Seraph

Voices from above — a choir and vocal processor for operatic metal vocals.

Work in progress. Seraph is pre-1.0 and under active development. Binaries for macOS and Windows are available from the Releases page (currently unsigned — see the release notes); building from source works too. Expect breaking changes until v1.0.0 ships (see Roadmap).

What it is

Seraph is a choir and vocal processor built for operatic metal vocals: it tames sibilance, adds airy openness above the vocal's natural top end, glues dynamics together with a gentle broadband compressor, and thickens a lead or choir line with a click-free four-voice doubler - all in one channel-strip-style plugin. AU / VST3 / Standalone.

See docs/manual.md for the full user manual (signal-flow explanation, complete parameter reference, and mixing tips).

Features

• De-Ess - a single-band, zero-latency dynamic EQ that detects sibilance energy around a tunable center frequency (DeEssFreq, ~5-9 kHz) with an adjustable detection bandwidth (DeEssWidth) and reduces it dynamically, without a lookahead delay. A Listen mode solos the detected band for tuning by ear.
• Air - a fixed-frequency (12 kHz) high-shelf with a wide, gentle transition for adding (or removing) openness above the vocal's presence range.
• Gentle Compressor - a single-knob, zero-latency broadband "glue" compressor (Comp, 0-100%) with a program-dependent auto-release, scaling threshold and ratio together up to a deliberately gentle 3:1 maximum, sitting after Air and before the Doubler so all doubled voices track a consistent level.
• Doubler - four short, independently modulated-delay voices at fixed per-voice pan positions (a small-choir spread, not a single symmetric L/R pair), slightly detuned (DoubleDetune, in cents) and spread across the stereo field (DoubleWidth), blended in (Double) on top of the centered dry signal - a classic vocal-doubling trick, implemented click-free (continuous delay modulation, never a discrete pitch-shift reset).
• Mix / Output - overall dry/wet blend and output trim.
• Presets - a preset bar with factory and user presets, save/rename/delete, and single-file/bank import-export.

Signal flow

input -> De-Ess (sibilance dynamic EQ, + Width + Listen mode) -> Air (high-shelf)
       -> Gentle Compressor (broadband glue, auto-release) -> Doubler (4 voices, per-voice pan)
       -> Output trim -> Mix -> output

See docs/architecture.md for the full diagram, the de-esser/compressor/doubler DSP design, and the real-time-safety notes. Seraph reports 0 samples of latency: nothing in the chain needs host-side plugin delay compensation.

Parameters

Parameter	Range	Default	Unit
De-Ess	0-100	30	%
De-Ess Freq	3,000-12,000	7,000	Hz
De-Ess Width	0-100	40	%
De-Ess Listen	off/on	off	-
Air	-6 to +9	+2	dB
Comp	0-100	0	%
Double	0-100	25	%
Double Detune	0-50	10	cents
Double Width	0-100	100	%
Mix	0-100	100	%
Output	-24 to +24	0	dB

Full descriptions of what each parameter does musically are in docs/manual.md; the sourced/reasoned design rationale behind the v0.2.0 ranges/defaults is in docs/design-brief.md.

Roadmap

Tracked as GitHub milestones and issues (M1 DSP & tests - done for v0.1.0 - · M2 presets/state - done for v0.2.0 - · M3 custom GUI & a11y · M4 release/signing/v1.0.0). Read them with gh issue list / gh api repos/basilica-audio/seraph/milestones.

Installation

No pre-built binaries are published yet (see the work-in-progress notice above). Once releases begin, installation will follow the standard plugin locations:

macOS

Format	Path
AU (Component)	~/Library/Audio/Plug-Ins/Components/
VST3	~/Library/Audio/Plug-Ins/VST3/

If Logic Pro doesn't pick up the plugin after installing, force a rescan by resetting the AU cache:

killall -9 AudioComponentRegistrar
auval -a

Windows

Format	Path
VST3	C:\Program Files\Common Files\VST3\

Building from source

Requires JUCE 8.0.14, C++20, and CMake ≥ 3.24. See docs/building.md for full prerequisites and step-by-step build/test commands for macOS and Windows.

cmake -B build -G Ninja -DCMAKE_BUILD_TYPE=Release
cmake --build build
ctest --test-dir build --output-on-failure

License

Seraph is licensed under the GNU Affero General Public License v3.0 (AGPLv3).

This project uses JUCE 8, whose open-source tier is licensed under AGPLv3 (as of JUCE 8; JUCE 7 and earlier used GPLv3), which is why this project is AGPLv3 rather than GPLv3. See docs/adr/0002-agplv3-licensing.md for the full reasoning.

VST is a registered trademark of Steinberg Media Technologies GmbH.

Seraph is an independent open-source project and is not affiliated with, endorsed by, or sponsored by any plugin manufacturer.