OPTIMOD-PC
OPERATION
3-73
Appendix A: Using the ITU BS.1770 and CBS Loud-
ness Meters to Measure Loudness Controller Per-
formance
[
Note:
This Appendix is a reprint of a stand-alone white paper. For this reason, it
contains some explanatory material regarding the CBS and BS.1770 meters that is
also found elsewhere in this manual.]
ITU-R BS.1770
In 2009, the ATSC released a 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 Act
, 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 mate-
rial, quiet passages tend to lower the measured value. To prevent this, the ITU add-
ed 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 mate-
rial whose loudness falls within a floating window extending from the loudest
sounds within the specified integration period to sounds that are 10 dB 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 up-
dated 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 technology
in its products for loudness control of sound for picture. De-
1
The CALM Act applies only to U.S. broadcasters and cable providers.
2
Jones, Bronwyn L.; Torick, Emil L., “A New Loudness Indicator for Use in Broadcast-
ing,” J. SMPTE September 1981, pp. 772-777.
Summary of Contents for Optimod-PC 1101
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