yep...a wave or aiff should use less CPU power as they are uncompressed data and can be played directly from file. mp3s are compressed and must be uncompressed before the data can be manipulated and played throught the system. this obviously uses more CPU power as it requires the uncompression to run prior to playing the track. now as to which uses more CPU power, lower or higher bitrate mp3s....hmmmmm. by the same logic, a 128 bitrate mp3 is more compressed than a 320 bitrate mp3 and would require more uncompressing. however, you have to rememeber that mp3 encoding is LOSSY compression meaning that you actually lose data during the compression. so while a 128 bitrate mp3 is smaller than a 320 bitrate mp3 because it is more compressed, it is also smaller because it contains less data. soooooooo.....quick answer is...i don't know.