I have 2 mobile configurations and one home configuration.
Mobile 1: My most common music editing equipment is just my laptop and headphones on the El. Most of the time spent editing, mixing and mastering this music has been while riding the train between the Loop and Evanston.
Mobile 2: When I need to record instrumentals, I can just add on an Edirol PCR-M30 controller as shown below. I can record and mix everything except the vocals and piano with this configuration.

Home Configuration: When I need more space, to record vocals or a full-size keyboard, I've got this configuration at home.
