The wah-wah pedal was originally developed to imitate a playing technique that the trumpeter Clyde McCoy popularized in the 1920s and 1930s with his mute. Therefore, the first wah pedal was also called the Clyde McCoy Wah-Wah and was manufactured by the Thomas Organ Company in California. Shortly afterwards, the V846 and the Cry-Baby from Vox followed, and the basic technical aspects of these are still manufactured in numerous versions by the Dunlop company today.

Technically speaking, the "wah-wah" effect is created by a sound filter that is described as a bandpass with a resonance peak; the resonance frequency is shifted within the spectrum. It is controlled by the pedal (= rocker), which allows the player to keep their hands free.
The position of this rocker is detected inside the housing by a specific component that influences the resonant frequency. This is usually done by means of a potentiometer operated by a rack, although there are models that use tunable coils or photoresistors controlled by a lighting system instead.

The sound quality is determined by the height of the resonance peak and the range of frequency variations. Some wah pedals offer the ability to adjust the Q of the filter, which allows for additional sound variations. In the classic design, the controlled component is located directly in the signal path. Due to dust buildup and mechanical wear, potentiometers can produce annoying noises over time, while modern designs with electronic control avoid such problems.

Since the 1980s, the Morley company has established itself as an important authority in the field of wah sounds, offering a softer and less aggressive sound alternative to the Cry Baby pedals. Morley uses these electro-optical controls, which are wear-free.

In the 1990s, switchless wah-wah pedals were added. Both Dunlop and Morley pedals have been used several times as the basis for signature pedals by artists such as Steve Vai, Mark Tremonti and George Lynch. Special mention should also be made of the WH-10 from Ibanez, which achieved cult status thanks to John Frusciante of the Red Hot Chili Peppers.
The inexpensive plastic version of this pedal offers a unique wah sound that, unlike many competing products, is produced without a coil.
Newer models change the resonance frequency via a control voltage that is integrated into a Voltage Controlled Filter (VCF). Such VCFs are typically found in synthesizers and can also be operated without a pedal. In variations such as Auto-Wah or Touch-Wah, the frequency is controlled by the strength of the player's touch, which makes this effect particularly attractive in the funk style.
Famous wah-wah users in the 1960s and 1970s were Jimi Hendrix, David Gilmour and Eric Clapton. Guitarists like Michael Schenker established the fixed-wah sound in their solos (where the wah-wah stays permanently in one position). Marc Knopfler used the wah-wah over his chord playing in the song "Money for nothing" and this pedal is also indispensable in hits by Guns'n'Roses and Steve Vai. The wah-wah has also been established in harder music genres since the 90s, for example with Kirk Hammett from "Metallica" or Tom Morello from "Rage Against The Machine".

The wah-wah pedal is undoubtedly one of the most popular effects for the electric guitar and is used in a variety of genres today.