Question How to fade-out audio

Hey,

I am fairly new to unity, but I have go 3 basic scenes:

Scene 1
Scene 2
And Main Menu

The audio continues from scene 1 onto scene 2, but I want the audio to fade before loading the main menu.

I have tried to find audio, but their is no solution for this

Music Continuance script below:

Code (CSharp):

1. using System.Collections;
2. using System.Collections.Generic;
3. using UnityEngine;
4.  
5. public class StartupMusic : MonoBehaviour
6. {
7.     static bool AudioBegin = false;
8.     void Awake()
9.     {
10.         if (!AudioBegin)
11.         {
12.             GetComponent<AudioSource>().Play();
13.             DontDestroyOnLoad(gameObject);
14.             AudioBegin = true;
15.         }
16.     }
17.     void Update()
18.     {
19.         if (Application.loadedLevelName == "main_menu")
20.         {
21.             GetComponent<AudioSource>().Stop();
22.             AudioBegin = false;
23.         }
24.     }
25. }

Here is the scene layout



Any help appreciated and thanks in advance