[Roadmap] den effects library — v1.0 → v3.0 master plan

[yuichkun]

[Roadmap] den effects library — v1.0 → v3.0 master plan

Related: #<parent-issue-number> ([Epic] Foundation for den). This roadmap is created after the foundation epic merges. Individual effects are filed as separate issues via .github/ISSUE_TEMPLATE/add-effect.yml and checked off below.

Purpose

This is the curated master list of effects den commits to implementing — ~58 user-facing classes across 5 phases (v1.0 → v3.0). Each effect lists its target version, reference source (from LICENSE-THIRDPARTY allow-list), key parameters, and implementation notes. New effects are added only via a separate chore(roadmap): propose <effect> issue and maintainer approval.

The goal is parity with the serious-producer workflow: after v2.0, a user can construct a complete mix bus and master chain inside the browser using only @denaudio/effects — comparable in capability (not necessarily flavor) to the FabFilter Pro bundle + iZotope Ozone/Neutron core modules.

How to read this document

Each effect has:

• Class: the exported TS class name (PascalCase)
• Module: Rust module file (crates/den-core/src/effects/<snake>.rs)
• Category: filter | dynamics | saturation | modulation | delay | reverb | pitch | spatial | utility | analysis
• Reference: short-name key from LICENSE-THIRDPARTY Tier A/B
• Params: top-level AudioParam list
• Notes: non-obvious implementation constraints

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v1.0 — MVP (~20 user-facing classes across 16 modules): a complete bus chain without leaving the browser

Counting note: We count by TS class (user-facing exports). Modules can ship multiple classes (e.g., high_pass.rs exports HighPass12 + HighPass24 from the same biquad-cascade kernel). Gain ships in Sub D's foundation epic and is not a v1.0 work item.

Goal: after v1.0, a user can route source → HPF → EQ → Comp → Limiter → out with pro-grade fidelity.

Utility

• Gain — Gain / gain.rs / utility / ref: rbj+textbook
  • Params: gain (linear, 0..10, a-rate)
  • Notes: delivered in Sub D (foundation epic)
• PolarityInvert — PolarityInvert / polarity_invert.rs / utility / ref: textbook
  • Params: active (0/1, k-rate)
  • Notes: trivial; good second effect to confirm scaffolder generality
• StereoWidth — StereoWidth / stereo_width.rs / spatial / ref: dafx ch.6 (Mid/Side)
  • Params: width (0..2, a-rate)
  • Notes: M/S encode → scale S → M/S decode. Classic formula.
• Mono — Mono / mono.rs / utility / ref: textbook
  • Params: none
  • Notes: out = (L+R)/2 duplicated. Useful as a bus check.
• DcFilter — DcFilter / dc_filter.rs / filter / ref: jos (DC blocker)
  • Params: none
  • Notes: 1-pole HPF at ~5 Hz, y[n] = x[n] − x[n−1] + 0.995·y[n−1]. Should be applied implicitly at input of every effect chain; we expose it explicitly too.

Filter

• HighPass12 / HighPass24 — HighPass12, HighPass24 / high_pass.rs / filter / ref: rbj
  • Params: frequency (20..20000 Hz, a-rate, exp), q (0.1..10, a-rate)
  • Notes: biquad single (12 dB/oct) or cascade-of-2 (24 dB/oct). Coefficients from RBJ cookbook.
• LowPass12 / LowPass24 — same file — ref: rbj
  • Params: frequency, q
• BandPass — BandPass / band_pass.rs / filter / ref: rbj
  • Params: frequency, q
• Notch — Notch / notch.rs / filter / ref: rbj
  • Params: frequency, q
• LowShelf / HighShelf — LowShelf, HighShelf / shelving.rs / filter / ref: rbj
  • Params: frequency, gain_db (-24..+24, a-rate), slope (0.1..2)
• PeakingEq — PeakingEq / peaking_eq.rs / filter / ref: rbj
  • Params: frequency, q, gain_db
  • Notes: single-band only in v1.0. Multi-band cascade is v1.1.

