Re: Frozen noise generation (David Robinson )

Subject: Re: Frozen noise generation
From:    David Robinson  <david(at)ROBINSON.ORG>
Date:    Fri, 13 Dec 2002 03:32:12 -0800

Enrique, With noise signals, there are at least two measures of "level". Spectrum Level, which is a measure of energy per unit bandwidth; and RMS energy, which is a measure of the energy of the signal as a whole. If you wish both signals to have the same spectrum level, use the same amplitude sine waves to generate each sample. On an idealised spectrum analyser, the flat top of both signals would be at the same height. If you wish both signals to have the same RMS energy, then measure this value after generation for each file, and adjust as appropriate. "Normalising" so that the peak sample value in each file is the same is NOT a method of matching Spectrum Level, RMS energy, SPL (unless each file contains a single pure low frequency sine wave), perceived loudness, or anything else! I can probably send you a poorly written and very slow MATLAB script to generate noise of any bandwidth, spectrum level, or RMS energy level. If this would be of help, send me an email. However, the principle is exactly what you're doing: sum sines of random phase. Filtering the output of a random number generator is a different approach, which may or may not be appropriate. It seems you will achieve exactly what you want simply by omitting the normalisation. Hope this is of some help - apologies if I have misunderstood the problem. Cheers, David.

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