In Sonor, n=128, and a 20-coefficient FIR filter is calculated.
where <n> is the integer value of n.
Sonor does not actually use FFT, it uses discrete cosine transform, or DCT for short, as it is more accurate:
s is a strength factor.
s is the amplitude of the wave from 0.0 to 1.0. f is the frequency of the sample.