Dan Dugan wrote:
> Walt, you wrote,
>
>
>>As I've noted it's a error to think ATRAC even keeps 20% of the original
>>data. The more I dug into it, the more it became clear that it should
>>rather be thought of as synthesizing a whole new set of data, and
>>storing instruction on how to do this. Yes, a approximation, but so is
>>anything that comes out of a A/D - D/A cycle.
>
>
> Since ATRAC has higher fidelity than, say, pre-Dolby analog master
> tape recording (compare to 15 ips 2-track: better s/n, flatter
> frequency response, lower distortion, better group delay), one could
> ask "what percentage of the data does tape recording throw away?"
Different world. One more or less assumes that analog recording methods
don't throw away data, a infinite amount of data points in and a
infinite amount out. But it may store it imperfectly. I suppose you
might could come up with something, since analog is a infinite amount of
data it would be some percentage of infinity.
And you are shooting at one of my original favorite recording methods.
Really hated it when cassette pushed reel to reel aside. I'm not
surprised by your statement, however.
In digital one has data points that one could count, in theory. So how
many are saved can also be counted. Because ATRAC occupies 20% of the
disk space that the uncompressed data it stored occupies there is this
leap that somehow it saves just 20% of the original data, each point it
saves unchanged. I can't see how 20% of the raw data saved like that
would come out all that good. And reading the descriptions of what's
saved and how leads to the conclusion it does not save the original data
at all. It saves a sort of description of what the original data
contained, a blueprint for making it. You certainly would not get
anything usable out of a D/A if you fed it what's recorded. The decoder
understands the description and using that makes a new set of data
points to feed the D/A. Not a mix of old and new points. The distinction
is a important one. As I'm sure we all know a description of a thing can
be many times smaller than a thing and yet describe it in a very
detailed manner. ATRAC manages to describe all of a sound's samples in
just 20% of the space the samples occupy.
Walt
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