Envelope filter pedals (often referred to as an ‘auto wah’) give you a wah sound without having to rock your foot back and forward on a wah-wah pedal. They are, unsurprisingly, hugely popular guitar pedals with funk players. Plus, they’re superb for experimentation as we’ll see.
If you’re in a rush, here’s a quick peek of the products we review further down the page:
At a Glance: Our Choice of the Best Envelope Filter Pedals on the Market
- Electro-Harmonix Q-Tron
- Electro-Harmonix Riddle: Q-Balls
- Source Audio SA127
- Pigtronix EP2
- Maxon 9-Series
Note: Clicking the above links will take you to further information, current prices and customer reviews on Amazon.
In this article, we’re going to go deep into these pedals. We’ll also recommend some of the favorite products on the market. Sound good? Let’s get to it.
- What is an Envelope Filter?
- Buyer’s Guide – What to Look for When Buying One
- Product Round-up & Mini Reviews
- So Which Should I Buy?
What is an Envelope Filter?
Envelope filters have much stronger tone changes than say a regular EQ. They use what’s known as ‘resonance’ to accentuate certain frequencies, creating the sort of sounds we associate with wah or funk – that distinct “quack” and “bow wow” sound. The “envelope” is the shape of each note you play, from the initial spike when you pluck or pick a note, through to the moment it trails off.
In essence they give you the ‘wah sound’ you’d normally get from a wah-wah pedal, with one key difference: the sound is triggered by how hard you play (i.e. how hard you pluck your strings, also called ‘your attack’) rather than having to rock your foot as you do on a normal wah. The harder the attack, the more it goes ‘wah.’
As mentioned in the introduction, these units are mostly used in funk music for that signature “quack” or “bow wow” sound.
Set it and Forget it
As discussed, they’re a set-it-and-forget-it option as opposed to a traditional wah pedal (which you need to control via the rocking switch with your foot). But there’s another less obvious benefit: using a wah pedal is sometimes incredibly impractical during a live performance, especially if you’re singing at the same time. Balancing on one leg while you wah with the other might not be the look you’re going for on stage.
Another massive benefit is speed. The circuits within envelope pedals react at a faster rate than we can physically move our feet, making a rapid wah sound possible. This effect is pervasive in funk music. As well as being capable of a faster speed than your foot can manage, the fact that it’s automatically controlled means that the rhythm of the sweeping will sort itself out.
It’s a bit like driving a manual (stick shift car) versus an automatic. Driving a stick shift gives you more ‘control,’ but do you need that control? Perhaps your attention is better placed elsewhere (i.e., on your guitar playing or singing). Don’t think for a minute that they’ll ‘dumb down’ your sound – the range control makes them very responsive, so the harder you pick, the more wah you get.
Range (Sweep) Control
The range control adjusts the frequencies affected by the ‘sweep’ effect, meaning you have more of the effect when you’re playing high notes than when you’re playing low notes or vice versa. It can be convenient: you might not want wah on every single note you pick hard.
Sometimes just called ‘filter,’ this lets you choose between a low-pass, high-pass or band-pass. These different filters pick out different frequencies that each gives you a different vibe: a high-pass filter allows anything above a particular frequency get through, the low-pass lets anything below a specific rate through, and the band-pass put a band in the middle and anything either side of it gets through.
Closely related, the resonance control lets you adjust the feedback of the filter. This allows you to set certain frequencies to amplify more than other frequencies. It can be the control that helps you to achieve a sharp, almost distorted tone, or a mellow, laid back sound.
Attack/Response and Decay Controls
Some pedals include an attack control (some models call this response), which controls how quickly sweep peaks. The decay control determines how soon it cuts out. A fast attack and a slower decay will provide a clear, rhythmic sound. Slower attacks can make your playing sound out of time, and decays which are too fast can also detract from the rhythm of your playing.
Buyer’s Guide – What to Look for When Buying One
StompBox Vs. Additional LFO
These pedals come in mainly two formats. First, there are the stompbox-style ones. These are small stompboxes that are easy to use and adjust. These will suit those who like to keep things simple. Then there are the ones with additional LFO (low-frequency oscillation). These are usually bigger, and suit those who want to experiment.
Where to Place it in Your Signal Chain?
There are two main ways to do it. A lot of guitarists choose to have them at the start of their chain – right next to their guitar. This enables a clean signal to reach the pedal, which is helpful as it’s responding to your picking attack. Other guitarists prefer to have them at the end of their chain – closest to the amplifier. This can be interesting as it means that other effects can potentially affect the signal going into the pedal, producing some interesting sounds.
Product Round-up & Mini Reviews
Electro Harmonix Q-Tron
Used by funk legends Bootsy Collins and George Clinton among others, this is one of the most popular envelope filter pedals ever built. There are multiple modes, boost and gain controls, and even a peak knob to give you control over the width of your sound. Newer models contain effects loops so that you can insert an additional effect between the pedal’s pre-amp and filter. This makes the pedal more responsive to your playing and gives you more sound options.
- Four filter modes, speed, volume, and intensity settings give you plenty of options for fine-tweaking and adjusting
- It’s solid and rather cool looking: it holds to its funk and disco roots in aesthetics as well as its tone.
