Hi, I'm sure a music expert would have some insight on this
But I would like to know why certain songs seem not have a set bpm? Hip hop seems to always have a set bpm but I'm trying to re-create some older reggae songs using software instruments and it makes it difficult because I'm having to perform the songs one instrument at the time from beginning to end, without being able to loop or quantize.
I feel like there has to be a way to make my job easier! Thanks!
A set, unwavering BPM is, most likely, even for the most disciplined and technical classical performers nearly impossible. This is, say, rock and roll from 3 decades ago, 'feels' different than now. I am not taking a side, I love both metronomic electronic beats, as well as loose, behind the beat or rushing rhythm.
I read an article/analysis, a few years ago, and on 'OK Computer', on one of the songs, (I unfortunately can't remember the song) Radiohead speeds up something like 15-20BPM. I am not referring to tempo changes for obvious different sections e.g. Paranoid Android) In music school for classical or jazz training, this is a big fat NO-NO. Unless of course it is part of the arrangement. But in the case of the Radiohead song, it is not. But then again, why is it a 'no-no'?
You might want to do an experiment. Pick an old reggae song you like. Try to find the average speed of the first 30 seconds, then try to find the average speed of the last 30 seconds. Is there is a difference? Did it happen somewhere specific, like in the chorus, or was it a gradual raising of BPM? Most musicians, can have a tendency, when playing with others, to speed up. We've all done it. I constantly hear it in my students. When we're playing. It's part of the excitement of music. But it can't be too much of change, or it might sound ridiculous.
If you set a gradual raise in the BPM of about 10bpm for a 4 minute song, and play a long with the metronome (or better yet drummer), I don't thing you'll notice it, and it may give it the some of the spirit of the old reggae tunes you're looking for.
(then again, knowing reggae's drug of choice, maybe many pieces slow down.