GullDSP has released Circulate, a free and open-source phase smearing plugin for Windows that delivers a unique take on all-pass filtering.
Circulate works by using banks of all-pass filters to delay and scatter the phase of your audio around a center frequency. The result is a phase smearing effect that sounds hollow and slightly reverberant.
The effect can sound very good with the right settings, and it’s especially effective on transient-heavy material like percussion, plucks, or bass hits.
It doesn’t change the frequency balance of your sound, just the way the phase relationships interact, which can make drums feel more spacious or give synth stabs that unusual, almost liquid movement.
If you’ve ever used Kilohearts’ Disperser, you’ll probably get similar vibes here. Still, Circulate absolutely does its own thing, with a different control scheme and the potential for a broader range of results.
You control the Center frequency (in Hz or via MIDI note), Focus (resonance or Q), Depth (number of all-pass stages), and Feed (feedback amount), while Pitch and Det provide subtle pitch-based modulation options.
I had only a short time to test Circulate on a friend’s Windows setup (I’m on macOS, which isn’t supported yet), but I was impressed. Try loading it on a percussive loop, adjusting Center and Focus until you hit a sweet spot, and then tweak Depth and Feed for intensity.
I also got some fun evolving textures by slightly automating Q and Focus. Automating it can add a bit of depth and movement, and the results are surprisingly musical.
What I really like about Circulate is that it’s different without being obscure. It’s not weird for the sake of weird; it’s genuinely a cool plugin for sound design and production, and that kind of originality is something the indie plugin scene could use more of.
The GUI is clean and minimal, easy to navigate, even though it’s not super-polished, and it invites you to experiment without confusion.
If you enjoy indie plugin releases, it’s worth mentioning that Ewan Bristow (developer of LOCD Distortion) recently announced that he’ll make all of his paid plugins free for a week once he hits 10,000 followers on X, so if you want to help make that happen, check out Ewan Bristow on X.
You can download Circulate for free and open source from GullDSP’s GitHub page. It’s available as a VST3 plugin for Windows.
Hopefully, we’ll see a macOS version in the future, although there’s been no announcement yet. But if you’re on Windows, this is a great freebie to explore right now.
Download: Circulate (Windows only)
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Last Updated on October 16, 2025 by Tomislav Zlatic.
