Bus Channel Strip

Seven modules. One chain. A hidden polish coat at the end. The glue your bus has been missing.

Built with NIH-Plug, Airwindows DSP, and vizia

Documentation & Presets | Download Latest Release

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Bus Channel Strip is a single plugin that replaces eight inserts on your master or stem bus. Load it once and run your mix through a console EQ, an Airwindows glue compressor, a passive tube EQ, a dynamic EQ with sidechain support, a vintage transformer stage, a psychoacoustic stereo widener, a transparent loudness maximizer, and a hidden master-end polish coat — in that order, or in any order you like (the first seven are reorderable; the polish coat is pinned at the end).

Every module is individually bypassable and fully automatable. Every parameter reads as a clean integer in your DAW's automation lanes. The signal chain has a global bypass for zero-latency passthrough and RMS-based Auto Gain compensation so level differences don't fool your ears when you're comparing.

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Download

Go to Releases and grab the archive for your platform:

Platform	File
Windows (x64)	Bus-Channel-Strip-windows.zip
macOS Apple Silicon	Bus-Channel-Strip-macos-arm64.tar.gz
macOS Intel	Bus-Channel-Strip-macos-intel.tar.gz
Linux (x64)	Bus-Channel-Strip-linux.tar.gz

Install paths:

Format	Windows	macOS	Linux
VST3	C:\Program Files\Common Files\VST3\	~/Library/Audio/Plug-Ins/VST3/	~/.vst3/
CLAP	C:\Program Files\Common Files\CLAP\	~/Library/Audio/Plug-Ins/CLAP/	~/.clap/

macOS Intel note: The Intel build ships without the GUI (Skia cross-compile limitation on Apple Silicon runners). All DSP is present and functional; use the ARM64 build if you need the visual interface.

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What's New in v1.0.0

Two major workstreams ship together: Sheen (a hidden master-end polish coat) and a full multi-fx rack UX redesign that finally makes module reordering feel native.

Sheen — master-end polish coat

A new pinned DSP stage at the end of the chain (post-Punch, pre-master-gain) that makes the chassis sound finished out of the box. The brushed-brass API brand plate in the chassis header is the only front-panel surface — click it to flip into a hidden back view with five sliders. Always-on by default at research-grounded factory tuning:

Stage	Algorithm	Factory default
BODY	Low shelf @ 100 Hz	+1.0 dB
PRESENCE	Peak EQ @ 3 kHz, Q=1.0	0.0 dB (transparent)
AIR	High shelf @ 14 kHz, Q=0.5	+1.8 dB
WARMTH	Sonnox Inflator polynomial @ Curve=0, 2× oversampled	20% mix
WIDTH	M/S side-only: HPF @ 150 Hz + shelf @ 500 Hz	+12.5% sides above 500 Hz, mono <150 Hz

Defaults are anchored in three parallel research reports — classic console-bus measurements (SSL G, Neve 33609, API 2500, Studer, Trident), polish-plugin teardowns (Slate Revival, Kush AR-1, Maag EQ4, Sonnox Inflator, Pensado, Vitamin, Ozone, PSP Vintage Warmer, bx_console), and tape + transformer harmonic profiles (Studer A800, Ampex ATR-102, Jensen, Lundahl, Carnhill). See docs/adr/0006-sheen-pinned-master-end-polish.md for citations and stage-by-stage rationale. Excluded from Auto Gain — auto-comp on a polish stage defeats its purpose.

Multi-fx rack redesign

The seven-slot rack got a ground-up UX overhaul:

• Native vizia drag-drop replaces the previous hand-rolled mouse-capture state machine that was silently failing under baseview's Win32 SetCapture lifecycle.
• Swap-or-insert semantics decided by cursor X within the target slot at release time: left third = insert before, middle = swap, right third = insert after.
• Live drop-position preview while dragging — bright cyan bar pinned to the target slot's left or right edge (insert) or full yellow ring around the slot (swap), so you see the resolved drop intent before releasing.
• Floating drag-ghost label tracks the cursor showing the dragged module's tag.
• Empty slots collapse by default to narrow dashed tabs; the library sidebar is now the sole "add module" affordance.
• Focus mode — press 1..7 to focus a real-module slot (collapses every other slot to a tab); Esc exits focus, cancels drag, or closes any open back view.
• Chain mini-map appears as a band above the chassis only when a slot is focused, hidden otherwise.
• Brushed-brass brand plate is the entry point to the Sheen back view; mutually exclusive with the DynEQ back view.
• Click-lag fix — the chassis-level MouseUp listener that previously routed every click through the broken drag state machine has been removed.

