A wah-wah pedal (or just wah pedal) is a type of guitar effects pedal that alters the 

tone of the signal to create a distinctive effect, intended to mimic the human voice. 

The pedal sweeps the peak response of a filter up and down in frequency to create the 

sound (spectral glide).

The Wah-Wah pedal has a very specific and technical circuitry and housing structure. 
Therefore, all other previous effects circuits and devices, prior to 1966, that share 
similarities with the wah-wah pedal are not actually affecting the signal in the same 
manner and cannot be considered early versions of the wah-wah pedal. The first pedal 
ever created was by Warwick Electronics Inc. / Thomas Organ Company in 
November 1966; this pedal is the original prototype wah-wah pedal made from a 
transistorized MRB potentiometer bread-boarded circuit and the housing of a 
Vox ContinentalOrgan volume pedal.