My response is specifically to jazzmammal's reply:

You say it'sthe nature of audio, however, Real Track #487 stretches fine from its 085bpm tempo to 110bpm, but Real Track #714 does not. #714 sounds pretty bad at tempos as low as 90bpm. These two tracks are both acoustic piano, and actually sound very similar, except that the pianist's style of playing on #714 is latin with an even ryhthm feel, while #487 is a swing feel. Why would one stretch and not the other, unless there is something wrong with the one that won't stretch?

Andy