Guitar Pedals Explained (Part 5): Filtering

Filtering pedals modify the frequency spectrum of the signal. You may know that any sound you generate is a combination of billions of sine waves, each at a given frequency, with a particular phase, and with different amplitudes.

It is very straightforward to visualize the effect of filtering pedals if you think that they simply change the amplitude of some sine waves (at single frequencies) within a given frequency span.

But these pedals are much more than simple tone equalization devices, as they can apply filtering in the time domain, which provides cool dynamics to the tone and creates synthesizer-like effects.

Apart from the basic filtering of the input signal via a graphic EQ, these pedals can produce awesome effects that you would instantly recognize as one of the most representative tones in the history of rock guitar.

In this category, you will see amazing end epic effects, like the Wah-wah that Jimmy Hendrix (once again) made so popular in the 60s. But you’ll also see other awesome effects that use envelope filters.

• Wah-wah pedals. I’m sure you know this effect. It takes its name for the kind of sound it generates. It is so great because you control it with your foot while playing.
• Filter pedals. Known as envelope filters, these stompboxes are really cool. Auto-wah could be included in this category.
• Auto-wah pedals. The effect it creates is very similar (even identical) to the one the conventional way pedal generates. However, you don’t control it with your foot. It’s created automatically.
• Equalizer pedals. These are really easy to understand. They allow you to equalize different frequency bands, very much like the tone controls of your amp, but with more versatility.

Wah-wah pedals

This effect takes its name from the kind of sound that it generates. It is another example of the great classic pedals of the 60s rock scene; it also took disco music and funk in the seventies to the next level.

Wah-wah pedals work in a very simple way: by rocking the pedal with your foot, you sweep the center frequency of an envelope filter, or band-pass filter, through the frequency spectrum.

When that peak is swept through the portion of the spectrum in which the current note or chord is being played, it emphasizes those frequencies and produces a characteristic wah-wah-like sound.

A Little History About Wah Pedals

Wah-wah sound has its origin back in the mid-twenties when trumpet and trombone players in the jazz scene produced such a sound when muting the instrument with their hand.

Regarding the guitar world, it seems that the wah-wah pedal was invented by accident. It was the mid-sixties when VOX engineers were tweaking old tube amps, and they accidentally came up with a weird sound that everybody just loved.

They wanted to replace the expensive Jennings 3-position MRB circuit switch with a transistorized solid state MRB circuit. After adjusting the circuit, they connected its output to a speaker, and the sound surprised everybody around.

They used it with a saxophone, and after that, they used a volume pedal to control the Wah with a guitar. The rest is history.

VOS wah pedal was released in 1967. Once again, Jimmy Hendrix was the first to amaze the whole world with what this pedal could do with the sound of the guitar. From then on, Wah is considered to be essential in rock music.

The other mythical wah pedal is the CryBaby, which got its name due to the similarity of the tone that it generates with a baby crying. It came out in 1968, and I would say that it’s the most widely used wah-pedal.

In the seventies, funk, soul, and disco music guitar players started massively using Wah, which took this sound to the next level.

Wah Pedals Controls and Features

Wah pedals are very simple devices. You won’t usually see any knobs in them, although there are some models that allow you to change the bandwidth of the envelope filter. This way, if you select a narrow bandwidth, you will get a sharper wah. On the contrary, if you increase the bandwidth, the effect will be less noticeable.

Now, all wah pedals look the same, just like an actual pedal. By firmly stomping on it, you will activate the pedal so you can start rocking.

Do I need a Wah pedal?

It is a classic, and every guitarist should have one, so yes, you need a wah pedal.

Envelope Filters Pedals

Filters (envelope filters) are very similar to wahs and auto-wahs, although more versatile because they include more controls that allow you to amazingly shape the tone of your guitar.

Most of them include a low-frequency oscillator (LFO) that is mixed with some of the controls that the filter has. In some cases, you can even modify the shape of the signal generated by this LFO (sine, square, triangle, etc.).

This is a wide category because there are very different filtering pedals with very different functionalities and tonal possibilities. Some of them (really complex devices) provide, just with filtering, synthesizer-like sounds that will take your guitar out from conventionality.

A Little History on Envelope Filters Pedals

The history of envelope filtering is very related to the history of synthesizers.

Just check some recordings of the early progressive rock in the seventies, and you will hear a lot of psychedelic synthesizers applying crazy filtering. Once again, I will refer to Pink Floyd and “The dark side of the moon” and their mastery (though being just novices experimenting) with the use of synthesizers in the studio.

The first envelope filter was the Mu-Tron III, first made in 1972 and quickly becoming an essential effect for many funk musicians. Other examples of envelope filter pedals include the MXR Envelope Filter and the Boss AW-2 Auto Wah.

Envelope filter pedals are not really mainstream pedals. Although most mainstream brands have an envelope filter in their catalog, there are not many models in the market (at least not as many as overdrives)

This pedal also shaped the sound of funk.

