Songs for Insomniacs 6: “Repent Walpurgis” by Procol Harum

Procol Harum is best known for “Whiter Shade of Pale.” But the dark and brooding final track on their debut (minus Gary Brooker’s soulful voice) illustrates other strengths of this seminal band, including Brooker’s piano solo (based on a Bach prelude), Robin Trower’s fierce guitar lines, and B. J. Wilson’s impassioned drumming.