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organisation |
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Super
Audio CD |
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Data organisation (cont.)
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Access
method
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SACD supports two
different access methods :
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Using a hierarchical TOC structure, with a Master
TOC and two Area TOCs
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Using a UDF
and/or an ISO 9660 file system
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All discs include the
TOC structure. The use of file system is optional.
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TOC
structure
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Unlike
Compact Disc, TOC in SACD has a two-level structure.
The highest level is the Master TOC and the lower
level is formed by two Area TOCs, one in the
2-Channel Stereo Area and one in the Multichannel
Area. The Extra Data Area does not contain an Area
TOC.
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The
Master TOC is stored in three locations, at sectors
510, 520 and 530. It contains general information on
the high-density layer and information on the size
and location of the Audio Areas. The second and
higher sectors of the Master TOC can optionally
contain a textual description of the disc, such as
the album title, artist, publisher,... This text can
be stored in up to 9 different languages / character
sets.
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The
Area TOCs are located at both, the start and the end
of the corresponding Audio Areas. An Area TOC
contains information on the Audio Area, such as the
sampling frequency of the audio signal, the bit
rate, the total playing time, the number of tracks,
the track list, and optional text channels. The text
channels may contain textual information such as
track titles, performers, composers,...
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File system
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The
high-density layer of a Super Audio CD optionally
contains an UDF and/or an ISO 9660 file system. The
directory structure of a SACD disc has the following
form :
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The
files master.toc, 2_ch.toc and m_ch.toc correspond
to the Master TOC, the 2-Channel Area TOC and the
Multichannel Area TOC respectively. The files
tracki.2ch and tracki.mch correspond to the
2-Channel Stereo and Multichannel audio tracks
respectively.
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Audio
tracks
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The
audio tracks contain a multiplex of elementary
streams. There are two types of elementary streams :
the audio elementary stream, a sequence of audio
frames, and the supplementary data elementary
stream, a sequence of supplementary data frames. The
multiplexed stream also contains headers to identify
and locate the different frames, and padding frames
to guarantee a fixed bit rate when reading data from
the disc, which are particularly used in the buffer
control stage (see Direct Stream Transfer). All
frames represent a time period of 1/75 seconds. Each
audio frame has a time code associated to it.
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Supplementary
data streams can contain text, graphics, still
pictures,...
A possible supplementary data text format is CD
Text. For CD Text, the stream is divided into ITTS
packets of 48 bytes. Another possibility is JPEG or
MPEG-2 still pictures.
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