> > | Compression as I understand it is an encoding and decoding process.
> > | Anything that is compressed will have to be "decompressed" in order to
> > | play it.
> >
> > CD-DA has this thing called a digital to analog converter for playback.
So
> > if analog to digital is compression then digital to analog is
decompression.
>
> But analog to digital conversion is not compression, so this is a moot
> point.
I agree with you, there is a big difference between compression and
compression, you can compress air, and you can compress digital data. When
we're talking about compression in the Computer Science sense of the word we
are talking digitally, we are talking bitstreams, datagrams and all that.
Compression in a digital fashion means that you make the bitwise
representation of the original smaller, and from that smaller bitwise
representation you can recreate the original to a reasonable extend. The
difference between the original and the reproduction is the loss of
information. In modern day compression you have lossless and lossy
compression, like has been said, all file packers like ZIP, RAR, ARJ and all
are lossless. other compression schemes like ATRAC, MP3, MPEG Video, JPEG
are lossy compression, the quality of the reproduction is less than the
quality of the original, though the designers of a lossy compression always
try to lose the stuff that is the least significant.
> > | Since if you cut the frequency response off at a certain point and can
> > | never recover the sounds above that frequency response, that is not
> > | compress. Compression allows you to recover a facsimile of the
original
> > | source. Just how different that is depends upon how lossy the
technique
> > | is.
> >
> > In what way is this facsimilie reproduction different from an audio CD
> > compared to the original analog source? Because that is what you are
> > getting out of the player: a facsimilie.
>
> Is an audio cassette then a "compressed" format because it's physically
> smaller than a record? Again, compression is something in the digital
> domain.
no comment
> > | But in the terms we think of it today (and the definition that I
accept
> > | (for what ever my opinion is worth) the term compression means
encoding
> > | and decoding.
> >
> > How is converting an analog signal to a digital data stream different
from
> > "encoding"? How is converting that digital signal back to analog not
> > "decoding"?
>
> Compresion is something that happens purely in the digital domain, by
> definition.
Indeed talking of ADC and DAC as a compression/decompression is absolute
nonsense, again there's a big difference between compression and
compression.
> > | MP3, ATRAC are compression techniques.
> >
> > Technically, ATRAC is not a traditional compression algorithm, but
bitwise
> > reduction. But we call it "compression" anyway because the end result
is
> > to make the data smaller. MP3 combines bitwise reduction and Huffman
> > coding (a lossless compression scheme).
>
> Please cite a source for your definition of compression that excludes
> ATRAC?
>
> "Data Compression Method: ATRAC"
> -Sony, on the spec sheet for the MZ-R90.
>
http://www.sel.sony.com/SEL/consumer/ss5/car/mdwalkmanrtm/playerrecorder/mz-
r90_specs.shtml
>
> "The ATRAC (Adaptive Transform Acoustic Coding) data compression system
> was therefor designed..."
> -the paper produced by the designers of the ATRAC algorithm in 1992.
>
> http://www.minidisc.org/aes_atrac.html
>
> It would appear that you have developed a unique definition of compression
> that includes some things and excludes others. If you are going to claim
> ATRAC is not compression, please cite a source.
ATRAC is a bitwise reduction as you are stating yourself, when there's a way
to get the original data back with a negligable or no data loss the it is a
compression by definition. ZIP is merely a bitwise reduction, it takes note
of all data and try's to remove all redundancy, ie merely a bitwise
reduction...
> > | Cutting frequency or limiting the difference between the quietest and
> > | loudest sound is not in my opinion what we think of today when we
speak
> > | about compress (although in the broadest sense removing or limiting
> > | anything probably could be called compression-I just don't think it is
in
> > | common usage of the word today.
> >
> > But that is what ATRAC does, and we call it compression. So it is
common
> > usage even if most people do not relize it.
>
> ATRAC does it by a different method; ATRAC compresses it to do this. If
> you use an analog cutoff filter to cut off all sounds above 5kHz, you
> haven't compressed the sound.
ATRAC doesn't do it that way indeed, ATRAC does a bitwise reduction with all
the information it gets from cutting frequency and limiting the difference
between the quitest and loudest sound, it doesn't actually do that. It's
actions result in a similar effect which is based upon those techniques.
Bye, Remko van der Vossen
[EMAIL PROTECTED]
The Black Angel [EMAIL PROTECTED]
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