// Listen to only Echo (not the original audio source)
    // Set the wet mix to 0 and you will disable the echo.
    @script RequireComponent(AudioSource)
    @script RequireComponent(AudioEchoFilter)
    function Start() {
        GetComponent(AudioEchoFilter).wetMix = 1.0;
        GetComponent(AudioEchoFilter).dryMix = 0.0;
    }

using UnityEngine;
using System.Collections;

[RequireComponent(typeof(AudioSource))]
[RequireComponent(typeof(AudioEchoFilter))]
public class example : MonoBehaviour {
    void Start() {
        GetComponent<AudioEchoFilter>().wetMix = 1.0F;
        GetComponent<AudioEchoFilter>().dryMix = 0.0F;
    }
}

import UnityEngine
import System.Collections

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

    def Start():
        GetComponent[of AudioEchoFilter]().wetMix = 1.0F
        GetComponent[of AudioEchoFilter]().dryMix = 0.0F