Dynamics

• Compressor — Compressor / compressor.rs / dynamics / ref: dafx ch.4, airwindows/Pressure5
  • Params: threshold_db, ratio, attack_ms, release_ms, knee_db, makeup_db, sidechain_hp_hz
  • Notes: feed-forward, RMS detection (sqrt of 1-pole smoothed square), soft-knee via quadratic interpolation around threshold. No look-ahead in v1.0. sidechain_hp_hz is an INTERNAL high-pass on the detector's RMS signal (not an external sidechain input channel) — the detector ignores energy below this frequency, useful for ducking only mid/high-frequency content. External sidechain (separate input channel) is a v2.0 follow-up.
• Limiter — Limiter / limiter.rs / dynamics / ref: dafx ch.4
  • Params: ceiling_db, release_ms
  • Notes: hard-knee, zero look-ahead ("brickwall-lite"). True-peak ISP limiter is v3.0.
• Gate — Gate / gate.rs / dynamics / ref: dafx ch.4
  • Params: threshold_db, attack_ms, release_ms, hold_ms, hysteresis_db

Saturation

• SoftClip — SoftClip / soft_clip.rs / saturation / ref: dafx ch.4 (tanh waveshaper), airwindows/Loud
  • Params: drive (1..10, a-rate), mix (0..1, a-rate)
• BitCrusher — BitCrusher / bit_crusher.rs / saturation / ref: dafx ch.4
  • Params: bits (1..16, k-rate), sample_rate_reduction (1..64, k-rate)

Modulation / Delay

• Tremolo — Tremolo / tremolo.rs / modulation / ref: dafx ch.5
  • Params: rate_hz, depth, shape (sine/triangle/square, k-rate enum)
• DigitalDelay — DigitalDelay / digital_delay.rs / delay / ref: dafx ch.2
  • Params: time_ms (0..2000), feedback (0..0.98), mix (0..1)
  • Notes: power-of-2 circular buffer, linear interpolation on fractional delays. Denormal flush. mix=0 ⇒ bypass fast-path.

---

v1.1 — Mix essentials (+10 effects): polished mix chain

• ParametricEq8 — ParametricEq8 / parametric_eq.rs / filter / ref: rbj, fundsp/Pro-Q-like
  • Params: 8 bands × {enabled, frequency, q, gain_db, type}. State per band, total ~2 KB.
  • Notes: cascade of biquads. Serialization of configurations from v2.0.
• Expander — Expander / expander.rs / dynamics / ref: dafx ch.4
• DeEsser — DeEsser / de_esser.rs / dynamics / ref: dafx ch.4
  • Notes: split-band (HPF ~4 kHz side chain into comp, subtract from signal, recombine)
• MultibandCompressor3 — MultibandCompressor3 / multiband_compressor.rs / dynamics / ref: fundsp, dafx
  • Notes: Linkwitz-Riley crossovers at 200 Hz / 2000 Hz; 3 independent compressors.
• HardClip — HardClip / hard_clip.rs / saturation / ref: textbook
• TapeSaturation — TapeSaturation / tape_saturation.rs / saturation / ref: airwindows/IronOxide5, dafx ch.7
  • Notes: pre-gain → asymmetric waveshaper → post-LPF + subtle HF rolloff. Airwindows port.
• TubeSaturation — TubeSaturation / tube_saturation.rs / saturation / ref: airwindows/Focus, dafx ch.7
  • Notes: asymmetric waveshaper (positive vs negative half different curves).
• PingPongDelay — PingPongDelay / ping_pong_delay.rs / delay / ref: dafx ch.2
  • Params: time_ms (0..2000, k-rate), feedback (0..0.95, a-rate), width (0..1, k-rate; 0=mono delay, 1=full ping-pong), mix (0..1, a-rate)
  • Notes: pair of cross-feedback delay lines (L→R, R→L), independent fractional read taps.
• TransientShaper — TransientShaper / transient_shaper.rs / dynamics / ref: airwindows/Slew2
  • Params: attack, sustain (each -24..+24 dB)
• AutoPan — AutoPan / auto_pan.rs / modulation / ref: dafx ch.5
  • Params: rate_hz, depth, shape

