Re: anti-aliasing

On Sun, 25 Nov 2007 18:46:00 -0800, John Larkin
<jjlarkin@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:



Suppose one (actually, me) were firing an adc at some fixed rate,
ballpark 12 KHz in this case, and the input to the adc was a sine wave
of fixed but unknown frequency. The adc will take a bunch of samples,
ballpark 1000 maybe, and I want to compute the mean (ie, dc value) and
the mean of the abs value of the samples (ie, the ac value). That
works, but sometimes the input frequency aliases against the sample
rate and messes up the data, like gives a big average dc value when
there's really none there.

(This is not a Nyquist issue; the sample rate may be above or below
the sinewave frequency.)

So maybe I can fuzz up the sample rate so that it can't alias against
any constant sinewave frequency.

I could add a pseudo-random delay after every adc sample shot; but the
mean sample rate wouldn't change a lot. Or I could add successive
delays, essentially sweeping the sample rate down.

Any ideas?

---
What's the input frequency range and, if you can vary the sample
rate, what's the maximum rate?


--
JF
.

Relevant Pages

  • Re: anti-aliasing
    ... ballpark 12 KHz in this case, and the input to the adc was a sine wave ... of fixed but unknown frequency. ... The adc will take a bunch of samples, ... The added delays wouldn't have to be Gaussian, you'd just want their spectrum to be fairly white. ...
    (sci.electronics.design)
  • Re: anti-aliasing
    ... John Larkin writes: ... Suppose one were firing an adc at some fixed rate, ... ballpark 12 KHz in this case, and the input to the adc was a sine wave ...
    (sci.electronics.design)
  • Re: anti-aliasing
    ... Suppose one were firing an adc at some fixed rate, ... ballpark 12 KHz in this case, and the input to the adc was a sine wave ... I could add a pseudo-random delay after every adc sample shot; ...
    (sci.electronics.design)
  • Re: anti-aliasing
    ... Suppose one were firing an adc at some fixed rate, ... ballpark 12 KHz in this case, and the input to the adc was a sine wave ... so I can't measure crossings to any useful accuracy. ...
    (sci.electronics.design)
  • Re: anti-aliasing
    ... Suppose one were firing an adc at some fixed rate, ... ballpark 12 KHz in this case, and the input to the adc was a sine wave ... If the granularity of your "pseudo-random delay" is small enough, ...
    (sci.electronics.design)