The bitdepth is an important but a bit a confusing concept since
its use varies among audio formats. The "classical" meaning is
applicable to PCM style encodings. When refering to mp3 or other
lossy type formats and DSD type formats the bitdepth is not used
in the same way. When referring to formats such as wav or aiff
the bitdepth is crucial to the dynamic range that is "encoded"
in the sound. Common Audio Bit Depths For a detailed explanation
on bit rates and their importance have a look at this wikipedia
article: http://en.wikipedia.org/wiki/Audio_bit_depth