January 19, 2007

Dolby Sounds Off

By Jim Barthold

While it is unclear how widespread the problem might be, the new generation of HDTVs with expanded Dolby Digital audio may not always sound as good as they look.

"Going from channel to channel ... some of these services may not be properly provisioning the dial norm parameter value in the bit stream which governs the reproduced loudness of the decoder," said Jeff Riedmiller, senior broadcast product manager for Dolby Laboratories. "We have developed tools and continue to develop tools for the broadcast and professional community to address that."

Simply put, sound is in the ear of the provider, and sound quality can fluctuate depending on what the broadcaster or programmer is pushing through. The pristine Dolby Digital audio that comes with high definition programming can be overwhelmed by the noncompressed analog sound coming from nonHD programs and advertisements, even on the same channel during the same program, if the programmer isn't careful. Thus, a consumer watching HD with Dolby Digital could, without warning, be audibly assaulted by a commercial or program break that slips back into more conventional, uncompressed audio.

"Some of this goes back to the broadcasters and the ability to set these parameters in the encoder," Riedmiller said. "The other piece is the set-top box. When you're switching between a Dolby Digital source and a nonDolby source, it comes out of that digital output on the set-top box."

From A to D

The analog is converted to digital, but it's not encoded in compressed Dolby Digital, so it doesn't match up with the higher quality, more heavily compressed digital audio. The result is a louder burst of sound when noncompressed audio slips through. Controlling this between channels is a nuisance, but doable; controlling it during programming breaks is more problematic and reminiscent of the early days of cable advertising when the message bearers shouted to get their points across.

Dolby is working on the problem from both sides – with programmers and providers like cable, telco and satellite operators using Dolby Digital and with end-user consumer devices using new Dolby Volume technology that the Labs introduced during the recent CES.

"Dolby Volume attacks the problem from another point of view and really is a way of providing the same kind of control for signals that don't include Dolby Digital," said Rocky Graham, director of broadcast products for Dolby Laboratories. "Dolby Volume is specifically designed for consumer implementations, so you'll find it initially in television sets and other kinds of consumer equipment."

Broadcasters, programmers, content and service providers already have access to Dolby Digital technology that "already contains this control mechanism so the broadcasters themselves and the content providers can control the loudness levels throughout the whole thing by adjusting the metadata parameters," said Graham.

The best way to fix the problem will be through education. While everyone seems concerned with picture quality – it is, after all, high definition television – audio demands the same attention to detail and the same amount of training to maintain quality levels.

Riedmiller said that the U.S. players need only look north for potential solution to the growing problem.

Canadian front

"All the cable MSOs in Canada, broadcasters and people in the post-production community, satellite turnaround and uplink facilities worked to actually go through and assess all the loudness discrepancies across all those services," he said. "We did some research for about a year-and-a-half and then wrote some procedures and documentation where we got the entire community up there – the entire industry, if you're a digital broadcast – to set these parameters more appropriately for your channel or service. That needs to happen here in the U.S., and we are trying to get some support ... to do this type of effort down here."

If something's not done and HDTVs continue to be connected to high-end audio systems, it's a pretty sure bet that cable, satellite and telco providers will get a nasty-sounding earful from their consumers.

- Jim Barthold