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Electronic Guitar: Filter vs. Wah

July 10, 2017

The wah-wah pedal was invented to let trumpet players electronically reproduce the physical muting effect of covering and uncovering the bell of the instrument. Having largely failed to catch on with horn players, it become a mainstay of electric guitar playing, driven by Skip Pitts’ classic work on “Shaft,” Eric Clapton’s “White Room,” and, of course, Jimi Hendrix’s creative use of the device as both a rhythmic effect and a moving or static filter.

If you’re looking for a wider variety of timbral effects for your own instrument, consider replacing the wah-wah on your pedalboard with an actual filter. Of course, a wah-wah pedal is itself a kind of filter: Its treadle sweeps the peak response of the filter’s frequency up and down to create the classic wah sound. However, its range is more limited than the kind of filtering found in electronic music—on synthesizers (modular or otherwise) or from DAW plug-ins.

In fact, you’ve probably already heard synth-style filtering employed by guitarists using envelope-filter pedals such as the Mu-Tron used by Jerry Garcia, from John Frusciante’s Moog pedals, and with Radiohead guitarist Jonny Greenwood’s DOD 440. In an envelope filter, the range of the filter’s sweep is controlled by your attack on the strings rather than your foot; harder attacks provide a greater range, whereas a lighter attack results in a more limited sweep. With some control of your picking dynamics, an envelope filter can offer some of the expressive power of a wah pedal, while freeing you to roam the stage rather than be tethered to a pedal.

Using an expression pedal with a filter, on the other hand, gives you control over not only the range of the frequency sweep, but also the time it lingers at each point. You can rock it rapidly for wah-like rhythms possessing a greater frequency range and a distinctly different character than your typical Cry Baby, or move the pedal slowly through the entire frequency range, from woofy lows to whistling highs. Like a wah, you can also leave it cocked at any point to carve out unusual guitar tones.


Fig. 1. As an alternative to a wah effect, you can use an expression pedal to change the rate of the Electro-Harmonix Blurst’s LFO (low-frequency oscillator).

Fig. 2. By choosing between down and up on the Stingray’s Depth control, you can change the “wah” sound to “ow.”

Fig. 3. With Source Audio’s Reflex Universal Expression Controller you can control the type of sweep and add an LFO to filters that don’t have one.

Filters such as the EarthQuaker Devices Interstellar Orbiter, Boss AW-3 Dynamic Wah, Death by Audio Evil Filter, and Subde-cay Prometheus DLX all include expression pedal inputs. I have been particularly enjoying the sounds I can create by plugging an expression pedal into the Electro-Harmonix Blurst and the Source Audio Stingray.

The Blurst offers a fat, synth-like analog filter, and I love using the pedal with an EBow to modulate the frequencies of the hand-held device’s drone. Moving the pedal down into the lowpass range takes the raspy edge off the EBow’s distortion, while slowly rocking the expression pedal back and forth gives some shifting color to the EBow’s typically monochromatic sound (see Figure 1).

Filtering is produced digitally in the Stingray, but the sounds remain fat and sassy, and digital processing gives it massive flexibility. I can easily change the sound produced by moving the expression pedal from heel to toe—from “wah” to “ow”—and choose an almost infinite variety of lowpass (letting mostly bass through) to highpass (letting mostly treble through) filters (see Figure 2). Distortion brings out the harmonics and overtones of a filtering effect, and the Stingray has some adjustable distortion right onboard. It is also programmable, so I can have two different filter effects on the two switches, or program 128 sounds that are accessible through Source Audio’s MIDI Hub.

Once you replace your wah with a filter pedal, you may find yourself using its LFO controls to create pulsating modulation, as well, replacing your tremolo, vibrato, phaser, or flanger pedals with this modern alternative (see Figure 3).

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