A wah pedal, also known as a tremolo, is an exceptionally versatile kind of electronic guitar effects pedal which changes the basic tone and pitches of the guitar sound to produce a unique sound, resembling the human voice commenting on the onomatopoeia (or sound) of the word 'wah'. In addition to producing sound similar to that produced by a musical wah, it can be used as a vibrato or added reverb to enhance the sound of a lead guitar, adding more richness to the sound. Guitarists who prefer the old school sound of a nylon string acoustic guitar often like to play with a wah pedal as it is easy to control the pitch of the reverb and the overall tone of the sound. But what other kinds of sounds are possible from a wah pedal?
Using the wah pedal to produce a sound similar to that of a musical vibrato is known as 'vibrato'. When you press down the wah pedal the strings vibrate producing a pitched sound. If you strike the sustain pedal the same as well, you will get a'rest' tone on the vibrato note, similar to an embouchure on the piano.
Other effects from wah pedals can be useful as effects. They can be used to create chorus effects when you use a combination of two wah pedals together. This is useful when you want the first sound to play continuously, whilst the second one is less frequent. Or, if you need to vary the pitch of a single signal, you can combine both. This way you can achieve two different octaves of pitch.
Fuzz is another effect that can be created using a wah pedal. The term 'fuzz' is used to describe any type of noise, without a sharp edge. Some examples of common wah pedal noises are pitched harmonic tones, chaos, reverb, slapback, and many others. To create a fizz effect, all you need to do is hit the sustain pedal whilst the wah pedal is pressed. If you release both pedals at the same time the sound will continue indefinitely.
A resonant peak filter is another type of effect which can be added to your pedalboard. A resonant peak filter takes a high frequency sound, such as a guitar, and changes its frequency slightly. This allows for a more gentle 'twangy' effect on the sound. A good resonant peak filter can also cut through noisy passages or be used purely for reverb. It's often found in the more expensive midi keyboards and plugins.
There are also a number of variable resistors which can be used on a wah pedal. A variable resistor allows the wah pedal to be turned on either by turning a one or two control leg into the input signal, or by turning the control leg in a clockwise direction to achieve a variable sweep. The most commonly used combination of a variable resistor and a potentiometer (one or two control legs each in a clockwise rotation about the potentiometer's axis) uses a low frequency oscillator. The sweep can be played in a variety of ways. As the resistors get closer to the center of the potentiometer's reading the wobble becomes noticeable. Also the sweep can be slowed down by turning the wah back and forth by varying the resistors.
One final component which you may find on a wah pedal if not already present is an expression pedal. An expression pedal allows you to control the volume of your wah pedal. The most common uses for this is to turn the wah pedal into a vibrato effect when you're playing. Another popular use is to turn it into a distortion effect. You will need a potentiometer to do this, but amateurs can create their own variation using a meter, a potentiometer, and a bridge rectifier like the BSC (battery cell multiplexer) mentioned above.
Another useful feature that can be found on a few different types of Wah Pedal is what I call the resonant frequency sweep. This is a feature that I've found is very useful in sound editing. Basically it allows you to sweep the sound around and change the resonant frequency as the sound passes through it. One popular use I've found for this is to make a drum loop sound like it's coming from a different genre. By doing this you can easily vary the sound of your lead wah pedal.