AkSoundEngine.GetRTPCValue not updating

Question

Hello

In Unity, I'm trying to determine whether or not music has been started so I can avoid it being started again and again over the top.

I've tried putting a Wwise meter on the music switch, and outputting that to an RTPC, and I've also tried setting the RTPC in the same event as the music_start event. 

In each case, I can see the RTPC going for it in the Game Sync Monitor, but in Unity it doesn't seem to be updating the variable at all.

Here's the code: 

public class MusicControl : MonoBehaviour {

    public int musicvolume = (int)RTPCValue_type.RTPCValue_GameObject;
    public float volume;
    // Use this for initialization
    void Start () {
            AkSoundEngine.PostEvent ("music_start", gameObject);
    }

    // Update is called once per frame
    void Update () {
        AkSoundEngine.GetRTPCValue ("music_volume", gameObject, out volume, ref musicvolume);
    }
}

If anyone has any ideas please let me know. 

Also, can anyone tell me what's best practice for triggering the music? Which game object should it be attached to?

Thanks