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Bus Channel Strip

Changelog

For full release notes, binaries, and platform-specific archives, see the GitHub Releases page.

v0.5.0 — 2026-04

Pultec EQ — authentic LCR resonance and bandwidth control

The LF section is completely remodeled to match the sound of the original EQP-1A hardware.

  • LCR resonant bump: A PeakingEQ at the shelf corner frequency (45% of shelf gain, Q=1.8) models the inductor resonance of the original hardware. This resonant peak is why Pultec LF boosts sound focused and punchy rather than soft and woolly.
  • 18 dB range for both LF Boost and LF Cut (extended from ~8 dB).
  • LF Boost Freq: now spans 20–300 Hz with skewed scaling (was stepped 20/30/60/100 Hz).
  • LF Cut Freq: now spans 20–400 Hz with skewed scaling (was 20–200 Hz).
  • New: LF Boost Bandwidth — controls shelf width from narrow (Q=1.0) to wide (Q=0.25). At the default of 0.67, the shelf spreads through the musical 100–300 Hz range. This is the difference between a Pultec that sounds sub-only and one that sounds full and present on guitars, keys, and mix buses.
  • New: LF Cut Bandwidth — same Q mapping as LF Boost BW.
  • All filter math now routes through shaping::biquad_coeffs to apply the correct Nyquist normalization (f0 * 2 / sr), fixing the biquad 0.5.0 frequency normalization bug that was placing every filter at 1/4 its intended corner frequency.

New module: Haas stereo widener

A psychoacoustic stereo widener using M/S encoding and Haas effect comb filtering.

  • Two modes: Side Comb (WOW-Thing style, mono-compatible) and Wide Comb (diffuse, L-R delay injection).
  • Delay time: 1–20 ms, Hermite-interpolated with one-pole smoothing (τ=20 ms) to prevent zipper noise on automation sweeps.
  • RMS-safe output trim: automatic gain compensation based on mid/side gains and comb depth.
  • Anti-denormal protection: Airwindows-style 1e-20 alternating dither in the delay line.
  • Default position: before Punch — so the clipper catches any widener-induced peaks before they hit the ceiling.
  • Feature flag: haas (enabled by default).

Plugin integration tests

New src/plugin_integration_tests.rs file exercises the full plugin pipeline rather than isolated module tests. Catches parameter wiring failures, bypass default regressions, and coefficient initialization bugs. Currently covers Pultec module end-to-end.

CI fix

src/haas.rs was missing from the repository (untracked locally). Added to git. The haas feature is in [features] default, so all CI targets were failing with E0583: file not found for module 'haas'.

v0.4.0 — 2026-03

ButterComp2 — new compression models

Three new compressor models join the original Airwindows Classic algorithm. Select the model from the dropdown at the top of the ButterComp2 module panel; the controls below update to match.

  • VCA — Hard-knee voltage-controlled amplifier compression. Fast, precise transient response. Threshold (dB), Ratio (1–20), Attack (ms), Release (ms), Character % (0–100, controls 1176-style color), Mix. Use on drum buses and any source where you want predictable, controllable gain reduction.
  • Optical (Opt) — Soft-knee program-dependent compression. Threshold (dB), Character % (0–100, controls program-dependent release behavior and tube warmth), Attack (ms), Release (ms), Mix. Use on vocal, acoustic instrument, and bass stems.
  • FET — Field-effect transistor compression driven by an input gain stage rather than a threshold control. Input (dB), Output (dB), Ratio (1–20), Attack (ms), Release (ms), Auto Release (toggle — enables program-dependent release), Mix. Use on drum buses and any stem where you want a forward, saturated character.
  • Classic — Airwindows ButterComp2 (original, unchanged). Bipolar interleaved compression with Compress, Output, and Dry/Wet. VCA, Optical, and FET are native Rust implementations; Classic compiles from Airwindows C++ via Rust FFI.

Parameter display — integer formatting

All non-percentage float parameters now display as integers throughout the UI, automation lanes, and parameter tooltips. This eliminates long decimal strings on thresholds, ratios, EQ gains, and timing values. Existing automation data is unaffected — the underlying parameter ranges are unchanged.

UI — API5500 EQ layout

  • LF and HF shelves moved to a two-column layout, freeing vertical space in the module slot
  • Parametric bands now ordered low-to-high: LMF, MF, HMF

UI — Pultec EQ

  • HF boost bandwidth control now visible in the panel
  • HF cut frequency and gain controls now visible

UI — Transformer

  • Output saturation control exposed
  • Panel sections structured as INPUT / OUTPUT / TONE for clarity

UI — ButterComp2 model panel

  • Model selector dropdown at top of module
  • Per-model control panel updates via Binding::new pattern — controls swap without resizing the module slot
  • Fixed-height panel prevents adjacent modules from shifting when switching models

DSP — global bypass

  • Global bypass now passes audio through with zero processing overhead via early return from process()
  • Previously, bypass still evaluated the module order dispatch loop

