var AudioContext = window.AudioContext || window.webkitAudioContext
var audioCtx = new AudioContext()

let gainNode = audioCtx.createGain()
gainNode.gain.value = 0.5

let osc = audioCtx.createOscillator()
osc.frequency.value = 50
osc.type = 'sine' 
osc.detune.value = 0 

osc.connect(gainNode)

osc.start()

gainNode.connect(audioCtx.destination)