Dan Dugan wrote:
>
> Walt, you wrote,
>
> >Since audio CD as played includes a step to deal with any missing bits,
> >playing is not a perfect reproduction.
>
> You're talking about error concealment, I think. To clarify:
>
> The audio CD system assumes that not all the bits will be read
> correctly from the disc. This is the -normal- state of affairs, a
> certain error rate. Same for DAT and any digital medium! Audio CD
> playback has three levels of dealing with errors:
>
> 1) Error correction: The player uses redundant coding to reconstruct
> missing data. This normally happens all the time. The result is
> perfect reproduction.
>
> 2) Error concealment: When the error rate rises so high that the
> redundant coding can't correct it, the player interpolates samples,
> i.e. makes up data that smooths over holes in the incoming stream.
> This process can be very subtle and impossible to hear. On my
> instrumented player, I only see error concealment flags where there
> is gross damage to the disc. I have a disc that I found in the street
> that has around 1000 error concealments per second. It still sounds
> like music.
>
> 3) Muting. This is the zipping, ripping sound that means the holes in
> the data are so big the player gives up.
>
> To repeat myself, any commercial pressed CD in good condition can be
> captured by a digital link with perfect reproduction. CDR playback
> may be compromised into error concealment or even muting by the low
> modulation level of the dyes used today. You can proof your system by
> reading a CDR back into the workstation digitally (synching to the
> digital input), slipping the files into bit-synchronization, and
> doing a subtraction test. If the files subtract to dead silence, the
> CDR is good.
I've rarely bothered with the last. But I agree, CD is good. And yep,
your discussion is more complete, but what I was referring to. The
difference between that and a computer audio file is the computer gives
up far earlier. They would rather not give you damaged data unless you
have special software to handle it.
As I noted I've not seen a problem with the new dyes, maybe because I'm
not easily seduced by fast burning times. And I stick with top brand media.
Walt
________________________________________________________________________
________________________________________________________________________
|