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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
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
kthomas
911 posts
 
Some of this is a question I have tried to understand the answer to for a long time, to no avail. It sounds trite (or obvious) to say that the job of transport is to read the data on the CD and deliver it faithfully to the destination, in the case of music, the DAC. Given that a $50 CD drive in a computer can read a CD at much faster rates than is required for audio playback from a redbood CD, and deliver it provably bit-for-bit to another location, all while in a horrible electrical environment and, if you like, with the computer sitting on it's side, leads me to wonder why any of these issues exist in the audio component world. I see only one of two possibilities:

1. They don't and the performance differences people confer don't actually exist, or

2. They exist because truly bad engineering in the transport-to-DAC design that is fundamental to ALL audio component CD players. Assuming everyone who hears a difference isn't looney (and I assume they're not), there should be a technical explanation that is understandable in engineering terms to describe why the cheap computer CD can do it but the audio CD player can't. I've never read one that was convincing.

I think the far greater difference you'll find between a Wadia 861 and a Sony SCD-1 will be in the filtering algorithms they apply to the data stream. -Kirk

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.
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