function modifyGain(stream){
    var AudioContext = window.AudioContext || window.webkitAudioContext;
  var ctx = new AudioContext();

  var src = ctx.createMediaStreamSource(stream);
  var dst = ctx.createMediaStreamDestination();

  var gainNode = ctx.createGain();
  gainNode.gain.value = 3.5;
  src.connect(gainNode);

  gainNode.connect(dst);
 
  return dst.stream;
}

webcamStream = await navigator.mediaDevices.getUserMedia(mediaConstraints);
webcamStream = modifyGain(webcamStream);

document.getElementById("local_video").srcObject = webcamStream;

webcamStream.getTracks().forEach(
        function (track){
            myPeerConnection.addTrack(track, webcamStream);
        });

webcamStream.getTracks().forEach(track => {
            track.stop();
        });
webcamStream = null;
localVideo.srcObject = null;