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

Ralf Mardorf ralf.mardorf at alice-dsl.net
Fri May 28 16:33:33 UTC 2010


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.
>
> Ciao,
>   

AM could be caused by residual ripple from the DC source, but the signal 
was clearly separated from any 50 Hz harmonics. So it wasn't LF noise on 
the voltage reference?



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