[LAD] A little quiz about audio measurements...

[torbenh]

On Fri, May 28, 2010 at 05:37:47PM +0200, fons at kokkinizita.net wrote:
> On Fri, May 28, 2010 at 08:30:54AM -0700, Niels Mayer wrote:
> 
> > Audio ADCs and DACs have three important inputs;
> > the signal input, the voltage reference, and the clock.
> > Noise and interference on the voltage reference causes
> > amplitude modulation, and jitter on the clock causes
> > phase modulation. The resulting modulation products
> > look very similar in the frequency domain. One of the
> > authors once spent several days trying to track down a
> > low-frequency jitter problem, only to find that it was
> > in fact a problem of LF noise on the voltage reference.
> 
> You're close. See the extra hint in a previous post.

is that an USB card ?
there is a "small" peak at 1000Hz which looks like a usb power drain at
isochronous packet frequency. 

maybe its the packets voltage lifting the local ground a bit.


> 
> Ciao,
> 
> -- 
> FA
> 
> O tu, che porte, correndo si ?
> E guerra e morte !
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-- 
torben Hohn