Pedal tone

The bell significantly raises all pitches in the series, particularly on the low end, while the mouthpiece lowers the higher harmonics, limiting the amount to which higher harmonics are raised by the bell.

The resulting compressed set of pitches resembles a new harmonic series that includes the even members.

The higher resonances of the new series help the lips vibrate at the fundamental frequency and allow the pitch to sound.

On trombone, pedal B♭1 is frequently seen in commercial scoring but much less often in symphonic music.

Notes below B♭ are called for only rarely as they "become increasingly difficult to produce and insecure in quality" with A♭1 or G1 being the bottom limit for most trombonists.