In article , John Phillips
wrote:
In article , Ian Molton wrote:

There may be some quirks to consider here too.

AIUI, a few years ago only CD-ROM transports used to have three-beam
lasers (as opposed to CD-DA transports with a single beam) and were
reported to have rather lower first-stage soft read error rates due to
better tracking of the CD.

My understanding is that the Philips mechanisms for CD-A started off with
single beam dither tracking, but the Sony ones started as three-beam. I
think this continued for many years, but am less sure of that.

So, maybe there is a hypothesis to test here concerning the error
performance of the CD transport.

This may well have been behind Meridian's use of CD-ROM transports in
their CD players years ago when others were still using CD-DA
transports. This seems to have changed over the last few years as many
audio CD players have come to use three-beam transports too.

My understanding is that they stayed with the transports they were familiar
with as they'd put a lot of work into developing their own in-house servo
control software, etc. So far as I know, the main distinction, though was
not between dither tracking and 3-beam, but between x1 and xN with
re-reads.

However, for low enough raw error rates (hard plus soft) this should all
get corrected anyway (although, again, CD-DA format error correction is
not as good as CD-ROM format error correction). My experience
recovering the data from physically damanged audio CDs is the same as
Ian M's: until a CD is really bad, multiple extractions on a three-beam
CD-ROM transport produce completely identical bitstreams (I'm not
including timing here).

My experience is the same as the above.

I have not followed the thread well enough to recall just what CD
transport was being used for Andy's initial observation but it is
certainly my observation that some transports are audibly worse than
others with damaged CDs. I can demonstrate that with the three current
transports I have (four including the car player).

My experience is similar. Indeed, I have had some faulty discs which
produced quite obvious clicks/pops/swishes in one player but not another.
This included players like the Quad 67 and the Meridian 200/263.

However I can also demonstrate to myself that the additional vibration
isolation I have tried (not the same thing as Andy tried) on my main CD
player - a three-beam transport - makes no audible difference for all
CDs I have tested (including the damaged ones).

My experience is the same as the above. I *have* felt that damping can
help, but for reasons that do not have anything to do with the actual
digital output of the transport.

Slainte,

Jim

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