03.09.2013 07:36 AM
Harris Broadcast experts discuss CALM Act, tools to modulate audio

Several factors have contributed to the increased attention that the issue of loudness is getting in the broadcast industry.

The CALM Act, for sure, has been a catalyst, but the proliferation of home theater systems capable of delivering a wide dynamic range is another key element. Over the course of the next several months, we hope to discuss the evolution of audio standards with representatives from a number of companies who manufacture audio equipment used in the broadcast production stream.

This time, we’re getting input from three members of the Harris Broadcast team. Paul Keller holds the title of Product Manager For Test and Measurement, and Randy Conrod is Product Manager For Digital Products.  Though retired, Jay Adrick has been retained by Harris to serve part time as a Technology Advisor.

Broadcast Engineering: The ATSC standard includes a component that deals with audio loudness.  Can you explain how A/85 came into existence?

Jay Adrick: “When Congress embarked on the Calm Act, rather than redefine loudness, they picked A/85 as the reference point. We thought that was unusual; to the best of our knowledge it was the first time that a standard created by an outside body was selected as the basis for legislation. A/85 deals with the variations of audio over time.”

BE: For traditionalists — I may be dating myself here — compression immediately comes to mind when the process of reducing the peaks and valleys in an audio path is considered. What part does compression play in today’s technologies?

Randy Conrod: “Compression is one technology that can be used to remediate loudness problems. Traditionally, compression has been used make audio as loud as possible without going into modulation.

“It’s important to understand that the measurement of loudness is not purely scientific.  Every human being hears differently. Through experimentation and listening tests, the industry landed on a method of measuring loudness that gives us a common tool to apply when dealing with the problem of avoiding fluctuations in volume. ITU.BS.1770 is a recommendation that we use to deal with this issue. Interestingly, people tend to agree on the loudness (or softness) of dialog, but there’s less agreement regarding music and sound effects. Again, the individual’s perception is a factor that manufacturers and engineers have to keep in mind.”

BE: So, we now have new legal requirements that mandate relatively consistent audio levels, and a new generation of tools being developed to help engineers in the field and in post production comply with them. 

What happened to the trusty old VU meter?

RC: “VU meters don’t measure loudness. They measure voltage, which isn’t equivalent.  Two audio streams may look the same on a VU meter, but will they can sound different with regard to loudness, which again, is based on perception, not power or voltage.

“While participating in an industry panel session, I heard a good analogy. The analogy is between the speedometer on your car and the tools that help you measure loudness.  Speedometers tell you how fast you’re going. The new loudness meters tell you how loud your signal is.”

BE: Wait a minute-a well tuned speedometer gives a reading that is absolute and accurate. Haven’t you been saying that loudness is, in part, a reflection of the individual’s perception of audio?

RC: “Very good! You’re right. The analogy is imperfect, but it’s still helpful, I think. The ITU.BS.1770 recommendation isn’t the only one; there are other models, but they’re harder to implement, and more expensive. The tools that have been developed to work with ITU.BS.1770 are being mass adopted worldwide. Audio engineers who use them can be confident that the product they turn out will be in compliance with the demands of the CALM Act.”

BE: What products does Harris have that specifically deal with the issues you’ve discussed today?

RC: “We incorporate DTS Neural Loudness Control processing across our video and audio processing product lines."  

Paul Keller: "We have three products for loudness measurement: the CMN-LA is geared for production. It displays loudness, metering, and has two different types of loudness monitoring, an oscilloscope and a spectrum display. This device is meant to be used in production.

PK: “The LLM-1770 is our loudness logger and monitor.  It’s a small box with numeric displays that maintains logs of loudness.  We also offer loudness measurement as an option for our TVM and VTM video series.”



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