AudioSource.mute

Un- / Mutes AudioSource. Mute устанавливает volume=0, Un-Mute восстанавливает первоначальный объем.

// Mutes-Unmutes the sound from this object each time the user presses space.
using UnityEngine;
using System.Collections;

public class ExampleClass : MonoBehaviour
{
    AudioSource audioSource;

    void Start()
    {
        audioSource = GetComponent<AudioSource>();
    }

    void Update()
    {
        if (Input.GetKeyDown(KeyCode.Space))
            audioSource.mute = !audioSource.mute;
    }
}