On Wed, Feb 22, 2006 at 12:16:18AM -0600, Travis H. wrote:
> 
> One of the things Terry Ritter mentioned when evaluating the Atom Age HWRNG
> (my page on it http://www.lightconsulting.com/~travis/atom_age/)

Very nice.  I was thinking a little bit about doing the same sort of
thing but packaging it in a rs-232 backshell.  Getting rid of stray
EMI was something that worried me quite a bit though, and rightly so
it seems :)

> is
> that we should take the *analog noise* and digitize it and do
> autocorrelation.  By passing it through a single-bit A/D, you're
> throwing away data that might be useful to recognize a pattern which
> is present though obscured in the digital data.  I'm sure you can
> imagine such a thing.
> 

Nup - you are fooling yourself.  You are forgetting the Nyquist
Theorem.  With _any_ sampled data system you are implicitly throwing
data from the analogue signal away, any frequencies above the sample
frequency are implicitly mapped to below the sample frequency.
Normally in a sampled data system you make your sample frequency two
times higher than the highest frequency you are interested in.
Theoretically, white noise has an infinite bandwidth so any sample
freqency you choose is going to band limit your noise - regardless of
the resolution of your a/d conversion.  All it would buy you is more
bits per sample period.

Regardless of the number of bits per sample, they should be amenable
to fourier analysis which would easily show up any strong frequency
correlations over time.  The problem is to make sure you have "real"
white noise you would need an infinite number of samples, to get a
decent correlation you would need a lot of samples otherwise you may
get a short term run that will skew things.

-- 
Brett Lymn