# [PD] Equation question

Frank Barknecht fbar at footils.org
Mon Nov 21 00:11:04 CET 2005

```Hallo,
day 5 hat gesagt: // day 5 wrote:

> what formula might one be using to determine periodicity as rate in ms ?
>
> For example, say you know total frames of a video file and you know
> this file is 24 fps. You can say that it vibrates at 24 Hz so what is
> the periodicity of the wave in ms ?

You just take the inverse to convert between period (or wavelength)
and frequency (like fps or Hz), so it's

[expr 1/\$f1].

If you want to drive a [metro] with that, you have to take into
account, that the metro wants milliseconds. So you'd use:

[expr 1000 * 1/\$f1] == [expr 1000/\$f1]

to convert from fps to a metro period, where the period is the time it
takes for one frame to pass.

It's similar with converting BPM to a [metro] period, however there
you have the additional problem, that BPM is beats per minute. As a
minute has 60 seconds and a second has 1000 milliseconds, you do this:

[expr 60*1000 * 1/\$f1] or better: [expr 60000/\$f1]

It works both ways: Sending 120 (BPM) into this will give you 500
(ms), and sending 500 (ms) into it wil give you 120 (BPM).

Ciao
--
Frank Barknecht                 _ ______footils.org_ __goto10.org__

```