🚀 go-pugleaf

>You obviously know what you are talking about. How does the 'bad data'
>flag get unset? I would have thought that a 'dumb copier' would not
>alter any of the incoming bitstream.

The "bad data" flag isn't part of the primary datastream... it isn't
part of the 16-bits-per-sample audio data.  It's auxiliary
information, calculated by the CD player hardware.

When you use a CD-ROM drive to read audio data from a CD, you get the
audio data (2352 bytes per block).  You do not, unfortunately, get the
"bad data" flags associated with the samples in the block.  As far as
I can tell, there's no standard for transferring a combined "data and
flag" data across the SCSI or IDE/ATAPI bus.

So, the "bad data" flag is lost at this point in the process.  At
best, you might get a status result from the READ command which tells
you "there's a bad sample somewhere in the data you just read"... but
I have yet to see this sort of feature actually implemented.

To make matters worse... when you "burn" the CD-R, you send the
2352-byte audio blocks to the drive via SCSI or ATAPI, and the drive
calculates a _new_ C1/C2/interleaved block structure and burns it to
the disc.  There's no way (as far as I know) to tell the CD-ROM drive
"Here, burn this sector of data... and, oh, by the way, I want you to
deliberately damage the CIRC data so that the following set of samples
will read back as 'bad' and be interpolated."

I'm sure there are some professional recorders which can be used to
burn arbitrary interleaved data to a CD-R (in order to deliberately
introduce errors for testing purposes) but this doesn't seem to be a
feature of standard consumer drives... and there's not really any good
reason to want to do it, anyhow.

So, the PC never sees the "bad data" flag, and couldn't pass it along
to the CD recorder even if it did.

-- 
Dave Platt                                        dplatt@feghoot.ml.org
Visit the Jade Warrior home page:   http://feghoot.ml.org/jade-warrior/
  I do _not_ wish to receive unsolicited commercial email, and I will
     boycott any company which has the gall to send me such ads!