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David Moulton

At the Friday, January 18, 2013 meeting...
The CALM Act and its Effect on TV Audio Levels
With TV Technology audio columnist David Moulton, Moulton Labs

By Marty Feldman

Audio educator/columnist and CALM Act guru David Moulton was the featured speaker at the SMPTE New England Section's January meeting held at Emerson College's Bordy Theater in Boston. The topic was the recently implemented CALM Act and its effect on television audio levels. The Act is essentially the ATSC's A/85 audio standard codified into law and is designed to reduce variations in loudness between program material and commercials. It's ultimate effect will likely reach beyond this goal as it requires broadcasters to take a closer listen to their audio.

Moulton, a noted audio engineer, educator, acoustician and author has been studying the problem of disparate TV audio levels since 2003 as part of his work for TV Technology Magazine. He began by describing the history of the problem and how the industry's rather inconsistent self-regulation of audio levels eventually led to this law's adoption.

He described the methodology of his research and its conclusions.

Moulton discovered early on that there were not only level differences between programs and commercials, but also between one channel and another. In fact, he became convinced that this related issue might even be a more irritating one to the average viewer than the more often vociferously expressed dissatisfaction with the level differences between programs and commercials.

A 5dB difference in average audio level, Moulton believes, will motivate a viewer to reach for the volume control. When Moulton began his research in 2003, such level differences were disturbingly quite common.

Happily, the situation has slowly but dramatically improved over the years even without a law. His current measurements indicate that level differences are currently way below his 5 dB irritation level.

Compliance with the CALM Act, using sophisticated monitoring, level adjustment and logging equipment will presumably only facilitate this positive trend.

Moulton described various types of level adjustment, monitoring and logging equipment and how to go about the task of insuring proper operation and compliance. He discussed the importance and significance of setting 'dialnorm', a method of using metadata to actually normalize the gain of a viewer's set top box or HDTV tuner to keep their audio level within a predetermined average value and keep it there. It was stressed that the average 'target loudness' and 'dialnorm' should always be set to agree.

He also described how metering has changed over the years, the meaning of LKFS and how audio 'weighting' is designed to set audio levels based on the way we actually hear.

L=level, K= 'K weighting', based on the way humans hear at about 70dB SPL and FS=full scale. -24 LKFS has become a very typical dialnorm setting.

Meters designed for CALM Act (ATSC A/85) compliance follow the B.S.1770 standard. The latest 'rev' of which is B.S. 1770-3.

Moulton stated that VU metering is no longer valid. Those involved in program production would do well to employ a B.S. 1770 meter at least along with other meters they may be more familiar using such as peak reading meters.

Dealing with legacy receivers that do not recognize 'dialnorm' was discussed as well as how to ride gain on live broadcasts including the use of systems that use digital delay to 'look ahead'.

It was also pointed out that when 5.1 surround programs are transmitted, LFE information is not included in the measurement. This sometimes results in audience complaints, when high gain, low-frequency information such as drum beats are reproduced by often misadjusted sub woofers. This sometimes occurs, for example, during network football broadcasts when rousing, motivational music is often played during breaks in the action or when leading into or out of commercial messages.

SMPTE New England wishes to express its thanks to David Moulton for visiting with us to share his knowledge of this critical and timely topic.

We also wish to thank EMERSON COLLEGE for making the beautifully restored and exceptionally well-equipped Bordy Theater available to us for this meeting as well as to our own Paul Beck for coordinating the myriad behind-the-scenes details that are vital to the success of any meeting.

Martin P. Feldman, Chair, SMPTE New England.

Click here for writeups of other past meetings

Posted: 22 January 2013
Bob Lamm, SMPTE/New England Newsletter/Web Page Editor
robert.e.lamm@gmail.com