---

v1.2 — Modulation & reverb (+10 effects): space and motion

• Chorus — Chorus / chorus.rs / modulation / ref: dafx ch.5, fundsp
  • Params: rate_hz, depth_ms, mix, voices (1..4, k-rate)
• Flanger — Flanger / flanger.rs / modulation / ref: dafx ch.5
  • Params: rate_hz, depth_ms, feedback, mix
• Phaser — Phaser / phaser.rs / modulation / ref: dafx ch.5, airwindows
  • Params: rate_hz, depth, stages (4/6/8/12, k-rate enum), feedback, mix
  • Notes: cascade of first-order allpass filters, swept by LFO.
• Vibrato — Vibrato / vibrato.rs / modulation / ref: dafx ch.5
  • Notes: delay-line-based; linear-interpolation fractional read.
• RingMod — RingMod / ring_mod.rs / modulation / ref: dafx ch.5
  • Params: frequency (5..5000 Hz, a-rate), mix
• PlateReverb — PlateReverb / plate_reverb.rs / reverb / ref: jos/physical, fundsp
  • Notes: four-tap delay + allpass network. Classic "plate" decay. Size ~8 KB of state.
• HallReverb — HallReverb / hall_reverb.rs / reverb / ref: jos/physical (FDN), fundsp
  • Notes: 8-node feedback delay network with Hadamard mixing matrix.
• RoomReverb — RoomReverb / room_reverb.rs / reverb / ref: jos/physical, fundsp
  • Notes: shorter decay, denser early reflections.
• TapeDelay — TapeDelay / tape_delay.rs / delay / ref: airwindows/TapeDelay
  • Notes: wow/flutter LFO on read head + saturator in feedback loop.
• DuckingDelay — DuckingDelay / ducking_delay.rs / delay / ref: dafx
  • Notes: sidechain compressor on delay output keyed by input.

---

v2.0 — Pitch, advanced mastering (+10 effects)

• PitchShifter — PitchShifter / pitch_shifter.rs / pitch / ref: dafx ch.8 (PSOLA)
  • Params: shift_semitones (-12..+12, a-rate), mix (0..1, a-rate), formant_preserve (0/1, k-rate)
  • Notes: PSOLA (Pitch-Synchronous Overlap-Add) is deterministic and avoids phase-vocoder window artifacts. Best for monophonic sources (vocals, leads, single-instrument tracks); polyphonic content will exhibit smearing. Document this caveat in the catalog page.
• FormantShifter — FormantShifter / formant_shifter.rs / pitch / ref: dafx ch.8
• Harmonizer — Harmonizer / harmonizer.rs / pitch / ref: dafx ch.8
  • Notes: multi-voice pitch shifter with configurable intervals.
• SpringReverb — SpringReverb / spring_reverb.rs / reverb / ref: jos/physical, airwindows
  • Notes: physical-model spring (dispersion via allpass cascade).
• ShimmerReverb — ShimmerReverb / shimmer_reverb.rs / reverb / ref: jos/physical
  • Notes: pitch-shift the reverb return +12 into feedback loop.
• ConvolutionReverb — ConvolutionReverb / convolution_reverb.rs / reverb / ref: dafx ch.9
  • Params: mix (0..1, a-rate), predelay_ms (0..200, k-rate), gain_db (-24..+12, a-rate)
  • Notes: partitioned block convolution (uniform partition for v2, non-uniform later). User supplies IR via loadIR(audioBuffer) method (decoded by user via ctx.decodeAudioData). No default IRs bundled with this effect — bundling commercial/copyrighted IRs would breach licensing. Companion package @denaudio/ir-library (v3.0) ships a curated set of CC0/public-domain IRs separately.
• DynamicEq — DynamicEq / dynamic_eq.rs / filter / ref: dafx ch.4 + ch.3
  • Notes: peaking band whose gain is modulated by a sidechain compressor envelope.
• LinearPhaseEq — LinearPhaseEq / linear_phase_eq.rs / filter / ref: jos/filters, dafx ch.3
  • Notes: FIR via overlap-add convolution. Substantial CPU; v2 target.
• Exciter — Exciter / exciter.rs / saturation / ref: dafx ch.7
  • Notes: HPF → saturate → mix back in, restores HF energy.
• HaasWidener — HaasWidener / haas_widener.rs / spatial / ref: dafx ch.6
  • Notes: sub-30 ms delay on one channel for stereo illusion.

