@jfg. Ah thank you so much, I will try that out.
I ended up giving up and just using all the sound for the level watcher. I was using Izzy to created a haunted house room, where the ambient sound played all the time but when triggered, the jump-scare scream goes off and light from projector hits the scary skeleton... reflecting in plexiglass so it forms a hologram, like a pepper's ghost. The sound level made the light flicker in time with the scream.
(edit: what I was missing was the AU sound level watcher, didn't know about that)
I'm sure there are hardware ways to do this especially if it was a permanent exhibit, more reliably over years, but for a one-night party Isadora was my instant choice.