Controls and Features

In the case of (envelope) filter pedals, the controls vary widely among different stompboxes.

In any case, these are the most commons controls that you can find in the majority of filters:

• Rate. With the rate, you will control the time in which the frequency sweep occurs. Think about a wah pedal that you control with your foot: the faster you rock the pedal, the faster the wah sound is generated. You can obtain the same effect by increasing the rate of an auto-wah.
• Depth. The depth knob changes the bandwidth of the envelope filter. At its minimum, you will get a subtle effect, whereas turned all the way up, you will reduce the bandwidth, obtaining a sharper wah tone.
• Sensitivity. Sometimes you can obtain a dynamic change in how the pedal reacts to your playing. If you play louder, the wah effect will be more pronounced. You will obtain more natural effects by tuning this control.
• LFO. With this knob, you can change the speed (frequency) of the LFO from a slight vibe-like affect up to a high-frequency helicopter-like high-speed tremolo.
• Envelope. Sometimes you can select between different shapes for the signal generated by the LFO (sine wave, triangular, square, etc.).
• Mode. Some really best pedals allow you to select between different modes of operation. Instead of having just a steady LFO with a constant output, they include a few presets with crazy oscillator patterns.

Do I need a filter pedal?

Not really. But trust me, they will boost your creativity because they allow you to sound so amazing that you will get inspired by the effect itself.

I must admit that, when I’m writing these lines, I am waiting for a present that I’ve made for myself. A friend of mine is about to come from NYC, where he got me a SolidGoldFx FUNKZILLA. What does this name suggest?

Do you like funk? Then you need a filter pedal.

Auto-wah pedals

Auto-wah is very similar to the classic Wah because it is also based on an envelope filter circuit.

However, you now don’t control the frequency characteristics of the filter with the foot; instead, this is done by the pedal automatically, depending on the dynamics of your playing and the settings of the pedal.

This is a really cool funky effect that gives you a sound kind of different than a classic wah. If you are into soul and funk music, you definitely must have one of those.

A Little History on Auto-wah pedals

Auto-wah can be considered as a particular case of envelope filtering, so the history of envelope filters applies here.

Controls and Features

Auto-wah pedals can be considered as a group within the envelope filters category. However, there are some models in the market with just-auto-wah functionality.

in general, they will share these controls:

• Rate. With the rate, you will control the time in which the frequency sweep occurs. Think about a wah pedal that you control with your foot: the faster you rock the pedal, the faster the wah sound is generated. You can obtain the same effect by increasing the rate of an auto-wah.
• Depth. The depth knob changes the bandwidth of the envelope filter. At its minimum, you will get a subtle effect, whereas turned all the way up, you will reduce the bandwidth, obtaining a sharper wah tone.
• Sensitivity. Sometimes you can obtain a dynamic change in how the pedal reacts to your playing. If you play louder, the wah effect will be more pronounced. You will obtain a more natural effect by tuning this control.

Do I need an auto-Wah pedal?

Unless you are into funky stuff, you won’t be thinking of including an auto-wah in your pedalboard. But, if you do like how synthesizers can color different sounds by adding filtering and LFOs, you will love what these pedals can do with a guitar.

Equalization (EQ) Pedals

This effect is pretty straightforward. It consists of a graphic EQ that includes a number of band pass filters at different frequencies.

Depending on how many bands the EQ has, you really can change the tone of your playing. EQ pedals usually have slider-based controls to tune each band that present a graphic image of the shape of your EQ settings.

A little history About EQ Pedals

Graphic equalizer pedals were widely used in the seventies. They’ve always been used to adequate the sound of the guitar when playing live at a particular venue.

The most popular EQ pedals were those offering 6 frequency bands. Everybody was offering EQ pedals, so you will find Electro Harmonix, Ibanez, DOD, and other guitar pedals brands competing since these first appeared.

Equalization Pedals Controls and features

Graphic equalizers are usually very simple devices to control. They usually have these controls:

• Volume. You can boost (or attenuate) the output of your guitar with volume control after having equalized the sound.
• Frequency band. You will be able to boost or attenuate different band frequencies independently with the respective knob or fader. Faders are very convenient because they give you a graphic view of how the frequency equalization is shaped. In fact, they sometimes include an led so you can see the frequency shape on stage.

Do I need an EQ pedal?

You may think that this pedal is not for you because you have enough EQ control with the knobs of your amplifier. Well, that is true if you are playing at home.

If you play live with a band, you will need some means of quickly equalizing the sound coming out of your amp. The sonic characteristics of the venue may impose to boost some signals while attenuating others. You could even need to notch a given frequency to avoid unwanted feedback from occurring.

In addition to that, an EQ can make your guitar sound like it was produced in a recording. They will provide you with a lot of flexibility.

As I said before, if you play in a band in relatively big venues or you just want to be able to change the tone of your guitar drastically, put an EQ pedal on your pedalboard!