Circular breathing is the act of pushing air out through the oral cavity while breathing in through the nostrils. When done correctly, the performer can sustain a buzz for as long as necessary, although small dips in sound level may be discernible at the crossover points between stored and fresh air. Many higher pitched wind instruments utilize this technique in their repertoire, but due to the high air demands of the tuba family, this technique is seldom called for in the contemporary tuba/euphonium repertoire. This technique is more approachable for the euphonist (which requires a slightly smaller amount of air than the larger tubas), but even then, this technique will be seldom seen among professional performers. It is still a valid technique for the tuba and euphonium, however! This technique must only be used if it is known for a certainty that the performer can comfortably circular breathe.
Although possible, it must however be said that circular breathing can be a very noisy affair on the tuba (and slightly less so on euphonium). The large amounts of air required for the tuba and euphonium necessitate a very rapid intake of a high volume of air through the nose, which creates a loud “sniff” sound. These sniff breaths must also be done at a rapid pace, due to the need for a constant air supply when performing even at soft dynamics on the tuba and euphonium.
Due to the active nature of this technique, it is most often used to create sustained sounds on the tuba and euphonium. Although it is possible to circular breathe and perform rapid passagework, this technique is not physically possible for some performers.
As with many of the techniques described in this guide, care must be taken to ensure that the intended performer of a new work is able and willing to circular breathe.
A simple score direction above a sustain note or passage will suffice to let the performer know that you wish for them to circular breathe. This is true whether the note is for a determined duration or is indeterminate. When articulations are called for within a section of circular breathing, they can be notated traditionally (assuming that it is obvious that there should not be a break—tuba and euphonium players often place breaths at articulation breaks).
Works to consider (bolded titles are particularly representative examples of this technique)
Jigsaw – Mikel Kuehn
Music for Tuba and Computer – Cort Lippe
 For a virtuosic example of this technique, listen to Dr. Benjamin Pierce’s recording of Peter Christoskov’s Moto Perpetuo, which features four minutes of circular breathing through a series of rapid passages.