tags: reaper jsfx

The sliders in Reaper are always linear. Perhaps one day they will have logarithmithic
sliders. For now, what we can do if we want frequencies logarithmically, we can use
MIDI pitches with fractional values, and possibly negative. Essentially our
slider value is \(s\), and the frequency \(f\) is given by
\[f=440\cdot 2^{\frac{s-69}{12}}\]
(The 440 comes from A440, which is midi note 69, so \(s=69\) will give \(f=440) which
is what we desire. We can then display this \(f\) using the `gfx` facilities in JSFX.

## JSFX
```
desc: jda log freq slider example

slider1:60<0,169,0.1> Freq Midi Pitch

@slider
cutoff_freq = 440*(pow(2,(slider1-69)/12)); // hack for logarithmic slider

@gfx 640 200
x = 640*(slider1/127.0);

gfx_set(1,1,1);
gfx_x = 10;
gfx_y = 10;
gfx_printf("Cutoff midi %.01f == %.02fHz\n",slider1,cutoff_freq);
```