How do I unmute my microphone in Teamviewer 12?

[RhinoCan]

I haven't used Teamviewer in several months so when I tried to use it yesterday, it offered me an update to version 12 (from 11) so I accepted it. But now, when I do a remote session where I try to help a friend with a problem, she can't hear me. I can hear her fine and the chat feature also works fine but life is going to be a lot easier if I can give her instructions by voice.

I suspect my microphone (on my headset) may be muted by default in Teamviewer but I can't find the setting in Teamviewer 12 that lets me unmute it. Can someone tell me where that setting is? It has apparently moved from where it was in Teamviewer 10 and 11. I've looked high and low but haven't found it after an extensive search.