Convert integer samples to float using a power-of-2 divisor

Convert integer samples to float using a power-of-2 divisor

This should cut down on unnecessary quantization noise (however minor) for 8-
and 16-bit samples. Unfortunately a power-of-2 multiple can't be used as easily
for converting float samples to integer, due to integer types having a non-
power-of-2 maximum amplitude (it'd require more per-sample clamping).