Improvement of the ITU loudness algorithm with a relative gate

Eelco Grimm chaired a ‘gating’ subgroup of the EBU PLOUD working group that wrote the R128 recommendation for broadcast loudness. The task of the subgroup was to address the problem that movies with large parts of near silence, such as ‘No Country for Old Men’ of the Coen Brothers would receive a too low overall loudness value to align them succesfully with commercial breaks. The solution was found in the addition of a ‘relative measurement gate’ that was later adopted by ITU and became part of the BS1770 standard.

At the 128th AES convention in London, Eelco presented the paper. The abstract is as follows:

Undesirable loudness jumps are a notorious problem in television broadcast. The solution consists in switching to loudness-based metering and program normalization. In Europe this development has been led by the EBU P/LOUD group, working towards a single target level for loudness normalization applying to all genres of programs. P/LOUD found that loudness normalization as specified by ITU-R BS.1770-1 works fairly well for the majority of broadcast programs. However, it was realized that wide loudness-range programs were not well-aligned with other programs when using ITU-R BS.1770-1 directly, but that adding a measurement-gate provided a simple yet effective solution. P/LOUD therefore conducted a formal listening experiment to perform a subjective evaluation of different gate parameters. This paper specifies the method of the subjective evaluation and presents the results in term of preferred gating parameters.

The paper is available in the AES e-library: Determining an Optimal Gated Loudness Measurement for TV Sound Normalization.

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