code: function buildLowshelf (context) {
    const lowshelf = context.createBiquadFilter()
  
    lowshelf.type = 'lowshelf'
    lowshelf.frequency.value = 750
    lowshelf.Q.value = 100
    lowshelf.gain.value = 30
  
    return lowshelf
  }
docs: /*global AudioContext:false, webkitAudioContext:false