Tempo modulation

At the end of this post is a demo file that demonstrates Polymeter's new tempo modulation feature. Tempo tracks are a bit tricky and need to be properly documented (like the entire application!) but for now hopefully this will help.

To create a tempo track, just change a track's Type to "Tempo". Set the track's steps to whatever shape you want the tempo change to have. Also set the Duration to some non-zero value, e.g. try 100. For tempo tracks, Duration is reused as the tempo change percentage. If you set it to 100, the tempo will vary from half-time (for a step value of -64), to double time (for a step value of +63). If you set Duration to 50, the range will be half as much. Tempo is logarithmic, much like frequency. The actual formula is:

current_tempo = base_tempo * pow(2, (step_value - 64) / 64 * Duration / 100)

Only one tempo track can be active (unmuted) at a time! If you have multiple tempo tracks unmuted at once, they will compete which probably isn't what you want. To get second order change (tempo changing in multiple ways at once) you should use tempo modulation instead.

Tempo modulation is when a tempo track (see above) is modulated by one or more modulator tracks having a modulation type of "Tempo". The modulator tracks also must have non-zero Duration, in other words each modulator has its own tempo change percentage, which specifies the range of tempo change that modulator causes. Initially you can just set them all to 100. Like the tempo track, the tempo modulator can have any function in its steps. The actual tempo at any time is the product of the base tempo, the tempo track, and all of its unmuted modulators.

The idea is that tempo can change in polymeter, meaning e.g. changing slowly in one meter, while changing faster in some other meter. This is what the demo file below demonstrates. You need the Polymeter application to open this file!

https://www.dropbox.com/s/qd4myou0k2yxwf6/tempo%20track%20test.plm?dl=0