If Art Ensemble Of Chicago's 2019 London Jazz Festival performance showed how inventive Roscoe Mitchell is when a dozen so musicians are on stage with him, then this vibrant concert is a timely reminder that four can also be a magic number. The Polish players who join Mitchell include the impressive drums and bass siblings, Qba and Slawek Janicki and multi-reedist Jerzy Mazzoll, and together they cohere as a pressure cooker unit that has faint echoes of some of Mitchell's small groups with the late Joseph Jarman. On one hand the ensemble pushes the notion of density and mass to thrilling heights, setting up daringly held drones on bass and bass clarinet that buzz and squelch tremulously while detail is added by way of clacking percussion or scurrying horn motifs. These pieces succeed for the great nuance found in repetition as well as the unbroken ferocity of the sound, but they are supplemented by more raucous moments in which Mitchell explores the outer limits of timbre, making his woodwinds so hoarse they suggest a bow scraping cello strings, or ballads where shadow and light, sound and silence, flow in and out of each other organically. As uncompromising and restlessly probing as one would expect of such personalities.