WebAudio：setTargetAtTime（）事件立即触发，而不是在计划的时间触发

Question

我有一个Oscillator连接到Gain Node，用于创建一个音量包络，该包络<大约1.5开始后几秒钟，我想在第二个[[2：

处执行以下操作取消所有计划的（将来的）信封增益更改。

创建新的时间表
• setTargetAtTime

以“淡出”声音。

问题是，“淡出” setTargetAtTime（）似乎立即被触发，这导致了JUMP IN VOLUME。是的，如果第二个参数（startTime）小于或等于audioContext.currentTime，则可以预期。但是这里不是这种情况。

function startSound() {
  //Audio context
  var audioCtx = new (window.AudioContext || window.webkitAudioContext)();
  var currentTime = audioCtx.currentTime;

  //Create Gain Node And Oscillator
  var gainNode = audioCtx.createGain();
  var oscillator = audioCtx.createOscillator();
  oscillator.type = "sine";
  oscillator.frequency.setValueAtTime(440, currentTime);

  //Connect Oscillator to Gain Node and Gain Node to audioCtx.destination
  oscillator.connect(gainNode);
  gainNode.connect(audioCtx.destination);
  oscillator.start(currentTime);

  //Create Gain (Volume Envelope)
  gainNode.gain.setValueAtTime(0.5, currentTime);
  gainNode.gain.linearRampToValueAtTime(0.5, currentTime + 0.5);
  gainNode.gain.linearRampToValueAtTime(0.25, currentTime + 2);
  gainNode.gain.linearRampToValueAtTime(0.000001, currentTime + 5);
  gainNode.gain.linearRampToValueAtTime(0.000001, currentTime + 999);

  //Approximately 1.5 seconds later, Cancel ALL Scheduled Envelope changes from second 2 and up, and create a FAST
  //"Fade Out" that lasts 0.1 seconds.
  var cancelAt = currentTime + 2;

  setTimeout(function () {
    StopEnvelope(audioCtx, gainNode, cancelAt);
  }, 1500);
}

function StopEnvelope(audioCtx, gainNode, cancelAt) {
  //This is never TRUE
  if (cancelAt <= audioCtx.currentTime) {
    console.log("cancelScheduledValues will happen immediately!");
  }

  gainNode.gain.cancelScheduledValues(cancelAt);
  gainNode.gain.setTargetAtTime(0.00001, cancelAt, 0.1);
}

<input type="button" value="Start Oscillator" onclick="startSound();" />

<p>
  You can hear a JUMP in Gain (Volume) at around 1.5 seconds. That is when <strong>gainNode.gain.setTargetAtTime(0.00001, cancelAt, 0.1);</strong> is executed.
  It's is like it is executed Immedately instead at cancelAt (at second 2).
</p>

<p style="color: red; font-weight: bold;">
  NOTE: this would be expected if cancelAt <= audioCtx.currentTime. But that is NOT the case here. </p>

非常奇怪的是，如果我将一点时间添加到预定的事件中，它的行为似乎与预期的一样。参见行[[cancelAt + = 0.0005;

 
function startSound() {
  //Audio context
  var audioCtx = new (window.AudioContext || window.webkitAudioContext)();
  var currentTime = audioCtx.currentTime;

  //Create Gain Node And Oscillator
  var gainNode = audioCtx.createGain();
  var oscillator = audioCtx.createOscillator();
  oscillator.type = "sine";
  oscillator.frequency.setValueAtTime(440, currentTime);

  //Connect Oscillator to Gain Node and Gain Node to audioCtx.destination
  oscillator.connect(gainNode);
  gainNode.connect(audioCtx.destination);
  oscillator.start(currentTime);

  //Create Gain (Volume Envelope)
  gainNode.gain.setValueAtTime(0.5, currentTime);
  gainNode.gain.linearRampToValueAtTime(0.5, currentTime + 0.5);
  gainNode.gain.linearRampToValueAtTime(0.25, currentTime + 2);
  gainNode.gain.linearRampToValueAtTime(0.000001, currentTime + 5);
  gainNode.gain.linearRampToValueAtTime(0.000001, currentTime + 999);

  //Approximately 1.5 seconds later, Cancel ALL Scheduled Envelope changes from second 2 and up, and create a FAST
  //"Fade Out" that lasts 0.1 seconds.
  var cancelAt = currentTime + 2;

  setTimeout(function () {
    StopEnvelope(audioCtx, gainNode, cancelAt);
  }, 1500);
}

function StopEnvelope(audioCtx, gainNode, cancelAt) {
  cancelAt += 0.0005;
  
  //This is never TRUE
  if (cancelAt <= audioCtx.currentTime) {
    console.log("cancelScheduledValues will happen immediately!");
  }

  gainNode.gain.cancelScheduledValues(cancelAt);
  gainNode.gain.setTargetAtTime(0.00001, cancelAt, 0.1);
}

<input type="button" value="Start Oscillator" onclick="startSound();" />

<p>
Now the "Fade Out" works as expected. The only change is that 0.0005 seconds is added to the <strong>cancelAt</strong> paramenter.
</p>

<p style="color: red; font-weight: bold;">
  NOTE: As before, cancelAt is NEVER less than or equal to  audioCtx.currentTime. </p>

Answer 1

您可以使用cancelScheduledValues()而不是cancelAndHoldAtTime()来实现所需的行为。它会保留上一个值，下一个自动化将从此处开始。