The path to IBOC


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Now that CES is over and IBOC has made its splash as HD Radio, many new questions are being raised just as broadcasters begin to understand the answers to the existing questions.

I'll skip ahead and bypass the elements of creating the digital signal in a hybrid transmission mode. Radio magazine has already covered this in many ways, and we will continue to do so as new developments arise. Now that stations are beginning to install IBOC systems on their own, the focus changes from how to install it, to how to do what might come next.

Beyond the technical issues, several existing questions remain. Return on investment is the primary concern, which covers a broad scope. The simple formula weighs the costs of installation and operation of an IBOC system with the eventual benefits. Ibiquity touts the improved audio performance, a greater immunity to transmission interference and the potential to transmit additional data services as a source of revenue. Let's look at these points with an eye to the future.

One audio plus is that IBOC removes the audio pre-emphasis and de-emphasis in the transmission system, which improves high-frequency clarity. IBOC also offers a wider audio frequency bandwidth than existing analog services.

The main audio drawback is that the system uses a data compression algorithm to cram the bits into a comparatively narrow pipe. It won't be linear audio. While the codec being used (Lucent's Perceptual Audio Coder, or PAC) sounds good, it's not perfect. This is not a fault of the algorithm, it is the design of all perceptual encoding methods. One advantage is that consumers are growing accustomed to data-reduced audio sources.

Depending on your preference, the severe data reduction carries an extra benefit or added nuisance. Heavy data reduction does not work well with high levels of audio compression. Stations that heavily process may need to rethink their processing approach. I have looked into this as part of my pre-NAB planning and have found that Harris has been working on this behind closed doors and will discuss these plans at NAB2003.

In addition to the new approach to processing, there will be no more pushing the modulation limit. The digital limit has no red zone. Full-level digital is full level and no more.

At some point we will see the IBOC equivalent to the modulation monitor. For now, the stations that are on the air follow the “if you can hear it, the levels are OK” approach. In IBOC, carrier deviation will not buy loudness, but stations will need a way to monitor occupied spectrum, bit-error rates and encoder accuracy. The system has limitations, but we will want to get the most from what we have.

What about the data? This is an area of development in its infancy. While FM has been able to transmit data with RBDS, this never really caught on in the United States for several reasons. It was a solution looking for a problem that never really worked well with the broadcast model in North America at the time it was introduced.

Now we have a data pipe and a software-driven transmission method. As features are added, stations can load updated operating systems, audio encoding algorithms and data standards as they are developed. The difficulty in making these changes to an existing consumer receiver base ensures that the advances must be backward compatible.

The IBOC rollout will take some time. Because it is not mandatory for stations to make the conversion, those who oppose the system can choose not to implement it. For now it supports only one audio stream and limited data. There are no formal plans to do more, but this continues to be a work in progress. As acceptance grows, transmitter manufacturers and data-capacity developers will work with Ibiquity to continue the evolution.

We're currently watching the rollout of IBOC 1.0. As the technology evolves, later upgrades may quell the current shortcomings, real or imagined. It's possible that a future technology will take us on another course as well. For now, watch the stations that are making the move. Learn from their experiences and continue fine-tuning your own plan for the future.

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