equalizer.js

const bassNode = new BiquadFilterNode(context, {
  type: 'lowshelf',
  frequency: 500
});

const midNode = new BiquadFilterNode(context, {
  type: 'peaking',
  Q: Math.SQRT1_2,
  frequency: 1500
});

const trebleNode = new BiquadFilterNode(context, {
  type: 'highshelf',
  frequency: 3000
});

// Decreasing bass level by 10 dB.
bassNode.gain.value = -10;

// Increasing middle level by 15 dB.
midNode.gain.value = 15;

// No boost.
trebleNode.gain.value = 0;