The Web MIDI API[0] used by the author has a built-in precise scheduler, that has higher precision and works better than the unreliable setTimeout approach used

The Web MIDI API[0] used by the author has a built-in precise scheduler, that has higher precision and works better than the unreliable setTimeout approach used by OP when coupled with the Performance API[1]. Pass a timestamp as the second argument to midiOutput.send(data, timestamp), calculated with performance.now. Something like midiOutput.send(data, performance.now() + offset) 0: https://developer.mozilla.org/en-US/docs/Web/API/MIDIOutput/send https://developer.mozilla.org/en-US/docs/Web/API/MIDIOutput/... 1: https://developer.mozilla.org/en-US/docs/Web/API/Performance/now https://developer.mozilla.org/en-US/docs/Web/API/Performance...