How to fade out audio/music between scenes?

Question

I'm trying to get some music to fade out when I start my android game. The music plays in the main menu and then should fade out when the player clicks play. I can get the music to stop, just not fade out.

Im trying to fade out using this:

using UnityEngine;
using System.Collections;

public class MusicScript : MonoBehaviour 
{
    static MusicScript instance;
    bool doneFading;

    void Start()
    {
        if(instance == null)
        {
            instance = this;
            DontDestroyOnLoad(gameObject);
        }

        else if (instance != this)
        {
            Destroy(gameObject);
        }
    }

    void Update()
    {
        if (Application.loadedLevelName == "Flappy Drone Gameplay Screen")
        {
            FadeMusic();
            if (doneFading == true)
            {
                Destroy(gameObject);
            }
        }
    }

    IEnumerator FadeMusic()
    {
        for (int i = 9; i > 0; i--)
        {
            Debug.Log("here");
            instance.audio.volume = i * 0.1f;
            yield return new WaitForSeconds(0.5f);
            Debug.Log("lowered volume");
        }
        doneFading = true;
    }

}

Any help is appreciated!

Answer 1

After a bit of playing about with Time.deltatime I found a simple way of doing a fade :)

Code for anyone in the same problem (this code fades out music on a particular scene but keeps the music playing for all other scenes):

using UnityEngine;
using System.Collections;

public class MusicScript : MonoBehaviour 
{
    static MusicScript instance;
    bool doneFading;

    float timer = 5f;

    void Start()
    {
        if(instance == null)
        {
            instance = this;
            DontDestroyOnLoad(gameObject);
        }

        else if (instance != this)
        {
            Destroy(gameObject);
        }
    }

    void Update()
    {
        if (Application.loadedLevelName == "Flappy Drone Gameplay Screen")
        {
            FadeMusic();
            if (doneFading == true)
            {
                Destroy(gameObject);
                Debug.Log ("Music destroyed.");
            }
        }
    }

    void FadeMusic()
    {
        if (timer > 0)
        {
            instance.audio.volume -= 0.015f;
            timer -= Time.deltaTime;
        }
        if (instance.audio.volume == 0)
        {
            doneFading = true;
        }

    }

}