Pedal tone
Pedal tones are special notes in the harmonic series
Harmonic series (music)
Pitched musical instruments are often based on an approximate harmonic oscillator such as a string or a column of air, which oscillates at numerous frequencies simultaneously. At these resonant frequencies, waves travel in both directions along the string or air column, reinforcing and canceling...

 of cylindrical-bore brass instrument
Brass instrument
A brass instrument is a musical instrument whose sound is produced by sympathetic vibration of air in a tubular resonator in sympathy with the vibration of the player's lips...

s. A pedal tone has the pitch of its harmonic series' fundamental tone. Its name comes from the pedals of a pipe-organ. Cylindrical brasses 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, and the mouthpiece limits the amount to which higher harmonics are raised. The resulting set of pitches is a new harmonic series altogether. This new series has all but one of its members present, instead of only the odd members.

The member not present in the new series is the fundamental. The original fundamental is not raised all the way to the new fundamental pitch, and the original third harmonic becomes the new second harmonic.

The new fundamental can be played, however, as a pedal tone. The higher resonances of the new series help the lips vibrate at the fundamental frequency and allow the pitch to sound. The resulting tone relies heavily on overtone
An overtone is any frequency higher than the fundamental frequency of a sound. The fundamental and the overtones together are called partials. Harmonics are partials whose frequencies are whole number multiples of the fundamental These overlapping terms are variously used when discussing the...

s for its perception, but in the hands of a skilled player, pedal tones can be controlled and can sound characteristic to the instrument.

Pedal tones are called for occasionally in advanced brass repertoire, particularly in that of the trombone
The trombone is a musical instrument in the brass family. Like all brass instruments, sound is produced when the player’s vibrating lips cause the air column inside the instrument to vibrate...

 and especially the bass trombone.
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