How to reproduce:

1. Open attached project
2. Open scene unity5-School.unity
3. Play the scene
4. Hum into the microphone, slowly increasing the pitch
- Note how the speedometer increases properly
5. Select the gameobject Canvas_meters
6. Mute the Audio Source
7. Hum into the microphone again
- Note that the speedometer does not react (unlike the people in the same room)
- A workaround is to route the Audio Source into a specific mixer channel with the channel's volume set to low

By Design:
- The behaviour of this has changed to fix the conceptually broken behaviour of GetOutputData.
- It doesn't make sense to have an AudioSource muted, effectively producing no signal, and have getOutputData return signal. This fix was put in place to bring the behaviour inline with what is conceptually happening with the signal path.
- To achieve the old behaviour, have the AudioSource route into an AudioGroup of an AudioMixer that is fully attenuated. That way the data can be read from the mic audioSource and not be played through the speakers.