The brain doesn't compute it, the cochlear is an fft! It is a cone shaped structure (that is curled up) that is covered in hairs and neurons. The fatter end is used for low freq and the thinner end is used for hi freq. So the brain takes audio in the frequency domain, not as continuous samples!
(I did an Anatomy degree almost 20years ago now, all from memory)
(I did an Anatomy degree almost 20years ago now, all from memory)