The guys here can give you the method they used, but whenever I’ve done it, I just get a tapper, tap to the beat of the song, use that as an estimate, and tweak it if it seems to get off sync. The other authors do matching that’s a little closer to the intended method, but I could never get it the way I liked it, so I do it a different way.
I tend to author songs with limited or no bpm changes, of course, so… yeah.
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