Convert linear audio signal to mu-law
mu = lin2mu(y)
mu = lin2mu(y) converts linear audio signal amplitudes in the range -1 ≤ Y ≤ 1 to mu-law encoded “flints” in the range 0 ≤ u ≤ 255.
-1 ≤ Y ≤ 1
0 ≤ u ≤ 255
mu2lin