One of the reasons Spektral Quartet have remained favorites of Chicago’s new music scene is their holistic interest in the trajectory of classical music and how it connects with contemporary repertoire. This superb new double album expands the way the group often programs its concerts. Yes, it’s strange to include a performance of Brahms’ String Quartet in C Minor in this column, but the group features the piece because the composer’s harmonic sense was celebrated by Arnold Schoenberg, the 20th century paradigm-shifter whose String Quartet No. 3 is also performed here. Also included is Ruth Crawford Seeger’s brilliant and perennially overlooked 1931 String Quartet. The second half of the collection zooms in on the present; the slashing intensity and radical dynamics of Sam Pluta’s “binary/momentary logics: flow state/joy state;” the transplanted harmonic language of jazz within a formal classical structure behind the splintered melodies of guest flutist Claire Chase on Anthony Cheung’s “Real Book of Fake Tunes;” the purely spontaneous electricity of the quartet’s splattery yet cogent collaboration with improvising vocalist Charmaine Lee on “Spinals;” and the, by turns, eerie, violent, serene, and percussive George Lewis work “String Quartet 1.5: Experiments in Living.” The second disc provides a potent sampler of some crucial threads in 21st century composition.