- Contains true bypass, so it won’t interfere with your signal when it’s not in use.
- Built in effects loop
- Although the four filter modes are pretty great, some models offer more than this.
- No expression-pedal options.
- Although not expensive by any measure, it doesn’t provide the best value for money
Electro-Harmonix Riddle: Q-Balls
This one is an upgrade from the Q-Tron, so take everything you liked about that pedal, and prepare for a little more. It’s only fractionally more expensive but provides much better value. It features multiple modes, attack, decay, blend and sensitivity knobs, but also has two controls which weren’t seen on the Q-Tron (the stop and start knobs which allow you to set the starting and ending points of the sweep giving you an excellent amount of controllability). It’s also in sturdy, chrome casing: made for taking on the road.
- All the circuitry is analog, which helps to keep the 70’s sound alive (who said disco is dead?) and doesn’t interfere with your signal if this is part of a chain
- There’s an input for an expression pedal giving you more intimate control of the filter’s sweep direction and depth
- Controls for attack, decay, sensitivity, and Q (how many frequencies are affected by the envelope pedal’s settings), as well as additional stop/start knobs to set the size of the sweep.
- Has one less filter compared to the Q-Tron
- The filter options which are available aren’t particularly creative, so if you were looking to experiment beyond the classic sounds of envelope filter pedals you’ll be disappointed by the lack of options
- It’s a rather basic design, and the small size of the dials can make it difficult to see the settings if you need to change them under poor lighting (which as well know can be a real pain for a gigging musician)
Source Audio SA127
The SA127 delights in playing with the adage that less is more. You get enough variety to play around with forever, but it’s all contained in an ultra-compact design. In keeping with the disco roots, it’s bright purple. It’s also excellent value for money, especially when compared to either of the Electro-Harmonix models. There are 21 filter sounds, an attack and decay control, and a knob to set the size of the sweep. Although it’s small, you still have quite a lot of control over your sound with this pedal.
- An insane array of choices, you get 21 filter options all controlled by a single dial
- Three additional dials for controlling attack, decay, sweep, range, and sensitivity
- The whole pedal has a remarkably slim profile considering all of the options available
- Many of the controls are merged. Although this works quite well most of the time thanks to the way they’ve been paired up, it can limit your options
- No expression pedal options
- Since the controls are combined into just four dials, you’ll have to spend a little time learning how they all work together to ensure the best results, unlike with other models where you can play with one setting at a time to learn its ins and outs
The Pigtronix EP2 is a little more expensive than the others but comes with some extremely great features that set it apart. It has an LFO option for a start, so you can control your auto-wah sounds using either the envelope or the low-pass filter. This gives you more options for controlling the response of the pedal: it can follow dynamics or be time operated. You can even use them both together, for some very interesting sounds. It also has a staccato function which adds an extra response to the envelope. It’s well suited to playing funk.
- Has not just one, but two inputs for expression pedals that allow you to control speed and sweep direction separately, plus an input for a “trigger” that allows the envelope filter to be controlled by other external sources.
- The Staccato switch enables the filter to adjust to every note even when playing at inhuman speeds to ensure perfect articulation even if you decide to bust out the shredding and sweep-picking.
- Has some truly fantastic tone, which you can endlessly play with thanks to the huge range of controls
- Although you get a lot in one package, this pedal is quite expensive, and if all you need is the standard funk/disco sound, you will do better to look at some of the other products on this list
- The complexity of the controls might take a while to get used to
- It uses an 18v battery, which gives great headroom but can put a bit of dent in your bank account as this thing runs through juice like you wouldn’t believe if you can’t use a mains power supply or a rechargeable battery
The Maxon AF-9 takes a straightforward approach. It looks a bit retro, but considering the sound it produces, perhaps that’s in line with what it should be. There are filter, range and drive switches, as well as sensitivity and peak controls. Although it’s small, you can still control quite a lot. It also features true bypass, so it won’t muddy your signal when it’s not in use.
- Built like a tank. There’s very little that’s vulnerable to damage, and it can safely be carried around from venue to venue with no problems at all for years. It can even take a hell of a beating, making it live up to the stomp part of “stompbox.”
- True bypass means it won’t ruin your tone when not in use
- Nice warm tone that closely resembles the legendary Jerry Garcia sound
- Lacks some of the extended functionality and fine tuning controls of more advanced models
- It’s quite expensive for its simplicity
- No expression pedal input available, so it does lack the option for intimate control
So Which Should I Buy?
The Pigtronix EP2 and the Source Audio SA127 are serious contenders. The EP2 offers a lot of fine-tuning, and the two expression pedal jacks put all of the control you could ever want in your hands (and feet). If you find all of the options a bit overwhelming and would rather just dive in, then the SA127 might be more your style thanks to its merged controls and the massive range of filters for quick exploration.
Ged is Founder and Editor-in-chief at Zing Instruments. He’s a guitarist for London based gypsy jazz band ‘Django Mango’ and a lover of all things music. When he’s not ripping up and down the fretboard, he’s tinkering with his ’79 Campervan.