How do vibrations in a CD player/transport cause jitter ?

[percy]

I have across mods to CD players that involve damping the chassis, covers, and internal parts of a CD player and transport against vibrations. Can someone please explain to me how exactly does vibration influence or induce jitter ?

[poynton]

Originally posted by percy
I have across mods to CD players that involve damping the chassis, covers, and internal parts of a CD player and transport against vibrations. Can someone please explain to me how exactly does vibration influence or induce jitter ?

Hi.

To give an easy example :-

Any capacitor acts as a microphone to a certain extent (hence 'capacitor microphones').

Therefore any vibration will cause the capacitors to introduce 'noise' into any circuit to which they are attached.

Reduce the induced vibration - reduce the induced noise - QED.

Andy

[ezkcdude]

Capacitor microphones are designed specifically so that one plate acts as a very thin diaphragm, while the other plate is fixed. Then, air pressure changes can change the distance between plates, and hence, the capacitance, voltage, etc.

That said, capacitors used for audio applications are not "designed" to do this, and I can't imagine that typical vibrations will change the capacitance by any significant amount (i.e. enough to hear). If someone has tried inducing vibrations to measure this effect, by all means, let me hear it. But, I really doubt that anyone can offer anything more than hand waiving arguments based on something they read in Stereophile or some other audiophile pub.

Something that potentially could cause problems are vibrations that effect the crystal timing.

[percy]

Originally posted by poynton

Therefore any vibration will cause the capacitors to introduce 'noise' into any circuit to which they are attached.

I realize that noise in the clock's signal and power lines can be held accountable for jitter, but are you saying that the mechanical vibrations from the drive are strong enough to create microphonics from capacitors ? which in turn are strong enough to pollute the clock lines ??

[percy]

Originally posted by ezkcdude
Something that potentially could cause problems are vibrations that effect the crystal timing.

I was hoping to hear something to that effect, but even in that case just isolating/damping the crystal - or the module/pcb on which the crystal sits - should be enough. Why the whole darn chassis ?

[poynton]

Originally posted by ezkcdude


That said, capacitors used for audio applications are not "designed" to do this, and I can't imagine that typical vibrations will change the capacitance by any significant amount (i.e. enough to hear).

I only gave the capacitor as an example since capacitor microphones exist. Yes, I know that they are not built to the same design as audio caps but they exist and therefore it is a fact that vibrations in caps can induce spurious voltages however small. When you discharge a flashgun cap., a noise is produced (try it) and the reverse is obviously so. Enough of caps. , it was an example ! Try Tubes / valves - also microphonic. Try flexing a phono-preamp pcb - you get a noise.

Many more examples exist - whether they increase jitter, I do not know but they can introduce noise.

Andy

[jeff mai]

Vibration modulates the *shared* power supply through the servo circuitry. If the disc moves, the laser has to track it. Motors draw current, etc.

I can tell you that the best transport I have heard was a relatively old and cheap CD player where someone had given a lot of attention to this. There was no part of the original chassis remaining. The transport mechanism was on a sprung platform. Worth doing.

[DragonMaster]

I think that it's mostly for the disc, if there are less vibrations, it has less tracking, focusing, etc. job to do, and less chances to skip.

Maybe the clock would be affected, but if a shock could change it's output, then an high-pass filter could remove it.

Also, I think that a lot of them are made by persons that want to make $$$, usually accompanied with a looong fake theory seeming a bit plausible. See : CD Demagnetizer, right next in the products page to $60 plugs, green CD markers, CD flashers, $125 system enhancer CDs and $10k/foot speaker cables, or the Clever Little Clock.

http://www.gcaudio.com/cgi-bin/store...uct.cgi?id=190
http://www.machinadynamica.com/machina41.htm

[Calimero]

http://www.6moons.com/industryfeatures/lurne/lurne.html

IMO our knowledge (at least mine) is insufficient to understand all effects within digital audio translation to music that effects its quality. There are a lot of partial theories, with various kinds of measurement/statistical backup. It comes down to 'what you want to believe'.

Henk

[seppstefano]

Originally posted by poynton


Any capacitor acts as a microphone to a certain extent (hence 'capacitor microphones').
...

Reduce the induced vibration - reduce the induced noise - QED.

Andy

Besides the xtal works through a piezoelectrical effect... If the xtal shakes, no doubt the signal output will be altered...

Stefano