Wah Wah Filter

According to Erickson, 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."  

All That Brass

The word for "wah-wah" effect is derived from the sound of the effect itself, in other words, an onomatopoeia of the word. Jazz player Barney Bigard noted one of the first recorded "wah-wah" sound effects. 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 1920s, with the brass players finding they could produce an expressive crying tone by moving a mute, or a plunger, in and out of the instrument's bell. In 1921, trumpet player Johnny Dunn's use of this style inspired Tricky Sam Nanton to use the mute with the trombone.

Guitar Wah-Wah

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 sometimes used the effect of leaving the pedal in a particular location. This created a 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. Hendrix's wah-wah sound became a trademark of the whole 1970s Funk and Soul subgenre.  

Screaming Sounds

Another unusual use of the wah-wah pedal can be heard in the Pink Floyd song "Echoes." They created screaming sounds by plugging the pedal back and forth, connecting the amplifier to the input and the guitar to the pedal's output.  

Spectral Glide

The wah-wah effect is produced mainly by foot-controlled signal processors containing a bandpass filter with variable frequency and small bandwidth. Moving the pedal back and forth changes the bandpass center frequency. The wah-wah effect then mixes with the direct signal. This effect leads to a spectrum shaping similar to speech, producing a speech-like "wah-wah" sound. Instead of manually changing the filter frequency, letting the low-frequency oscillator control the center frequency is possible. 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.