ITU-R BS.1770 is the foundational recommendation that defines how loudness is measured, and almost every loudness rule in the world is built on it. Its algorithm has two key parts: a K-weighting filter that shapes the signal to approximate the ear's frequency response, and a gating stage that ignores silences and very quiet passages so they don't drag the average down. The output is a single loudness figure in LUFS (called LKFS in the ATSC world — the same thing). EBU R128, ATSC A/85, and every streaming target are essentially BS.1770 with a chosen number attached. Later revisions refined the gating and added true-peak measurement.
The book · Volume 4 of 7
Audio for Video: A Complete Guide to Sound in Video Products: From PCM and Codecs to Loudness, Accessibility, and Real-Time Voice Processing
ITU-R BS.1770 is the measurement every loudness spec quotes, so a meter that implements it slightly wrong fails every downstream check. This volume explains BS.1770 in depth, from K-weighting and gating to LUFS, true peak and the EBU R128 and ATSC A/85 targets built on it, so your measurements match what broadcasters and platforms see. Written by Nikolay Sapunov, CEO at Fora Soft.
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