Free stereo widener: wider without losing mono
A stereo widener makes a sound feel bigger by changing what differs between the left and right channels. Done carelessly it collapses in mono or smears the low end. Here's how to widen safely, and the free tools that do it.
COLONY: the free multi-effect plugin from 13x Audio
Add warmth, width, space and movement to drums, keys, bass and loops — six effects in one plugin, moved together by one ENERGY knob.
How stereo widening works
Any stereo signal can be split into mid - what both channels have in common - and side - what differs between them. Turning the side up makes a sound wider; turning it down narrows it. Some wideners also create new side content, from short delays or detuned copies of the signal.
In mono, left and right are added together and the side part cancels out. That's the catch: widening that relies on delaying one channel against the other can comb-filter or thin out when the mix is played on one speaker.
Keep it mono-compatible
- Prefer widening that works on the side signal and leaves the mid alone: then the mono sum doesn't change at all.
- Keep the low end centred. Removing side content below roughly 100-150 Hz keeps kick and bass solid on club systems and in mono.
- Check in mono every time you widen, and listen for the part getting quieter or hollow.
- Don't widen everything. A mix where every part is wide has no width, because nothing is narrow next to it.
Where widening helps
Pads, chord stacks, backing vocals, synth layers and reverb returns benefit most. Leave kick, bass, the lead vocal and the snare in the middle, where they carry the mix on any system.
Widening in COLONY
COLONY's WIDTH Cell is a mid/side widener. It leaves the mid untouched and works only on the side: it raises it and adds delay voices made from the mid. So the mono sum of your track never changes, however far you push it. Six styles set the character: Ensemble, Micro, Chorus, Side, Air and Huge.
Mono Below is a steep 24 dB-per-octave high-pass on the side signal, adjustable from 20 to 500 Hz and set to 120 Hz by default, so the low end stays centred whenever WIDTH is on. Mix blends the widened sound with the original.
What it doesn't do: WIDTH only widens - it can't narrow a sound or fold it to mono - and COLONY has no correlation meter or vectorscope, so check mono with your DAW's tools.
Other free stereo wideners
All free, as their makers list them (checked 2 October 2026). Some need an account or an email address to download.
- Wider · Polyverse MusicOfficial page ↗
Mono-compatible widening up to 200%, with an option to leave the low end out and a mono check.
Free · Windows, macOS · VST2, VST3, AU, AAX - Ozone Imager · iZotopeOfficial page ↗
A width control with Stereoize modes and vectorscopes that show what the widening does.
Free download · Windows, macOS · AU, AAX, VST2, VST3 - Stereo and Haas (Kilohearts Essentials) · KiloheartsOfficial page ↗
Part of a free effects bundle: Stereo controls width and pan, Haas widens by delaying one channel (check those in mono).
Free with a Kilohearts account · Windows, macOS · VST2, VST3, AU, AAX
COLONY: the free multi-effect plugin from 13x Audio
Add warmth, width, space and movement to drums, keys, bass and loops — six effects in one plugin, moved together by one ENERGY knob.
What does a stereo widener do?
It changes the balance between what the left and right channels share (mid) and what differs (side). Raising the side, or creating side content from short delays, makes a sound feel wider.
Are stereo wideners mono compatible?
Not all of them. Wideners that delay one channel against the other can comb-filter in mono. Mid/side widening that leaves the mid alone keeps the mono sum unchanged.
Should I widen bass?
Usually not. Keep everything below roughly 100-150 Hz centred so the low end stays solid in mono and on club systems; widen the upper harmonics instead.
Does COLONY's WIDTH change the mono sum?
No. WIDTH leaves the mid signal untouched and only works on the side, so the mono sum stays the same. Mono Below also keeps the low end centred.