Perhaps the most famous guitar effect, the V847 is a wah-wah modulation effect guitar pedal introduced by VOX in the 1960s.
The Wah-Wah effect is basically a tone control. The frequency response of it is a band-pass filter which boosts the resonant frequency and attenuates above and below harmonics. The action of rocketing the pedal shifts the resonant frequency. When the pedal is pushed all the way down, the high frequencies are emphasized, and conversely, when the pedal is all the way up, the bass is boosted.
The frequency response is characterized by a resonant peak which is centered in 750 Hz (pedal in a mid position) and can be swept up and down from 450 Hz to 1.6 KHz. The selected frequencies are amplified up to 18dB while the surrounding ones are attenuated.
The Gear Rack