Rob A. Wrote: 
> You and I are perhaps debating two different points. While I don't want
> to devolve the conversation, the point I was debating was that it's
> nearly impossible to have a bit-for-bit copy of a CD. I wasn't debating
> the merits of the website "accuraterip.com", or the merits of C2 or
> other error correction algorithms.  
> 
> Rob

AFAIK it is perfectly possible to have a bit for bit copy of a cd.  If
3 people rip different originals of the same album on different
hardware and get the same data it is very unlikely that they don't have
a bit for bit copy of the data on the cd.

I think the confusion is caused by the fact that the bits will be
different BEFORE any error correction takes place.  As I understand it
there are two levels of error correction that can take place.  The
first deals with normal read/write errors that occur all the time, and
is capable of completely correcting those  errors.  This error
correction is then re-generated when the cd is written again, thus
giving an exact copy of the original.  The second level of error
correction is used when there are too many corrupt bits for the 1st to
deal with, and this is where we lose bit accuracy, as samples are made
up to fill the gaps.

The way the data is written to a cd can be thought of like a RAID5
array, using 3 disks, you lose 1/3 the total capacity, but if one disk
fails, all the data can always be extracted from the remaining two. ie
around 1/3 or more of the data physically on the cd is a duplication of
the real data.  If it wasn't for this, the slightest scratch, bit of
dust, or manufacturing defect would ruin the cd.


-- 
bludragon
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