Date: Fri, 17 Sep 1999 12:52:21 +0200 (CEST) From: Oliver Fromme <olli@dorifer.heim3.tu-clausthal.de> To: freebsd-multimedia@FreeBSD.ORG Subject: Re: Atapi CD audio ripper quality? Message-ID: <199909171052.MAA14465@dorifer.heim3.tu-clausthal.de>
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Daniel O'Connor wrote in list.freebsd-multimedia:
> > Presumably, because it's a digital medium, there is only one "correct"
> > version. Right?
>
> Thats true, but gsince CD audio has no checksum information you don't KNOW if
> you're getting the right data.
That's not exactly correct. "Red Book" CDs (audio CDs) have
two layers of error detection _and_ correction information.
These are should be handled by the CD-ROM drive and not be
visible to the software running o the computer. (CD-ROM has
an additional third layer of error correction, at least for
mode1 tracks -- that's why a CD-ROM has a lower effective
capacity than an audio CD.)
However, if any non-correctable errors occur, the drive will
usually _not_ signal an error condition to the host when
reading an audio CD, but it will try to just send "similar"
data to the host ("similar" regarding the perception of the
human ears). Different drives have different algorithms for
that. Usually you can't hear it if such corrections occur,
unless the CD is severely broken which leads to skipping and
"clicking".
Of course, when reading CD-ROM data tracks, the drive should
always report an error to the host if a situation occurs in
which the digital data can not be reproduced 100% correctly.
> > So how do I tell which setting (if any) is giving me the correct output?
In your case, it rather sounds like a software problem.
If it gives you identical output most of the time when using
the same options, then the CD and your drive are probably OK.
If you get different results when using different options,
I'd say your "grab" software is to blame.
On the other hand, most IDE CD-ROM drives require so-called
"jitter correction", which your grab software must support.
using different options might affect the way the data comes
out in that case.
My recommendation is, of course, to buy a decent SCSI drive
and use a grab utility such as cdd or tosha. :)
Regards
Oliver
--
Oliver Fromme, Leibnizstr. 18/61, 38678 Clausthal, Germany
(Info: finger userinfo:olli@dorifer.heim3.tu-clausthal.de)
"In jedem Stück Kohle wartet ein Diamant auf seine Geburt"
(Terry Pratchett)
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