Vicki Powys wrote:
> What is the compression rate for currently
> available minidisc?
ATRAC takes less space to store a
recording by significantly transforming
the original digital sound data. An
instruction set is created that can be
used to reproduce the sounds at playback.
Sony, creators of ATRAC, needed to
achieve enough data reduction to fit the
contents of a standard music CD (~700MB)
onto a 74 minute minidisc (~150MB). That's
a ratio of 22%. This is called ATRAC SP
in minidisc recorders today.
22% is about the same data reduction as
is achieved using MPEG1 Level 2 (aka MP2)
techniques. When played back, ATRAC SP
and MP2 files sound very much like the
original.
Later, to compete with MP3 players, Sony
created new versions of ATRAC that squeeze
more music into less space. The most
recent ATRAC for minidisc is called ATRAC3,
and it achieves a data reduction ratio of
about 10% (that is, the ATRAC file is only
10% the size of the original digital audio
file).
10% is about the same data reduction as is
achieved using MPEG1 Level 3 (MP3) techniques.
Most people notice a reduction in sound
quality at this level of data reduction.
There's even an ATRAC3plus, which achieves
a reduction to 5%. But no minidisc player
has been released to take advantage of this
format. Instead Sony uses ATRAC3plus in
some of its solid-state walkman products.
--oryoki
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