Compatibility

11 new automation params (Sheen) on top of the existing ~75 — no reused IDs. Existing DAW sessions load with Sheen ON at factory defaults; playback will subtly differ from pre-1.0 sessions. For bit-identical playback, flip the back-panel master Sheen bypass.

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Coming in v2.0

Theme: "Stop sounding digital." A perceived-quality release targeting the four artifacts that read as "digital" to a trained ear — top-octave aliasing, midrange phase smear, lifeless memoryless saturation, and overly-precise stereo imaging. ~3-month scope. Full requirements in docs/V2_ROADMAP.md.

DSP track (weeks 1-6)

• Universal 4× internal oversampling across every module containing a nonlinearity (ButterComp2, Pultec tube saturation, Transformer, Sheen WARMTH). Punch oversampling normalized as a global quality preset.
• TPT (topology-preserving transform) state-variable filter cores replace biquad direct-form-1 in API5500, Pultec, DynamicEQ, and Sheen EQ stages — eliminates phase smear at extreme Q and cleanly accepts coefficient automation.
• Optional linear-phase mode on Pultec (mastering EQ) — windowed-sinc FIR with FFT convolution, ~512-sample latency at 4×.
• Single-cell Preisach hysteresis model in Transformer core + as an opt-in "tape" mode on Sheen WARMTH — gives saturation actual memory (output depends on input history, not just present input), which is what "lifeless" really means perceptually.
• Per-channel coefficient micro-detuning (TMT-style ±0.3%) on API5500, Pultec, Transformer, Sheen — produces natural stereo decorrelation rather than the unnaturally precise center image of identical L/R coefficients.
• ButterComp2 adaptive envelope — program-dependent attack curve that softens on transient-dense material (drum bus auto-softening, vocal bus auto-tightening).
• Punch true-peak detection (ITU-R BS.1770-4) with intersample peak metering and a -1 dBTP default ceiling.

UI track (weeks 4-10)

• Resizable window (1100×750 to 2400×1400, locked aspect) with HiDPI awareness — currently locked at 1300×860.
• Preset system — 20 factory presets across genres (rock drum bus, pop vocal bus, hip-hop master, jazz acoustic, EDM master, podcast voice, classical orchestra, etc.), browser UI with categories, user save/load to ~/Documents/Bus Channel Strip/Presets/, current-preset name in chassis header with diff indicator.
• Per-module inline metering — tiny reactive spectrum strip atop each EQ module, consistent GR meters on compressors, saturation meters on Transformer / Punch / Sheen WARMTH.
• Visual polish pass — typography rhythm (12/14/16/20/24px scale), spacing rhythm (4/8/12/16/24px grid), knob spring-back micro-interactions, follow-cursor value tooltips during drag, custom SVG icon set replacing Unicode glyphs.
• Theming — ships with two curated themes (Studio dark, Daylight bright). User-customizable colors deferred to v2.1.
• Tooltips — hover any control >800ms for control name + one-sentence description (text lives in src/tooltips.rs).

Foundation work (opportunistic, no dedicated track)

• lib.rs refactor — extract per-module parameter definitions into a params/ module (forced by the preset system work).
• CI/CD fix — repair the macOS / Linux GitHub Actions builds that currently fail (forced by the signed-installer work).
• macOS code signing + notarization — required for "broader audience" distribution.
• Installer packages (Windows MSI, macOS pkg) replacing zip extraction.
• Test coverage expansion — every new DSP module tested at the same density as Sheen.

Compatibility notes (planned)

• Parameter IDs from v1.0 stay stable.
• TPT EQ migration is a breaking sound change — sessions saved in v1.0 will load and play in v2.0 but null within ~0.1 dB of the biquad versions at moderate settings, larger at extreme Q.
• Hysteresis on Transformer is a bigger sound change — a new transformer_hysteresis_bypass BoolParam (default OFF, i.e. hysteresis on) lets users flip back to v1.0 behavior for bit-identical playback.

Deferred to v2.1+

A/B compare snapshots · MIDI parameter learn · multi-instance link · sidechain routing for non-DynEQ modules · new DSP modules · user-customizable theme colors · workflow features generally.

