As soloists, double reedist Kyle Bruckmann and trumpeter Ernst Karel are versatile and fluent, but as the electroacoustic duo EKG their sound world is scrupulously bounded. Using analog electronics, they generate Geiger-counter blips, shortwave crackles, and lonesome feedback whistles. Their horns, typically routed through effects or amplified so that an intake of breath sounds like a gale-force wind, fit right in; it’s a bit of a shock when Karel blows a lovely blue phrase at the beginning of “Days,” a piece from their new CD, No Sign (Sedimental). The album reminds me of electron micrographs of viruses–initially imperceptible elements turn out to have marvelous shapes. Karel assembled the tracks from improvisations recorded over a three-year period, but his edits are so subtle that the pieces sound like continuous performances. EKG shares the bill (and members) with openers Relay Signals and headliners Who Cares How Long You Sink, two local acts that both released albums last year on the Spanish label Lucky Kitchen. On the excellent Relay Signals, percussionist Tim Daisy alternates abstract solos and elegant small-group performances with Karel and bassist Jason Ajemian. Ajemian assembled a nine-piece ensemble that includes Bruckmann and Karel for Who Cares How Long You Sink; his compositions feature some lovely textures, but he doesn’t do much with them. EKG also plays a free show with the Books on Saturday 5/7 at 10 PM, at the Reynolds Club at the University of Chicago; call 773-702-8289. Bruckmann appears earlier this week in the trio Disney & the Muslims; see Monday. Also, the Kyle Bruckmann Group opens for the trio of Jason Adasiewicz, Nate McBride, and Dave Rempis on Thursday at 9:30 PM at 3030, 3030 W. Cortland; call 773-862-3616. Wed 5/4, 9:30 PM, Empty Bottle, 1035 N. Western, 773-276-3600 or 800-594-8499, $5.