Wah-wah 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). Although this effect is thought of almost exclusively as the electric guitar wah-wah pedal, it is also used in other contexts, listed here.
Wah-wah in trumpet and trombone playing
Although perhaps best known from the electric guitar's wah-wah pedal, the sound is much older, having been significantly developed by trumpet and trombone players using mutes in the early days of jazz.
Joe "King" Oliver recorded "Wawawa" in the '20s. Bubber Miley, Cootie Williams, trumpeters, and Tricky Sam Nanton, trombonist, of the Duke Ellington Orchestra pioneered in using plunger mutes ("plumber's helper") to create wah-wah sounds.
The effect was used in the '30s on "Sugar Blues" by commercial Dixieland trumpeter Clyde McCoy, who built a long career around the sound, and even today has a popular wah-wah pedal by VOX named after him. "The Fat Man", the first hit by Fats Domino, features Fats singing vocal trumpet wah-wah. Another New Orleans singer, Chuck Carbo frequently performs vocal wah-wah. "Tuxedo Junction," a signature tune for the Glenn Miller Orchestra, uses the effect prominently in its trombone parts.
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, p.73).
The animated Peanuts film and television specials used a trombone with a plunger mute to stand in for the voices of adults, who were always off-screen when they spoke.
Wah-wah in electronic music
In electronic music, wah-wah effects are easy to produce by controlling any number of filter types with a modulation envelope.
Wah-wah effects can also be achieved by using a vocoder to modulate an instrument sound, and speaking "wah-wah" into the modulation control input of the vocoder. The vocoder then impresses the formants of the spoken sound into the musical sound.
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