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.