EDN Access -- 10.13.94 DSP technique generates arbitrary nois
Design Ideas:October 13, 1994
DSP technique generates arbitrary noise
Flight Safety International, Broken Arrow, OK
A simple addressing technique can yield long bursts of pseudorandom noise without performing strenuous real-time computations or consuming large amounts of memory. The trick is first to fill memory with a short, precalculated pseudorandom sequence and then to access the samples in that sequence indirectly using a randomly generated pointer.
The method in Ref 1 generates and then averages 16 random numbers to achieve noise with a Gaussian distribution. Ref 1's algorithm is too complex for hectic real-time processing but is fine for generating a pseudorandom sequence with which to preload memory.
If you were to load memory with 16 ksamples of noise--only 1 sec's worth at a 16-ksample/sec output rate--the following code fragment would stretch that 1 sec's worth of samples to many times its apparent length:
This code fragment generates noise having any desired distribution, as long as you preload memory with proper noise samples. (DI 1590)
Salibrici, Bill, "Fixed-point DSP chip can generate real-time random noise," EDN April 29, 1993, pg 119.