Crate audiobook_creation_exchange 

ACX-compliant audio post-processing pipeline for speech audio.

Validates and repairs raw L16 mono PCM against the ACX audiobook specification (−23…−18 dBFS RMS, −3 dBFS true-peak, −60 dBFS noise floor) per https://www.acx.com/help/acx-producer-standards/201456300.

Pipeline (applied in order by process)

1. Click suppression — removes sub-10 ms transient spikes via cubic Hermite interpolation.
2. DC offset removal — subtract the mean sample value.
3. Noise reduction — Wiener spectral subtraction profiled from the leading silence (disabled by default; requires a silent lead-in — see AcxConfig::denoise_enabled).
4. EQ warmth — low-shelf (+2 dB @ 180 Hz) + high-shelf (+1.5 dB @ 5 kHz) biquad IIR.
5. De-essing — OLA STFT; reduces 5–8 kHz sibilance band by up to −6 dB.
6. Plosive suppression — OLA STFT; attenuates sub-150 Hz bins on plosive windows.
7. Multiband compression — 3-band LR4 crossover compressor (250 Hz / 3 kHz crossovers); runs before normalisation so the level step sees the compressed spectrum.
8. Normalise — linear gain to −20.5 dBFS, pre-compensated for bookend energy dilution.
9. Limit — 5 ms lookahead brickwall limiter; no peak (including 4× interpolated) exceeds −3 dBFS.
10. Breath removal — breath-band windows replaced with room tone (disabled by default).
11. Pause normalisation — caps over-long inter-sentence pauses to natural targets (sentence 120 ms, paragraph 400 ms, scene break 700 ms); skips leading/trailing silence.
12. Gate — sub-threshold 50 ms windows replaced with 1/f pink noise room tone.
13. Bookend padding — first 1 s and last 3 s forced to room tone with 10 ms crossfades.
14. Verify — second analysis pass; returns Err(AcxError::StillNonCompliant) only when audio is irrecoverably broken.

Standalone utilities

• crossfade() — equal-power segment transition
• consistency_check — batch RMS variance check across multiple segments
• LoudnessPreset — pre-built AcxConfig variants for different delivery loudness levels

Re-exports

pub use analyse::AcxReport;

pub use analyse::analyse;

pub use bitstream::CbrReport;

pub use bitstream::Id3Report;

pub use bitstream::check_cbr;

pub use bitstream::check_id3_tags;

pub use consistency::ConsistencyReport;

pub use consistency::consistency_check;

pub use crossfade::crossfade;

pub use error::AcxError;

pub use loudness_preset::LoudnessPreset;

pub use lufs::LufsReport;

pub use lufs::integrated_lufs;

pub use lufs::loudness_range;

pub use multiband::MultibandParams;

pub use spectral::SpectralViolation;

pub use spectral::SpectralViolationKind;

pub use spectral::scan as spectral_scan;

pub use temporal::DeadAirViolation;

pub use temporal::check_bookends;

pub use temporal::count_digital_zero_runs;

pub use temporal::detect_dead_air;

pub use temporal::max_dead_air;

Modules

analyse

bitstream

MP3 bitstream validation: CBR frame consistency and ID3v2 tag completeness.

breath

Breath removal: detect and suppress audible breath sounds in speech audio.

click

Click and impulse suppressor.

consistency

Inter-episode loudness consistency check.

crossfade

Chapter crossfade using equal-power (constant-power) fade curves.

dc_offset

DC offset detection and removal.

deess

Frequency-selective de-esser for TTS sibilance reduction.

denoise

Wiener spectral subtraction noise reducer.

eq

Warmth shelving equaliser — two biquad IIR filters applied in a single pass.

error

gate

limiter

loudness_preset

Loudness preset factory — maps a delivery character to a tuned AcxConfig.

lufs

LUFS (Loudness Units relative to Full Scale) measurement per ITU-R BS.1770-4.

multiband

Three-band feed-forward RMS compressor.

normalise

pause_norm

Inter-sentence pause normaliser.

plosive

Plosive suppression: gentle low-frequency shelving below 150 Hz.

room_tone

spectral

FFT-based spectral analysis for sibilance and plosive detection.

temporal

Temporal silence validation: dead air, head/tail bookends, and digital zero detection.

Structs

AcxConfig

Audio processing configuration.

DiagnosticReport

Full diagnostic report produced by validate.

Functions

bytes_to_samples

Convert raw L16-LE bytes to i16 samples.

process

Run the full ACX post-processing pipeline on raw L16-LE PCM bytes.

process_with_config

Like process but with a custom AcxConfig.

samples_to_bytes

Convert i16 samples back to L16-LE bytes.

validate

Run a full diagnostic pass on raw L16-LE PCM bytes without modifying them.

validate_with_config

Like validate but with a custom AcxConfig.