[sdiy] Best software noise algorithm?

[Scott Gravenhorst]

Tom Wiltshire <tom at electricdruid.net> wrote:
>Hi All,
>
>What's the most efficient software pseudo-random noise algorithm?
>
>I have previously used LFSRs, which are reasonably quick and can  
>produce very long sequences quite easily, but I'm looking for  
>something really quick and dirty.
>
>I looked into Linear Congruential Generators, and found lots of sites  
>that said that these can be very quick if you ensure the modulus is a  
>power of two. But most examples are actually with the Parks-Miller  
>numbers, which aren't a power of two.
>
>I'll be doing this in dsPIC assembly as usual, and I've currently got  
>a 64-bit LFSR that generates a new 16-bit number in 19 cycles. The  
>quality and sequence length of that are more than I really need, so  
>I'd like to speed it up.
>
>Have people got any good tricks to share for making random numbers  
>quickly ?
>

I'm an LFSR freak...

http://home1.gte.net/res0658s/electronics/LFSRtaps.html

The above is a table of taps for maximal LFSRs, some require only 2 taps.  The
execution time, I assume, depends on the number of XOR operations (among other
things) so to reduce the taps is to speed it up.  

I like Eric's idea of using an internal CRC generator if it's got enough bits.

I also like Dave's idea of adding an FPGA.  

Also - Could a CPLD do this?  

As long as the topic is noise algorithms - see this thread wherein there are some
samples of an FPGA noise synth I'm working on:

http://electro-music.com/forum/viewtopic.php?p=284333#284333

The synth is implemented on the little Avnet Spartan-3A dev board.

-- ScottG
________________________________________________________________________
-- Scott Gravenhorst
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