THE most common filter for guitarists is a wah pedal. This simple effect can add percussive effects, bring rhythm parts to life, or add extra vocal expression to solos.
Wah pedals usually create a band-pass filter (see diagram on page 54), and the ‘centre frequency’ of the wah sound is changed using the rocker pedal. In classic wah examples such as the Dunlop Cry Baby, the rocker pedal is attached to a control pot, similar to the ones you find on your guitar.
When the pedal is swept from the heel-down to toe-down setting, the pot turns and the wah-wah sound corresponds to the movement. Mechanical pots can often wear out, introducing a scratchy sound to your pedal, or they can even stop working entirely. To combat this, companies such as Morley make wah pedals that use a sensor inside, rather than a moving pot.
Wah pedals don’t usually have any controls apart from the rocker pedal and an on/off switch, but some come with additional circuits to increase the vocal quality of the pedal or add overdrive.