SEAM-LTM — Learning Through Making

A pedagogical VST3 plugin suite for the SEAM project (Sustained Electro-Acoustic Music).

Sixteen plugins built directly on the Steinberg VST3 SDK — no JUCE, no frameworks. Clean C++17, VSTGUI for the interface, and the minimum code needed to do the job.

Plugins

The suite falls into three families: converters that move a signal from one spatial format to another, generators that produce the test signals a room is measured with, and the measurement and processing tools that listen to the result. Every window follows the same grammar, described in doc/style/ui-style.md and enforced by tools/check-uidesc.py as part of ctest.

Format converters and rotators

Plugin	I/O	Description
SDMX	stereo → stereo	Sum and Difference Matrix (Blumlein M/S). The matrix is involutory (A = A⁻¹), so one instance encodes LR → MS and a second one decodes MS → LR
B2XROT	B-format 4ch → AmbiX 4ch	B-format (FuMa) to AmbiX with rotation: W is scaled by √2, channels are reordered to ACN/SN3D, then Yaw/Pitch/Roll is applied
XYPRROT	AmbiX 4ch → AmbiX 4ch	First-order AmbiX rotation (Yaw, Pitch, Roll). Channel A0 is omnidirectional and passes through untouched
M2XHGR	mono → AmbiX 4ch	Mono to AmbiX via Haar Decomposition: the Haar QMF bank haarmn(1) spreads one channel across four spatial components, which are then rotated by Yaw/Pitch/Roll
LR2XHGR	stereo → AmbiX 4ch	Stereo to AmbiX via Haar (Silvi's method): each channel is Haar-decomposed, placed by a Divergence half-angle, summed, and finally oriented by a global Yaw/Pitch/Roll
ABMODULEX	A-format 4ch → AmbiX 4ch	Tetrahedral microphone A-format to first-order AmbiX: LFU RFD RBU LBD → A0 A1 A2 A3. Pure matrix, involutory (M² = I), the inverse of BAMODULEX, and the front end of the TETRAREC chain
BAMODULEX	AmbiX 4ch → tetrahedral 4ch	Gerzon's BA-module in the AmbiX domain: a decoder to the LFU · RFD · RBU · LBD vertices, which are the four drivers of a STONE loudspeaker. The Gerzon compensation shelves are omitted by design — the STONE amplifier corrects HF/LF downstream
X2UHJ	AmbiX 4ch → UHJ C-format 4ch	First-order AmbiX (ACN/SN3D) to UHJ C-format (L, R, T, Q) — the "UHJ decoder" that makes an Ambisonic mix audible on two channels. The ±90° quadrature pair is designed live at the host sample rate by the shared seam_quadrature engine, and the GUI reads out the resulting coefficients together with the achieved maximum phase error

Signal generators

Plugin	I/O	Description
LTBURST	none → mono	Linkwitz shaped tone-burst: N = 5 cycles of a sine under a Hann window, repeated at a fixed frequency. Frequency, Dwell and Level are the whole interface
LTGLIDE	none → mono	Linkwitz glissando tone-burst: the carrier of each N = 5 grain is latched from a linear or exponential sweep F0 → F1 spread over a Sweep Time, with grains spaced in step or gap timing. It loops, declares a STONE id, and publishes what it is playing on the calibration bus
MULTIPINK	none → 1..64ch	Multichannel pink noise drawn from a shared 64-slot logical pool, so that separate instances never emit the same stream. Layout-adaptive from mono to 64 channels, RMS-calibrated (-23/-20/-18 dBFS RMS reference, ±6 dB trim), with a POWER switch, a STONE id, and a calibration-bus announcement

