Walk up to the tallest tree1) in the Common Ground between the pond and the bar. Look at the glowing red circle where it's written prominently FOCUS HERE AND THINK TO AFFECT ACOUSTICS, and think something; If there's a music that can be made of it, you'll hear it wafting throughout the gardens immediately.
It was an AI2) originally created by NesQuarX to serve as a security monitor for his tree in the Common Ground. It was later retrofitted with speakers that look like normal leaf bunches in trees all over the CG, a thought sensor which is the aforementioned glowing red coil mounted at a convenient height on a region of the tree painted black. It detects commands from any thoughts focused on the coil and interprets them as music. It knows most pre-EMP popular music but always plays them with an improbable twist. It can also synthesize music if you just think up the nature of it.
Apart from being the watchman to the tree and playing music, the AI also monitors the Common Ground and can interface with most other electronics, though it won't accept any unauthorized commands to do that.