[superjc]

Well, they way I do it is make a perfect loop of the original in Wavelab, load that into Recycle, and it will tell me the exact BPM. Then when I load the acapella into Cubase, set the master bpm to that tempo. If it starts to vary, look/listen to the waveform with the metronome playing- is it getting behind, or speeding ahead of the clock? Sometimes I have to use the awesome "time warp" tool where you drag the bar TO THE WAVEFORM and Cubase will calculate a tempo adjustment out to .0009 of one beat. I have seen songs that had changes/wobble from R.Kelly, Timbaland, and others (could be from 2" tape transfers or whatever).