[sdiy] PRN Noise Gennie Question

[Antti Huovilainen]

On Tue, 29 Mar 2005, Harry Bissell Jr wrote:

> If you took the DAC outputs from widely
> spaced shift register points (assuming that you could
> as in a hardware implementation)... wouldn't that
> also remove the lowpass characteristic.

No, that simply moves the taps around.

As far as the output is concerned, an N-bit LFSR with a single input can 
be considered an N-bit delay line. If you take out more than one tap, it 
is same as using (maximally) N coefficient FIR filter (with possible zero 
coefficients). As the samplerate is usually around 1 MHz or more, you 
can't use this for pink noise etc. But if you for example need audibly 
white noise with gaussian amplitude distribution (for dither), you can 
apply a short FIR filter followed by a simple RC filter. This produces 
more even distribution for "low" clock rates than simple RC filter.

Jon Dattorro has a paper that covers this topic pretty well at
http://www.stanford.edu/~dattorro/EffectDesignPart3.pdf

Antti

"No boom today. Boom tomorrow. There's always a boom tomorrow"
   -- Lt. Cmdr. Ivanova