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Anti-jitter RAM buffer in DACs, Which have one ?
Pio2001
post Aug 3 2003, 10:00
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In, http://www.tc.umn.edu/~erick205/Papers/pap...html#principles we can read about RAM buffers :

QUOTE
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 ?
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d_kay303
post Aug 14 2003, 08:44
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QUOTE (ChristianHJW @ Aug 7 2003, 07:01 AM)
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 wink.gif ....

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
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Posts in this topic
- Pio2001   Anti-jitter RAM buffer in DACs   Aug 3 2003, 10:00
- - Patsoe   Since it's the cheapest thing, I can't ima...   Aug 3 2003, 19:58
- - F1Sushi   All CD players contain buffer memory between the E...   Aug 3 2003, 21:13
- - Halcyon   QUOTE As far as jitter at the DAC stage is concern...   Aug 4 2003, 09:36
- - 2Bdecided   Pio, I agree with the importance of your question...   Aug 4 2003, 11:27
- - F1Sushi   QUOTE (Pio2001 @ Aug 3 2003, 05:00 AM)So, do ...   Aug 4 2003, 12:53
- - F1Sushi   QUOTE (Halcyon @ Aug 4 2003, 04:36 AM)Does th...   Aug 4 2003, 13:44
- - Patsoe   Those are interesting side notes, F1Sushi. Could ...   Aug 4 2003, 14:05
- - F1Sushi   QUOTE (Patsoe @ Aug 4 2003, 09:05 AM)Those ar...   Aug 4 2003, 14:25
- - Patsoe   QUOTE (F1Sushi @ Aug 4 2003, 02:25 PM)http://...   Aug 4 2003, 14:44
- - Pio2001   Thanks, all of you for the answers. There was a pa...   Aug 4 2003, 14:54
- - F1Sushi   QUOTE (Patsoe @ Aug 4 2003, 09:44 AM)QUOTE As...   Aug 4 2003, 15:01
- - Pio2001   Sorry, I completely lost the link. It was an old s...   Aug 4 2003, 21:13
- - F1Sushi   QUOTE (Pio2001 @ Aug 4 2003, 04:13 PM)Sorry, ...   Aug 4 2003, 21:21
- - Pio2001   No sorry, there was no color, it was all about jit...   Aug 4 2003, 22:02
- - F1Sushi   QUOTE (Pio2001 @ Aug 4 2003, 05:02 PM)No sorr...   Aug 4 2003, 22:13
- - Halcyon   F1Sushi, thanks for the clarification! More ...   Aug 5 2003, 08:52
- - F1Sushi   QUOTE (F1Sushi @ Aug 4 2003, 04:21 PM)QUOTE (...   Aug 6 2003, 03:23
- - F1Sushi   QUOTE (Patsoe @ Aug 4 2003, 09:05 AM)Those ar...   Aug 6 2003, 04:10
- - Pio2001   QUOTE (F1Sushi @ Aug 6 2003, 05:23 AM)Could t...   Aug 6 2003, 12:49
- - TrNSZ   There is a device available from most high-end aud...   Aug 6 2003, 13:24
- - F1Sushi   QUOTE (TrNSZ @ Aug 6 2003, 08:24 AM)There is ...   Aug 6 2003, 14:17
- - F1Sushi   Found it - actually it's from Monarchy Audio, ...   Aug 6 2003, 14:36
- - Patsoe   Actually, from the description I'd suspect it ...   Aug 6 2003, 15:22
- - F1Sushi   QUOTE (Patsoe @ Aug 6 2003, 10:22 AM)Actually...   Aug 6 2003, 15:34
- - TrNSZ   To clarify on the "Monarchy Audio" DIP D...   Aug 6 2003, 15:57
- - F1Sushi   QUOTE (TrNSZ @ Aug 6 2003, 10:57 AM)To clarif...   Aug 6 2003, 16:20
- - 2Bdecided   In the current (September!) issue of Hi-Fi New...   Aug 6 2003, 16:32
- - F1Sushi   QUOTE (2Bdecided @ Aug 6 2003, 11:32 AM)The o...   Aug 6 2003, 16:42
- - Halcyon   2Bdecided, do you know of studies/measurements an...   Aug 6 2003, 19:25
- - F1Sushi   QUOTE (Halcyon @ Aug 6 2003, 02:25 PM)However...   Aug 6 2003, 19:44
- - Pio2001   You can always record an SPDIF output with an SB l...   Aug 6 2003, 21:19
- - Patsoe   QUOTE (F1Sushi @ Aug 6 2003, 03:34 PM)QUOTE (...   Aug 7 2003, 08:30
- - F1Sushi   My take on it is that the statement about "ab...   Aug 7 2003, 12:46
- - Patsoe   QUOTE (F1Sushi @ Aug 7 2003, 12:46 PM)Thought...   Aug 7 2003, 15:23
- - 2Bdecided   QUOTE (Patsoe @ Aug 7 2003, 02:23 PM)QUOTE (F...   Aug 7 2003, 15:36
- - F1Sushi   QUOTE (2Bdecided @ Aug 7 2003, 10:36 AM)QUOTE...   Aug 7 2003, 15:42
- - ChristianHJW   This thread confirms a couple of opinions i have s...   Aug 7 2003, 16:01
- - Patsoe   QUOTE (ChristianHJW @ Aug 7 2003, 04:01 PM).....   Aug 7 2003, 18:56
- - Halcyon   Shhh... don't tell them. It's reserved for...   Aug 7 2003, 20:09
- - F1Sushi   Just came across this link, which raises several t...   Aug 7 2003, 20:42
- - 2Bdecided   This thread should be in the FAQ! Cheers, Dav...   Aug 8 2003, 09:51
- - F1Sushi   Here's a Monarchy Audio DIP on a chip: http:/...   Aug 8 2003, 16:36
- - d_kay303   QUOTE (ChristianHJW @ Aug 7 2003, 07:01 AM)Th...   Aug 14 2003, 08:44
- - Patsoe   You're pointing out the exact reason why a two...   Aug 14 2003, 09:25
- - Pio2001   As 2Bdecided explained, this is only valid for che...   Aug 14 2003, 12:17


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