Beats per minute from real-time audio input

Question

I'd like to write a simple C# application to monitor the line-in audio and give me the current (well, the rolling average) beats per minute.

I've seen this gamedev article, and that was absolutely no help. I went through and tried to implement what he was doing but it just wasn't working.

I know there have to be tons of solutions for this, because lots of DJ software does it, but I'm not having any luck in finding any open-source library or instructions on doing it myself.

Answer 1

I'd recommend checking out the BASS audio library and the BASS.NET wrapper. It has a built in BPMCounter class.

Details for this specific function can be found at http://bass.radio42.com/help/html/0833aa5a-3be9-037c-66f2-9adfd42a8512.htm.

Answer 2

Not that I have a clue how to implement this, but from an audio engineering perspective you'd need to filter first. Bass drum hits would be the first to check. A low pass filter that gives you anything under about 200Hz should give you a pretty clear picture of the bass drum. A gate might also be necessary to cleanup any clutter from other instruments with harmonics that low.

The next to check would be snare hits. You'd have to EQ this one. The "crack" from a snare is around 1.5kHz from memory, but you'd need to definitely gate this one.

The next challenge would be to work out an algorithm for funky beats. How would you programatically find beat 1? I guess you'd keep track of previous beats and use a pattern matching something-or-other. So, you'd probably need a few bars to accurately find the beat. Then there's timing issues like 4/4, 3/4, 6/8, wow, I can't imagine what would be required to do this accurately! I'm sure it'd be worth some serious money to audio hardware/software companies.