Date: Tue, 08 Jul 2003 18:43:44 -0400 From: Chuck Swiger <cswiger@mac.com> To: Ion-Mihai Tetcu <itetcu2@xnet.ro> Cc: questions@freebsd.org Subject: Re: dd an audio cd on 5.x ? Message-ID: <3F0B4920.2030503@mac.com> In-Reply-To: <200307090101.52233.itetcu2@xnet.ro> References: <200307081546.52889.itetcu2@xnet.ro> <200307082309.37378.itetcu2@xnet.ro> <3F0B2CDB.8090800@mac.com> <200307090101.52233.itetcu2@xnet.ro>
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Ion-Mihai Tetcu wrote:
[ ... ]
>> You'd have to obtain the glass master used to press the original to
>> get an absolutely exact copy. "bit-by-bit" accuracy of the raw CD is
>> not very easy or even desirable to obtain due to ECC hardware fixing
>> minor errors: for audio, you want a "bit-by-bit" accurate copy of the
>> data after ECC processing, not before.
>
> OK, do you know any method to do it under BSD ? There are some cdtools
> in the ports that claim to do DAE - but I haven't the time to look in
> the code to see how it is done and if there is any difference between
> using a SCSI an an IDE drive.
Modern CD-ROM burners use the SCSI command set and thus behave much like a SCSI
device modulo various per-device quirks: the ATAPICAM module connects IDE
CD-ROM's ("ATAPI CD-ROM's") via the SCSI CAM system.
>> Better CD-burners let you do something known as DAO+96 ot TAO+96,
>> which lets you override the ECC hardware when reading or writing, and
>> thus copy even the errors from the original, which can be useful for
>> copy-protected data CD's rather than for audio....
>
> We have a potential client who asked about studying both cases and make
> him a app that could say if it's an "original" or not so this sounds
> interesting (we're pretty new on this).
2048 bytes of "actual data" get turned into ~2536 bytes of Reed-Solomon ECC
encoded data. There is also a 94 byte subchannel + 2 byte checksum (for "96")
which is used to contain CD+G data and other information, which is probably a
part of what you'll need to consider to have the CDDB diskid match.
For example, "man burncd" has the following:
vcd Set the write mode to produce VCD/SVCD tracks for the fol-
lowing image files on the command line. This automatically
sets DAO (-d) and ``no gaps'' (-n) modes.
A good copy of a professionally mastered audio disk obviously will not have
2-second gaps between tracks (burned DAO and not TAO), will be closed
("fixate"), etc. I'm not an expert, however-- perhaps talk to <sos at
freebsd.org> who wrote a goodly portion of this infrastructure for FreeBSD...
--
-Chuck
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