footstep audio sync probs

Hi. SECOND time writing this out, thanks a lot UDN!!

anyway, grumbling aside I'm having trouble synching footsteps sounds to prerendered spritesheets.

previously I had written a script that played audio based on 3 things:

1.the frames in the animation

2.the frame where the first footfall is

3.and the second

this worked for a while, but I'm noticing the audio getting out of sync over time.

I'm sure there is some way to do it using Time.deltaTime, but I still cant fully get my head around that.

Also to add more complexity (of course, nothing is easy! :P ) different animations have different FPS's.

Here's the script I currently have:

 using UnityEngine;
 using System.Collections;
 
 public class WalkingAudio : MonoBehaviour {
     
     public AudioClip[] GrassSteps; // contains grass step sounds    
     public AudioClip[] StoneSteps; // contains stone step sounds
     public AudioClip[] GravelSteps; // contains gravel step sounds
     public AudioClip[] MetalSteps; // contains metal step sounds
     public AudioClip[] WoodSteps; // contains metal step sounds
     
     public bool isMoving = false; // is the character moving?
     
     public int firstFootfall; // the frame number where the first foot hits the ground
     
     public int secondFootfall; // the frame number where the second foot hits the ground
     
     public int framesInAnimation; // the amount of frames in the animation
     
     public enum GroundType {Grass, Stone, Gravel, Metal, Wood}; // what kind of surface is the character on
     
     private float currentFrame; // the current frame
     
     AudioClip[][] AudioArrayHolder = new AudioClip[5][]; // create an array to hold the three different audio arrays
     
     private int surface;    // 
     
     public GroundType ground;
     
     public GroundType previous;
     
     public float audioMax;
     
     public float audioMin;
     
     public float volDipTime;
     
     float audioMaxStart; // saves the original 
     
     float audioMinStart;
     
     bool dipVolume = false; // should the vol be dipped?
     
     // Use th for initialization
     void Start () {
         
         /*if (ground == null){
         ground = GroundType.Stone;
         }*/
         StartCoroutine("NewMaterial");    
     }
     
     void Awake(){
         currentFrame = 1;
         AudioArrayHolder[0] = GrassSteps;
         AudioArrayHolder[1] = StoneSteps;
         AudioArrayHolder[2] = GravelSteps;
         AudioArrayHolder[3] = MetalSteps;
         
         audioMaxStart = audioMax; // save original values to reset
         audioMinStart = audioMin;
         
         //Debug.Log("audioMaxStart in Start"+audioMaxStart);
     }
     // Update is called once per frame
     void Update () {
         
         //    Debug.Log("isMoving "+isMoving);
         //what kind of ground is the character on?
         switch (ground){
             
         case GroundType.Grass:
             surface = 0;
             
         break;
             
         case GroundType.Stone:
             surface = 1;
             //StartCoroutine("NewMaterial");
         break;
             
         case GroundType.Gravel:
             surface = 2;    
             //StartCoroutine("NewMaterial");
         break;
             
         case GroundType.Metal:
             surface = 3;
             //StartCoroutine("NewMaterial");
         break;
             
         case GroundType.Wood:
             surface = 3;    
             //StartCoroutine("NewMaterial");
         break;
         }
         
         
         // if the character is moving play the sounds
         if (isMoving){
             //Debug.Log("surfacee no is:"+surface);
             currentFrame ++;//
             
             //Debug.Log("currentFrame "+currentFrame);
             
             //play the first footfall on the relevant frame
             if (currentFrame == firstFootfall){
                 audio.volume = Random.Range(audioMin,audioMax );
                 audio.PlayOneShot(AudioArrayHolder[surface][Random.Range(0, (AudioArrayHolder[surface].Length-1))]);    
                 
                 //Debug.Log("playing footf1");
             }
             
             //play the second footfall on the relevant frame
             if (currentFrame == secondFootfall){
                 audio.volume = Random.Range(audioMin,audioMax );
                 audio.PlayOneShot(AudioArrayHolder[surface][Random.Range(0, (AudioArrayHolder[surface].Length-1))]);    
                 
                 //Debug.Log("playing footf2");
             }
             // if we have reached the end of the animation end go back to the start
             if (currentFrame == framesInAnimation ) {
                 currentFrame = 1;    
             }
         }
     //    Debug.Log("dipVolume"+dipVolume);
         
         if (dipVolume ){
             //Debug.Log("audiomax reducing");
             //Debug.Log("audiomaxstart"+audioMaxStart);
             if (audioMax > audioMaxStart/2 || audioMax == audioMaxStart ){
                 audioMax -= 0.01f; 
             }
         }
     }
     
     public void StartMoving() {
         isMoving = true;
         //Debug.Log("started moving "+isMoving);
     }
     
     public void StopMoving() {
         isMoving = false;
         //Debug.Log("stopped moving "+isMoving);
     }
     
     
     
 }