No expression pedal input, and it's a standard filter, reacts to your dynamics. Because of the effects loop though there is a nifty little trick you can do. Plug whatever you want to trigger the filter (say the bass drum mic) into the input, then plug your bass into the return of the effects loop. It will be your bass sound coming through, but the filter will only be controlled by the kick drum So you can essentially sync the filter to be triggered by whatever you like, but have it effect your bass.
Edit: Here's a vid that shows you what I mean.