Re: What's the use of a 192 kHz sample rate?

On Tue, 13 May 2008 18:08:19 GMT, nospam@[EMAIL PROTECTED]
 (Don Pearce)
wrote:

>On Tue, 13 May 2008 11:04:09 -0700, Eric Jacobsen
><eric.jacobsen@[EMAIL PROTECTED]
> wrote:
>
>>On Mon, 12 May 2008 19:42:31 -0400, "Arny Krueger" <arnyk@[EMAIL PROTECTED]
>
>>wrote:
>>
>>
>>>
>>>A properly-operating CD player playing discs in good condition probably
has 
>>>less than one erroneous sample per full side (72 minutes). There are a 
>>>modest number of correctable and corrected errors.
>>
>>Then they were mighty foolish to add a lot of interleaving and FEC to
>>correct the errors.    Those foolish, foolish engineers.
>>
>Only a fool would design a system that needed everything to be perfect
>in order to operate. Plenty of error correction means that CDs still
>play after your daughter has danced on them.
>
>d

Not only that, but if somebody had designed CDs so that the raw error
rate was extremely low, it'd be very easy for somebody else to come
along with a competing technology that squeezed in more data and
traded that off with a reasonably high-rate ECC to clean it back up.
Doing it sensibly would give a net increase in data density.

But they already did that on CDs, since the inner (28,24) Reed-Solomon
code plus the (14,8) EFM is there specifically to handle the fact that
reading optical data is prone to errors, even with pristine media.   I
worked briefly on an optical storage system in the early 90s, and at
the time (which was contemporary with CDs being pretty fresh
technology), the raw error rate for optical storage, of pretty much
any kind, was Pe = 10e-3.

If it weren't prone to errors, the obvious thing to do would be to
increase the data density until the error rate was something
reasonably easy to clean up with a high-rate FEC or ECC.  Clearly
that's exactly what they did.

The outer code, after the first interleaver, on a CD is what cleans up
scratches and things like holes drilled in the media.  The inner code
cleans up the errors that will exist even with pristine media and a
healthy reader.

Eric Jacobsen
Minister of Algorithms
Abineau Communications
http://www.ericjacobsen.org