Measurement and processing

Plugin	I/O	Description
STRX	stereo → stereo	Stereo M/S Analyser: goniometer, overlaid M/S Welch spectra, and In L / In R / M / S / Width meters, plus a status line fed by the calibration bus. It observes only — the audio is passed through unchanged and there are no automatable parameters
DSLAR	mono → mono	Agostino Di Scipio's LAR homeostatic loop, hand-ported from LAR.pd: the feedforward half of a Larsen system whose loop is closed acoustically by the room. Drive, loop delay, decorrelation, target, steepness and control smoothing, with live r (Hann RMS) and g (loop gain) readouts
DDELAY	4ch → 4ch	Quad Alignment Delay for loudspeaker time-alignment. A distance in metres becomes an integer-sample delay at c = 331.4 m/s, rounded up to the next prime so that several instances stay incommensurable. All four channels share one value
HILBERT	mono → stereo	Wideband Quadrature Transformer: one input becomes an in-phase and a quadrature branch held −90° apart from 20 Hz to 20 kHz. Both outputs are all-pass filtered, since the relationship belongs to the pair rather than to either signal. Two topologies — RBJ biquad cascade and Niemitalo polyphase — are selectable live and redesigned per sample rate by the same seam_quadrature engine X2UHJ uses internally
ADDELAY	4ch → 4ch	Air-Absorption Delay: inherits DDELAY's exact metres-to-samples integer delay (next-prime rounding included) and adds a minimum-phase air-absorption filter fitted to the ISO 9613-1 α·d distance-dependent high-frequency roll-off. Shelf and three-section RBJ high-shelf cascade topologies are switchable live, with an optional 1/r geometric-spreading attenuation. All four channels share one distance, so the inter-channel phase is preserved

Screenshots

All sixteen windows, photographed after the UI standard landed, in the order of the three families above.

SDMX	B2XROT	XYPRROT	M2XHGR

LR2XHGR	ABMODULEX	BAMODULEX	X2UHJ

LTBURST	LTGLIDE	MULTIPINK

STRX	DSLAR	DDELAY	HILBERT

ADDELAY

Installation

Prebuilt VST3 bundles are attached to each release. The macOS builds are universal binaries (Intel x86_64 + Apple Silicon arm64).

To build from source instead, skip to Requirements.

macOS

The bundles are not code-signed or notarized (no Apple Developer ID). Gatekeeper will therefore quarantine them on download and refuse to load them until you clear the quarantine attribute. This is a one-time step per download.

# 1. Unzip the downloaded bundle(s)
cd ~/Downloads
unzip 'multipink-*-macOS.vst3.zip'

# 2. Install into the standard user VST3 path
cp -R multipink.vst3 ~/Library/Audio/Plug-Ins/VST3/

# 3. Clear the Gatekeeper quarantine flag (-r: .vst3 is a bundle/directory)
xattr -dr com.apple.quarantine ~/Library/Audio/Plug-Ins/VST3/multipink.vst3

# 4. Rescan plugins in your DAW

To install and unblock all plugins at once:

xattr -dr com.apple.quarantine ~/Library/Audio/Plug-Ins/VST3/*.vst3

Verify a bundle is clean (the command should print no com.apple.quarantine line):

xattr -l ~/Library/Audio/Plug-Ins/VST3/multipink.vst3

Alternatively, after the first blocked load attempt you can authorize each plugin via System Settings → Privacy & Security → "Open Anyway" — but the xattr route is faster and covers every plugin in one command.

Linux

Copy the .vst3 bundles into a standard VST3 search path:

mkdir -p ~/.vst3
cp -R *.vst3 ~/.vst3/

No quarantine mechanism exists on Linux; the plugins load once your host rescans them.

Requirements

VST3 SDK

The plugins depend on the VST3 SDK, cloned with submodules alongside this repo:

git clone --recursive https://github.com/steinbergmedia/vst3sdk.git

Note: the --recursive flag is essential — it pulls VSTGUI and other components needed for the build.

