Sympiano · Free reverb

The inside of a grand piano, as a reverb.

Sympiano is a free, physically modeled piano string-resonance effect. Feed it any signal and it blooms with the sympathetic ring of undamped strings, the halo you hear when you hold the sustain pedal on a real piano.

Download free Hear it first

No cost · no account · macOS and Windows

Real instruments, played into the strings: pedal down, dampers up.

Acoustic piano A piano, reverberating in a piano

Snare drum Every hit blooms across 230 strings

Cello Bowed strings meet struck-string resonance

A voice, inside the piano The strings answer; listen for the tail

What it is

230 strings, listening to your music.

Hold the sustain pedal of a grand piano and sing into it: every string that shares a frequency with your voice hums back. Sympiano is that effect, as a plug-in: a physical model of all 230 strings of a grand (or upright), each one a tuned resonator with real inharmonicity, coupled at the bridge, damped by felt, and picked up by a virtual piezo you can slide along the string.

It is not a convolution of a piano. It is the piano itself, strings, dampers and pedal, resonating with whatever you feed it. Put it on an insert or a send and send it audio: drums, keys, vocals, guitars, synths. MIDI is optional and only chooses which strings are free to ring.

Sympiano is free because it is the doorway to the rest of the catalog: the same physics and the same care as our paid plug-ins, aimed at one beautiful effect.

The mechanism

What the knobs are attached to.

MIDI dampers

Route MIDI at it and only the strings you hold resonate. The sustain pedal works, including half-pedaling, and the top octaves stay open, damper-free, exactly like the real instrument.

Scale-aware resonance

No MIDI? Choose a root and one of 21 scales, from Ionian to Altered to Bebop, and only in-key strings ring. A reverb that always lands in the key of your track.

A movable piezo

Slide the pickup along the strings: near the bridge for glassy close-mic bite, at the halfway point to hollow out every even partial. It is physics, not EQ.

Freeze

Lock the strings at zero loss and the current resonance hangs forever: an instant tuned pad. Feed it new audio while frozen, or let it stand.

Grand and upright

Two physically distinct pianos. String lengths, stiffness, decay and the overstrung bass crossing all change: the upright growls, the grand sings.

The standard kit

Pre-delay, ducking, wet low and high cut, unison detune from concert-fresh to saloon, stretch tuning, four temperaments, una corda, felt mute, stereo width.

Under the hood

For the technically curious.

Sympiano is not a convolution reverb and contains no samples or impulse responses. It is a real-time digital-waveguide physical model, solved live, every sample, for every string.

230 living strings

Each string is its own waveguide loop with Fletcher-Rossing inharmonicity fitted per register. Change the tuning and the physics follows: there is nothing pre-rendered to go stale.

The Weinreich aftersound

Unison strings are genuinely coupled at the bridge, so the famous two-stage piano decay and slow unison beating emerge from energy exchange. They are not chorus effects painted on top.

Practical or experimental

At low mix it is glue: a tuned, always-in-key sheen no algorithmic reverb produces. Pushed hard, with freeze, max coupling, saloon detune and a bridge-close pickup, it becomes a drone machine, a resonant filter bank, a texture generator.

Light enough to spend freely

The whole model runs at roughly a tenth of one CPU core at 48 kHz, independent of buffer size down to 32 samples: fit for live use and for stacking across a session.

Physics all the way out

The pickup control is a real tap position on the string (its comb filtering falls out of the wave equation), half-pedaling morphs actual damper loss, and the top octaves ring free because real pianos have no dampers up there.

Engineered, then audited

Over a million automated assertions on tuning (within 3 cents), decay times, stability and hostile-input handling, plus an independent security review, before version 1.0 shipped.

Skins

Choose your look.

Eight skins, from the default Brasswork to Neon Grid '86. Right-click anywhere on the plug-in to switch; the sound never changes.

Six Sympiano skins side by side: Brasswork, Brushed Steel, Driftwood '77, Space Age '66, Neon Grid '86 and Nightwire. — Brasswork, Brushed Steel, Driftwood '77, Space Age '66, Neon Grid '86 and Nightwire (six of the eight).

Download

Get Sympiano.

