Why is HD Radio such an unsuitable digital radio model? (especially in Brazil)

I have a post on my old blog, https://rnradio.blogspot.com/2008/12/sistema-de-rdio-digital-brasileiro.html, from December 2008, where I already anticipated the failure of Brazil’s decision to bet on the HD Radio system as a solution for radio digitalization in the country.

It’s now 2025, and in Brazil the topic "digital radio" hasn’t even been mentioned for years, as if there had been a tacit abandonment by the government, the regulatory agency, and the broadcasters themselves, especially those from São Paulo, who were the most enthusiastic and directly involved with the very expensive and technically controversial HD Radio.

Unlike other models adopted around the world, which rely on separate bands for digital and analog signals, HD Radio attempted to force both signals to coexist on the same frequency a fragile boundary between functionality and mutual interference. The result? The digital signal had to be heavily attenuated to avoid destroying the analog signal, which compromised coverage, quality, and reliability of the new system.

I understand that the attempt to coexist side by side with analog and digital transmission is not exclusive to HD Radio, but the difficulty that HD Radio brings to broadcasters has proven to be significantly more pronounced. Even the elimination of royalties leaves a mark of insecurity regarding various issues, including the fact that suppliers of equipment and software for the system may face some form of cost increase for their products due to the controls of the centralized system.

I will try to express myself beyond my own perceptions.

I've been reading about objective tests of signal robustness and even about the subjective perception of what it delivers — something quite complex to translate into judgment. That’s why I focus much more on its ability to overcome distances, barriers, and handle interference and effects like multipath. And at least from my perspective, HD Radio came out as the one that performed the worst.

Centralization can leave us indefinitely held hostage, no matter how tempting the concessions from the HD Radio controllers may seem fantastics at the moment. This is one of the key differences when compared to DRM, which presents itself as more like open-source and democratic.

I understand that digital radio, at its current stage, has not yet reached a scale that allows for significant price reductions. However, we must consider that for this to happen, simplification, cooperation, and a broad network of stakeholders involved in the ecosystem are key elements of a formula likely to succeed in bringing better prices and wider adoption in the future. It tends to function as a living organism, constantly evolving and improving, without relying on centralization.

My colleagues from São Paulo would say to me: “Hey, Ricardo, it’s amazing — you’re going to love it!” But I know very well what it means to set up a controlled environment, with the transmitter right next to you and everything carefully arranged to look perfect — when in the real world, those conditions would change with every step you take.

Why did digital TV succeed?

In digital TV, a well-established reality in Brazil, despite being much more expensive, we didn’t have this problem precisely because there was no attempt to overlap signals. You may recall analog channel 11 and notice that today there's still a digital channel 11. But in practice, the actual transmission frequency is completely different; only the “nickname” of the channel remained.

We need to implement a practical and functional digital radio! The difference in sound quality is striking. The complete absence of static and the clarity of the audio make for an extremely pleasant experience, a huge differentiator for traditional radio, especially in an age where streaming already offers ultra-high fidelity in car audio systems.

Below is a summary of what I envisioned back then:

December 2008 Blog Post

Title: Brazilian Digital Radio System

Link: https://rnradio.blogspot.com/2008/12/sistema-de-rdio-digital-brasileiro.html

The digital radio system I dreamed of!

Given the fog surrounding the HD Radio system — which the Minister himself acknowledged — I dared to propose ideas for a Brazilian digital radio system.

Let’s start by attacking some myths.

Assumption: Operation on the same frequency (IBOC)

The first correction I would make is to the fundamental guideline that the station should operate digitally on the same frequency as the analog signal.

Reason behind this directive: to maintain the station’s identity and audience.

Note: there’s fundamentally no such thing as operating on the exact same frequency in both analog and digital modes. What exists is digital broadcasting on sidebands very close to the analog frequency (IBOC is more of an “optical illusion” of frequency sharing). Many AM stations experience interference from their own digital signal to the analog one, as well as destruction of adjacent emissions from other broadcasters. As a result, stations are instructed to reduce the digital transmission power.

What I envisioned was a blend of what I had seen used worldwide — elements from the Japanese model, a bit of DAB, and even other lesser-known systems with no marketing lobby.

Alternative Proposal: Double Channel

(To make it marketable worldwide, I would call it “DOUBLE CHANNEL”)

I understand that maintaining operation on the same frequency is essential — but only for analog. As a solution, all stations would automatically be assigned a second frequency in another band — likely the only available one would be a few dozen UHF channels. Existing TV channels (if any) would be relocated up or down the band. This band would be exclusively reserved for digital broadcasting, with power levels equivalent to analog (i.e., without the necessary reductions currently required to coexist with analog during the hybrid period).

Note: Stations could offer different programming on the digital and analog channels (multicast, which was also praised by the minister). Analog broadcasts would not be allowed on the digital-designated band. I imagine the initial audience would be higher-income listeners, so there would be a need for differentiated programming to build a primary audience on the system.

Possible questions:

1 – Wouldn’t it be more expensive to have two transmitters in the DOUBLE CHANNEL model?A: The technical instability of co-located frequencies in IBOC means ongoing costs (specialized technicians, equipment made only by iBiquity-licensed manufacturers, etc.). It ends up being more expensive. Plus, iBiquity charges royalties for the entire operational lifespan (similar to the old DirecTV subscription model).

2 – Won’t listeners have trouble tuning in to the digital frequencies?

A: IBOC doesn’t solve that either, because to hear the digital transmission, the listener must buy a new IBOC-compatible device (in 2008, it cost about US$100). With DOUBLE CHANNEL, the new devices (and any digital system will require a device upgrade) would at least offer organized channel navigation in the digital band (e.g., Channel 01 = Universitária; Channel 02 = empty; Channel 03 = 89FM; Channel 04 = Rádio Cidade…). Analog bands would still be included for those who haven’t migrated or just want to enjoy a bit of “static nostalgia.”

