const MonoToStereoEffect = ({ input, output }) => {
  for (let i = 0; i < input.length; i ++) {
    output[0][i] = input[i];
    output[1][i] = input[i];
  }
};

this.constructDevice = () => constructPerBufferDevice({
  implementation: MonoToStereoEffect,
  inputs: {
    input: mono('In'),
  },
  outputs: {
    output: stereo('Out'),
  }
});
