I know of an especially tedious method of finding the points in time where the
beats of a song occur using open source software. It involves opening the audio
track in Audacity and making some inferences about the shape of the waveform
(WRONG terminology). Then you move the cursor along and write down the time in
seconds for each bump in the waveform you're interested in.

Q: Is there a more automatic or accurate way of doing this?

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gregjohn wrote:
> I know of an especially tedious method of finding the points in time where the
> beats of a song occur using open source software. It involves opening the audio
> track in Audacity and making some inferences about the shape of the waveform
> (WRONG terminology). Then you move the cursor along and write down the time in
> seconds for each bump in the waveform you're interested in.
> 
> Q: Is there a more automatic or accurate way of doing this?

Several. Depends on exactly what information you want.

Maybe you just want to know how many beats per minute the track is? In 
that case, you can probably just find the first few beats manually and 
then fit them to an arithmetic progression. That should enable you to 
easily compute the location of all further beats. Assuming the rhythem 
is simple and unchanging. (!)

Alternatively, maybe you want to find all the actual beats? As in, every 
audible drum hit. In that case, you're probably going to have to look 
for spikes in the wave amplitude - possibly after filtering it for 
various frequency band(s) of interest. (No, I don't know of any program 
that does this, off the top of my head.)

If you could be a bit more specific about what you want and why you want 
it...?

PS. Maybe now is a good moment to explain how I did my own music video. 
Some of you may recall I started work on a video for the Prodigy's "No 
Good / Start the Dance". Liam Howlett did me a great favour here; the 
track runs at *exactly* 92 beats per minute. And the way the record is 
cut, beat #0 happens at 0 seconds in. So I wrote a trivial POV-Ray 
script that puts a beat every 92/60 seconds, starting from frame #0. And 
the result looks beautifully synchronised.

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Why, I wanted it to put on my own music videos!  I guess my questions were about
whether there were an easier way to pick out the beats, rather than how to do
arithmetic on the time slices I wrote down. :)


Invisible <voi### [at] devnull> wrote:
> So I wrote a trivial POV-Ray script that puts a beat
> every 92/60 seconds, starting from frame #0. And
> the result looks beautifully synchronised.


< partisanship = on >
One of the songs I was looking at ages ago had some floating point number of
seconds per beat, not an easy ratio like the one that you had.  Isn't this one
case where povray would be superior over most of the other raytracing apps that
require you to think exclusively in terms of *frames*.

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gregjohn wrote:
> Q: Is there a more automatic or accurate way of doing this?

I've never used it, but you might try this:

http://www.elec.qmul.ac.uk/people/simond/beatroot/

If you want to search for more, the Google terms you're looking for are 
`beat detection' and `beat tracking'.  Hope this helps!

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