ActionScript 3: How can I keep an accurate BPM counter?

Question

I'm looking to create a drum machine in ActionScript 3 (as an Adobe AIR Android app), which will keep to a user defined tempo (BPM).

I am struggling to find a way to keep the project in time, I have, at the moment, made it so that 5 different sounds are represented in rows of 8 squares, and the user can click each square to choose when to play that sound (hope this makes sense).

At the moment I am using Timer to keep the project in time, which is very laggy and inconsistent.

Answer 1

using timer is a bad idea for this, there I said it...

The issue is that the timer has a drift and fires several milliseconds later. Try a simple test where you have a timer that executes every 500ms, and then compare the getTimer() count. What I have found in my experiments that the timer is continually off and it looks like it doesn't self correct. I've tried using a self-correcting timer, that changes the firing time based on the getTimer() difference since last run, but it's still not reliable. and anytime your processor's load picks up, the timer will be off anyway.

The correct way of dealing with this is to use byteArray data as a source for the sound. Based on the calculation of sampling resolution you can populate the stream with the data in advance, and the sound will play on time, pretty much guaranteed. I haven't gone as far as to create something that does this myself. But there are several libraries that you can utilize that can help you with this.

My top two decremented libraries are SiON and tonfall

you can see a sample of SiON here http://wonderfl.net/c/qf4b
and tonfall example at http://tonematrix.audiotool.com/

While I haven't tried them on android, I think either should work