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CD Transports: Data Drops Etc...

Please forgive the wordiness in advance. Having searched back and found a great series of posts on the technical aspects/sources of jitter (in a thread about differences in digital cable dating from last December), I find myself confronted with the following questions:

1) Is "jitter" purely a question of clock mismatch between the transmission of digital signal from the pickup and its reception by the DAC (whether separate or in-box)?

2) What is the source of so-called "data drops" (those data "errors" other than jitter) in reproducing the digital signal encoded on a CD? Is it vibration, something else?

And what may seem to be a dumber corollary question...
3) What effect does vibration have on the ability of the laser pickup to read data correctly? [looking for the technical answer]

This from a newbie trying to decide on a CDP/transport and wondering if build-quality should actually make a difference (Wadia 861 on a super-hard surface sounds better than on a table, wondering if rigid build-quality on Sony SCD-1 makes a difference or whether it could be built with plastic and have the same sound, and wondering whether what appears to be an ultra-rigid disc-clamping system made by TEAC reduces data errors)...

A big thank you in advance to all of those of you who contribute and make this forum interesting and informative to those of us just starting out...
t_bone

Showing 4 responses by aragain

aragain
39 posts
 
This isn't what you want to hear but - You can't get there from here.

The analysis you are attempting is an interesting intellectual excercise but will have no correlation to picking a cd player that you actually like!

I'm on my third set of speakers, third power amp, second pre-amp, went through 2 dacs and 2 cd players - all because I tried to 'figure out' the answer ahead of time. It would have been much easier to invest the time listening to as many components as I could and simply pick what I liked best.

There are so many factors that determine the final sound that you can't really break it down to pieces, add the individual scores and then assume the final product will equal the total score.

I know this is agonizingly low-tech but you just have to listen to as many players as you can in your own system and pick the one you like best.

Happy Listening!

- A
aragain
39 posts
 
For KThomas -

In the case of jitter the issue is insuring that the input of the dac sees the exact series of bits that came off the drive.

It is possible that the bits come off the drive properly but are seen as a different series of bits by the dac.

The dac wants to know the value of a bit at each clock tick and this involves sensing changes in voltage. A variety of factors can lead to the dac sensing an incorrect value.

So, reading the bits from the cd accurately is different than getting those bits into the dac with the proper timing.

I have intentionally not attempted to explain things that are beyond my knowledge. Hopefully an expert can jump in and provide more details.
aragain
39 posts
 
Hi KThomas -

I'm in the computer game also and this same cd drive question has bugged me for a while.

One analogy is the old 'framing error' on a modem's uart where the uart's clock got out of sync with the sender's clock.

Still, it seems like this is a problem that has been solved already and could be built into a cd player.

I am trying to remember where I read a bunch of stuff about jitter. I suppose a web search would eventually turn up something insightful.

Cheers,
A
aragain
39 posts
 
Ghost - Thanks for the info!

Still, this seems like a standard async communication problem (particularly in the single-box players) which has been solved in the computer data communications world. I think the serial rate on SPDIF is 2 mhz or 4 mhz.

If the dac is viewed as an async receiver (which I don't know if that's a valid view) then it seems existing engineering is available to get it right.

Still puzzled -
A
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