     
     @IBAction func playFastAUdio(sender: AnyObject) {
         // MARK: task 2
-        audioPlayer.stop()
-        audioEngine.stop()
-        audioEngine.reset()
+        stopAudioPlaying()
         
         // MARK: play audio fast
         stopButton.hidden = false
-        audioPlayer.stop()
         audioPlayer.currentTime = 0
         audioPlayer.rate = 2
         audioPlayer.play()

    
    
    func playAudioWithVariablePitch(pitch: Float){
        audioPlayer.stop()
        audioEngine.stop()
        audioEngine.reset()
        
        let audioPlayerNode = AVAudioPlayerNode()
        audioEngine.attachNode(audioPlayerNode)

    }
    
    @IBAction func playSlowAudio(sender: UIButton) {
        stopAudioPlaying()
        
        // MARK: play audio slow
        stopButton.hidden = false
        audioPlayer.currentTime = 0
        audioPlayer.rate = 0.5
        audioPlayer.play()