DSP — global auto gain

  • New global Auto Gain compensation: RMS level measured pre- and post-processing chain
  • ~5-second smoothing time constant; ±18 dB correction range
  • Compensates for level changes introduced by heavy compression or EQ boost without manual output trimming

Fix — NaN sentinel values

  • Replaced NaN-based dirty-check sentinels in the compressor model switching logic
  • Previously, switching models could leave NaN values in internal state, causing audio silence until the plugin was reset

v0.3.0 — 2026-03

Documentation site

  • Migrated documentation from MkDocs to Astro 5 + Starlight 0.32 for improved navigation, search, and theming
  • Added Architecture, Contributing, Changelog, and Parameter Reference pages
  • Live site deployed to GitHub Pages at fsecada01.github.io/bus_channel_strip

CI/CD pipeline fixes

  • Replaced deprecated actions/create-release@v1 with gh release create and GITHUB_TOKEN permissions
  • Fixed Skia cross-compile failure on macOS ARM64 runners: Xcode’s clang on aarch64 blocks x86 SIMD intrinsic headers (mmintrin.h, emmintrin.h) even when targeting x86_64-apple-darwin. Fix: ARM64 builds include GUI, Intel builds compile core modules only without Skia
  • Removed gui from [features] default in Cargo.toml to prevent Skia from compiling on all CI targets regardless of --features flags passed to xtask bundle
  • Used actions/download-artifact@v4 with merge-multiple: true for flat artifact glob upload to releases

Release artifacts (4 platform targets)

  • windows-x86_64 — VST3 + CLAP with GUI (Skia built from source with LLVM 19)
  • linux-x86_64 — VST3 + CLAP with GUI
  • macos-aarch64 (Apple Silicon) — VST3 + CLAP with GUI
  • macos-x86_64 (Intel) — VST3 + CLAP, core modules only, no GUI (Skia cross-compile limitation, tracked as Issue #1)

v0.2.x

Punch module

  • New Punch module: clipper + transient shaper with 8x oversampling
  • Three clip modes: Hard, Soft (tanh), Cubic (polynomial soft knee)
  • Transient detection with configurable attack/release times and sensitivity
  • Pumping fix: moved transient detection + shaping to pre-clip stage. Previously, post-clip transient shaping created time-varying gain modulation that audibly pumped on every note attack
  • Downsample IIR pole reduced from 0.3 → 0.05, further eliminating pumping artifacts
  • Transient detector now uses native sample rate (not the oversampled rate)
  • Punch module is bypassed by default — user must enable it intentionally

Module reordering UI

  • Drag-to-swap module ordering implemented in the vizia GUI
  • Click the drag handle (≡) to select a slot as swap source
  • Click another slot’s handle to swap positions
  • Visual feedback: white border + yellow module name on selected slot
  • Handle label changes reactively: “MOVE” (self) / “SWAP HERE” (others) / “CANCEL”

vizia-plug GUI integration

  • Replaced placeholder GUI with full vizia-plug integration (September 2025)
  • Fixed dependency configuration: removed conflicting skia-safe direct dependency
  • Switched to nightly Rust toolchain (required by vizia-plug)
  • Skia builds from source on Windows x86_64 using LLVM 19 + MSVC STL
  • Window: 1820×820 px, six module slots with per-module color coding
  • Spectrum analyzer canvas with real-time FFT display, band tint overlays, and GR bars

Dynamic EQ — sidechain masking analysis

  • Optional stereo sidechain input (second audio I/O layout in CLAP/VST3)
  • Lock-free one-shot analysis pipeline: GUI arms analysis, audio thread runs FFT on sidechain snapshot, results delivered via AtomicBool + AnalysisResult
  • Spectral overlap detection: overlap[k] = main_fft_mag[k] * sc_fft_mag[k]
  • Suggests threshold and target frequency for masking band
  • Two-step UX: “ANALYZE SC” arms; “APPLY RESULT” sets DynEQ parameters

v0.1.x

Initial implementation

  • Core plugin skeleton with NIH-Plug framework
  • API5500 EQ: 5-band semi-parametric (LF shelf, LMF/MF/HMF parametric, HF shelf)
  • ButterComp2: Airwindows C++ module wrapped via extern "C" FFI, compiled with cc crate
  • Pultec EQ: EQP-1A style with simultaneous boost/cut and tube saturation (tanh shaping)
  • Transformer: 4 vintage transformer models (Vintage, Iron, Modern, Warm) with input/output saturation
  • Dynamic EQ: 4-band frequency-dependent compression with configurable mode (compress downward / expand upward)
  • Module reordering system: six EnumParam<ModuleType> parameters for runtime signal chain ordering
  • Lock-free audio thread: no allocations, no locks, no panics in process()
  • Migrated from biquad v0.4 to v0.5.0 API: filter constructors now require gain parameter (Type::PeakingEQ(gain_db), Type::LowShelf(gain_db), Type::HighShelf(gain_db)); .set_gain() removed
  • Sample-accurate automation enabled (SAMPLE_ACCURATE_AUTOMATION: bool = true)