Editor’s note: With this article, we begin a series of high-level presentations from industry experts on issues of importance to the science and practice of broadcast and production technology. We are pleased to launch the Broadcast Forum with an in-depth examination of loudness and measurement with a feature article by Robert Orban.
In 2009, the ATSC released “Recommended Practice: Techniques for Establishing and Maintaining Audio Loudness for Digital Television (A/85:2009).” This was later updated as A/85:2011. A/85 specifies use of a long-term loudness meter based on the ITU BS.1770 algorithm for measuring the loudness of DTV broadcasts.
In December 2011, the FCC adopted rules implementing the CALM Act1, which, by law, forbids commercials from being louder than non-commercial program material. The new FCC rules incorporated ATSC A/85 (and, by implication, the BS.1770 meter) as an objective means of verifying that the rule was being obeyed.
Because loudness measurement per BS.1770 uniformly integrates all program material, quiet passages tend to lower the measured value. To prevent this, the ITU added gating to the BS.1770 standard, which was revised as BS.1770-2 in March 2011. The gating causes the meter to ignore silence and to integrate only program material whose loudness falls within a floating window extending from the loudest sounds within the specified integration period to sounds that are 10dB quieter than the loudest sounds. This is because humans tend to assess loudness based on the louder sounds in a given program. As of this writing, ATSC A/85 has not been updated to incorporate the BS.1770-2 standard.
The ATSC A/85 2011, ITU-R BS.1770-2 and EBU R 128 documents are available as free downloads and can easily be located with a search engine.
CBS loudness meter
For many years, Orban has used the Jones & Torick loudness controller and loudness measuring technology2 in its products for loudness control of sound for picture. Developed after 15 years of psychoacoustic research at CBS Laboratories, the CBS loudness controller accurately estimates the amount of perceived loudness in a given piece of program material. If the loudness exceeds a preset threshold, the controller automatically reduces it to that threshold. The CBS algorithm has proven its effectiveness by processing millions of hours of on-air programming and greatly reducing viewer complaints caused by loud commercials. Orban first licensed the CBS algorithm and began using it in products in the early 1980s.
Comparing meters
Because the ATSC recommends the BS.1770 algorithm, many broadcast and cable engineers facing the problem of controlling broadcast loudness have wondered how the CBS and BS.1770 technologies compare. An earlier version of an Orban white paper compared the CBS and BS.1770-1 (non-gated) meter. This presentation was revised in March 2012 to incorporate results from tests using the BS.1770-2 algorithm and EBU - TECH 3342 “Loudness Range” algorithm. The new measurements were performed using Version 2 of the Orban Loudness Meter3. This article compares the CBS and BS.1770-2 meters because it is expected that the ATSC will eventually update A/85 to specify BS.1770-2, which will more closely harmonize A/85 with its European counterpart, EBU R 128.
