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 ?

[d_kay303]

This thread confirms a couple of opinions i have since quite some time now :

1. A well tuned CD player, with drive speed controlled by the DAC timer/buffer does always ( say, in most cases ) sound better then external drive / DAC combo's, however expensive they might be

2. SPDIF sucks in terms of preserving highest possible quality ( its practical, easy to handle, but thats about it )

3. MISSION people knew what they were doing when inventing a new digital interface ( no SPDIF on these devices ) for their hi-quality CD drive / DAC combo's , with good old handshake signals to sync the timing ....

I did some simple pen and paper exercise, and this is what I found out:

Let's say our CD-player reads twice as slow as our DAC reads from FIFO buffer.
Datastream is a,b,c,d bits)

clock
CD__DAC__BUFFER (3bit)
1___Pause__000
2_________00a
3_________0ba
4_________cba
5____1 ____0cb
- ____2____ 00c
6____3 _____00d
-____4_____000
7____5 _____000 (bit e just makes it!)
-____6_____000 underrun!

Let's say our CD-player reads twice as fast as our DAC reads from FIFO buffer.
Datastream is a,b,c bits. We have 4 bit's FIFO


clock
CD__DAC_ BUFFER (4bit)
1___Pause_000
2________000a
3________00ba
4________0cba
5___1____0dcb
6________edcb
7___2____fedc
8________buffer overrun!


Ok, so what, no CD player works this way. They're not that stupid.

BUT.. say the clock in the CD-player would be 0.00001% slower or faster, eventually it would either underrun or overrun. Even if it's unstable being sometimes faster sometimes slower(jitter) it would have a meantime that is either slower or faster, and that will also eventually overrun/underrun the buffer. So what to do?, well.. two way communication would be nice. I guess most CD-player adapt their reading speed with regards to how full their FIFO buffer is.

How big is this problem in real life?, no idea. I think I'll buy an external USB DAC to my computer when there is a good one available.

This post has been edited by d_kay303: Aug 14 2003, 08:50