Date: Mon, 8 Sep 1997 08:40:37 +0200 From: j@uriah.heep.sax.de (J Wunsch) To: freebsd-hackers@FreeBSD.ORG Cc: jamil@counterintelligence.ml.org (Jamil J. Weatherbee) Subject: Re: i refuse to spend the $$$ Message-ID: <19970908084037.MZ56268@uriah.heep.sax.de> In-Reply-To: <Pine.BSF.3.96.970907225228.1391A-100000@counterintelligence.ml.org>; from Jamil J. Weatherbee on Sep 7, 1997 22:54:37 -0700 References: <19970908072530.ZD14625@uriah.heep.sax.de> <Pine.BSF.3.96.970907225228.1391A-100000@counterintelligence.ml.org>
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As Jamil J. Weatherbee wrote: > Can someone explain the real difference between an audio CD and a data CD? > I seen mentions of things like "jitter correction" etc. that I don't > really understand, I have a somewhat decent grip on data cd's but as for > audio --- are these made differently or what? Sorry to beat on you: but if you don't even know details, why are you starting to whine then that FreeBSD doesn't do this and FreeBSD doesn't do that? The difference is that lousy drives tend to lose track every now and then. For CD-ROM data, this can be compensated, since part of the redundant data (only 2048 bytes of data have to be obtained out of 2352 bytes per CD block) is a block sequence number, so once you've lost track, you simply wait until the desired block passes the laser again. For CD-DA, all 2352 bytes are user data, so once the drive lost track, it has to guess where to start again. Also, as you can see above, the redundancy in CD-ROM data allows for a fair amount of ECC error correction (298 ECC bytes per block), so even larger damages can be compensated completely. With CD-DA, only the lower-level error correction is available (Reed-Solomon, IIRC), potentially returning you slightly erroneous data. Yet another reason for why you need a high-quality drive if you're going into digitally processed CD-DA. Perhaps you know understand why those few people who have been working on CD-DA by now (Charles Henrich, Amancio Hasty etc.) did concentrate on SCSI first. -- cheers, J"org joerg_wunsch@uriah.heep.sax.de -- http://www.sax.de/~joerg/ -- NIC: JW11-RIPE Never trust an operating system you don't have sources for. ;-)
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