Tone.js timing inaccuracy

tone-timing.js

import Tone from 'tone'

const bpm = 120.0
const QUARTER_NOTE_MS = 60000.0 / bpm

var lastTime

Tone.Transport.bpm.value = bpm;

// Measure time delta since last call, warn if early or late
function measureInterval(time) {
  var currentTime = Date.now()
  if (lastTime !== undefined) {
    const deltaTime = currentTime - lastTime
    const errorTime = deltaTime - QUARTER_NOTE_MS
    if (errorTime > 0.0) {
      console.warn("Transport fired", errorTime, "ms LATE");
    } else if (errorTime < 0.0) {
      console.warn("Transport fired", -errorTime, "ms EARLY");
    }
  }
  lastTime = currentTime
}

// NOTE: timing is frequently off by >20ms
// e.g.
//     Transport fired 25 ms LATE
//     Transport fired 9 ms EARLY
//     Transport fired 6 ms EARLY
//     Transport fired 22 ms LATE
//     Transport fired 7 ms EARLY
//     Transport fired 9 ms EARLY
//     Transport fired 18 ms LATE
Tone.Transport.scheduleRepeat(measureInterval, "4n")

// // COMPARE WITH setInterval: timing is never off by >1ms
// setInterval(measureInterval, QUARTER_NOTE_MS)

Tone.Transport.start()