Wah-wah (or wa-wa) is an imitative word (or onomatopoeia) for the sound of altering the resonance of musical notes to extend expressiveness, sounding much like a human voice saying the syllable wah. The wah-wah effect is a spectral glide, a "modification of the vowel quality of a tone" (Erickson 1975, p. 72).
The word is derived from the sound of the effect itself; an imitative or onomatopoeia word. The effect's "wa-wa" sound was noted by jazz player Barney Bigard when he heard Tricky Sam Nanton use the effect on his trombone in the early 1920s (Nadal n.d.).
The wah-wah effect is believed to have originated in the 1920s, with brass instrument players finding they could produce an expressive crying tone by moving a mute, or plunger, in and out of the instrument's bell (Du Noyer 2003, 375). In 1921, trumpet player Johnny Dunn's use of this style inspired Tricky Sam Nanton to use the mute with the trombone (Nadal n.d.).
The method of production varies from one type of instrument to another. On brass instruments, it is usually created by means of a mute, particularly with the harmon (also called a "wa-wa" mute) or plunger mute. Woodwind instruments may use "false fingerings" to produce the effect.
Any electrified instrument may use an auxiliary signal-processing device, or pedal. Often it is controlled by movement of the player's foot on a rocking pedal connected to a potentiometer. An alternative to players directly controlling the amount of effect is an 'auto-wah'. These devices, usually make harder hit notes more trembly with a more prominent wah wah effect (Hunter 2008). Wah-wah effects are often used for soloing or for creating a "wacka-wacka" funk rhythm on guitar (Du Noyer 2003, 375). Although these electronic means are most often on electric guitar, they are also often used on electric piano (Kernfeld 2002).
The wah-wah effect is produced by periodically bringing in and out of play treble frequencies while a note is sustained. Therefore, the effect is a type of spectral glide, a "modification of the vowel quality of a tone" (Erickson 1975, 72).
The Electronic wah-wah effects are produced by controlling tone filters with a pedal (Keen 1999). An envelope follower circuit is used in the 'auto-wah'.(Hunter 2008). Subtractive synthesis can produce a similar effect.
Tricky Sam Nanton's wah-wah on trombone in Duke Ellington's Orchestra became well known as part of the so-called "jungle effects" of the band in the late 1920s (Nanton n.d.). This technique has been used in contemporary music. Karlheinz Stockhausen notates the use of the wah-wah mute in his Punkte (1952/1962) in terms of transitions between open to close using open and closed circles connected by a line (Erickson 1975, 73). Although the most common method of producing wah-wah on brass instruments is with a mute, some players have used electronic filtering, notably Miles Davis on trumpet (Kernfeld 2002).