Pedal tone

Pedal tones or "pedals" are special low notes on brass instruments that sound at the fundamental tone of the instrument's harmonic series. The name pedal comes from the pedal keyboard of a pipe organ, played with the feet to sound the 16′ and 32′ contrabass registers. Brasses with a bell do not naturally vibrate at this frequency.

A closed cylinder vibrates at only the odd members of its harmonic series. This set of pitches is too sparse to be musically useful for brass instruments; therefore, the bells and mouthpieces of brasses are crafted to adjust these pitches. 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. This new series is similar to that of a stopped conical tube, with the exception of the fundamental, which is no longer incorporated in the harmonic series.