Excerpt from Hembree's PhD dissertation:
Ouroboros and Apocryphal Chrysopoeia: Aesthetics and Techniques (2015)
Introduction from the Article:
"Over the past few years, I researched the relatively new terrain of brass split-tone multiphonics as a way to find distortion like sounds. Multiphonics in general are instrumental techniques, first developed on woodwind instruments, that involve the apparent production of more than one fundamental frequency, simultaneously, on a monophonic instrument.
In brass music, split-tone multiphonics have been more prevalent in the literature for and about the trombone, perhaps because its larger mouthpiece more easily allows for two side-by-side buzz-points to form on the lips (see below). Stuart Dempster's (b. 1936) book The Modern Trombone (1979) provides a good description of the technique, along with a method of learning how to produce it with regularity.
Split-tones on the trumpet are less well researched and less prevalent in the notated trumpet literature. Extended technique manuals by Paul Smoker, Attilio Tribuzi, William Denton and Amy Cherry, did not reveal any mention of the existence of split-tone multiphonics on the trumpet. They did mention singing while simultaneously playing, which produces similar, but less aggressively distorted sounds. Italian Gabriele Cassone mentions the technique, but without providing an example of the technique in trumpet literature.
In my modest survey of notated trumpet music, I was able to find a handful of pieces that use the technique, notably Liza Lim's Ehwaz (2010) and Eduardo Moguillansky's brutally difficult Limites (2006-2008), which requires the player to buzz on two trumpets, both with multiphonics, simultaneously. These works would not be possible without their virtuoso premiere players, Tristram Williams (b. 1978) in the case of Ehwaz and ValentÃn Garvie (b. 1973) in the case of Limites.
Split-tones have existed outside of the realm of notated music, in improvisations and non-notated music by jazz and experimental musicians, notably Wadada Leo Smith and Peter Evans. Evans has explored split-tones as a compositional resource extensively and in a truly idiomatic fashion in the non-notated piece The Chamber, from his album Nature/Culture. I was able to work with Evans during a UC San Diego residency of the International Contemporary Ensemble, which served to confirm that my experiments on my own instrument were indeed fairly universally applicable to other instruments as well as players.During the residency, Evans recorded my piece Blue Sky Catastrophe (2010/13), which was later premiered by composer-trumpeter Sam Wells. Blue Sky Catstrophe as an appendix to this document. Trumpeter Rachel Allen played on the premiere of Ouroboros, which featured a substantial trumpet solo using split-tones in the second movement."
Browse online:
Watch Ouroboros, Movement 2:
Listen to Blue Sky Catastrophe: