The Electro-Harmonix Pico Swello is a digital attack envelope pedal released in 2025. It takes the Attack Effect from EHX's POG2 and puts it into a standalone pedal in the company's compact Pico chassis1. Where a volume pedal or a slow attack setting on an amp makes your whole signal fade in, the Swello's polyphonic envelope applies a separate swell to each individual note, even when you play chords or fast arpeggios12.
Used subtly, Electro-Harmonix says the pedal adjusts your guitar's attack to sound smooth and flowing even while playing fast lines and arpeggios, and that heavier settings create dramatic swells for ambient soundscapes and synth style pads1. Guitar Pedal X framed it at launch as a utility for violin and cello like swells3.
What it does and where it came from
The Swello is a standalone version of the POG2's Attack Effect1. Guitar World's Trevor Curwen noted that the Attack slider, first seen in the POG2, "is a feature that has particularly hit the spot with players," which explains why EHX pulled it out into its own small pedal4.
The core of the pedal is a polyphonic attack filter that generates polyphonic and reverse sounds1. Because the envelope tracks each note rather than the whole signal, a strummed chord swells note by note instead of as one block, and fast arpeggios keep their individual swells12. Gearnews described the result as a POG2 style auto-swell in the Pico format, and noted that pressing the Filter button can transform the pedal into an envelope filter or auto-wah2.
The controls
The pedal keeps the Pico format's minimal control set: three knobs, the ATTACK knob, FREQ knob, and VOL knob, one FILTER button, and one footswitch1.
| Control | What it does |
|---|---|
| ATTACK knob | Controls the attack envelope time. Turning it clockwise increases the attack time, producing a slower swell or reverse effect1 |
| VOL knob | Adjusts the output volume1 |
| FREQ knob | Controls the cutoff frequency of the low-pass filter when it is active (LED orange or red). With filter modulation enabled it sets the filter's maximum frequency. The filter is fully disabled when the LED is green1 |
| FILTER button | Enables the low-pass filter and chooses the resonance setting1 |
| Footswitch | Engages or bypasses the effect. The LED color indicates the selected mode and is off in bypass1 |
The FILTER button
The FILTER button is a three-way switch, and its color tells you where you are314:
- Green: the filter is disabled1
- Orange: the filter is enabled with low resonance1
- Red: the filter is enabled with high resonance1
Guitar Pedal X listed the same three states as green disabled, amber low resonance, red high resonance3. Guitar World added that the resonance settings can be adjusted from the factory settings to your own preference if desired4.
With the filter engaged, the pedal becomes more than a swell box: Gearnews described the two filter types selectable via the Filter button as turning the Swello into an envelope filter or auto-wah2. That places it alongside EHX's other filter pedals such as the Micro Q-Tron and Doctor Q, though those are analog envelope followers that react to your picking dynamics across the whole signal rather than swelling each note polyphonically.
Power
The Pico Swello runs on the included 9.6VDC 200mA power adapter, and draws 100mA at 9.0VDC1.
No battery option is given, so plan on powering the pedal from a pedalboard power supply or the included adapter.
What reviewers said
Guitar World's Trevor Curwen reviewed the pedal and was positive about it:
"A really musical effect, perfectly implemented in a convenient tiny footprint, the Pico Swello is a joy to use and is capable of giving you an alternative voice whenever needed"4
Guitar Pedal X called it fully polyphonic and priced it at $150 on the EHX Webstore at launch3. UK availability was slow at first: Guitar Pedal X noted in September 2025 that UK stock had yet to arrive3, and later reported the pedal would reach UK shops on 31 October 202535.
That Pedal Show covered the Swello in an episode alongside pedals from Mythos, Cornerstone, TWA and Dinosaural, with the EHX Swello sounds starting at 42:196.
Videos
Tory Slusher
Dimitri
Ambiverb Pt.19
News
Questions
Is the Pico Swello polyphonic?
Yes. The pedal's polyphonic attack envelope applies a swell to each individual note you play, so chords and fast arpeggios get a separate swell on every note rather than one swell for the whole chord. Guitar Pedal X described it as fully polyphonic when it launched.
Is the EHX Pico Swello true bypass?
No. Electro-Harmonix specifies buffered bypass for the Pico Swello. The footswitch engages or bypasses the effect, and the LED is off when the pedal is in bypass.
Is the Pico Swello analog or digital?
It is a digital pedal. Electro-Harmonix lists it as digital on the product page, which is what allows the attack envelope to track and swell each note in a chord independently.
Does the Pico Swello come with a power supply?
Yes. Electro-Harmonix includes a 9.6VDC 200mA power adapter with the pedal. Current draw is 100mA at 9.0VDC, so it needs a proper power supply rather than a battery.
What does the Swello filter button do?
The FILTER button enables the low-pass filter and picks its resonance setting. Green means the filter is off, orange turns it on with low resonance, and red turns it on with high resonance. The LED color shows which mode is selected.
Sources (6)
- Pico Swello, Electro-Harmonix
- EHX Pico Swello: POG2- Style Mini Auto Swell, gearnews.com, 2025-09-22
- Guitar Pedal X, Guitar Pedal X, 2025-09-17
- Electro-Harmonix Pico Swello review, Guitar World, 2025-11-22
- New Pedal: Electro-Harmonix Pico Swello, Delicious Audio, 2025-10-31
- So Much Tone! Mythos Big Puft, Cornerstone Nucleo, TWA Source Code, EHX Swello & Dinosaural Hypoid, That Pedal Show, 2025-10-10
