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EDN Access -- 10.13.94 DSP technique generates arbitrary nois

-October 13, 1994

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Design Ideas:October 13, 1994

DSP technique generates arbitrary noise


Jeff Shadely,
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)

Reference

  1. Salibrici, Bill, "Fixed-point DSP chip can generate real-time random noise," EDN April 29, 1993, pg 119.


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