// drums -------------------------------------
p1.player('hihat').start(Tone.now());
if ([0, 4, 8, 12].indexOf(idx) >= 0)
p1.player('kick').start();
if ([2, 6, 10, 14].indexOf(idx) >= 0)
p1.player('snare').start();
// synth -------------------------------------
const chords = [
['C3', 'E3', 'G3'], // I
['G3', 'B3', 'D3'], // V
['A3', 'C3', 'E3'], // VI
['F3', 'A3', 'C3'], // IV
];
let chordIndex = -1;
if (idx === 0) chordIndex = 0;
if (idx === 4) chordIndex = 1;
if (idx === 8) chordIndex = 2;
if (idx === 12) chordIndex = 3;
if (chordIndex >= 0) {
polySynth.triggerAttackRelease(chords[chordIndex][0], '16n');
polySynth.triggerAttackRelease(chords[chordIndex][1], '16n', '+8n');
polySynth.triggerAttackRelease(chords[chordIndex][2], '16n', '+4n');
}