[pax]

либо

var nextSound: float=0;
var soundStep: float = 0.2;

function Update()
{
    if(Input.GetKey(KeyCode.W))
    {
        if(nextSound< Time.realtimeSinceStartup  )
        {
            audio.Play(); 
            nextSound = Time.realtimeSinceStartup + soundStep;
        }
    }
}