Anti-jitter RAM buffer in DACs, Which have one ? Options

[Pio2001]

In, http://www.tc.umn.edu/~erick205/Papers/pap...html#principles we can read about RAM buffers :

This process is referred to as timebase correction and as stated before, any quality piece of equipment will implement it.

That has been the ritual answer to jitter concerns since I'm on the Internet.

But... if "any quality piece of equipment will implement it", then some non-quality pieces of equipment don't implement it. My question is : which ones ?

The statement "quality piece of equipment" is completely subjective and doesn't give any information. For my grandfather, a "quality" CD reader will be a portable radio-cassette-CD-speakers combo for 100 $ in the supermarket. The "non-quality" one will be the Fisher-Price toy for children from 3 to 7.
For an audiophile friend, the "quality" CD player will be the 25,000 $ Wadia CD Transport+DAC, while any player under 1,500 $ is just worthless crap.

So, do a 200 $ CD Player always have a RAM buffer ? Or is it not considered a quality piece of equipment ? What about a 300 $ CD Player from 1990 ?

[Halcyon]

As far as jitter at the DAC stage is concerned, there isn't any, save for the jitter in the master clock. No amount of buffering will help that. Each stage from the CIRC decoder to the DAC filter is slaved and synchronized to the chipset's master clock (which has an arithmetic relationship with Fs).

Please correct me if I'm wrong. I'm straying a little off-topic here perhaps, but eventually hopefully covering what Pio2001 asks also.

With external bitstream feed, the master clock (from the perspective of the DA circuit) can be 1) the incoming bitstream's (when using SPDIF) original master clock generator OR 2) the master clock that is near the DAC itself (creating a new reference clock for the DAC, rather than using the clock from the incoming stream).

In many (if not most) cheap receivers, the DAC is slaved to the incoming (SPDIF) bitstream clock. The jitter contained in that signal will not be rejected and will most likely become part of the DA-converted signal's noisefloor (if random and not data induced).

In some receivers (this can be generalised to some external DACs and CD players) the input bitstream to DAC is buffered / jitter attenuated (there is a trade-off between attenuation frequency and power) and signal is fed to the DAC using a new hopefully more stable reference clock with diminished jitter levels.

An example of this aproach is the Chord DAC64 external DAC:

http://www.stereophile.com/printarchives.cgi?624:6

I don't want to debate the goodness/badness of that unit. Just pointing it out as an example of a dedicated RAM buffer for jitter attenuation.

Now, back to Pio2001's original question:

Yes, even simple/cheap cd-players contain a simple FIFO buffer.

Does this mean that their output does not contain jitter or that their internal DA conversion is immune to jitter?

No it does not. Jitter in DA stage is often linked to poor clock (deviation can be measured in hundreds of nanoseconds rather than hundreds of picoseconds), inadequate power filtering (e.g. power available to different parts modulates with the input data) and some other issues that can be avoided with a little bit more careful (and usually a little bit more expensive) electronics.

Does this mean such jitter in cheaper cd players is audible (now just talking about jitter, not I/V conversion, op amps and the analog stage after DAC in general)?

Somewhat debated area. Julian Dunn (in his Jitter Theory App Notes for Audiotech) has discussed the audibility of jitter at various levels using various signals.

Does it mean that the cheap cd-player can be used as a reference quality cd transport (assuming it does the disc reading / error correction properly) when combined with a superior jitter attenuation DAC?

To my knowledge, yes.

regards,
Halcyon