Urgent! Need to animate volume

Hi, I really need to know this like, yesterday, so if you could help me out I'd be very grateful.

I need to alter volume of my scene. It needs to be silent for 10 seconds at the start and then go to full volume. I have created a master volume control with the following code :

var master = 0;

function Update () {

AudioListener.volume = master;

}

I need to be able to change this from 0 to 1 after 10 seconds of the scene loading. However I cannot seem to animate the variable "master" so I am stuck. I'm sure this is easy but I have tried several ways and I have not worked it out.

Please help

Thankyou

function Start()
{
    Invoke("ChangeVolume", 10);
}

function ChangeVolume()
{
    AudioListener.volume = 1;
}

that is the simplest way really - if you want it to gradually fade in after the 10s silence, it's a bit more code