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Re: [vox-tech] update on the audio CD problem
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Re: [vox-tech] update on the audio CD problem

On Fri, Jan 27, 2006 at 04:05:23PM -0500, Peter Jay Salzman wrote:
> No.  The CPU is involved in many read-copy operations when the signal passes
> through the sound card.

It was my understanding that in this "analog" CD audio playback scheme,
the data is extracted by the CD Drive itself, converted to analog with the
drive's own built-in DAC (just like what's in a CD Walkman or a stereo),
and then wired directly to the sound card's "Line In" pins, and passed
along to the speakers.  (Mixed on the card in an analog state.)

So in this case, the only time the PC's CPU is used is to tell the CD player
"Play", then it sits idle.  Everything is done by the CDROM drive.
(This really _must_ be the case, since the earliest CDROMs could play music
just fine, even on 486s.)

In the "digital extraction" mode (which Norm has to do -- perhaps because
that little wire connecting the CD drive to the soundcard is missing),
the CPU is used to actually take the data off the CD and send it to the
sound card (via the motherboard, rather than that little wire).  I'm not
very knowledgable about audio formats used by either CD _or_ soundcards,
so it could just be a matter of 1:1 copying the data.

(In the amaroK example I gave, I think it may have been ripping and
encoding to MP3, and then _decoding_ the MP3 to play it, which is
absolutely retarded.  But, that's just a guess... after trying it once
and asking in #amarok on IRC, I learned it was just something you didn't
want to try yet, and to stick with KsCD.)

-bill!                                    Tux Paint 2006 wall calendar,
bill@newbreedsoftware.com                CDROM, bumper sticker & apparel
http://www.newbreedsoftware.com/       http://www.cafepress.com/newbreedsw
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