Sorry, poorly phrased that. Obviously all A\D's are simply voltage
measurement. I was referring to the information you wanted to get.

I'd only seen the Nyquist theorem related to the conversion of periodic
signals into constituent sine waves. I know if you take simple voltage
measurements ignoring the Nyquist frequency and then try to get the
constituent sine waves that will be wrong.

But if you simply sample the voltage every 0.5ms and convert that to a value
in the range 0-128 will the aliasing have a noticeable effect? (Answer from
your previous mail would be there is an effect. Is it noticeable?)

So, in my system with 16 knobs and a 1MSPS ADC that's 62500 samples per knob
per second theroetically. So would I filter at ~125000kHz would I? Well, I
know I can't turn a knob 62500 times a second so
I ain't gonna introduce that frequency. And there's a bit or breathing room
with the 50-60Hz hum. So I guess the only thing I'd need to filter is EMI.
Is there an inordinately high ammount of EMI >125kHz? If not then it
shouldn't need the filter as if enough high end EMI is getting through
there'll be too much low freq. EMI anyway.

Thanks very much,
Tom.
----- Original Message -----
From: Robert A. LaBudde <ral@LCFLTD.COM>
Subject: Re: A/D Challenge


> At 01:34 PM 9/22/99 +1000, Thomas Brandon wrote:
> >Does anti-aliasing (filtering anything of frequency greater than half
> >sampling rate) apply to simple voltage measurment. I had gathered
> >anti-aliasing occured in the seperation into multiple sine waves.
>
> ALL ADC measurements are simple voltage measurements!
>
> ================================================================
> Robert A. LaBudde, PhD, PAS, Dpl. ACAFS  e-mail: ral@lcfltd.com
> Least Cost Formulations, Ltd.                   URL: http://lcfltd.com/
> 824 Timberlake Drive                            Tel: 757-467-0954
> Virginia Beach, VA 23464-3239                   Fax: 757-467-2947
>
> "Vere scire est per causae scire"
> ================================================================