It’s quite simple really. Just combine a fondness for classic jazz composers (e.g., Monk, Roland Kirk, and Sonny Rollins) with a sensibility that allows for elasticized solo sections, the occasional synthesizer foray, and a goofily clever humor; include evocative newer pieces by the likes of Ornette Coleman and even Robert Fripp; fashion a vibrant sound that falls somewhere between the moonstruck ensemble work of the Microscopic Septet and the polished modernism of the Mel Lewis Orchestra; convince each of the band’s dozen or so members that he’s actually playing in a combo; and abracadabra, it’s the Either/Orchestra. Based in Boston, the E/O made their first midwest visit last fall, and it proved to be among the year’s best musical moments. (Jazz connoisseurs may hear, in the horn-guitar textures, traces of the late lamented Boston band called the Year of the Ear.) This time, we get to hear them on April 1, which is fitting, because these guys are jokesters in the best sense: they use wit and a touch of mischief to serious ends (in this case, the simultaneous maintenance and updating of the big-band tradition). Saturday, 8 PM, Green Mill, 4802 N. Broadway; 878-5552.