Use this when you want to use a custom rolloff.

Note: Currently is not possible to modify the volume curve via scripting.

	// Sets the rolloff of the audio source attached to
	// this script to custom.
	@script RequireComponent(AudioSource)
	function Start() {
		audio.rolloffMode = AudioRolloffMode.Custom;
	}

using UnityEngine;
using System.Collections;

[RequireComponent(typeof(AudioSource))]
public class Example : MonoBehaviour {
    void Start() {
        audio.rolloffMode = AudioRolloffMode.Custom;
    }
}

import UnityEngine
import System.Collections

[RequireComponent(typeof(AudioSource))]
public class Example(MonoBehaviour):

	def Start() as void:
		audio.rolloffMode = AudioRolloffMode.Custom