fixes pitch detection mem leak (#688)

Author: joeyklee

src/PitchDetection/index.js

@@ -83,14 +83,16 @@ class PitchDetection {
      * @public
      */
     this.results = {};
-    const centMapping = tf.add(tf.linspace(0, 7180, 360), tf.tensor(1997.3794084376191));
+    
     PitchDetection.resample(event.inputBuffer, (resampled) => {
       tf.tidy(() => {
         /**
          * A boolean value stating whether the model instance is running or not.
          * @type {boolean}
          * @public
          */
+        const centMapping = tf.add(tf.linspace(0, 7180, 360), tf.tensor(1997.3794084376191));
+        
         this.running = true;
         const frame = tf.tensor(resampled.slice(0, 1024));
         const zeromean = tf.sub(frame, tf.mean(frame));