Dolby Volume and Dolby Digital an Overall Loudness Solution

January 15, 2007

DOLBY VOLUME AND DOLBY DIGITAL AN OVERALL LOUDNESS SOLUTION

This week at the International Consumer Electronics Show in Las Vegas, Dolby Laboratories introduced a new consumer technology named Dolby® Volume. To explain how this relates to the AC-3 system used by broadcasters, Rocky Graham, Director, Broadcast Products at Dolby Laboratories, wrote the following article for TV TechCheck.

Dolby Volume is a unique technology that performs measurement, analysis, and control of television volume levels according to a psychoacoustic model based on the characteristics of human hearing. Dolby Volume complements Dolby Digital (AC-3), the standard audio system for DTV broadcasting in North America, in providing an overall solution for controlling loudness over a wide range of consumer media formats.

Dolby Digital contains a mechanism for controlling loudness through the digital broadcast chain by the use of audio metadata, and specifically the dialnorm parameter. Dolby Volume, on the other hand, addresses loudness variation issues for program sources other than Dolby Digital. These include analogue television, other audio formats used in some digital television systems, gaming, and additional consumer entertainment media. A consumer technology, Dolby Volume is not designed for use in professional audio equipment. It does not replace metadata but offers consumer electronics manufacturers an elegant solution to loudness control for audio sources other than Dolby Digital.

Some basic points about the operation of Dolby Digital metadata are worth mentioning, as they relate to the choices made by the broadcaster in an effort to control program loudness. First, the dialnorm parameter does not operate independently—it is part of a system of interrelated processes that combine to provide consistent loudness levels while maintaining the capability for reproducing the original program’s full dynamic range. The ability to deliver the full range is one of the great benefits that a digital transmission system offers, and preservation of that capability is important.

Additional metadata parameters known collectively as dynamic range control are sometimes used in Dolby Digital decoders to purposely constrain the dynamic range when desired by the consumer (late- night viewing, for example) or in situations where downmixing from 5.1 to stereo or mono is required. In order for dynamic range control to work as intended, the dialnorm parameter must be set to accurately represent the average dialogue level of the program. Otherwise, the typical dialogue in the program may be subject to extreme “protection limiting” in order to avoid overload. Broadcasters should understand that even Dolby Volume cannot undo the effects of improperly set dialnorm, and it should not be used as a way to avoid paying attention to metadata.

Another point to keep in mind is that anytime processing is applied to an audio signal there is a great benefit in monitoring the effects of that processing during the production process. Using metadata as the method for controlling loudness provides a means for this monitoring as emulation tools allow the audio mixer or production engineer to track the ultimate effects of the metadata as it will be applied during reproduction in the home.

As broadcasters are well aware, loudness issues are receiving a lot of attention lately. At Dolby, we learned years ago that there is no magic bullet for solving all the loudness problems in the home listening environment, and as the number of choices in home entertainment increases, the problem becomes more complex. With the capabilities built into the Dolby Digital system we have a method

TV TechCheck © 2007, NAB. TV TechCheck may not be reproduced or retransmitted without permission. for addressing the issue within the digital television environment. Hundreds of channels of programming are now on-air over terrestrial and cable transmission systems that have successfully implemented dialnorm and in the process have reduced viewer complaints dramatically. With Dolby Volume, we now also have an effective solution for the many other sources of entertainment that are available to the consumer today.

Information on Dolby products and systems is available at http://www.dolby.com./