What Are Wah-Wah Guitar Effects Pedals & How Do They Work?


Wah is one of the most famous effects for guitar and wah pedals are among the most expressive to play through. The sound of wah can be heard across many genres and on plenty of records and wah pedals can be found on pedalboards and jam spaces around the world.

What are wah pedals and how do they work? Wah pedals are nearly always expression-based pedal (they have a treadle-style control) and work by modulating the EQ of the signal to produce an almost vowel-like “wah” sound in the guitar (or other instrument) signal. Wah achieves this effect by sweeping bell-type peaks across the EQ.

In this article, we’ll focus on understanding wah pedals and how they affect our guitar signals. I’ll share a few wah pedals as examples and offer some tips on how to get the most out of your wah pedal(s).


Table Of Contents


What Is The Wah-Wah Effect?

The wah-wah effect (of simply “wah”) is a frequency-filtering effect for guitar, bass and some other instruments. It provides us a way of producing a spectral glide in instruments that typically wouldn’t be capable of such a thing.

A spectral glide, in music, is loosely defined as the modification of the vowel quality of a tone.

This “vowel quality” is largerly defined by the frequency response and overtones of a sound wave (or audio signal). So then, a spectral glide effectively alters the frequency response and overtones of a sound/signal. As it is a glide, these characteristic move continuously from one characteristic vowel quality to another.

This is most obviously heard in human speech.

The sound of each vowel is largely defined by its formants.

Formants are distinctive frequencies that help define a vowel (or consonant) sound. Each vowel will have its own formants, which have a bit more energy than the other frequencies in the sound wave.

As humans, we need to hear these formants in order to distinguish between different phonemes and understand language.

Here is a chart of IPA (International Phonetic Alphabet) vowels with their typical formants:

Vowel
(IPA format)
First Formant
F1 (Hz)
Second Formant
F2 (Hz)
Frequency Difference
F2 – F1 (Hz)
y23521001865
i24024002160
u250595345
ɯ30013901090
o360640280
ø37019001530
e39023001910
ɤ4601310850
ɔ500700200
œ58517101125
ʌ6001170570
ɛ61019001290
ɒ70076060
ɑ750940190
ɶ8201530710
a8501610760

What do these vowels sound like? It’s often best to use examples to describe the sounds of vowels. However, words are pronounced differently depending on a person’s accent. Rather than trying to list out word examples (of which there are none from the English language), I’ll share a link to Wikipedia where you can listen to each of the listed vowel sounds among others.

Here is a graph that plots the vowel sounds according to their first and second formants.

So we can alter the formants of our vocals quite easily by shaping our lips, mouth and tongue. We can effectively produce the wah-wah effect by simple saying “wah wah”.

Horns can also achieve an acoustic wah-wah effect with the use of a mute. Altering the position of the mute at the bell of the horn will alter the formant characteristics of the sound.

Brass instruments can produce some modification of vowel quality. The larger the mouthpiece, the better in this regard.

The didgeridoo is another notable acoustic instrument capable of producing a variety of different formants.

Woodwind instruments offer a bit of acoustic formant modulation but it’s really not remarkable.

Strings, like those on guitar and bass, are practically incapable of producing vowel-like sounds. Of course, we’re talking about acoustics here and the sound produced by the vibration of a string.

This is where the wah-wah effect pedal comes into play. This is an electronic device that can affect the guitar’s (or bass’s) audio signal to produce a wah-wah effect that would be impossible to produce acoustically.

We’ll get to wah pedals and their inner workings in a moment. For now, let’s discuss the term “wah-wah”.

The wah-wah effect is named after an onomatopoeia. The effect is simply what it sounds like. That’s why I went through the trouble of explaining formants and vowels earlier.

Saying the phrase “wah-wah” may seem simple. We’re only tasked with repeating a single syllable twice. However, if we break it down further, there are plenty of sounds to pass through in the phrase.

“Wah-wah”, when slowed down could be made to sound like:

“oo”-“wa”-“ah”-“oh”–“ow”-“oo”-“wa”-“ah”-“oh”–“ow”

In IPA, it could be u-w-ɑ-ə-ɒ-æ-oʊ-aʊ-u-w-ɑ-ə-ɒ-æ-oʊ-aʊ (or something along those lines). That’s a lot of formant modulation for a relatively simple phrase.

The wah-wah effect, electrically speaking, aims to emulate these formant changes by effectively filtering the signal to produce the resonances required.

Wah extends the magic of the spectral glide to stringed instruments, though i can certainly use used to affect other audio sources as well.


What Are Wah Pedals & How Do They Work?

Now that we have a solid idea of what the wah effect is, let’s turn our attention the main discussion of this article. That is, the wah pedal.

