Obviously there are differences in mp3 encoders - the algorithms and settings used to produce a file. But for a given mp3 file, should it decode to exactly one WAV file, or can there also be differences in the decoding?

Some decoders are not written properly and some don't implement the entire standard, thus not all will not give the same results with all mp3 files. There has particularly been a lack in many portable mp3 players. Many are restricted to a limited range of bitrates and sometimes will only handle CBR files.

Even in "compliant" decoders, there is different rounding at the least significant bit level, and sometimes dither.

http://mp3decoders.mp3-tech.org/

Cheers,
David.

Also, some decoders might sacrifice accuracy for a gain of speed by using less precision during the synthesis filterbank.

How is the ipod's decoding? better than other players, about even??? what bitrates and filetypes does it decode best?