Re: [LAU] Extracting the tempo track from a MIDI file

On Tue, Sep 25, 2007 at 10:08:57AM -0700, Ken Restivo wrote:
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> On Tue, Sep 25, 2007 at 09:21:06AM +0200, Alexandre Ratchov wrote:
> > On Mon, Sep 24, 2007 at 07:00:38PM -0700, Ken Restivo wrote:
> > >
> > > Is there any command-line tool to extract and print the tempo of
> > > a MIDI file?
> > >
> >
> > hi,
> >
> > you could use midish for that: import the .mid file, and use the
> > songtimeinfo function; example:
> >
> > $ rmidish
> > send EOF character (control-D) to quit
> > 1> songimportsmf "sample.mid"
> > 2> songtimeinfo
> > {
> > timesig 4 24
> > tempo 400000
> > }
> > 3>
> >
>
> Thanks! However, I haven't found any explanation of what those numbers mean. I need the tempo in BPM.
>
> I found this formula in the Rosegarden source:
> qpm = (60.0 * beatTime) / (beatSec * quarter)
>
> But of the three numbers that songtimeinfo spits out, I haven't been able to figure out which one is beatTime, beatSec, and quarter.
>

oops, forgot to say what units are; 400000 is the diration of a
MIDI tic in 24th of microseconds. To get the BPM:

        bpm = 60 * 24000000 / (tempo * ticks_per_beat)
            = 60 * 24000000 / (400000 * 24)
            = 150

(ticks_per_beat is the second parameter of the time signature).

[...]

However, in this case it's simpler to use "songgettempo" function,
example:

        $ rmidish
        send EOF character (control-D) to quit
        1> songimportsmf "sample.mid"
        2> print [songgettempo -1]
        150

songgettempo returns the tempo (in BPM) at the given measure
number, -1 means the end of the song. This function is not in 0.3.1
release, its only in the last snapshot:

         http://caoua.org/midish/midish.tar.gz

cheers,

-- Alexandre
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Received on Wed Sep 26 00:15:02 2007