---

v3.0 — Mastering-grade + analysis (+8 effects)

• TruePeakLimiter — TruePeakLimiter / true_peak_limiter.rs / dynamics / ref: dafx ch.4, jos
  • Notes: 4× oversampled look-ahead limiter with ISP awareness.
• LoudnessMeter — LoudnessMeter / loudness_meter.rs / analysis / ref: ITU BS.1770
  • Notes: integrated LUFS, short-term LUFS, momentary LUFS, true peak.
• SpectrumAnalyzer — SpectrumAnalyzer / spectrum_analyzer.rs / analysis / ref: jos/sasp
  • Notes: streaming FFT. Exposes magnitude array via MessagePort to main thread.
• StereoImager — StereoImager / stereo_imager.rs / spatial / ref: dafx ch.6
  • Notes: multi-band width control + vectorscope data.
• MultibandSaturator — MultibandSaturator / multiband_saturator.rs / saturation / ref: dafx ch.7
• WaveFolder — WaveFolder / wave_folder.rs / saturation / ref: dafx ch.7
• BinauralPan — BinauralPan / binaural_pan.rs / spatial / ref: kemar (MIT Media Lab HRTF dataset, free for commercial/non-commercial use)
  • Params: azimuth_deg (-180..+180, a-rate), elevation_deg (-40..+90, a-rate), mix (0..1, a-rate)
  • Notes: HRTF convolution. Bundle a small default subset of the KEMAR dataset (~500 KB) under vendor-licenses/KEMAR/. Attribution required: "KEMAR HRTF measurements © MIT Media Lab".
• ConvolutionIrLibrary — not an effect per se; companion package @denaudio/ir-library with curated CC0 IR files + loader helper.
  • Requires monorepo addition: this package is NOT in Sub A's initial layout (packages/core, worklet, effects, test-utils, examples). Adding it requires a separate chore(scaffold): add @denaudio/ir-library package issue before this checkbox can land.

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Tracking

Counts are TS user-facing classes, not Rust modules (some modules export multiple classes; some classes share a module).

• v1.0: ~20 classes (16 modules) — goal: 3–4 months post-foundation
• v1.1: +10 classes — goal: 6 months
• v1.2: +10 classes — goal: 9 months
• v2.0: +10 classes — goal: 12 months
• v3.0: +8 classes — goal: 18 months

Total at v3.0: ~58 user-facing classes. Dates are aspirational, not contractual. Each checkbox above links to its own implementation issue (filed via the Add-Effect template) as work begins.

How to contribute

1. Pick an unchecked effect from the list.
2. Open a new issue using .github/ISSUE_TEMPLATE/add-effect.yml with the effect name/ref from this roadmap.
3. Follow CONTRIBUTING.md §3.
4. Upon merge, check the box here.

How to propose a NEW effect (not on the list)

Open an issue titled chore(roadmap): propose <EffectName> with:

• Category (from the 9 listed)
• Target version (v1.x / v2.x / v3.x)
• Reference source (must already be in Tier A/B of LICENSE-THIRDPARTY, or propose its addition first)
• Justification (why does this belong in den?)

Maintainer approves → the effect is added here → an Add-Effect issue is filed to implement it.

What we will NOT build (explicit rejects)

• Sequencers / MIDI processing — den is effects, not composition.
• Synthesizers — arguably overlap, but v1.0–v3.0 are strictly effects. A sibling library @denaudio/synth might exist in the future; out of scope here.
• Generic delay lines, buffers, utility signal-flow primitives for users to build their own effects — those belong in @denaudio/core or a future @denaudio/graph. The user-facing library is "effects, ready to use."
• Anything GPL-encumbered — see LICENSE-THIRDPARTY.

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This roadmap lives at ROADMAP.md in the repo; changes go through PR.