[sdiy] OT: Scratchy CDs

[ChristianH]

Hi all,

not particularly synth diy related, but maybe someone has run into this
as well.

I recently happened to notice typical vinyl type scratch noises coming
>from a CD. At first I supected clipping in the analog audio path, but
after digitally grabbing the track into a WAV file, I found that
sometimes there are runs of about 7 to 15 audio samples with equal value,
similar to a s&h. If this happens within a waveform slope, it generates
those scratchy noises.

I tried grabbing with 3 different CDR drives, and an audio CD player
into the analog sound card input - and it turns out, that each drive
exhibits this behaviour at varying degrees, comparing the very same
location of the song. Only one drive (and that's the oldest one...)
delivers an apparently clean waveform. Seems to me that the error
correction isn't quite able to fix drop outs, depending on laser age or
other parameters.

The particular CD in question isn't really he problem (an el cheapo
T.Rex record released by the, um, honorable Pickwick label, bought back
in the 80s), but I found at least one other CD where it shows very
prominently - our very own Tony Allgood's Takla Makan (and that's more
of a loss, I might say ;-)

What worries me is the thought of CDs not being as durable as we all
wish they were. And it makes me wonder about long term CD-ROM reliability
as well.

cu
Christian