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The Signal Chain

[API5500 EQ] -> [ButterComp2] -> [Pultec EQ] -> [Dynamic EQ] -> [Transformer] -> [Haas] -> [Punch] -> [Sheen]

The first seven modules occupy reorderable slots — drag any module's body to swap it with another slot, insert it before, or insert it after, with a live cyan/yellow drop indicator showing where it'll land. Sheen is pinned at the master end (post-Punch, pre-master-gain); it's the chassis-level "polish coat" exposed via the brushed-brass brand plate. Every module is individually bypassable. The chain is fully automatable — all ~86 parameters are exposed to your DAW.

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Modules

Module	Category	What it does to your mix
API5500 EQ — 5-band semi-parametric	Console EQ	Broad, musical shelving on the lows and highs, three overlapping parametric bands (LMF / MF / HMF) for surgical or broad-brush tonal shaping, and a high-pass filter. Gives the mix the forward, punchy character of a large-format API console.
ButterComp2 — Airwindows bipolar interleaved	Glue Compressor	The richest glue compressor in the chain. Chris Johnson's bipolar interleaved algorithm knits elements together without dulling transients. Four models — Classic (original Airwindows), VCA, Optical, and FET — give you density with attitude. Built-in NY parallel blend lets you dial in exactly how much cement you pour.
Pultec EQ — EQP-1A passive tube	Tone Shaper	Simultaneous boost and cut on the same low frequency band: the classic Pultec trick for adding weight without muddiness. An authentic LCR resonant bump at the shelf corner models the original hardware's inductor resonance. LF Boost and Cut up to 18 dB each with independent bandwidth controls. Tube saturation adds harmonic richness.
Dynamic EQ — 4-band frequency-dependent dynamics	Surgical Dynamics	Compresses, expands, or gates each of four frequency bands independently — only when the level in that band crosses its threshold. A real-time spectral analyzer shows you what's happening while GR meters show how hard each band is working. Optional sidechain input for frequency-targeted ducking or de-essing driven by another signal.
Transformer — 4 vintage hardware models	Saturation / Color	Runs your signal through an emulated transformer core in four flavors: Vintage (Neve-style iron warmth), Modern (API-style punch), British (SSL-style clarity and grit), and American (custom character). Independent input and output transformer stages let you push the front end hard and tame the output separately. Frequency response shaping from the transformer model is included.
Haas — Psychoacoustic stereo widener	Stereo Width	M/S encoding with independent mid/side gain, then Haas effect comb filtering in two modes: Side Comb (mono-compatible, WOW-Thing style) or (diffuse L-R delay injection). Hermite interpolation keeps automation smooth and click-free. RMS-safe automatic output trim. Positioned before Punch so the clipper catches any widener-induced peaks.

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Global Controls

• Global Bypass — Engages zero-latency passthrough for the entire chain (including Sheen). Use it for A/B comparisons at a glance.
• Auto Gain — RMS-based output compensation (~5 second time constant) that matches the processed and bypassed levels. Sheen is intentionally excluded from this calculation — auto-comp on a polish stage defeats its purpose.
• Module Reordering — Click and drag any reorderable slot's body to a new position. Drop in the left third of a target to insert before, the middle to swap, the right third to insert after. A live cyan bar (insert) or yellow ring (swap) shows the resolved drop intent before you release. Drop on an empty slot to move there. A floating ghost label tracks the cursor showing what you're moving.
• Focus Mode — Press 1..7 to focus a real-module slot (collapses every other slot to a tab so the focused module gets the full chassis width). Press Esc to exit.
• Brushed-Brass Plate — The "API Bus Channel Strip" brand mark in the chassis header is clickable; it opens the hidden Sheen back view. Mutually exclusive with the Dynamic EQ back view.

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Build From Source

Requirements

Dependency	Version	Notes
Rust nightly	latest	Required by vizia-plug
LLVM / Clang	19+	Windows only — required for Skia bindgen
VS Build Tools	2022	Windows only — C++ FFI compilation

Quick Commands

just check        # Fast type-check (no codegen)
just bundle       # Production VST3 + CLAP bundle with GUI
just deploy       # bundle + install to system plugin directories
just qa           # fmt-check + lint + test

Windows — Full Bundle Command

set LLVM_HOME=C:\Program Files\LLVM
set LIBCLANG_PATH=C:\Program Files\LLVM\bin
cargo +nightly run --package xtask -- bundle bus_channel_strip --release --features "api5500,buttercomp2,pultec,transformer,punch,haas,dynamic_eq,sheen,gui"

Bundles output to target/bundled/.

