lufs

Purpose

lufs contains the kernel of BS.1770-4 loudness measurement: the per-block mean-square energy calculation, the BS.1770 channel-weighted summation, the energy-to-LUFS conversion, and the streaming IntegratedLoudness accumulator that implements the two-gate algorithm (absolute gate at −70 LUFS, then a relative gate 10 LU below the ungated mean of survivors). The kernels are document-agnostic — they consume Float32Array[] blocks and numbers — so a true-peak limiter can pull momentaryLufs without instantiating a meter.

Features

Pure functions: blockMeanSquare, combineChannelEnergies, energyToLufs, momentaryLufs, shortTermLufs.
Streaming IntegratedLoudness class with two-gate integration.
BS.1770 channel weights — L/R/C at 1.0, surround at 1.41, LFE excluded.
Finite silence floor (LUFS_SILENCE_FLOOR = -100) instead of -Infinity.

Usage: Basic

import { momentaryLufs } from "@suaveplan/audio-analysis-loudness/algorithms/lufs";

const lufs = momentaryLufs(kWeightedBlock);

Usage: Advanced

import { IntegratedLoudness } from "@suaveplan/audio-analysis-loudness/algorithms/lufs";

const integrator = new IntegratedLoudness(2);
for (const block of kWeightedGatingBlocks) integrator.pushBlock(block);
const integrated = integrator.integrated();
console.log({ integrated, surviving: integrator.gatedBlockCount });

API Reference

LUFS_SILENCE_FLOOR, ABSOLUTE_GATE_LUFS, RELATIVE_GATE_OFFSET_LU, CHANNEL_WEIGHTS_BS1770 — frozen constants.
channelWeight(index), blockMeanSquare(block), combineChannelEnergies(perChannel), energyToLufs(weightedMS), momentaryLufs(block), shortTermLufs(block).
class IntegratedLoudness — pushBlock, integrated, reset, gatedBlockCount.

Implementation Notes

The integrator stores the linear weighted mean-square values that survived the absolute gate rather than their LUFS counterparts, because the relative gate is itself derived from the linear mean. This avoids a second Math.pow(10, …) pass per block. The silence floor is the BS.1770-4 minimum reported value (−70 LUFS for "no programme") rounded down to −100 to give downstream UI meters a stable bottom.

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