diff --git a/src/effects/PitchEffect.js b/src/effects/PitchEffect.js
index 2281eba..7cebc44 100644
--- a/src/effects/PitchEffect.js
+++ b/src/effects/PitchEffect.js
@@ -49,7 +49,7 @@ class PitchEffect {
     * @returns {number} a playback ratio
     */
     getRatio (val) {
-        return intervalToFrequencyRatio(val / 10);
+        return this.intervalToFrequencyRatio(val / 10);
     }
 
     /**