Important: Do not set BINDGEN_EXTRA_CLANG_ARGS, CC, or CXX when building with the gui feature — they conflict with Skia's build system. Windows builds Skia from source; LLVM 19+ is required for MSVC STL compatibility.

All Justfile Recipes

just check        # Fast type-check
just build        # Debug build (no GUI)
just build-gui    # Debug build with GUI
just bundle       # Production VST3+CLAP bundle
just bundle-core  # Bundle without GUI (faster iteration)
just install      # Install to system plugin dirs
just deploy       # bundle + install
just test         # Unit tests
just lint         # Clippy -D warnings
just fmt          # nightly rustfmt
just qa           # fmt-check + lint + test
just env          # Show build environment

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Architecture Notes

Audio Thread Guarantees

All process() paths are allocation-free, lock-free, panic-free, and I/O-free. No heap allocation, no mutexes, no .unwrap(), no file or system calls. Parameter communication between the GUI and the audio thread uses atomics only.

Implementation Details

• Biquad filter coefficients update via update_coefficients() — no state reset on parameter changes
• ButterComp2 FFI is called once per buffer, not once per sample
• Dynamic EQ uses a 0.05 dB hysteresis gate on coefficient updates to skip trigonometric calls when the envelope is stable
• Transformer parameter caching gates update_frequency_response() to actual changes only
• Punch oversampling uses linear interpolation upsample and IIR downsample (pole = 0.05); transient shaping runs pre-clip to prevent pumping

Technology Stack

• NIH-Plug — plugin framework (~86 parameters, VST3 + CLAP output)
• vizia-plug — GUI framework (Skia GPU backend, ECS reactive architecture); v1.0.0 uses vizia's native on_drag / on_drop API for rack drag-drop
• biquad 0.6.0 — filter implementations (routed through shaping::biquad_coeffs, originally a workaround for the v0.5.0 frequency-normalization bug fixed in 0.6.0)
• Airwindows ButterComp2 — C++ FFI via extern "C" wrapper in cpp/
• realfft — FFT for the spectral analyzer

Source Layout

src/
  lib.rs           # Plugin entry, parameter definitions, process() dispatch (slot loop + Sheen tail)
  api5500.rs       # 5-band semi-parametric EQ
  buttercomp2.rs   # Airwindows ButterComp2 FFI wrapper
  pultec.rs        # Pultec EQP-1A tube EQ
  dynamic_eq.rs    # 4-band dynamic EQ
  transformer.rs   # Transformer saturation module
  haas.rs          # Psychoacoustic stereo widener (M/S + Haas comb)
  punch.rs         # Clipper + transient shaper with oversampling
  sheen.rs         # Pinned master-end polish coat (5 stages, default-on)
  editor.rs        # vizia GUI: chassis header + brass plate + library sidebar +
                   #   scrollable rack with native drag-drop / live drop preview /
                   #   floating ghost / focus mode / mini-map / DynEQ + Sheen back views
  components.rs    # Reusable GUI components
  spectral.rs      # FFT analysis + gain reduction metering
  shaping.rs       # DSP math utilities + biquad_coeffs workaround
  styles.rs        # vizia CSS-like styles (includes brass plate + Sheen back-view themes)

cpp/               # C++ Airwindows FFI wrappers
xtask/             # Build tooling (bundle, install)
docs/              # Internal docs: ADRs (docs/adr/), SYSTEM_PROMPT.md, TESTING.md, etc.
site/              # Published Astro/Starlight docs site (GitHub Pages)

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Documentation

Full control reference, genre signal chain examples, and preset descriptions:

fsecada01.github.io/bus_channel_strip

Internal design documents in docs/:

• docs/adr/ — Architecture Decision Records: Sheen design (ADR-0006), rack UX/drag-drop (ADR-0007), GUI framework/layout (ADR-0009), Punch design (ADR-0005), and more
• CLIPPING_INSIGHTS.md — Professional loudness techniques

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License

GPL-3.0-or-later. See LICENSE.

Airwindows source code is copyright Chris Johnson, released under the MIT license.