Walt, you're mis-using terminology here, and I feel the need to
explain for those who are here for education:
>DAT is lossy compression, hard disk digital is lossy compression, every
>single digital sampling method for sound is lossy. The question is not
>is it lossy, they all are. The question is what does that mean. Saying
>it's lossy is just the beginning, not the end of the discussion.
By "lossy compression" above, you seem to be meaning "imperfect."
This imprecise way of speaking is a bad thing to do in an educational
forum. "Lossy compression" refers to certain psychoacoustic data
reduction techniques, and it's confusing when you use it to describe
the other losses that happen in recording processes.
Digital recording on DAT or hard disk is imperfect to the degree that
it is limited by the quality of the converters, the 16-bit dynamic
range, and 44.1 or 48K sampling rate. With today's converters, all of
these limitiations are of little consequence. Many of the finest
classical music CDs you buy were recorded on DAT! The problem with
DAT is reliability, not fidelity. Most recordists are changing to
hard disk recording because they can use higher standards for
conversion (24-bit, 96K), always desirable in master recording, and
it's more reliable.
Those who are into the engineering know that a DAT recording system
is constantly making errors, and correcting them completely by using
a redundant data coding scheme. This process is invisible to the
user. The result is perfect up to the point where there are too many
errors, and failure. The same thing goes for CD reproduction, with
the addition of a "gentle" first failure mode called error
concealment.
Lossy compression systems (ATRAC, MP3, Dolby Digital movies, the new
AAC) are a whole different kettle of fish. They analyze the sound,
record the analysis parameters, and reconstruct it from that, rather
than recording the straight digital audio samples. It's unfortunate
that the term "compression" seems to have stuck, because it makes it
difficult to explain to newcomers that the word now means two
completely different things in audio engineering, depending on the
context!
-Dan Dugan
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