ITU-R BS.1770

Overview

ITU-R BS.1770 specifies how to measure program loudness and true-peak levels using a K-weighted algorithm. It underpins loudness regulations and best practices across broadcast and streaming, and increasingly informs nearfield deliverables for films. By standardizing measurement, it ensures mixes translate predictably between theaters, televisions, and mobile devices.

Measurement Concepts

K-weighting applies a frequency curve approximating human loudness perception, integrating over time to produce a single value (in LKFS/LUFS). Short-term and momentary windows capture dynamics without being fooled by brief transients. True-peak uses oversampled detection to estimate inter-sample peaks that can clip consumer DACs even when sample-peak meters look safe. Together, these metrics guide mixers toward consistent dialog intelligibility and controlled headroom.

Film and Streaming Deliverables

Theatrical printmasters target calibrated rooms rather than a fixed loudness number, but streaming and broadcast versions are typically normalized to regional specs derived from BS.1770 (e.g., −24 LKFS ±2 for legacy broadcast, or service-specific targets such as −27/−23/−18 LKFS with true-peak caps). Deliverable sheets should state target, tolerance, gating mode, and measurement tool versions to avoid disputes.

Practical Mixing Notes

Dialog anchor approaches measure only speech segments to set overall gain; integrated approaches consider the whole program. Mixers should watch true-peak especially on bright effects and encoded music; overs can sneak in during downmix or encode. Loudness range (LRA) helps judge macro-dynamics—too wide risks inaudibility at home; too narrow feels fatiguing.

Related Terms

• LKFS/LUFS, true-peak, LRA, loudness normalization.