Free for macOS and Windows. No account, no email, no license key.

macOS (universal, signed and notarized)

Installer 1.0.7 (.pkg) Zip (manual install)

Windows (64-bit, code-signed)

Installer 1.0.7 (.exe) Zip (manual install)

Installing on Windows

The build is code-signed (publisher: Benjamin Guerrero), so Windows does not flag an unknown publisher. Two small things you may still see:

Installer (.exe): a new signed publisher can briefly show a browser "isn't commonly downloaded" notice. Choose Keep (Chrome) or Keep anyway (Edge); this fades as reputation builds.
Zip: before extracting, right-click the zip, choose Properties, tick Unblock, then OK (otherwise your DAW may not list the plug-in). Then copy Sympiano.vst3 into C:\Program Files\Common Files\VST3.

Windows 10 or later, including Windows on Arm. Nothing else to install.

Mirror on GitHub · Release notes · Documentation · Support

Specifications

macOS	11 Big Sur or later, universal (Apple Silicon and Intel), notarized. macOS 10.x (High Sierra, Mojave, Catalina) is not supported.
Windows	Windows 10 or 11, 64-bit (x64 and Arm64), signed installer
Formats	AU, VST3, and Standalone (macOS); VST3 and Standalone (Windows)
Host	Any 64-bit VST3 host, or AU on macOS, or the included standalone app
In Logic	Find Sympiano under MIDI-controlled Effects on an instrument track, then feed it audio with the side-chain picker. Full guide in the download.
MIDI	Optional. It controls which strings ring (dampers and sustain pedal); it does not play notes.
Engine	230 digital-waveguide strings, 88 unison groups, bridge-coupled. About 10% of one core at 48 kHz (Apple M-series), about 20% at 96 kHz; Eco mode about 4%. Buffer-size independent down to 32 samples.
Sample rates	44.1, 48, 96, 192 kHz
Footprint	About 40 MB disk, 100 MB RAM
Privacy	One optional, anonymous version check per day to our update server; you can turn it off in the plug-in. Nothing else leaves your machine.
Price	Free. No account, no email, no dongle.

Release notes

What changed, version by version.

1.0.7 · Sep 2026 (current)

The preset menu button (three dots) is easy to see on every skin, including the default Brasswork.
Switched-on buttons (MIDI Dampers, Freeze, Eco) read clearly on every skin.

Earlier versions (1.0.0 to 1.0.6)

1.0.6 · Sep 2026	Runs on macOS 11 and later. Earlier Mac builds only loaded on macOS 26 by mistake, so Sympiano would not load in Cubase, Numerology or VCV Rack on older Macs. Windows: nothing extra to install (no Visual C++ Redistributable), Windows 10 or later, plus a native Windows on Arm build. Opens on the brass Brasswork skin by default; right-click anywhere for Zoom and Skin. Sympiano joins Reso Audio.
1.0.5 · Sep 2026	New User presets: save your own settings and recall them from the preset bar. Selectable skins, with a refreshed default look; the plug-in opened on the ResoModern theme. A Getting Started guide ships inside the download. Windows builds are code-signed (publisher: Benjamin Guerrero), so Windows no longer flags an unknown publisher. Fixed The editor no longer grabs your DAW's keyboard focus, so host shortcuts (the spacebar transport and friends) keep working while the plug-in window is open. More dependable MIDI: correct per-channel damper (sustain) behavior, and safer handling of unusual MIDI and audio files. Smoother, more accurate retuning under heavy MIDI, without audio-thread hitches. More reliable saving and recall of your settings with the project, including tuning. Long Root and Scale menus display correctly again.
1.0.4 · Sep 2026	New Resizable UI with zoom; the window remembers its size between sessions. Fixed Offline bounces capture the full reverb tail: the plug-in reports its real decay and freeze tail length instead of a fixed 30 seconds, so long Decay settings are no longer clipped when rendering. Resonance and tuning are identical regardless of the host's audio buffer size (coupling and retune are block-size independent). MIDI notes and the CC64 sustain pedal are applied at their exact sample offset within each block, for tighter timing. The fundamental's decay time stays accurate at the darkest brightness settings. More accurate hover readouts, menu fixes, and closing the editor no longer blocks.
1.0.3 · Aug 2026	Now runs on Windows, as VST3 and standalone. A one-click macOS installer joins the zip. Every knob answers on hover, and a new "?" opens the story of the plug-in and a line to the maker.
1.0.2 · Aug 2026	Dropdown menus open inside the plug-in window, which restores them in Audacity and other hosts with strict window management. The maker's full name on the nameplate.
1.0.1 · Aug 2026	The binaries report their true version number; 1.0.0 introduced itself as 0.1.0 and showed a phantom update notice.
1.0.0 · Aug 2026	First public release. 230 strings, tuned and delivered.