Loudness Range (LRA) is a measure of the variation of loudness on a macroscopic time-scale. Essentially, LRA is the difference in loudness level between the soft and loud parts of a programme. In 2009 the algorithm for computing LRA was published by TC Electronic, and was then included in the EBU R-128 recommendation for loudness normalisation. This paper describes the design choices underlying of the LRA algorithm. For each of its parameters the interval of optimal values is presented, supported by analyses of audio examples. Consequences of setting parameter values outside these intervals are also described. Although the LRA has already proven its usefulness in practice, this paper provides background knowledge that could support further refinement and standardisation of the LRA measure.
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