Wah pedals are stompbox-style units with treadle-style expression foot pedals designed to receive guitar, bass or other instrument signals. Their circuits are designed to modulate the formants of the sound by modulating one or more resonance peaks in the signal’s frequency response. Wah pedals do the with the use of filters and EQ.

Before we dive in, let’s have a look at a wah pedal. Pictured below is one of the many famed Cry Baby Wah Pedals from Dunlop. This one, in particular, is the Dunlop Cry Baby GCB-95 (link to check the price on Amazon).

Dunlop Cry Baby GCB-95

Dunlop is featured in My New Microphone’s Top 11 Best Guitar/Bass Effects Pedal Brands To Know & Use.

We see that the Cry Baby has a treadle-style foot pedal that allows us to rock back and forth between heel-down and toe-down positions.

At tow-down, there is a footswitch typical of most guitar/bass pedals that, when pressed, turns the pedal on or puts the pedal in bypass mode. Note that most wah pedals will require a bit of extra force to engage their on/bypass switches. This allows the user to rock all the way the pedal all the way to the toe-down position without turning the pedal on and off each time.

The treadle/rocking pedal is connected to a potentiometer that effectively controls the spectral glide of the guitar (or other instrument) signal and produces the wah-wah effect.

The question, then, is how does this all work? Let’s get into it without diving into complex circuit analysis (I’ll leave that to the electrical engineers).

The most important circuit of a wah pedal, when it comes to the effect itself (really, the entire design is critical to the pedal), is the filter.

The filter is either:

  • A bandpass filter.
  • An overcoupled lowpass filter that exhibits a resonant peak at its lowpass roll-off frequency.

As the name suggests, a band-pass filter passes a band of frequencies while cutting the frequencies below and above the defined band. It can be thought of as a combination of a high-pass filter and a low-pass filter.

In order to achieve the wah effect, the filter must produce a distinct resonance. This mimics the effect of a formant and gets us close to a vowel-like sound.

A low-pass filter passes low-frequencies while removing high-frequencies above its cutoff point. By over-coupling a LP filter, we can produce a resonance (increase in energy) at its cut-off frequency just before the higher frequencies begin getting cut out.

Turning a wah pedal on engages this band-pass or low-pass circuit (depending on the pedal design).

Here’s a simple illustration of a band-pass filter with a resonant frequency :

And here’s a simple illustration of an over-damped low-pass filter:

The band-pass filter (or low-pass filter) circuit is typically an LC (inductor-capacitor) circuit with a variable resistor (potentiometer). Of course, it’s more complex than that but this LC circuit is the basic design.

The fixed inductor plays a role in the sonic nature of the pedal. It’s partly responsible for determining the smoothness or aggressiveness of the sweep.

The fixed value of the capacitor also plays a tone-shaping role. Smaller capacitors increase the sweeping range while larger capacitors decrease it.

All this talk about sweep brings us to the variable resistor.

The variable resistance of the potentiometer is controlled by the treadle of the wah pedal. As the resistance is altered, the centre point of the filter is shifted upward and downward across the frequency spectrum.

On top of that, the value(s) of the variable resistor shape the sharpness or resonance of the wah effect. Higher resistance values narrow the resonance (increase Q) to make the peaks sharper while lower resistance values widen the resonance (decrease Q) to make the effect less distinct.

So then, rocking the pedal between heel-down and toe-down positions will sweep a resonant frequency across the frequency spectrum.

As we’ve discussed in the early parts of this article, resonances sound an awful lot like formants. Sweeping formants in speech gives us different vowel sounds. Sweeping resonances in a guitar or bass signal gives us the wah-wah effect!

The actual filter of a swept wah pedal would actually look something like this:

The yellow response curve represents the heel-down position while the dark blue response curve represents the toe-down position. The other curves represent certain instances during the sweep.

As the resonant frequency sweep along the response, it causes a “waaaoooh” sound from heel-to-toe as the resonant frequency glides upward and a reverse “hooooaaaaw” sound from toe-to-heel as the resonant frequency glides downward.

Some pedals allow us to switch the direction of the pedal’s effect on the frequency response.

So all wah pedals are built on the same premise:

  • Some sort of filter that has a resonant frequency and that removes high-end content from the signal (typically a band-pass or low-pass).
  • This filter is swept up and down the frequency response to create the spectral glide effect known as wah-wah.

The main differences between the various wah pedals on the market have to do with the parameters.

Q or quality factor is a major parameter. This affects the sharpness of the resonant frequency. Higher Q values make the resonant boost narrower and produces a sharper, more aggressive sound. Lower Q values widen the resonant boost and bring up more of the surrounding frequencies, resulting in a smother sound.

Some pedals offer Q control.

