🚀 go-pugleaf

In article <F308098DC0C8DC2F.31FD14AE39298D33.674812088DCBAA2A@library-proxy.airnews.net>,
Chung <kclee@hk.gin.net> wrote:

>Audio CD format has no error correction such as the "Check sum" of
>Computer CD ROM.  So, even error, the transport (or reader) don't know
>and will no correction made.  Only the DAC will check for reasonable
>signal and correct it.

This turns out not to be the case.  The audio CD format has quite a
lot of error correction... although it's true that CD-ROM has more.

Audio CDs have a two-level cross-interleaved Reed-Solomon error
correction.  Mode 1 CD-ROMs have three levels (the same two as an
audio CD, plus one additional layer).

A CD transport can and does correct the vast majority of the bit
errors it encounters. It does so, in almost all cases, without
bothering to "notify" the downstream DAC that this has happened.  If
this correction weren't taking place, _every_ audio CD would be
unbearably noisy (dozens of pops and ticks per second).

Most transports will do a pretty respectable job of identifying
audio-CD data which is so badly damaged that the C1/C2 corrector
cannot recover all of the bits.  This bad data is "flagged" when it's
transmitted to the DAC, and the DAC can choose to interpolate or mute
the audio signal to conceal the effect of the error.

-- 
Dave Platt                                        dplatt@feghoot.ml.org
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