Frequency spectrum

<div class="wrap">
  <div class="bars" id="bars"></div>
  <button class="play" id="play" type="button" aria-label="play sound"><span class="tri"></span></button>
</div>

.wrap{position:relative;width:92%;height:86%;display:flex;align-items:flex-end}
.bars{display:flex;align-items:flex-end;gap:3%;width:100%;height:100%;padding-bottom:4%}
.bars i{flex:1;background:linear-gradient(180deg,var(--accent),var(--accent-3));border-radius:3px 3px 0 0;height:6%}
.play{position:absolute;right:0;top:0;width:clamp(26px,14%,38px);aspect-ratio:1;border-radius:50%;border:1px solid var(--line);background:var(--surface);display:grid;place-items:center;cursor:pointer;box-shadow:0 2px 8px rgba(0,0,0,.12)}
.play .tri{width:0;height:0;border-style:solid;border-width:6px 0 6px 9px;border-color:transparent transparent transparent var(--fg);margin-left:2px}
.play:active{transform:scale(.92)}

const N = 16;
const barsEl = document.getElementById('bars');
const bars = [];
for (let i = 0; i < N; i++) { const b = document.createElement('i'); barsEl.appendChild(b); bars.push(b); }
let playing = false, analyser = null, data = null;
function idleFrame(t) {
  if (playing && analyser) {
    analyser.getByteFrequencyData(data);
    const step = Math.floor(data.length / N) || 1;
    bars.forEach((b, i) => { b.style.height = Math.max(6, (data[i * step] / 255) * 96) + '%'; });
  } else {
    bars.forEach((b, i) => {
      const v = 10 + Math.abs(Math.sin(t * 0.0016 + i * 0.5)) * 55 * Math.exp(-i * 0.045);
      b.style.height = v + '%';
    });
  }
  requestAnimationFrame(idleFrame);
}
requestAnimationFrame(idleFrame);
document.getElementById('play').addEventListener('click', () => {
  const ctx = new (window.AudioContext || window.webkitAudioContext)();
  analyser = ctx.createAnalyser();
  analyser.fftSize = 128;
  data = new Uint8Array(analyser.frequencyBinCount);
  const master = ctx.createGain();
  const now = ctx.currentTime;
  master.gain.setValueAtTime(0.0001, now);
  master.gain.linearRampToValueAtTime(0.02, now + 0.03);
  master.gain.exponentialRampToValueAtTime(0.0001, now + 1);
  master.connect(analyser).connect(ctx.destination);
  [110, 220, 330, 440, 660, 880, 1320].forEach((f) => {
    const osc = ctx.createOscillator();
    osc.type = 'sawtooth';
    osc.frequency.value = f;
    osc.connect(master);
    osc.start(now);
    osc.stop(now + 1);
  });
  playing = true;
  setTimeout(() => { playing = false; ctx.close(); }, 1050);
});