AudioChorusFilter.rate  

// Set the rate on the chorus filter to 15hz.

@script RequireComponent(AudioSource)
@script RequireComponent(AudioChorusFilter)

function Start() {
    GetComponent(AudioChorusFilter).rate = 15;
}

using UnityEngine;
using System.Collections;

[RequireComponent(typeof(AudioSource))]
[RequireComponent(typeof(AudioChorusFilter))]
public class example : MonoBehaviour {
    void Start() {
        GetComponent<AudioChorusFilter>().rate = 15;
    }
}

import UnityEngine
import System.Collections

[RequireComponent(AudioSource)]
[RequireComponent(AudioChorusFilter)]
class example(MonoBehaviour):

    def Start():
        GetComponent[of AudioChorusFilter]().rate = 15