One of the noteworthy recordings released in 2016 is the Kepler Quartet’s third volume of string quartets by Ben Johnston (New World Records). Johnston, who turned ninety this year, is well known for his work in unconventional tuning systems, namely extended just intonation. The complexity of some of his works in this system, notably the Seventh Quartet, included on Kepler’s volume 3, ranks up there with some of the toughest chamber works in the literature. Even a seemingly more straightforward piece, such as his Fourth Quartet, a trope on “Amazing Grace,” can provide both formidable pitch and rhythmic challenges. Recently,