config.json
Copy this and save it to CIRCUITPY/config.json. The demo uses the
first four presets, one per red LED; spot 0 is the clean passthrough. It also uses
the first four samples, one per white LED, walked with MIDDLE and played with BOTTOM.
$handle is supplied by the demo to preset effects only: 0.0 handle out,
1.0 squeezed in.