Pulitzer Prize-winning composer and Bang on A Can co-founder David Lang brings his pensive evening-length piece, darker, to EMPAC. Performed by Ensemble Signal. Scored for 12 strings, darker is a slow exploration of sound. At times, it gives the ensemble the feel of a giant pipe organ or, with the aid of visual artist Suzanne Bocanegra’s live projections, the feel of splattering rain on an immoveable wall. As much a hypnotic sonic and visual object as it is a piece of music, darker weaves its intricate solo lines into a delicate and subtly emotional fabric.