NPR’s Bold Move to Add Secondary Audio Might Drive Consumer Demand for HD Radio Receivers
As you’ve read in this column and elsewhere, there is considerable concern that the audio quality increase of HD Radio alone will not be sufficient to generate mainstream acceptance of the new format, and that the technology may languish as a result. This would lay waste to the considerable investment made by broadcasters, not to mention the R&D efforts of Ibiquity and others in designing the IBOC systems.
Nevertheless, hope may not be lost, thanks to a new initiative of public broadcasters and equipment manufacturers.
Despite the Ibiquity design that requires a broadcaster’s IBOC digital audio service to be a simulcast of its analog audio program, and the FCC’s initial rulemaking that mandates this approach, National Public Radio has launched its Tomorrow Radio project (see Feb. 12, page 6), which would place secondary audio services in the auxiliary data portion of the IBOC signal.
The concept would reduce the bit rate of the FM-IBOC main digital audio channel from 96 kilobits per second to 64 kbps, and assign 32 to 36 kbps of the IBOC datacasting bandwidth to a second compressed digital audio stream. At that bit rate, the second audio channel would be of limited quality, but it could serve well for a mono voice service, quite suitable for much of the programming that public radio stations often provide.
(Note also that the concept affects only the FM-IBOC service, again addressing the specifics of the public radio environment, where most stations are FM.)
This arrangement would allow each public radio FM station to provide a digital simulcast of its analog service, along with another lower fidelity channel for a second service.
Implementing this at the station would not be too difficult from a technical perspective, requiring fairly straightforward modifications to IBOC encoder and exciter designs, or perhaps even a simple sidecar extension to first-generation devices in the field.
The real challenge to this model arises on the receive end, where substantial design changes might be required to feed auxiliary data into the PAC audio decoder – originally intended to be fed only by the main digital audio channel’s bitstream. (Alternatively, a separate codec could be dedicated to the second audio service, using a different algorithm optimized for the lower bit rate audio envisioned in the Tomorrow Radio design.)
Also, some method of switching between primary and secondary digital audio services would be required in the receiver. IBOC radio manufacturers already plan the inclusion of soft keys on a front-panel display screen, so one of these buttons could be programmed to serve such a switching function when a second audio signal is detected.
Project plans
NPR has launched the Tomorrow Radio project with the expectation that it will run for five to seven years. Initial partners Harris Broadcast, Kenwood and KKJZ(FM) in Long Beach, Calif., may be joined by others soon. Several manufacturers have already expressed interest in doing so.
Current plans call for development of an experimental dual-service broadcast over KKJZ using Harris exciters and Kenwood receivers. A Texas Instruments chipset involved in the receiver prototype should be completed in the summer, and the on-air testing is expected to commence in the fall.
The primary goal of the initial test is to prove the feasibility of the concept, particularly with respect to the robustness of a second audio service that has no analog backup. The goal is to show that at least within the primary coverage zone of a station (down to ~40dBu) that a low-bit rate, digital-only second audio service can be reliably received on a mobile platform, while retaining acceptable quality in a slightly reduced bit rate for the primary digital audio (analog simulcast) signal.
The concept calls for an HD Radio receiver to default back to the primary digital signal should the secondary audio signal become unusable, perhaps with the insertion of an aural and/or graphical message that the secondary signal had been lost.
If the initial tests are successful, subsequent rounds will refine the design, and second-generation IBOC receivers with secondary audio channel capability could be available by late 2004.
Driving Miss HD
Although this service was not included in the initial design of HD Radio, and a simulcast-only model for digital conversion was supported by commercial broadcasters, public radio’s needs are divergent. For the latter group, a quantitative expansion is important, given the large availability of (and listener demand for) non-commercial content, and the limited shelf space in which to broadcast it.
Mike Starling, NPR’s vice president of engineering and Tomorrow Radio project leader, stresses that this second service is not a true doubling of the spectrum, but would allow any broadcaster that wished to include some additional content in its signal, on a full- or part-time basis, to do so flexibly.
While this effort has had to originate from the outside and as a second-generation add-on, Starling states that, “Ibiquity has assured its support for the Tomorrow Radio project.” In fact, he feels the industry at large is supportive.
“I’m pretty gratified at the response from manufacturers,” he said, adding, “No one has stood in the way of this, and in fact some manufacturers have cleared a lot of roadblocks to allow us to pursue this activity.”
Starling believes that secondary-audio capable IBOC receivers could eventually become the de facto standard, likening them to FM stereo receivers, which ultimately far outsold the mono designs of the original standard, even though the additional capability was optional.
Starling also expects that the FCC rulemaking on digital radio will be an iterative process, and he points out that several commissioners already have expressed interest in their initial rulemaking that such future service expansions might be offered.
“We’re cautiously optimistic at this point,” Starling said, and thinks that at some appropriate point the Tomorrow Radio project may result in a contribution to the rulemaking that adds secondary audio service as a standardized feature of U.S. digital radio.
Certainly this project faces an uphill climb, and its success will only come with considerable sales of currently hypothetical second-generation IBOC receivers. Yet the economics of public radio – where content for such second services already exists (some public stations currently provide this content on an AM sister station), and considerable revenue comes directly from satisfied listeners – might allow for the successful evolution of, and a comfortable transition to such technology in ways that a commercial environment might not.
Ultimately, the entirety of IBOC technology might benefit through accelerated acceptance, and once established, some commercial broadcasters could eventually choose to incorporate the technology, as well.
It’s too bad this capability wasn’t in the initial design of HD Radio, and ironic that non-commercial interests may come to the rescue of the American radio industry’s digital future. We’ll keep an ear turned to Tomorrow Radio, so stay tuned for updates on the project’s progress in future columns.
