mu2lin — mu-law encoding to linear signal
mu=lin2mu(y)
Utility fct: y=mu2lin(mu) converts mu-law encoded 8-bit audio signals,
stored in the range 0 <= mu <= 255, to linear signal amplitude in
the range -s < y < s where s = 32124/32768 ~= .9803.
The input mu is often obtained using mget(...,'uc') to read
byte-encoded audio files. Translation of C program by Craig Reese:
IDA/Supercomputing Research Center Joe Campbell: Department of Defense