问如何控制(音频缓冲区) AudioContext()的音量？

EN

var gainNode = aCtx.createGain()
gainNode.gain.value = 0.1 // 10 %
gainNode.connect(aCtx.destination)

// now instead of connecting to aCtx.destination, connect to the gainNode
source.connect(gainNode)

const aCtx = new AudioContext();

const gainNode = aCtx.createGain();
gainNode.gain.value = 0.1; // setting it to 10%
gainNode.connect(aCtx.destination);

let source = aCtx.createBufferSource();
let buf;
fetch('https://dl.dropboxusercontent.com/s/knpo4d2yooe2u4h/tank_driven.wav') // can be XHR as well
  .then(resp => resp.arrayBuffer())
  .then(buf => aCtx.decodeAudioData(buf)) // can be callback as well
  .then(decoded => {
    source.buffer = buf = decoded;
    source.loop = true;
    source.connect(gainNode);

    check.disabled = false;
  });

check.onchange = e => {
  if (check.checked) {
    source.start(0); // start our bufferSource
  } else {
    source.stop(0); // this destroys the buffer source
    source = aCtx.createBufferSource(); // so we need to create a new one
    source.buffer = buf;
    source.loop = true;
    source.connect(gainNode);
    
  }
};

<label>Start Playing</label>
<input type="checkbox" id="check" disabled><br>
<br>Its volume is 100%. Please help me to reduce it to 10%.

    const aCtx = new AudioContext();
    let source = aCtx.createBufferSource();
    let buf;

    var gainNode = aCtx.createGain(); // Create a gainNode reference.
    gainNode.connect(aCtx.destination); // Add context to gainNode

fetch('https://dl.dropboxusercontent.com/s/knpo4d2yooe2u4h/tank_driven.wav') // can be XHR as well
      .then(resp => resp.arrayBuffer())
      .then(buf => aCtx.decodeAudioData(buf)) // can be callback as well
      .then(decoded => {
        source.buffer = buf = decoded;
        source.loop = true;

        source.connect(gainNode);   //Connecting gain to source
        gainNode.gain.value = 1;  // 100% VOLUME RANGE OF VALUE IS 0-1

        check.disabled = false;
      });


   check.onchange = e => {
      if (check.checked) {
        source.start(0); // start our bufferSource
      } else {
        source.stop(0); // this destroys the buffer source
        source = aCtx.createBufferSource(); // so we need to create a new one
        source.buffer = buf;
        source.loop = true;

        source.connect(gainNode);   //Connecting gain to source
        gainNode.gain.value = 0.1;  // 10% VOLUME RANGE OF VALUE IS 0-1
      }
    };