bit rate is mostly irrelevant, and is mostly for compression of sound,
eg the audio is 16 bit (bit depth) 44100hz (sample rate) 320 kbs (bit rate)
I have seen cases where bit rate effects the speed, like on sound click high bit rates would play faster. this is mostly irrelevant.
bit depth, directly affects the signal and is like reducing colors of a digital image. eg. 12 bit audio, or 24 bit audio.
http://en.wikipedia.org/wiki/Audio_bit_depth
sample rate.
http://en.wikipedia.org/wiki/Sampling_rate
this is what speeds up and slows down a sample, when you load different Sample Rates into the 404, it plays the sample at different speeds, because it interprets them as 44100hz when actually they are not, so the play back speed is different.
ill explain further when i have a space bar for my keyboard.
I/O - EHT - Evangelist.