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From: acgd@ihlpf.att.com (Andrew Charles)
Newsgroups: rec.audio.high-end
Subject: Photo-detectors in CD players
Message-ID: <12783@uwm.edu>
Date: 5 Jun 91 12:54:23 GMT
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I have some questions which may not make sense (due to a lack of technical
background on my part). However, I'll give it a try:

What factors affect the output voltage of a photocell such as those used
in CD players? What factors affect the time it takes a photocell to reach
its "expected" output?

Is it possible that circumstances could arise in a CD player which would
affect the photocell sufficiently in these ways to either cause a misreading
of a bit (wrong voltage value reached) or cause "jitter" (photocell reaction
time is too long or too short)? If the answer to either of these is "yes",
could these circumstances arise under normal operation if the player is
not broken? If "jitter" is possible here, can it be large enough to affect
the sound?

Another way to approach this is to ask: how can a photocell fail? and if it
does (or is degrading over time) what symptoms would one expect to see at
the system level?

I've just started reading Pohlman's "Principals of Digital Audio" (2nd Ed.)
and haven't found any discussion of this. Of course, I may not have seen
it yet if it's there.

Generally, I'm wondering how much the choice of photocell matters when
a CD player is being designed.

Email or posted answers would be welcome. Technical references would also
be welcome if they aren't beyond my technical grasp (Pohlman's book is
in my range).

If I'm coming way out of left field I apologize and ask that you bear in
mind the disclaimer in the first line of this message.

Thanks,

Andrew Charles
acgd@ihlpf.att.com