The expected directory layout is:

some-folder/
├── vst3sdk/       ← git clone --recursive here
└── seam-ltm/      ← this repo

If your SDK is elsewhere, pass the path at configure time:

cmake -B build-release -DSEAM_VST3SDK_DIR=/path/to/vst3sdk

CMake

• CMake 3.25+

macOS

• Xcode (not just Command Line Tools — the SDK cmake needs the full app)
• Tested on macOS 15 Sequoia

Linux (Arch / Manjaro)

sudo pacman -S base-devel cmake gcc pkg-config \
    libx11 libxcb xcb-util xcb-util-cursor \
    cairo pango fontconfig freetype2 \
    libxkbcommon gtk3

Linux (Debian / Ubuntu)

sudo apt install build-essential cmake pkg-config \
    libx11-dev libxcb1-dev libxcb-util-dev libxcb-cursor-dev \
    libcairo2-dev libpango1.0-dev libfontconfig1-dev libfreetype6-dev \
    libxkbcommon-dev libgtk-3-dev

GCC 15 note

The VSTGUI header iplatformtaskexecutor.h is missing #include <cstdint>, which causes a build failure on GCC 15+ (Arch, Manjaro, Fedora). The CMake configuration patches this automatically at configure time — no manual intervention needed.

Build

macOS

cmake -B build-release -DCMAKE_BUILD_TYPE=Release -GXcode
cmake --build build-release --config Release -j8

Plugins are output to build-release/VST3/Release/ and automatically symlinked to ~/Library/Audio/Plug-Ins/VST3/.

Linux

cmake -B build-release -DCMAKE_BUILD_TYPE=Release
cmake --build build-release --config Release -j$(nproc)

Plugins are output to build-release/VST3/Release/. To install system-wide:

# Copy all .vst3 bundles to the standard VST3 path
cp -r build-release/VST3/Release/*.vst3 ~/.vst3/

Most Linux DAWs (Ardour, REAPER, Bitwig, Carla) scan ~/.vst3/ automatically.

Design

DSP

Each plugin implements its DSP in a single processMatrix, processBlock or processAudio template, supporting both 32-bit and 64-bit sample formats. The math follows the Faust reference implementations in the SEAM Faust libraries — seam.stereophony.lib, seam.ambisonics.lib, seam.analyzers.lib, seam.linkwitz.lib, seam.noises.lib, seam.discipio.lib and seam.math.lib. Faust is the specification and readable C++ is the deliverable: every processor header opens with a FAUST REFERENCE block naming the definition it re-implements by hand, so that a student can read the DSP from the source in front of them. Code shared between plugins lives in plugins/_common/ — the Haar bank, the quadrature designer, the FFT, the rotation matrices, the meters — and the peer-aware calibration bus lives in plugins/_common/calbus/, compiled once into its own dylib because static state does not cross .vst3 module boundaries.

GUI

All plugins share a consistent visual identity:

• Two formats decided by the control count: S, 300 px wide and a single column, up to about five fine controls; L, 460 px or wider and two columns, from about six. Height varies with content
• Zones in a fixed vertical order: HEADER, SETUP, OPS, FINE, FOOTER
• Source Code Pro Light monospace font throughout
• Dark background (#292c2f), light text
• Horizontal sliders with center-origin fill (bipolar rotation controls)
• SEAM logo at bottom

The window grammar is written down in doc/style/ui-style.md, started from plugins/_template/, and checked by tools/check-uidesc.py as part of ctest.

Architecture

Built on SingleComponentEffect (processor + controller in one class). No external dependencies beyond the VST3 SDK and VSTGUI. Cross-platform: macOS (Xcode) and Linux (GCC/Clang).

Theory

The plugin suite covers the Blumlein → Gerzon lineage of spatial audio, the measurement practice that a loudspeaker array needs, and one work of live electronics:

• Blumlein (1933): sum-and-difference matrix for MS stereophony
• Gerzon (1973): Ambisonics as a generalization of Blumlein's principles
• Haar transform: orthogonal encoding of stereo/mono signals into Ambisonic B-format
• Linkwitz (1978, 1980): shaped tone-burst testing, the signal LTBURST and LTGLIDE emit
• Di Scipio: the LAR homeostatic feedback system that DSLAR re-implements

License

GPL-3.0 — see LICENSE.

Author

Giuseppe Silvi — s-e-a-m