MOTM

Excellent and all to often overlooked point about the "ideal" LPF.

Jitter: all you need is a reclocking D/A. I have a $200 
DAC-in-the-box (yes, that's what it is really named) that beats the 
pants off of converters at ten times the price.

I just finished Datarius "CD/DVD School" at the top of my class (I 
was the only student ;-). Anyway, I can now analyze CD jitter on 
our new $53K Datarius System http://www.datarius.com on the 
order of 1 ns or less and I can assure most CDs have many ns 
of jitter (often in the hundreds).

Reclock for playback (and clock for recording) using a good 
clock, AardSync http://www.aardvark-pro.com is highly 
recommended, and be amazed by the difference, even with a 
so-so transport , D/A, etc.

Barry

--- In motm@y..., "Paul Schreiber" <synth1@a...> wrote:
> 
> 
> > > The Nyquist criterion states that any sample rate of more 
than twice
> > > the highest frequency is all thats needed for accurate 
reproduction,
> >
> 
> OK, this is pet peeve time!
> 
> NO, it DOES NOT say this. Because this is 1/2 of the 
statement. No one quotes the OTHER half
> because few people take graduate-level DSP and calculus. 
The second half can be *simplified* to
> say:
> 
> "for accurate reproduction.....assuming an IDEAL lowpass 
filter."
> 
> The ideal filter needs to have sin (x)/x response, which is a 
PHYSICAL impossibility. So, you
> have to approximate it.
> 
> Also, there is a mathematical "assumption" made about the 
sampling part: that the "jitter" is
> zero. Meaning, the sample period is PERFECTLY periodic, not 
within say 1ns but better than
> 0.001ps! That is also PHYSICALLY impossible. In fact, having 
low-jitter sample rate clock is MORE
> AUDIBLE than just about anything else. That's the ONE point I 
agree with Stereophile: the better
> CD players have extremely low sample-rate jitter. This is 
something you can plot as a histogram.
> That's why Yamaha and Crystal Semi sell boatloads of jitter 
PLLs.
> 
> Paul S.