trying to make a Sound Trigger

Hi Im hoping someone could help me work out how to bring up the fader from one end of a trigger from 0 at the edge of the trigger to 100 percent by the time you get to the middle then back down to 0 when you walk out the other side. I have drawn a diagram to try to explain what I mean.

 

This is what I have so far, sorry I'm not the best coder.

Code (CSharp):

1. using UnityEngine;
2. using System.Collections;
3. using UnityEngine.Audio;
4.  
5. public class AudioTrigger : MonoBehaviour
6. {
7.     //Audio stuff
8.     public AudioMixer mixer;
9.     public AudioMixerSnapshot[] snapshots;
10.  
11.     //Box Collider stuff
12.     public Collider audioTriggerBox;
13.     public Bounds bounds;
14.  
15.     private Transform centreOfBounds;
16.     private Transform edgeOfBounds;
17.     private float[] weights;
18.     private Transform Player;
19.  
20.     // Use this for initialization
21.     void Start ()
22.     {
23.         //find the centre of the collider
24.         bounds = audioTriggerBox.bounds;
25.         centreOfBounds.position = bounds.center;
26.         edgeOfBounds.position = bounds.extents;
27.  
28.     }
29.    
30.     // Update is called once per frame
31.     void Update ()
32.     {
33.         weights[0] = 0.0f;  //at the edge of the Collider
34.      
35.         weights[100] = 1.0f; //In the middle of the Collider
36.  
37.         mixer.TransitionToSnapshots(snapshots, weights , 1.0f);
38.         //at the centre of the Bounding box
39.    
40.     }
41. }

 

well if you want that to work as a trigger you'll need to be using OnTriggerEnter, OnTriggerExit and OnTriggerStay...

https://unity3d.com/learn/tutorials/topics/physics