Logic Pro X Scripter script for assigning MIDI NoteOn events to random channels

random-channel.js

// assigns incoming MIDI NoteOn events to a "random" channel in a given range
// channel assignment is deterministic based on position in song and specified seed
// for Logic Pro X Scripter plugin
// written by jae kaplan, 2020
// twitter.com/jkap
// github.com/jkap
// MIT licensed

var NeedsTimingInfo = true;

function randomSeeded(seed) {
  const x = Math.sin(seed) * 10000;
  return x - Math.floor(x);
}

var PluginParameters = [
  {
    name: "Min Channel",
    defaultValue: 1,
    minValue: 1,
    maxValue: 15,
    numberOfSteps: 14,
  },
  {
    name: "Max Channel",
    defaultValue: 7,
    minValue: 2,
    maxValue: 16,
    numberOfSteps: 14,
  },
  {
    name: "Fixed Seed",
    defaultValue: 69,
    minValue: 1,
    maxValue: 100,
    numberOfSteps: 99,
  },
];

const noteMap = new Map();

function HandleMIDI(event) {
  const minChannel = GetParameter("Min Channel");
  const maxChannel = GetParameter("Max Channel");
  const fixedSeed = GetParameter("Fixed Seed");
  let channel =
    Math.floor(
      randomSeeded(event.beatPos + fixedSeed) * (maxChannel + 1 - minChannel)
    ) + minChannel;
  if (event instanceof NoteOn) {
    noteMap.set(event.pitch, channel);
  } else if (event instanceof NoteOff) {
    channel = noteMap.get(event.pitch) || 1;
  }
  event.channel = channel;
  event.trace();
  event.send();
}