@audio/dynamics-unlimit

Classical de-limiter: transient-gated upward expansion restoring crest a brickwall limiter flattened

npm install @audio/dynamics-unlimit

import unlimit from '@audio/dynamics-unlimit'

De-limiter. iZotope Ozone 12's "Unlimiter" (Sept 2025) created the de-limiting category with a trained ML model; this atom is the classical counterpart — transient-synchronous upward expansion, restoring the crest factor a brickwall limiter (or an over-eager bus compressor) flattened. Program-adaptive upward expansion gated to transients, not level — one more cell in the four-quadrant dynamics taxonomy (Giannoulis, Massberg & Reiss 2012, JAES 60(6); Izhaki, Mixing Audio), built on expander's upwardExpanderGain curve.

A fast envelope (fastAttack/fastRelease, near-instant) and a slow envelope (slowAttack/slowRelease, sluggish) both track the input; their gap in dB — transientness — rises sharply on attacks and sits near zero on sustained material. Gain lift follows transientness, not absolute level: an absolute-level upward expander would pump sustains; gating on the fast/slow gap instead is what makes this a de-limiter rather than a leveler.

import { unlimit } from '@audio/dynamics'

unlimit(data, { amount: 9, drive: 2 })                  // deliberate restoration
unlimit(data, { amount: 9, drive: 2, ceiling: -1 })      // guard restored peaks at -1 dBFS

| Param | Default | | |---|---|---| | amount | 6 | dB, max crest restoration (range 0–18) | | drive | 1 | scales the deficit-driven restoration (1 = restore attacks to crestTarget); in adaptive: false mode, dB of lift per dB of transientness | | adaptive | true | deficit mode (see below); false = raw proportional transient-following (a transient exaggerator, for manual sound design) | | crestTarget | 10 | dB of transientness a healthy attack is expected to show; flattened attacks get lifted by what they're missing | | ceiling | null | dBFS; post guard so restored peaks don't exceed it. null (default): peaks may exceed 0 dBFS by design (float domain) | | fastAttack | 0.5 | ms | | fastRelease | 20 | ms | | slowAttack | 20 | ms | | slowRelease | 200 | ms |

The default mode lifts by transient deficit, not transient presence — the inverse-limiter insight: a brickwall limiter's fingerprint is attacks that are too small (3–8 dB of fast-over-slow transientness where healthy program shows 12–25 dB), so each onset gets back crestTarget − measured dB, and a naturally healthy attack gets structurally zero lift. Safety on dynamic material is a property of the curve, not a timid default: measured on the test fixture, defaults change never-limited program by ≤ 0.2 dB RMS while amount: 9 recovers ~4.5 dB of crest from a 9 dB-crushed brickwall (see tests). Three gates make that separation robust — peak-hold (deficit is judged against an attack's peak transientness, not its rise samples), a 10 ms attack window (a decaying tail keeps the fast envelope above the slow one for its whole length; a decay is not an onset), and a ~3 ms confirmation ramp (a healthy attack outruns crestTarget in ~1.5 ms, collapsing its own deficit before lift confirms; a limiter-flattened plateau is still standing).

Honest scope: this restores dynamics/crest — it cannot recover information a clipper already destroyed (pair with @audio/denoise-declip for that), and it does not un-mix limiter pumping artifacts baked into the waveform's history. Over-driving amount/drive invents transients that were never there. v1 is zero-latency with no lookahead — it reacts to a transient already underway, it cannot anticipate one; lookahead attack-anticipation is a future option.

Use when: restoring life to over-limited masters, streaming-loudness-flattened stems, squashed dialogue or game audio. Not for: recovering clipped/distorted peaks — use a declipper. Undoing audible limiter pumping — remix from an earlier, unlimited stage if one exists.

Part of @audio/dynamics — the dynamics family umbrella. This README is generated from the umbrella docs.

MIT © audiojs