Pedal notes of brass instruments, a mysterious regime of oscillation

Abstract

In reed and brass instruments, sound is produced by self‐sustained mechanical oscillations driven by an airflow coming from a pressure supply such as the player's lungs. Most of the time, the fundamental frequency of a periodic oscillation is close to, and mainly controlled by one given acoustic mode. Even though, these oscillations are the result of a complex non‐linear coupling between all the acoustic modes and the mechanical valve. The pedal note, which is the lowest note that can be sounded on a brass instrument, is well‐known as a counter‐example. Eighty years ago, Bouasse did an experiment by replacing the brass mouthpiece by a reed mouthpiece on a brass instrument, and obtained a pedal note a fifth below! An elementary model dedicated to both cane‐reed and lip‐reed instruments can be used. In order to investigate the sound production of pedal notes, a simulation method based on modal decomposition of bore and reed dynamics has been carried out. Then, the periodic solutions of this model are obtained, and the mysterious oscillation regimes of Bouasse experiment are discussed.