Calculating BPM changes

Does anyone know of efficient ways to mathematically calculate gradual increases or decreases in song BPM? An example would be Wild Rush or Saint Goes Marching.

1. Open a DAW and throw in the music
2. Try and match up waveform as best you can with a ton of guessing and checking
3. Slam head against wall repeatedly
4. say fuck it mid sync and step something constant bpm instead

There's no real clear cut procedure because next to no gradual increases/decreases are the same.

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@SM MaXX

What is a DAW?

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Usually, I just look up if someone's made a simfile for the song before I have, and use the timing data of that simfile. From what I can tell, gradual slowdowns and non-multiple BPM changes are mostly just trial-and-error.

http://lmgtfy.com/?q=DAW

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Yeah I figured there was no clear cut way on how to do this. There are a few songs I would like to produce simfiles out of that have these gradual slowdowns and increases. Being the perfectionist I am I would be darned if even one value is incorrect. rapidemboar gave a good example to use data from another simfile and make the comparison from there. But if no one has used that song before and you're the first to do it, it's going to take a lot of work. I wonder how they calculated the BPM changes for the Vertex songs?

The easiest procedure I can think of is to cut the song in fragments, then analyze the BPM of each of those pieces where BPM changes are present. If even one of those pieces gets an incorrect value it won't be any good.

That's exactly what I was about to suggest.

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I was personally thinking of measuring the time of each 1/4 measure, and doing some calculations off of that. Granted, I've never stepped a song with weird BPM changes. Maybe BPM analysis is a better idea. Of course, the only DAW I have is Garageband, and that's kinda finicky to work with...

Lately I have been using DDReam Studio for checking weird BPMs or for songs with live BPMs. It's time consuming, yes, but it's not so hard to use and yields good results.

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