[linux-audio-dev] Some help with my BPM algorithm?

[Simon Jenkins]

Jay Dolan wrote:

>--- Simon Jenkins <sjenkins at blueyonder.co.uk> wrote:
>
>>Try this?
>>[...]
>>
>Definitely closer!  I'm embarassed to admit how long
>I've looked at this code and didn't see that I was
>initializing lowestDiffFound (was previousDiff) to 0,
>doh!
>
>It's now returning 120.0 (g_minBpm) for every file,
>tho.  So there's still a problem somewhere.  Perhaps
>in phaseShift?  I've re-attached the improved version.
> Thank you for your help.
>
ok:

~ Downsampling by 50???  That's *got* to require some
filtering. In keeping with your need for speed - not to mention
my lack of DSP guru-head - i've implemented the crudest
imagineable.

~ fseek()-ing the pipe wasn't working. I've removed the
first fseek(), but that means that g_startTime is no longer
honoured and must be left at zero. The (ahem) "filter" i
added means the second fseek() is no longer required.

~ A couple of math corrections.

~ Widened expected bpm range: It now looks for 100 - 199 bpm.
You should probably narrow that back down again if you know
your source is in a narrower range.

I actually ran it a couple of times and it seems to produce plausible
results now though i don't have the exact bpms for the mp3s i tried.
Also, my test mp3s contained looped samples and/or programmed
drum parts. I'm not sure this algorithm will work so well (or at
all for that matter) on less regular material.

Simon Jenkins
(Bristol, UK)

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