Subject: Re: [linux-audio-dev] time stretching and compression under Linux ?
From: Erik de Castro Lopo (erikd-lad_AT_mega-nerd.com)
Date: Tue Nov 13 2001 - 22:24:57 EET
It really blew my mind when Tim Goetze <tim_AT_quitte.de> said:
> >> Assuming the clocks on the cards really *are* running at constant
> >> rates. I wonder how consistent those things are? (I'm not a (digital)
> >> hardware guy...)
> >
> >I was and I can tell you they will drift relative to one another. It
> >will probably be less than 50 part per million.
>
> i wonder why they don't just take the PCI clock and divide it to generate
> the sample word clock.
Two problems:
- Most of the A-D and D-A converter chips use delta-sigma technology which
requires an input clock at 128 times the word clock.
- Generating 128 times word clock for a number of different sample rate
frequencies (22k05, 32k, 44k1, 48k, etc) from the PCI clock of 33MHz
with low jitter would require a very difficult to design Phase Locked
Loop. I know because I designed one.
Erik
--
+-----------------------------------------------------------+
Erik de Castro Lopo nospam_AT_mega-nerd.com (Yes it's valid)
+-----------------------------------------------------------+
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