3 – I’d rather not switch bands!

A: That might not be such an advantage. Since digital and analog signals in IBOC are crammed on adjacent frequencies, the digital signal has to be much weaker to avoid interfering with the analog. This results in areas where the digital signal is so weak it keeps switching back and forth with the analog one — a frustrating “time-travel” experience. Changing bands isn’t that hard — you already do it when switching between AM and FM.

4 – On different bands, can the digital signal use more power?

A: Bingo! Exactly. Since there's no risk of damaging the analog signal, full power can be used.

5 – Two bands for the same station (digital + analog)? Isn’t that a waste?

A: Dozens of UHF channels filled only with pink noise (off-air) — now that’s a waste!

6 – And what about maintenance?

A: IBOC presents an added risk: fixing a digital problem can cause a new analog issue and vice versa. Diagnosing problems is also harder. With two separate transmitters (analog + digital), managing the system is far easier.

Back in 2008, I wrote this text titled “Brazilian Digital Radio System, the digital radio system I dreamed of.” Based on technical, cultural, and market observations, I was already predicting that the hybrid HD Radio system was not suitable for Brazil. Now, in 2025, I can sadly (but unsurprisingly) confirm that it failed.

Brazil tried to push HD Radio as a viable digital radio solution, a foreign system, poorly adapted to Brazilian realities, based on the flimsy premise that analog and digital signals could operate “on the same frequency.” In practice, what we saw were interference, severe technical limitations, and, above all, a complete lack of public adoption.

The promises were ambitious: high-quality sound, multimedia features, new channels. What was delivered was an expensive, elitist system with very few receivers available on the market. Meanwhile, traditional radio kept going strong with good old FM, and ironically, real “digitalization” happened via the internet, through streaming, apps, and audio platforms.

In that 2008 article, I proposed an alternative: the “Double Channel” model. The idea was simple, keep analog as it is, but open a separate band (such as a portion of UHF) exclusively for digital radio. No forced coexistence of incompatible signals. Each mode in its own space, with technical and editorial freedom. Broadcasters could even offer different content for digital and analog, creating new audiences and formats.

Was it a utopia? Maybe. But it was a more plausible and honest utopia than what they tried to implement, a technically sound, commercially viable solution that respected the audience’s transition time. It didn’t require “technological miracles” or assume people were too dumb to tune in a digital station.

HD Radio transmissions were experimental and eventually abandoned. The dream of a national, efficient, and popular digital radio system remains unrealized.

If there’s a lesson here, it’s that technology can’t be imposed by decree, it needs real adoption. Radio, like culture, needs solutions that speak to local contexts, not ready-made packages pushed by lobby groups or temporary conveniences.

There’s still time to rethink it all. Brazil can still develop a digital radio system that is simple, robust, fair, and future-proof.

But for that to happen, we need to overcome the fear of changing frequencies. We’re in 2025, and look — the prediction from December 2008 came true. HD Radio didn’t take off, and we’ve made no real progress toward digital radio in Brazil.

The AM Band for DIGITAL RADIO

AM is just a frequency band, not a limit on sound quality. And yes, it is perfectly possible to run digital radio over the AM band. This presents a concrete opportunity to begin, in an organized and trauma-free way, the digital transition for stations currently on the AM dial.

Here’s my proposal: FM stations would continue their regular broadcasts, but they would also be granted a digital channel on the AM band. The digital signal's power would be proportional to the FM station's current power, though not identical, since AM and FM have very different technical behaviors, especially regarding range and signal propagation.

It would probably be necessary to use variable powerfull transmission during the day and reduced power at night, due to AM's extended reach after sunset, which could cause interference with analog stations in neighboring countries. A categorization model based on power and distance would be essential to avoid international conflicts.

Brazil could naturally lead this transition to AM digital, opening up a promising new market for domestic equipment manufacturing. It’s hard to imagine countries like Argentina, Uruguay, and others not following this path, especially after seeing its technical and commercial benefits.

This would only be the first step toward total digitalization. In the AM band, there’s an open highway, adopting a digital technology there could happen organically and gain momentum quickly.

Let’s stop insisting on the hybrid system

The hybrid HD Radio system never truly took off in Brazil — it became a “technological zombie”: present in some tests and speeches but absent from everyday life.

Key issues:

• Digital receivers remain expensive, rare, and with minimal adoption.

• Coexistence between digital and analog still causes interference and limits digital signal power.

• The Brazilian industry has shown resistance: with no clear business model and high costs, digital radio has never been a real priority.

• The attempt to keep everything on the “same frequency” was a mistake: the IBOC system still feels more like a sophisticated hack than an efficient solution.

• Government planning was poor: there was never a clear, consistent public policy with achievable goals.

Here’s an idea I have that I believe is practical for introducing digital radio in Brazil, I hereby name it “ Collateral DRM”

Collateral DRM: The right granted to a broadcaster to transmit on two different frequencies: one for digital transmission and the other for analog. In practical terms, in Brazil, with the AM band now practically vacant, all FM stations could use this AM band for their DRM transmissions — that is, digital broadcasts — and gradually guide listeners to experience the audio quality and features of the new system!! Is this case: A Collateral DRM FMtoAM

A simple, parallel, and more flexible model — like “Double Channel” — would have been more technically honest and easier for the public to grasp. Interestingly, something along these lines (using separate bands for pure digital) was even discussed in technical forums in recent years, but always stalled by the IBOC/iBiquity lobby.