The Xotic XW-1 (link to check the price on Amazon) is a great example of a wah pedal with adjustable Q.

Xotic XW-1

The other big parameters include the sweeping range or how far the resonant frequency can be swept (from the lowest possible frequency to the highest) and the type of filter being used (band-pass or low-pass).

Many wah pedal designs utilize a mechanical gear-type connection between the treadle pedal and the potentiometer.

The Vox V847A (link to check the price on Amazon) is a popular wah pedal. We can see its mechanical gear/tooth link underneath the footpedal in the picture below:

Vox V847A

Some other wah pedals, often referred to as “switchless wahs”, utilize optical methods (the use of light) to connect the footpedal to the potentiometer.

The Morley PWO (link to check the price on Amazon) is an example of such an optical wah:

Morley PWO

In a way, a wah pedal could be thought of as a foot-controlled tone knob, like the one (or several) found on your guitar. This comparison works at a surface level. However, wah pedal designs generally have a much more pronounced effect on the signal’s frequency response than tone knobs.

Before we move on I want to address a key point.

In the earlier parts of this article I discussed the vocal formants for a number of different vowel sounds. Each vowel sound had two distinct formants. These formants represent the high-energy frequencies of whatever the vowel sound may be.

We’ve likened these formants to the resonant frequencies of wah pedal circuits.

However, wah pedals, as we’ve discussed, only have one resonant frequency or “electronically-produced formant”. Therefore, while the wah pedal sounds similar to a voice saying “wah”, it’s technically quite different.

This was worth mentioning to help clear up any confusion.


Potential Parameter Controls For Wah Pedals

Wah pedals, like most effects pedals, have controls to alter their performance.

The most obvious control is the expression pedal. Practically all wah pedals have this control (or an input to connect an external expression pedal). Many wah pedals actually only have this single control.

However, for those that have more, this section will help explain.

Potential parameter controls for wah pedals include:

Expression Pedal

The expression pedal is the treadle/rocking pedal seen on practically all wah pedals.

This pedal controls a potentiometer inside the wah pedal that sweeps the resonant frequency of the wah filter up and down the frequency spectrum. It is the main control of the wah pedal.

Most wah pedals will have their on/bypass button under the toe of the expression pedal. This allows us to effectively turn the pedal on and off by pressing just a bit harder while in tow-down position.

Q Controls

The Q (quality factor) is a dimensionless unit that represents the width of the resonance peak. High Q values produce a narrow, more aggressive boost in the wah pedal’s filter while low Q values produce a wide, more mellow boost in the filter.

Note that the Q doesn’t affect the amount of boost at the peak though it does affect the residual boost of nearby frequencies.

The Q is a major determining factor in the wah’s overall character.

Range

The range control will affect the overall range of the wah filter’s sweep. It could shift the entire sweep up or down the frequency spectrum and/or it could increase or decrease the overall range.

EQ (Bass, Mids, Treble)

Some wah pedals include an addition EQ circuit with static EQ controls. This can help improve the overall mix of the wah pedal by cutting some of the harsh frequencies and/or boosting some frequencies that need to be heard.

The EQ circuit of a wah pedal is typically put after the wah circuit in terms of signal flow in order to help “clean up” any ill effects of the wah.

Level

The level control brings the overall output of the wah pedal up or down in amplitude.


Tips On Using A Wah Pedal

Wah pedals are among the most expressive in the world. These instantly recognizable yet highly versatile pedals can be used in many different ways.

Here are a few tips to get the most out of your wah pedals:

Give It A Break

As discussed, wah is very noticeable when applied to guitar.

It can be used to a greater effect if we were to only engage it during musical parts that would truly benefit from its effect. It may be counter-intuitive but we can actually get “more” out of our wah pedal by using it less.

Sync Up Your Hands And Feet

A wah pedal offers plenty of versatility with its treadle-style pedal.

A lot of expression can come from synchronizing the notes your play with the motion of the treadle. Take this tip in whatever way suits you best.

Perhaps you could rock back and forth each time a new note is played; maybe you could rock the pedal one way each note and reset before playing a new note. Find what works best for expressing your playing.

Rock To The Rhythm

Working the pedal to tempo of the song is another great way to get more out of your wah pedal.

This technique sounds awesome when combined with more percussive and funky styles of playing.

Keep The Pedal Toward The Front Of The Pedal Chain

Though I always encourage experimentation when it comes to music, keeping the wah pedal near the front of the pedal chain (but after synth, fuzz, and pitch-shifting pedals) can get you a better sound out of your wah and from your rig overall.

Try It Out Stationary

Parking a wah pedal at a stationary position along its tread can yield an interesting EQ on the signal that can get us a different sound from our instrument. Setting it so that the resonance frequency fills a spot in the mix can be a great way to make the guitar pop out for certain passages of music.

