     
     @IBAction func stopPlayAudio(sender: UIButton) {
         // MARK: stop play audio
-        audioPlayer.currentTime = 0
-        audioPlayer.stop()
+        stopAudioPlaying()
         stopButton.hidden = true
     }
     

        audioEngine.reset()
        
        audioPlayer.stop()
    }
    
    @IBAction func playSlowAudio(sender: UIButton) {

        
        // MARK: play audio fast
        stopButton.hidden = false
        audioPlayer.rate = 2
        audioPlayer.play()
    }
