CD transports and resonance
 

In article , Paul Dormer
wrote:
"Dave Plowman (News)" emitted :

A well worn disc is also likely to produce higher error rates
(naturally).

Wear suggests something which occurs normally with use - as happens
with an LP. CDs don't appear to wear as such - my very first one ever
still plays as new.

Damage would be a better term.

Well I did say "well worn", by which I meant to infer scratched or
grazed, but OK I accept your correction..

Does a properly setup turntable actually cause audible wear with each
and every use?? I've never owned a high end turntable long enough to
know. I do have a few elderly CD's which have gained pinholes in the
metal layer just sitting on the shelf.. :-(

Can't say for sure about 'audible' wear on LPs as - after any possible
damage that occurs on the first playing (which will affect the first
hearing, so isn't normally subject to be noticed as a change between
playings) I'd expect any further damage to be slight per playing.
(Exculding effects due to dust or a damaged stylus.)

However I have seen photos taken using microscopes that show clear signs of
stylus wear on the groove walls of LPs. IIRC there were also - many years
ago - articles on this. Not seen results for current stylii/cartriges,
though. Only ones for some years ago.

FWIW I'm currently reading through various old articles on LP performance,
but am concentrating on factors like noise level and distortion/mistracking
rather than wear. I think, though, there are some papers on this in the
JAES that I've skipped over in passing.

The snag is that modern MC cartridges seem to often have lower compliances
and higher masses than something like the 'old' V15 series. Hence they can
be expected to wear the LP more than a V15 given a comparable stylus shape.
Alas, I can't recall many modern reviews even noting this effect, let alone
any systematic work on it.

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

CD transports and resonance
 

In article , Paul Dormer
wrote:
"Jim Lesurf" emitted :

. A CD-Rom vibrates quite a bit in your hand,

Indeed. However when spinning at speeds above x1 it can re-read the
disc to ensure consistent and reliable data recovery before sending out
the resulting bitstream.

In a realtime playback situation, isn't it tricky for a CD drive to
accurately relocate itself to the correct position on a re-read, due to
the very nature of audio CD's which are not timestamped??

The data is timestamped, but not on a per-sample basis. It is stamped in
data blocks. Hence re-reads can be performed on a 'block' basis and once
aligned, the relevant bits/bytes/samples compared and collated.

What a specific CD reader does, though, is a matter for the maker of that
particular drive... :-)

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

CD transports and resonance
 

In article , Paul Dormer
wrote:
"Jim Lesurf" emitted :

The assumption - and I think it's not unreasonable - is that
stabilising a cd mechanism brings audible benefits.

As a vague and unspecific generalisation that is fine. However it does
not establish that this *is* the case in this specific instance. For
that we require suitable tests to obtain relevant evidence.

For sake of argument, wouldn't it be quicker and more fun for Andy to
just make whatever changes he feels improves his CD drive to his ears,
and get on with his life rather than conducting a series of boring
tests?? ;-)

Yes. However he *did* ask us for reasons/explanations for what he feels he
hears. Once he does this we then need more info. However if he does not
wish to determine any reasons... :-)


I mean.. permutations of stabilization technique could be very long
winded. Eg, try some feet under it.. does it sound better? Yes/No... OK
let's move on...

This is the snag with making obervations without reliable measurements. You
end up having to try things 'at random' in the hope some might seem better,
but not then be sure if or why...

Not scientific but less tedious... :-)

Far simpler IMHO to buy a Meridian and listen to the music. :-)

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

CD transports and resonance
 

In article , Paul Dormer
wrote:
"Dave Plowman (News)" emitted :



I do have a few elderly CD's which have gained pinholes in the metal
layer just sitting on the shelf.. :-(

I've heard of this but not experienced it.


Yep.. happened to a few of mine. This is out of a collection of several
thousand though, so percentage-wise a small number. Have to say.. it's
not necessarily obvious!! You can see the holes if you hold the disc up
to the light, otherwise can easily be missed. I have one right here..
not a prime example, but I'll see if it picks up on the scanner. A
legendary Nimbus rot job..


I have some CDs with pinholes. However so far as can tell, these have had
them since purchase, and they have not altered. They seem playable with not
audible problems I have noticed. The Philips Red Book spec caters for quite
large holes in the info layer without this necessarily preventing recovery
of the correct sample values.

I've also had a number of the PDO Blackburn 'brown rot' discs, and they
have replaced them all FOC when returned to them. However these don't show
holes. Just a brown discolouration of the metal.

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

CD transports and resonance
 

Dave Plowman (News) wrote:

I do have a few elderly CD's which have gained pinholes in the
metal layer just sitting on the shelf.. :-(

I've heard of this but not experienced it.

I've found pinholes in brand new CDs.

some play, some dont. luck of the draw.

CD transports and resonance
 

Paul Dormer wrote:

Audibly?? Have you performed the necessary scientific tests to confirm
this degradation with each subsequent listen? ;-)

Having seen vinyl swarf peeling off a record I can guarantee the wear is
audible once it gets bad enough.

CD transports and resonance
 

Paul Dormer wrote:

In a realtime playback situation, isn't it tricky for a CD drive to
accurately relocate itself to the correct position on a re-read, due
to the very nature of audio CD's which are not timestamped??

Not quite true. the problem is that the resolution of the timestamps is
only one frame (IIRC 1/75th of a second).

Define 'difficult'. My CD-ROM can read audio at over 30 speed.

CD transports and resonance
 

Paul Dormer wrote:
"Ian Molton" emitted :


Audibly?? Have you performed the necessary scientific tests to confirm
this degradation with each subsequent listen? ;-)

Having seen vinyl swarf peeling off a record I can guarantee the wear is
audible once it gets bad enough.


Yikes!! What kind of turntable was that on?? Did it have a nail for a
stylus? ;-)

"not mine" is all that I care about ;-)

CD transports and resonance
 

Paul Dormer wrote:
"Ian Molton" emitted :


I've found pinholes in brand new CDs.

some play, some dont. luck of the draw.

What.. some of them don't play *at all*?

Well I tend to bin CDs once they fail to play properly. (Id do the same
if it was vinyl too ;-)

CD transports and resonance
 

Paul Dormer wrote:
"Ian Molton" emitted :


In a realtime playback situation, isn't it tricky for a CD drive to
accurately relocate itself to the correct position on a re-read, due
to the very nature of audio CD's which are not timestamped??

Not quite true. the problem is that the resolution of the timestamps is
only one frame (IIRC 1/75th of a second).

Define 'difficult'. My CD-ROM can read audio at over 30 speed.


I was thinking more of a dedicated CD player or transport.

Is your drive capable of reliable DAE at that speed?? Pretty impressed
if so!

I think Im remembering it right. its certainly able to do a full CD in
under 5 mins, which makes it 20 speed or better.