The Advanced Television Systems Committee (ATSC) has delivered an updated version of ATSC A/85, the core technology mandated by the Commercial Advertisement Loudness Mitigation (CALM) Act in the USA.
As approved by ATSC members, the revised version of A/85 includes an update of the reference to the International Telecommunications Union (ITU) recommendation for “algorithms to measure audio programme loudness and true-peak audio level.”
The revised A/85 now references ITU-R BS.1770-3. Version 3 of BS.1770, adds “gating” (excluding low level passages from the measured value) to the measurement algorithm. In addition, version 3 of BS.1770 includes some minor editorial updates to the loudness measurement text and a minor correction to the true-peak measurement algorithm. Beyond the reference change, A/85 now includes improved guidance for measuring the loudness of surround programming in both its multichannel format and in its 2-channel downmix. This is important because many consumers utilize the stereo downmix of surround programming and it is possible to have loudness disparity between the two modes. In addition, A/85 is now specific about the differences between loudness and dynamic range.
The updated ATSC Recommended Practice A/85:2013, dated March 12, 2013, is the successor document to Recommended Practice A/85:2011, dated May 25, 2011.
This brings A/85 even closer to the EBU R128 recommendation and will make it even easier to deliver loudness content across multiple territories.