This is yet another way to get more out of your wah. It doesn’t always have to be modulating!

Clean Up With EQ After The Fact

Wah pedals are awesome but sometimes they can get a bit piercing as their resonance peak crosses certain frequency bands. Too much energy at any frequency band can cause issues that are unpleasant to the ear.

To counteract these harsh frequencies, we can reduce them after the way pedal with a selective EQ.

To learn more about EQ pedals, check out my article What Are EQ Pedals (Guitar/Bass) & How Do They Work?


Where Should A Wah Pedal Go In The Signal Chain?

Wah pedals typically sound best when put near the front of the pedal chain since they affect the EQ and tonal characteristics of the signal.

However, if you’re running utility (buffers, tuners), synth, and/or pitch-shifting pedals, a wah will likely perform better when put after these pedals.

It’s also common to put wah pedals after distortion-type pedals (including overdrive and fuzz) to get a fatter tone. However, putting the wah before the distortion may allow for increased wah reactivity and more harmonic content in the high-end.

Wah pedals generally sound better when put before modulation and time-based effects.

That all being said, experiment with the position of your wah pedal within the pedal chain to find the best spot for your rig.

To learn more about ordering pedals in the signal chain, check out my article How To Order Guitar/Bass Pedals (Ultimate Signal Flow Guide).


Other EQ Modulation Effects

Now that we understand wah pedals, let’s have a look at other effects that utilize variations in a signal’s frequency response:

Note that any effect that alters the tone of the signal will have some effect on the frequency response. That’s in the nature of changing any audio signal in any way.

Modulation effects (chorus, vibrato, flanger, etc.) are effects that effectively produce modulation in the frequency response of the output signal. However, they do not actually achieve the effect through EQ. Phasers are special caveat to this, as we’ll discuss in a moment.

Envelope Filters Pedals

Envelope filter pedals are commonly referred to as “auto-wah” pedals.

This is a dynamic EQ-type effect that alters the EQ of the signal relative to the amplitude of the signal.

When a note is played on a guitar, bass or any other instrument, a transient is produced. The harder/louder the note is played, the larger the transient.

The transient is a fast increase and decrease in amplitude (of a sound wave or audio signal) that contains much of the harmonic content and timbre of the sound/signal.

Here’s an illustration of a waveform and its transient:

So as transients are produced in the signal, the envelope filter will trigger its EQ filtering. As the signal amplitude drops, the filter will move across the frequency spectrum back toward “rest position”.

The spectral glide (wah effect) caused by an envelope filter, then, is controlled via the envelope (of which the transient is a part) of the signal, hence the name.

The MXR M82 Bass Envelope (link to check the price on Amazon) is a great example of an envelope filter designed for bass guitar.

MXR M82

Phaser Pedals

You may be thinking to yourself “but phaser is a phase-modulating effect”. Well, that’s the category it fits into and indeed a phaser does modulate the phase of its signal. However, the way it achieves this effect is largely based on modulation EQ.

Phaser pedals produce their distinguished effect by modulating a series of all-pass filters. Yes, all-pass filters are filters that pass all frequencies and do not actually really filter anything. This seems strange, I know.

The way an all-pass filter works, at least in a phaser, is by splitting the input signal in two; phase-inverting one copy, and then sending the dry signal through a low-pass filter and the inverted signal through a high-pass filter (or vice versa).

The result is that all frequencies pass through but the phase of these frequencies changes. Phasers string multiple all-pass filter “stages” together and modulate the cutoffs of the all-pass filters’ HP and LP filters to produce their effect.

So then, technically speaking, phasers are EQ-modulation pedals, too.

The Electro-Harmonix Small Stone (link to check the price on Amazon) is a simple example of a phaser pedal.

Electro-Harmonix Small Stone

For more in-depth information on phaser pedals, check out my article What Are Phaser Pedals (Guitar/Bass FX) & How Do They Work?

MXR and Electro-Harmonix are featured in My New Microphone’s Top 11 Best Guitar/Bass Effects Pedal Brands To Know & Use.


Should I use the effects loop on my amp? Effects loops effectively put effects units/pedals between the preamp and power amp of the guitar amplifier. If you’re running the amp’s preamp clean, putting pedals before or after won’t make a big difference. If, say, you’re using a distortion channel with reverb, you may want to put certain pedal in the loop and other in front.

Do I need a compressor pedal? Compressor pedals help balance out the dynamic of our playing by reducing the dynamic range of the audio signal. They are by no means necessary, though they may help increase perceived loudness; add sustain; improve transients, and make the guitar or bass fit better in the mix.

Related article: What Are Compressor Pedals (Guitar/Bass) & How Do They Work?

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