Nth Octave Test Signal

Returns an Nth Octave Test Signal similar to a warble tone.

random_band is the main program and it outputs a test signal which has a constant level. The instanatenous frequency varies randomly within the specified Nth octave band range.

The program outputs three plots: time record of the instantaneous frequency, time record of the instantaneous level, and a histogram of the spectral content.

The test signal is constructed by generating a a set of random number for the instantaneous frequency as a function of time.
The instantaneous frequency is integrated to yield the phase angle. The trigonometric sin function is used to construct the real part of the amplitude.

Filtering and normalizing is used to remove artifacts from the random number generation. The resulting test signal is not a warble tone and it is not pink, white, or brown noise.

The resulting test signal has characteristics of a warble tone.
The level is more constant and the frequency is band limited
like a warble tone. There is still some random variation in
instantaneous frequency like white noise.