room :: Pattern Double -> ControlPattern
room controls reverb. It turns a number pattern (ranging from 0 to 1) into a control pattern that controls how much of the audio is signal is sent into the reverb effect.
d1 $ sound "bd feel odx drum" # room "0 1 0.25 0.75" # size 0.5 # orbit 1
As room is a global effect, you will want to use it in tandem with orbit (unless you're only running one pattern at a time).
The size function controls the reverb size.