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Composer's Handbook
A pedal point is a sustained note, usually in the bass, held while harmonies change above it.
Hold C in the bass while the chords above move F, G, C.
F/C (C–F–A–C), G/C (C–G–B–D), C (C–E–G–C).
Bach, Prelude in C major, BWV 846 (closing bars)