Vibrato method

vibrato.js

const defaultLFO = {
  type: 'sine',
  freq: 12,
  volume: 40,
};

// Uses same `duration` as "source" oscillator
vibrato(duration, options = {}) {
  const config = Object.assign(defaultLFO, options);

  this.lfo = this.context.createOscillator();
  this.lfoGainNode = this.context.createGain();

  this.lfo.type = config.type;
  this.lfo.frequency.value = config.freq;
  // Volume will control the intensity of the effect
  this.lfoGainNode.gain.value = config.volume;

  // Instead of connecting the LFO to the AudioContext.destination,
  // we connect it to the "source" oscillator's frequency instead
  this.lfo.connect(this.lfoGainNode);
  this.lfoGainNode.connect(this.oscillator.frequency);

  this.lfo.start();
  this.lfo.stop(duration);
}