct dtpackedbcd hour;
               struct dtpackedbcd min;
               struct dtpackedbcd sec;
               unchar parity;
            };

    Catalog Number
      The catalog number pack gives the catalog number expressed in 13 BCD
      digits according to the UPS/EAN-Code.  It is stored in a struct
      dtcatalogpack defined in dataudio.h as follows:

            /* pack for catalog number */
            struct dtcatalogpack {
               unchar id:4, n1:4;
               struct dtpackedbcd nrest[6];
               unchar parity;
            };

      The catalog number does not change on a tape.  When this item is present
      it occupies at least one of 100 successive frames.

    International Standard Recording Code
      The ISRC gives a unique identification code to a recording.  It is stored
      in a struct dtidentpack which is defined in dataudio.h as follows:

            /* pack for ISRC */
            struct dtidentpack {
               unchar id:4, point:2, fill:2;
               union {
                   struct {
                       unchar country[2];
                       unchar owner[3];
                       unchar fill;
                   } point0;
                   struct {
                       struct dtpackedbcd year;
                       struct dtpackedbcd serial[3]; /* serial is 1st 5 digits */
                       unchar fill[2];
                   } point1;
               } data;
               unchar parity;
            };

      When point is zero the pack contains the country and owner codes.  When
      point is one the pack contains the year and serial number.  Country and
      owner are encoded in a six-bit code representing digits and upper case
      letters.  [See cdframe(4) for the code.]  Year and serial number are BCD
      digits.

      The ISRC can only change immediately after the program number changes.

      When this item is present it occupies at least one of 100 successive
      frames.

    Pro Binary
      The Pro Binary pack contains either the binary group data of IEC (SMPTE)
      time code or the status data of Pro DIO time code.  It is stored in a
      struct dtprobinarypack which is defined in dataudio.h as follows:

            /* pack for pro-binary */
            struct dtprobinarypack {
               unchar id:4, fill:2, sid:2;
               union {
                   struct bgd {
                       unchar fill;
                       unchar tcbits;
                       struct dtpackedbcd bg[4];
                   } bgd;  /* binary group data of IEC time code */
                   struct csid {

                       unchar csbytes[6];
                   } csid; /* channel status id of Pro DIO time code */
                   struct cod {
                       unchar fill[2];
                       unchar cod[4];
                   } cod; /* alphanumeric origin data of Pro DIO */
                   struct cdd {
                       unchar fill[1];
                       unchar flags;
                       unchar cdd[4];
                   } cdd;  /* alphanumeric destination data of Pro DIO */
               } data;
               unchar parity;
            };

      sid is a subpack identification identifying what is in this pack as
      follows:

           value   content
           00      binary group data of IEC (SMPTE) time code
           01      channel status ID of Pro DIO time code
           10      alphanumeric origin data of Pro DIO
           11      alphanumeric destination data of Pro DIO

      The IEC (SMPTE) binary group data consists of binary group and time code
      bits.  The binary groups are stored as BCD digits in bg. The eighth
      binary group is stored in bg[0].dhi. The seventh binary group is stored
      in bg[0].dlo. The groups continue in descending order through the array
      with the second group in bg[3].dhi and the first group in bg[3].dlo.

      The time code bits are used as follows:

           bit   IEC bit   525/60              625/50
           0     10        drop frame          unassigned
           1     11        color frame         color lock
           2     27        phase correction    binary group flag
           3     43        binary group flag   binary group flag
           4     58        unassigned          unassigned
           5     59        binary group flag   phase correction
           6               not used
           7               not used

      When the IEC (SMPTE) time code is recorded for a given frame, the binary
      group data must also be recorded.

      The channel status ID consists of bytes 0 to 5 of the channel status data
      of the IEC serial digital interface stored in bytes 0 to 5 of
      data.cdid.csbytes.

      The alphanumeric channel origin data consists of bytes 6 to 9 of the
      channel status data of the IEC serial digital interface stored in bytes 0
      to 3 of data.cod.cod.

      The alphanumeric channel destination data consists of byte 22 of the
      channel status data of the IEC serial digital interface stored in
      data.cdd.flags and bytes 10 to 13 of the channel status data stored in
      bytes 0 to 4 of data.cdd.cdd.

    Pack Parity
      The last byte of a pack is a parity checksum which is computed as the
      exclusive-OR of the first seven bytes.  During playback, the DAT drive
      executes a parity check and only returns packs with correct parity.
      During recording, the correct parity value must be computed and written
      into the parity field before the pack is written to the tape.

  SEE ALSO

      The Digital Audio Tape Recorder System published by The DAT Conference.
      c/o Electronic Industries Association of Japan, Engineering Department.
      Tokyo Chamber of Commerce & Industry Building 2-2, 3-chome, Marunouchi,
      Chiyoda-ku, Tokyo 100, Japan

      DAT for Professional Use.  The DAT Conference. c/o Electronic Industries
      Association of Japan, Engineering Department.  Tokyo Chamber of Commerce
      & Industry Building 2-2, 3-chome, Marunouchi, Chiyoda-ku, Tokyo 100,
      Japan

  AUTHOR

      Mark Callow

Copyright © 1993-2006 Silicon Graphics, Inc. All rights reserved.


