New HD Radio Applications Seek to Fix System Flaws

There’ve been a couple of interesting developments out of the HD Radio trenches over the last few months. Both are touted as advanced “applications” for utilizing the HD Radio system — but in reality they’re band-aids that seek to fix fundamental flaws with the technology itself.
The first involves transmitter-manufacturer Nautel and its experiments with FM-HD multiplexing. This practice is inherent to the DAB/DAB+ radio systems adopted in Europe, Asia, and elsewhere: instead of every station having its own transmission infrastructure, stations send a stream to a multiplex transmitter where it’s combined with other stations and broadcast as a unifed signal. Instead of tuning to a particular frequency, DAB/DAB+ receivers look for the data-flags of the desired station and, once found, decode only that stream. In this configuration, DAB/DAB+ multiplexes can broadcast 10 or more channels of programming on a single unified digital radio signal.
Nautel is bringing the same concept to FM-HD as part of its “HD PowerBoost” system — this is basically a chipset and software onboard Nautel transmitters that allows them to more effectively combine the FM-HD signal with its analog host. According to Nautel, PowerBoost’s primary benefit is allowing stations to broadcast more robust digital signals with less electrical consumption.
Nautel says that multiplexing works by removing the analog FM signal from the IBOC waveform and replacing it with digital data. Doing so allows as many as three stations to be consolidated into a single transmitter to provide up to nine program streams using the current 400 KHz that an FM-HD signal occupies. If a transmitter’s spectral footprint is expanded to 600 KHz, the system can accommodate up to 15 streams, all encoded at a combination of bitrates ranging between 14-32 kilobits per second (kbps).
At present, this technology is experimental, both in the eyes of the industry and the FCC, and it is not cross-compatible with the all-digital configuration of the FM-HD system (which as not yet even been tested to any significant degree), although Nautel says it “can co-exist in-band with FM stations and iBiquity-defined all-digital service modes (when available).” It does not have plans to implement the technology until it receives adequate “feedback from broadcasters,” but it does plan to conduct on-air testing of the multiplexing application later this year. No word either on how much this application might add to the cost of a Nautel HD transmission system.
The implementation of FM-HD multiplexing would require some additional regulatory tweaks. In the analog regime, stations are allocated 200 KHz of spectrum on which to broadcast; this is surrounded by an emissions mask that was originally designed as guard-bands between stations to prevent interference from spurious emissions. Under the current configuration of FM-HD Radio, that emissions mask has been appropriated as additional spectrum on which the digital sidebands reside — effectively doubling the footprint of every HD-enabled FM station on the air. Although fattening stations’ signals opens up the potential for interference, this convolution was absolutely necessary for FM-HD to even exist.
Nautel’s multiplexing application proposes to fatten FM-HD signals even more — up to 600 KHz — and while it claims that this technology can coexist with analog FM and hybrid FM-HD signals, it’s hard to see how occupying three FM channels’ worth of spectrum with a single signal actually represents a more efficient use of that spectrum.
Furthermore, Nautel’s multiplexing application would reduce the bitrate available to each program stream in order to fit them into the transmission. Current FM-HD broadasts typically use anywhere from 24-64 kbps per channel, with the majority using between 24-48 kbps. Nautel’s plan requires stations to cap the availale bitrate per channel at what is effectively the low-end of current FM-HD configurations. I’m assuming that Nautel assumes digital audio codecs will become more efficient over time, allowing stations to provide higher-fidelity streams with less bandwidth. However, this is not guaranteed, and current FM-HD bandwidth allocations are designed to provide signals that (by and large) are comparable with analog FM quality. One of the criticisms of DAB/DAB+ is that multiplexes have chosen to maximize the number of channels available to the detriment of their audio quality, so adopting FM-HD multiplexing would make for a calculated risk.
The second new development in the HD Radio space is the creation of an audio processing box by Inovonics that purports to solve FM-HD Radio’s dreaded time-alignment issue. Under the current IBOC system, digital receivers work by first acquiring the main analog FM signal and then switching over to the HD signal when the receiver has buffered enough data. For this to work properly, both analog and digital signals must be properly aligned. But this isn’t an easy process — what often ends up happening is that as an HD receiver switches over from analog to digital, there’s a stuttering or skip in the audio.
According to Inovonics President/CEO Ben Barber, “Everyone is used to tuning in their radio and hearing music start playing. That’s great, and that still happens even with the presence of HD Radio, but the difference now is that a few seconds later they hear a stutter or a skip in the audio and wonder what just happened. Is my radio broken? If it’s a brand-new car and you just paid big bucks for it, this is not acceptable. If you pressed your foot on the accelerator pedal and the car “hiccupped” or “stuttered” a few seconds later, you bet you’d drive that car back to the dealer and demand that they fix it.
“This is exactly what happens when the FM and HD Radio time alignments are off. Car dealers are getting the brunt of the frustration and they don’t have the power to do anything. Worse than that, if someone tunes in station “A” and the problem happens because they are an HD Radio station with their time alignment off, and station “B” is a traditional FM station without HD Radio, station “B” sounds better because you don’t have the stutter or echo effect.
“The problem is exacerbated even worse if your listeners are in a fringe area and the radio is blending in and out of FM/HD Radio mode on a continual basis.”
Inovonics’ Justin 808 HD Delay Processor gets around this problem by doubling the delay of FM-HD signals (from eight to 16 seconds) and providing on-board monitoring of the analog and FM-HD signals. Providing an increasing blend-time as well as a feedback loop of what the two signals actually sound like on the air allows for better synchronization — so much so that skips and stutters all but disappear. Barber says you can thank “an amazing amount of math” for this accomplishment, which also allows for the volume levels of analog and digital signals to be properly harmonized.
So, for the factory-listed price of $3,400, FM-HD stations can virtually eliminate one of the technical problems that inhibit their listenability. Inovonics expects to go into full-production mode on the Justin 808 in late July.
It’s difficult to see these developments as great leaps forward in the HD space since one seeks to fix an inherent flaw in the system (Justin 808) while the other attempts to more efficiently utilize currently-available FM-HD spectrum, since there is virtually zero movement on the further development or eventual implementation of the all-digital FM-HD mode (multicasting). Both are the products of third-parties, not the system developer (iBiquity) and for broadcasters to take advantage of them they’d have to invest in particular brands of HD transmission and audio processing equipment.
This may give Nautel and Inovonics a leg up on competitors who don’t have these applications — but this is a far cry from an open innovation environment where system improvements are shared and ultimately benefit the platform as a whole, and both will require additional investment by broadcasters who seek to adopt HD technology.
Ultimately, these “innovations” are piecemeal and reactionary, and they signify fragmentary development activity regarding the HD Radio system. This is directly attributable to the closed paradigm that iBiquity has chosen to impose on the system itself. Will existing HD broadcasters be willing to shell out thousands (or tens of thousands) of additional dollars to enhance a transmission technology that already exists on the margins? As it has been for the entirety of HD Radio’s history, I guess it’ll be up to the marketplace to decide.