[Lab] Controlling Light with Sound

[The Big Plan - Chris B]

Hi!

Looking for some advice for an art installation. I'd like to have a  
light or set of lights respond to an auditory
input. I'd like the lights to turn on in time with the sound of a  
ventilator (a medical one). So when the ventilator is
not doing a breath, the lights would be off, but then when the  
ventilator starts doing a breath they would
turn on for the duration of the breath. I'd like the lights to light  
up and dim gradually, not just on an off.

What's a simple or best way to do this?

Thanks!

Chris