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Abstract

This document describes breifly some of the terms and techniques that are used to describe and control the loudness and level of audio in broadcasting. Sometimes misunderstanding can occur because of loose or inaccurate use of terminology. The purpose of this document is to reduce that.

The kind of terms that are often used, are things like dB, dBFS, LUFS, LU, LKFS, dBu, dBm, V, alignment level, programme reference level, target level, dialogue level, loudness level, together with a range of "standard" numbers: 0.775, 0, -18, -20, -23, -24, -27, -31.

A description of dBFS, LU, LUFS, and related terms is given, together with an explanation of some of the common numerical values that are associated with measurements that use these units. Two methods of loudness normalisation using meta-data are briefly described and compared.

True peaks of an audio signal can exceed the highest sample value (the sample peak) when the signal is processed, potentially leading to clipping. Proper metering and control of levels is therefore necessary.

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