add feedback delay effect

packages/webaudio/feedbackdelay.mjs

@@ -0,0 +1,28 @@
+class FeedbackDelayNode extends DelayNode {
+  constructor(ac, wet, time, feedback) {
+    super(ac);
+    wet = Math.abs(wet);
+    this.delayTime.value = time;
+
+    const feedbackGain = ac.createGain();
+    feedbackGain.gain.value = Math.min(Math.abs(feedback), 0.995);
+
+    const delayGain = ac.createGain();
+    delayGain.gain.value = wet;
+    this.delayGain = delayGain;
+
+    this.connect(feedbackGain);
+    this.connect(delayGain);
+    feedbackGain.connect(this);
+
+    this.connect = (target) => delayGain.connect(target);
+    return this;
+  }
+  start(t) {
+    this.delayGain.gain.setValueAtTime(this.delayGain.gain.value, t + this.delayTime.value);
+  }
+}
+
+AudioContext.prototype.createFeedbackDelay = function (wet, time, feedback) {
+  return new FeedbackDelayNode(this, wet, time, feedback);
+};