You know the pedal steel guitar: those beautiful sliding chords that shimmer in country music and the talking notes that enliven gospel. Well, you don't know the full scope of the pedal steel until you hear Susan Alcorn take the instrument for a wild ride. Alcorn emerged from the Baltimore scene playing pedal steel in C&W bands. Then she started exploring what the pedal steel might bring to the compositions of classical composers like Messiaen and Varèse or the tangos of Astor Piazzolla. It wasn't long before she slid into the realms of world music and free jazz. The sky's the limit when Alcorn takes the stage at the Bop Shop Monday.