If Bob Vaillancourt, Engineering Manager for local NBCU O&O KNSD has anything to say about it, San Diego’s TV audio is about to improve. In spite of great new pictures with high definition broadcast TV, one of the lingering complaints about the technology is the audio. It’s all over the place. Compressed commercials can blow out the audience after a soft dramatic scene. Local material doesn’t always match network material in an automated master control. And different local stations can have very different levels as viewers surf through channels.
Bob said he had recently spoken with NBCU’s Advanced Technology guru, Jim Starzynski, who laid out a plan to address loudness using the Dolby dialnorm setting that is a part of the Advanced Television Systems (ATSC) standard. That plan starts with each of the ten network owned and operated stations, but he said it needs to spread to the other digital stations in each market, and ultimately to all ATSC stations.
Dolby dialnorm is part of the specification written into ATSC that helps normalize audio levels based on metadata that rides along with the audio. Normalization, unlike compression or limiting, doesn’t change the dynamic range—only the level of audio. Researchers learned that people who watch TV like to set their volume levels based on dialog instead of music or background. Dialog normalization, or dialnorm, attempts to automatically adjust dialog levels based on the standard of the source. Without dialnorm, Dolby interprets the dialog amplitude as being averaged around -31 dBFS. With a Fox dialnorm setting of -25, they are commanding the end viewer’s Dolby decoder to release its audio to the amplifier with a 6 dB attenuation. With a local setting of -23, the decoder attenuates the local material 8 dB.
How do you derive those settings? That’s where Bob comes in. NBCU bought for KNSD a Dolby LM-100 Loudness Meter that specifically reads loudness with respect to digital full scale only during dialog. Bob sampled all the San Diego area English language DTV stations over a two-week period in early July. He took readings during primetime, fringe, daytime, and even overnight. He put the readings into a large spreadsheet to share with local broadcasters.
The results are interesting. First, all the stations in the market except KNSD and KPBS had their dialnorm settings on their Dolby encoders at the Tandberg default of -27. KPBS had theirs at -31–the setting that signals Dolby decoders not to normalize levels. Bob had set KNSD’s dialnorm at -22 to begin with, then adjusted it during the week to -23. He recommends XETV FOX6 set its dialnorm to -23 based on an average of 43 loudness readings ranging from -20 to -29. Readings at KPBS swung the most, as you might expect of a public station with widely varying content and no dialnorm action. Readings at KUSI were the most consistent, as you might expect of an independent station heavy with news and talk content.
XETV has adjusted its dialnorm to -25 based on a recommendation from Fox Network, though we intend to adjust that figure after analyzing it more. Jim DeFilippis, Fox VP of Engineering, said that they will be working with affiliate stations and the other networks to implement dialnorm. FOX6 will soon be applying normalization to all local recorded content.
Bob says that they now have the Dolby Loudness Meter at their ingest station where operators use it to help them set levels. He is looking forward to working with all local engineering crews to get their dialnorm settings programmed. Once this is done, viewers should hear more consistent loudness when switching between stations as well as when the stations switch between local and network content.
You can learn more about dialnorm in this Broadcast Engineering magazine article.
