| Sectors
and ECC |
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Super
Audio CD |
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Sector format,
error correction and channel modulation
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Data
are recorded in the Information Area of the disc. It
consists of 3 parts : the Lead-In Area, the Data
Area and the Lead-Out Area. The present chapter
explains how data are physically recorded in these
areas. Structure of the information on a Super Audio
Disc is detailed in the next
chapter.
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As
in Compact Disc, information recorded on the
high-density layer of a SACD disc is formatted into
Sectors. A Sector is the smallest addressable part
of the information track that can be accessed
independently. Depending on the stage of the signal
processing, a sector (or group of sectors) is called
: a Data Sector, an ECC block, a Recording Sector or
a Physical Sector.
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A
Data Sector is 2064 bytes longs, and consists of
2048 bytes of Main Data, 12 bytes of Identification
Data (ID) and 4 bytes of Error Detection Code (EDC).
This is hundred bytes shorter than for CD's Sector
format.
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After
scrambling the Main Data in the Data Sectors,
Reed-Solomon error correction coding information is
added to each group of 16 Data Sectors to form an
ECC block with supplementary inner-code parity (PI)
and outer-code parity (PO) bytes.
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The
Recording Sectors are formed by interleaving the
PO-rows in the ECC block and dividing such a block
again into 16 sectors.
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Finally,
EFM+ channel modulation creates a Physical Sector,
which is the actual format recorded on the disc.
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Data Sector
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As
shown in the following diagram, the first part of a
SACD Data Sector contains, among other things, 4
bytes of Identification Data (ID). This includes
Sector information, such as Sector format type,
tracking method,
reflectivity, area type and data
type. The Identification Data are protected by an
additional error detection code (IED).
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| Identification
Data (ID) |
4
bytes |
| ID
Error Detection (IED) |
2
bytes |
| Reserved |
6
bytes |
| Main Data |
2048
bytes |
| Error
Detection Code (EDC) |
4
bytes |
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Synchronisation
data, as used in CD format, is not needed any more
in SACD, thanks to an advanced synchronisation
method at the EFM level. Besides, the extra ECC
layer as used in CD format is superfluous, because
the normal error correction incorporated in SACD is
much more powerful than the CIRC in CD. The EDC is
however maintained, because it gives a very easy and
powerful error detection capability at Sector level.
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