// Shuts down the source.
 private void ShutdownSoundfield()
 {
     if (id >= 0)
     {
         for (int channelSet = 0; channelSet < audioSources.Length; ++channelSet)
         {
             ShutdownChannelSet(audioSources[channelSet], channelSet);
         }
         GvrAudio.DestroyAudioSoundfield(id);
         id = -1;
     }
 }