iOS : Delayed response to touch began?

Hi,

Starting from a new empty scene on Unity iOS, I'm simply adding an AudioSource and the following script to the main camera (purely for testing purposes). The script simply play a sound upon any touch. After launching on the iPad2, there is an approx 0.5 second delay between touching the screen and the audio playing! Is this the bottom-line performance, or should I be doing something else to improve the response of touches?

(Naturally, a similar script responds immediately when testing for a KeyDown on the Mac, so the delay is purely down to Touch it would seem.)

 function Update () {
     
     for (var i = 0; i < Input.touchCount; i++)
       {
         var touch : Touch = Input.GetTouch(i);
           if (touch.phase == TouchPhase.Began)
           {
               audio.Play();
           }
       }
 }