I’m relatively new to university teaching but something I found useful right from the start is the use of music in lectures. Inspired by a Times Higher Education article on lecture trailers, I have been using Spotify on my backup laptop to play music as a signal to students that talking is encouraged at that time.
When I want to end a discussion, I will gradually ramp up the volume to the point of noticeability and then cut the music: Any of us who have seen the spread of causeless hush in a crowded room know how contagious silence can be. It might just be my scant experience so far, but I find a transition to silence to work far better than a transition from silence to yelling, as a way of re-consolidating a lecture theatre.
I started out by running lecture trailers in the form suggested in the linked article: A rolling slideshow of “coming up today” content, set to quiet music. Noticing how effectively it quietened down the room when used at 10:05am to signal the start of the lecture, I also use music during the discussion phase of Peer Instruction, with similarly useful effects.