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Frozen noise generation

Dear list,

We would appreciate your expertise in the following problem.

We wish to generate two ".wav" files, each containing a burst of frozen
noise (N1 and N2) of the same duration (say 200 ms) but with different
frequency content.  Let's say that N1 has frequency components from 10 Hz
to 3000 Hz, and N2 from 3001 Hz to 4000 Hz.  Most importanly, we wish that
the SPL level for all frequencies be equal within each noise and equal for
the two noises.

So far, we have attempted to generate the noise by adding a large number of
equal-amplitude, random phase tones (phases are uniformly distributed
between 0 and 2pi).  We then normalize each of the noises to their maximum
amplitudes to produce a wav file.  The result is that the spectrum of each
noise is flat over their respective frequencies.  However, the levels are
different for the two noises (remember we wish for them to be equal).  It
is lower for the noise with the largest number of frequency
components.  This is probably the result of the normalization prior to
producing the wav file.

Is there a clever (analytical) solution to our problem, or do we have to
adjust the level of noises manually to make them equal?

Thank you very much in anticipation.

-- Enrique

Please note my new e-mail address:  Enrique.LopezPoveda@uclm.es

Dr. Enrique A. Lopez-Poveda
Facultad de Medicina                Tel. +34-967599325
Universidad de Castilla-La Mancha   Fax. +34-967599327 / 967599272 / 967599204
Campus Universitario                http://www.med-ab.uclm.es
02071 Albacete, Spain