Essential Robin Trower

Credible guitar heroes were in short supply when Robin Trower left Procol Harum in 1971 (which had long since swapped the baroque subtleties of ''A Whiter Shade of Pale'' for harder rock) to claim the spotlight for himself. A commanding, evocative soloist with a substantial stylistic debt to Jimi Hendrix, Trower formed a trio and made several powerful blues-infected rock albums in the mid-'70s. The nine songs in Essential Robin Trower that belong to his first three records — including ''Too Rolling Stoned'' and ''I Can't Wait Much Longer'' — find excitement in the taut contrast between Trower's fluid playing and bassist Jim Dewar's whisky gruff singing. But other than one worthy souvenir from Tower's 1981 collaboration with ex-Cream bassist Jack Bruce, the rest of the tracks are redundant, lacking the early work's freshness and fire. B-