function Start() {
    audio.rolloffMode = AudioRolloffMode.Linear;
}

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
    void Start() {
        audio.rolloffMode = AudioRolloffMode.Linear;
    }
}

import UnityEngine
import System.Collections

class example(MonoBehaviour):

    def Start():
        audio.rolloffMode = AudioRolloffMode.Linear