Chasing perfection

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Chasing perfection

Dec 1, 2003 12:00 PM, Chriss Scherer, editor

After the release of HDC as the audio codec for the Ibiquity IBOC system, I expected to see many positive comments about the progress on the digital radio transmission system. The performance of the HDC codec is substantially better than PAC, the algorithm previously used. But instead of spurring optimistic statements about IBOC coming of age, the news has had the opposite effect in some circles. The HDC demo CD, which I evaluated in Viewpoint in the October issue, provides several examples of the codec as well as the original source material and an analog broadcast example. In personal conversations as well as online debates in e-mail discussion groups, there are many dissenters as to the success of HDC and IBOC in general.

Overall, many feel that HDC provides an acceptable encoding quality for IBOC. It's not a perfect system � any perceptual audio encoder will have flaws � but a perceptual encoder is designed to offer a compromise between required bandwidth and perceived audio quality. The negative remarks state that the trade-off in audio quality is unacceptable. Some cited that even at the 96kb/s data rate (the highest data rate on the demo), the encoding artifacts were unacceptable. In my listening, I felt that there were some detectable artifacts, but without comparing the encoded version to the original, most listeners would be hard-pressed to detect these errors. Some in the discussion agreed.

In addition, some performed a subtractive mono sum (left minus right) on the mono material to evaluate the grunge and artifacts that appeared. While no listener would ever make this kind of a detailed analysis, it could be argued that some listeners will detect the added noise and artifacts in the encoded audio quality of HDC. My feeling is that this pool of audio-purist listeners also objects to the bandwidth limitations of the current AM analog system and the pre-emphasis of the FM analog system. You can't please all the people all the time.

The IBOC system locks the transmission to certain data rates, all of which are 96kb/s or less. As broadband connectivity increases in data rates (and popularity), these data rates will seem like stone knives and bearskins compared to newer technologies. A saving grace may be the continued improvement of the audio encoding algorithm used, assuming that it will be possible to upgrade receivers in the field as the technology develops.

In addition to the audio quality arguments, the discussions turned to the overall system performance of IBOC. The usual topic relating to the problems of AM IBOC at night is the most popular argument. Some want to see another option, such as that suggested by Leonard Kahn with Cam-D. Like I said in last's month's Viewpoint, so far Cam-D has been unproven, untested claims and rhetoric.

Other arguments include the reduction in digital coverage compared to the analog signal, the effect that IBOC will have on distance-listening (DXing) and the uncertainty about the theoretical data services. A paper at NAB2003 by Paul Signorelli of Impulse Radio and Dave Maxson of Broadcast Signal Lab recommended a baseline data standard to be established today so that the data services can begin that much sooner.

In the end, technology is a race that cannot be won. While we choose a system and lock in to its parameters today, the advances in technology will continue. An update path must be available to the broadcasters and the consumer receivers or the debate will arise again in another 10 years.

The common theme of the discussions is that IBOC is flawed and should not be accepted until it is perfect. Most of these comments are made in closed circles where the participants are the only ones who hear them. These mental exercises produce some interesting ideas, but unless they are shared with Ibiquity, the NRSC, the FCC, the station owners or any other group that can act on them, they are a wasted effort.

Don't debate the issue in a vacuum. Get the facts and speak your voice. If you don't like the path that IBOC is showing us, speak now or forever hold your peace.

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