Our "That Pedal Show" Blog

The World of Auto Wah with Boss, EarthQuaker, And Electro-Harmonix

By Andy Perrin | November 24, 2017

That Pedal Show 11/17/2017

Envelope filters. Often underutilized and regularly misunderstood. After a few weeks on the road, Dan & Mick were back in the TPS shed and dove headlong into the sweeping sounds of a set of envelope filter pedals (a.k.a., auto wahs). From true-to-form classics like the Mu-Tron and Meatball to more recent takes from Electro-Harmonix, Boss, and EarthQuaker Devices, Dan & Mick’s take on the topic proved two things. (1) Like wahs, you can’t play an envelope filter without your mouth automatically mimicking the “wows” coming out of the amp. This is true guitarist ventriloquism. (2) Envelope filters are more than meets the eye (or ear) and proved to be a versatile effect and inspirational tool.

Here’s a rundown of where the story with envelope filters started and where it’s taken us recently with some analog and digital pedals.

Chapter One: The Short Story of Auto Wahs Starting With The Mu-Tron

When it comes to effects that are a bit off the beaten track, knowing what we’re dealing with at the outset makes the rest of the journey so much easier.

As Dan described, an envelope filter “works in much the same way as a wah pedal.” The difference, however, is that for a wah you’re in control of the duration and spread of the envelope filter sweep. In laymen’s terms, as your foot rocks back and forth, you get more or less “wah-chicka.” Dan continued, “but the same as a wah pedal, [an envelope filter] will accentuate certain frequencies and [automatically] sweeps up and down.”

Any history of envelope filters has to start with the Mu-Tron way back in 1972. Regulars of TPS will recognize this pedal that was forever perched behind Mick on a shelf, waiting to be played. Today was the day it came of the wall and onto the board. As Dan noted, “This is the one that started it all…I don’t know if it’s because this sound was in so many things, but whenever I hear it, it’s just great!”

The challenge is the Mu-Tron is on the endangered species list. Rare, sought after, and pricey. Thankfully, that prototypical sound has inspired a number of other pedals in recent years. So, if you’re in need of some auto wah there’s a number of gear items to consider.

A Modern Classic: The Electro-Harmonix Q-Tron Plus

As Mick underscored at the outset, “when Electro-Harmonix makes a pedal that’s well-priced, well-designed, and sounds good it usually tends to be a top-seller.” The Q-Tron Plus checks off all of those boxes.

The Q-Tron Plus has a massive frequency range as well as a gain setting to push the amp even harder across the board. When dimed out to full, the gain boost also sets the filter wide-open so that the biting sound of the sweep is ever-present in the mix. With the gain control scaled back to more reasonable levels, the “peak” and “range” knobs set the scope and scale of the filter.

As Mick noted after a few riffs through, “It’s really cool and quite addictive.”

EarthQuaker Devices On The Verge of Stompbox and Synth Sounds

An effect is never just an effect with EarthQuaker. It’s and experience. That is undoubtedly the case with the Spatial Delivery. While the pedal takes its cue from the heritage of auto-wahs and can be used in that classic sense, there are a few tricks up its sleeve for extended range and functionality and tone shaping.

On the simpler side of things, the Spatial Delivery has three knobs that set the types parameters you’d expect of an envelope filter (“range,” “resonance,” and “filter”). When it came to nailing some of classic funk sounds, Dan noted “There’s something really vocal about it.” With a mid-ship three way toggle, the pedal also allows for choosing the direction of the frequency pitch. It’ll either push your EQ range up after the attack or rock it down low after hitting a note. And then there’s secret option number three, engineered straight out of EarthQuaker’s lab of engineering insanity in Akron, Ohio…

When flipped to the sample and hold mode, the pedal used the envelope filtering in an almost synth-like sense. As Mick noted, the Spatial Delivery is technically applying a step filter: “The step filter, instead of sweeping smoothly through the frequencies, [it’s breaking up the frequency filter] and not necessarily in the same order.” The pedal samples part of the sound and sends it through the filter’s random voltages.

Boss’ Big Box of Modulation Tricks: Auto Wah In The Boss MD-500

Since its inception and launch, the Boss 500 series has become a major contender in the market for meticulously crafted and infinitely customizable effects. The MD-500 opens up that universe into modulation, with envelope filter effects being just one of many sounds onboard for the journey. As Mick noted, “Assuming that you don’t have the pedalboard real estate to carry around a Meatball [envelope filter], a [Boss] CE-1, and an [Electro-Harmonix] Electric Mistress, you can get versions of all of that inside one of these in programmable, digital recreations.”

When it came to the auto-wah, the MD-500 offers up several renditions of classic sounds and nearly endless parameters for tinkering.

For example, it can be set to an auto speed to change the cycle and pace of the frequency sweep. The MD-500 also included settings geared toward guitar and bass, which added further depth and character to the filters and effect. If you were enamored by the syth-like sounds of a step filter, Boss has you covered. It’s here too and you can even change the frequency of all the steps. Deep customization.

In addition to all of these sounds and many more, the MD-500 includes parameters common to any auto wah pedal—range, frequency, resonance, etc. They’re are all readily accessible and awaiting your own sonic engineering on the intuitive and easy-on-the-eyes interface. As Mick summed up, “There’s immense tweakability if you’re into filters.”

Tone Engineering And Inspiration

Drawing things to a close, Dan reflected that “The thing I love about filters is they force me to play differently. Anything that makes me play differently, that leads me down a different avenue, I’m always up for that.”

If you’re ready to take a trip down a dark and under-accessed alley of the world of envelope filters, head over to Riff City and click through the many options for modulation and auto-wah pedals. This episode of TPS was a good reminder that gear is not only about trying to recreate that sound in your head or picking the right pedals for that one part of the song, items of gear are also inspirational tools.

TPS Rig Rundown:

Guitars: Fender American Vintage Stratocaster; Fender Custom Shop 1963 Telecaster.

Pedals: D’Addario Pedal Tuner; Musitronics Mu-Tron III; Lovetone Meatball; Electro-Harmonix Q-Tron Plus; EarthQuaker Devices Spatial Delivery; Boss MD-500; Z-Vex Fuzz Factory; Fulltone OCD.

Amps: Two Rock Classic Reverb Signature with 2x12 cabinet; Marshall 1987x with 2x12 20161x cabinet.