The definition for the wah-wah effect, according to Erickson in 1975, is that the 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”
All that brass
The word for Wah Wah effect derived from the sound of the effect itself, in other words, an onomatopoeia of the word. One of the first recorded “wah-wah” sound effects was noted by Jazz player Barney Bigard. This happened after hearing Tricky Sam Nanton use the effect on his trombone in the early 1920`s. So bearing this in mind we can say that the effect originated in the 1920`s, with the brass players finding they can produce an expressive crying tone by moving a mute, or a plunger, in and out of the instruments bell. In 1921, trumpet player Johnny Dunn’s use of this style inspired Tricky Sam Nanton to use the mute with the trombone.
The guitar wah-wah effect was developed almost by accident. The engineers at Vox were working on a solid-state, Beatles endorsed amp when a junior accidentally created a circuit with odd, audible effects. The team housed it in an organ volume pedal chassis and began experimenting with brass instruments. (brass players in big-bands frequently used these effects, after all).
Jimi’s guitar pedal
The ”wah wah” effect is incredibly expressive. People associate it with whole genres of music. Additionally, you can hear it on many of the most influential recordings of funk, soul, jazz and rock in the past 50 years. Jimi Hendrix would sometimes use the effect with leaving the pedal in particular location. This created the unique effect that did not change over time. However, in his song “Voodoo Child” Hendrix muted the strummed strings while rocking the pedal, creating a percussive effect. The sweeping of the wah-wah pedal is more dramatic in the louder verse and the chorus, emphasizing the song`s blues styling. The wah-wah sound that Hendrix created became a trademark of the whole subgenre of the 1970’s funk and soul.
Another unusual use of the wah-wah pedal can be heard on the Pink Floyd song “Echoes”. They created screaming sounds by plugging in the pedal back and forth. That is, the amplifier was connected to the input and the guitar was connected to the pedal`s output.
The wah-wah effect is produced mostly by foot-controlled signal processors containing a bandpass filter with variable frequency and small bandwidth. Moving the pedal back and forth changes the bandpass centre frequency. The wah-wah effect then mixes with the direct signal. This effect leads to a spectrum shaping similar to speech and therefore produces speech-like “wah-wah” sound. Instead of manually changing the filter frequency, it is also possible to let the low-frequency oscillator control the centre frequency. Parameters derived from the input signal control this. This is an auto ”wah-wah” filter. On the other hand, a tremolo wah filter occurs after combining the effect with a low-frequency amplitude variation, which produces a tremolo
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