[sdiy] Digital noise sources

Eric Brombaugh ebrombaugh at earthlink.net
Fri Mar 28 15:52:46 CET 2008


Tom Wiltshire wrote:
> Sorry to go back to this again, but I wonder if someone could clear 
> something up for me. There's something I don't understand:
> 
> What's the difference between outputting a random stream of bits at high 
> frequency (1-bit digital noise) and outputting a  series of random bytes 
> to a DAC (8-bit digital noise)?
> 
> Are they equivalent? Is one better than the other?
> 
> If someone who understands digital better than I could explain this, I'd 
> be very grateful.

Tom,

That's a good question and one that's often occurred to me as well. I 
built up some Octave code to investigate this and what I found was that 
there really is no spectral difference between 1-bit and 8-bit random 
noise. The only noticeable difference is that if the max values of the 
8-bit noise line up with the max values of the 1-bit noise then the 
overall power in the 8-bit noise will be a few dB lower.

The most critical aspect of your noise generator is ensuring that it has 
a long period and uniform distribution.

Eric



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