A multiphonic is an extended technique on a monophonic musical instrument (one that generally produces only one note at a time) in which several notes are produced at once. This includes wind, reed, and brass instruments, as well as the human voice. Multiphonic-like sounds on string instruments, both bowed and hammered, have also been called multiphonics, for lack of better terminology and scarcity of research. Multiphonics on wind instruments are primarily a 20th-century technique, though the brass technique of singing while playing has been known since the 18th century and used by composers such as Carl Maria von Weber. Commonly, no more than four notes will be produced at once, though for some chords on some instruments it is possible to get several more. Technique Woodwind instruments On woodwind instruments—e.g., saxophone, clarinet, oboe, bassoon, flute, and recorder—multiphonics can be produced either with new fingerings, by using different embouchures, or voicing the throat with conventional fingerings. There have been numerous fingering guides published for the woodwind player to achieve harmonics. Multiphonics on reed instruments can also be produced in the manners described below for brass instruments. It is said to be impossible to recreate exactly the conditions between one player and the next, due to minute differences in instruments, reeds, embouchure, and other things. This, however, is not entirely true; the multiphonic will depend on the room temperature and other such things, but essentially multiphonics sound the same due to the harmonic structure of the multiphonic. A multiphonic fingering that works for one player may not work for that same player on a different instrument, or a different player on the same instrument, or even after switching reeds. This is often the result of slightly different construction of two instruments from different makers. Brass instruments In brass instruments, the most common method of producing multiphonics is by simultaneously playing the instrument and singing into it. When the sung note has a different frequency than the played note (preferably within the harmonic series of the played note), several new notes that are the sums/differences of the frequencies of the sung note and the played note are produced; leading to the popular term trumpet/trombone/horn growl. This technique is also called "horn chords". The tone sung doesn't necessarily have to be in the played tone's harmonic series, but the effect is more audible if it is. The tone quality of brass multiphonics is influenced