Petter Reinholdtsen

Measuring and adjusting the loudness of a TV channel using bs1770gain
11th June 2015

Television loudness is the source of frustration for viewers everywhere. Some channels are very load, others are less loud, and ads tend to shout very high to get the attention of the viewers, and the viewers do not like this. This fact is well known to the TV channels. See for example the BBC white paper "Terminology for loudness and level dBTP, LU, and all that" from 2011 for a summary of the problem domain. To better address the need for even loadness, the TV channels got together several years ago to agree on a new way to measure loudness in digital files as one step in standardizing loudness. From this came the ITU-R standard BS.1770, "Algorithms to measure audio programme loudness and true-peak audio level".

The ITU-R BS.1770 specification describe an algorithm to measure loadness in LUFS (Loudness Units, referenced to Full Scale). But having a way to measure is not enough. To get the same loudness across TV channels, one also need to decide which value to standardize on. For European TV channels, this was done in the EBU Recommondaton R128, "Loudness normalisation and permitted maximum level of audio signals", which specifies a recommended level of -23 LUFS. In Norway, I have been told that NRK, TV2, MTG and SBS have decided among themselves to follow the R128 recommondation for playout from 2016-03-01.

There are free software available to measure and adjust the loudness level using the LUFS. In Debian, I am aware of a library named libebur128 able to measure the loudness and since yesterday morning a new binary named bs1770gain capable of both measuring and adjusting was uploaded and is waiting for NEW processing. I plan to maintain the latter in Debian under the Debian multimedia umbrella.

The free software based TV channel I am involved in, Frikanalen, plan to follow the R128 recommondation ourself as soon as we can adjust the software to do so, and the bs1770gain tool seem like a good fit for that part of the puzzle to measure loudness on new video uploaded to Frikanalen. Personally, I plan to use bs1770gain to adjust the loudness of videos I upload to Frikanalen on behalf of the NUUG member organisation. The program seem to be able to measure the LUFS value of any media file handled by ffmpeg, but I've only successfully adjusted the LUFS value of WAV files. I suspect it should be able to adjust it for all the formats handled by ffmpeg.

Tags: english, frikanalen, multimedia, video.

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