On Thursday the 22nd of March, 2007 the Federal Communications Commission approved all facets of digital broadcasting in the USA. In particular, AM stations will soon be authorized to begin 24/7 use of their first adjacent frequencies for digital sidebands.
What this does is open the door to significant interference to all AM stations. A 50kw clear channel station can run a digital transmitter at far more power than would be authorized for any conventional station in that location on those two adjacent frequencies. It will be interesting from a rather perverse sense to see what happens at night..
I have had two HD Radios, and found that the digital signals are very fragile, and cover about half the radius (1/4 the area) of a good analog signal. Electrical noise from many sources like car ignition, light dimmers and bad wiring can easily disrupt things.
The programming is the real draw to a station, and HD Radio on AM will provide no change at all. A talk show in digital "high quality" is still a talk show. In the 35+ years I've been a broadcast engineer, I have seen a small handful of complaints about audio quality. These have always been when there is some correctable flaw, like a hum. Quality is not the issue and never has been.
I saw an interesting comment. Name and location deleted to protect the writer:
"The latest e mail from xxxxxx in xxxxxx said that the reason the big boys in the big markets are so pro IBOC is because they like the hash as it wipes out distant signals getting into their market. There is no way to stop skip, but if the IBOC hash wipes the signal out, then the locals will have to listen to their local station. Kind of like legal jamming. Considering that, then even if the public does not buy the radios, keeping the IBOC signal might be worth their while."
Jamming is illegal in many ways. If some entity has manipulated this process to allow it, then appropriate action should be taken to shut it off.
One possible result is many smaller non-IBOC stations refusing to drop power at night in an attempt to keep their current coverage area. Or, installing bigger transmitters to outright cheat to keep the coverage radius they had pre-IBOC. That would make a very interesting case, should it ever go to court. Two wrongs don't make a right, but when one of the wrongs is legalized, all bets are off.
Shouldn't the digital sideband powers be calculated by the same rules as used for analog signals? Just plopping in a new signal on a frequency without any regard for it's interfering effects is a recipe for chaos. No new station could be allocated today without a full allocation study. Why are these new digital allocations exempt? In effect, they are really two new stations in themselves.
What if there are unequal powers allocated for the upper and lower sidebands? For technical reasons, IBOC requires the two sidebands to be of equal strength to minimize interference to the analog signal. Didn't they see all this in the formulation stage? Or did they simply decide to ignore the obvious and forge ahead, oblivious?
There are some stations that have directional arrays that may never be able to be compliant with the specs for IBOC transmission. As a result, they will not be able to run it. Is it fair that some can and some cannot be digital? If digital-only operations are mandated, will these stations be forced to go dark? Is that fair to their communities? It would seem that many small town stations cannot afford the license nor the technical upgrades. Again, if digital is mandated, do these small towns simply lose their station, even if it is the only one? That seems grossly unfair.
Customers are staying away from these radios. Market penetration is very much below the radar. They hope to sell two million HD Radios by the year 2010. That's about how many iPods sell in a month.
Many years ago WLW had a project for HiFi radio. They made sure their transmitting plant was flat out to +/- 20KHz. There were receivers in that time that were up to that task as well. I would dearly love to hear that setup today, and compare it to the HD signal.
Instead of inventing this intrusive technology, they could have spent their efforts on DSP-based receivers to minimize impulse noise and other interference. A good DSP decoder can null out a coherent tone such as a 10KHz heterodyne without a negative effect on the audio. It could also compare the upper and lower sidebands to determine what would give the better sound. It could narrow the bandwidth to the most efficient point for best reception. And, the DSP decoder could look over a wide swath of spectrum to detect wideband noise and remove it. The technology is there, but they chose to ignore it.
Heck, if they could get such a good analog signal decades ago, what happened? What if a station today decided to use the mask designed for IBOC and implement a wideband analog signal? Would it be legal? How would that sound compared to the HD version,. assuming a good wideband receiver could be found? What if it even sounds better than HD Radio?
One of the significant problems of AM these days is the shielding effects of newer steel and concrete building construction. AM simply doesn't penetrate. Why did they think that overlaying a digital signal on the same band would penetrate these buildings any better?
A better overall plan would have been to embrace streaming technology. WiFi access is exploding, and WiFi-enabled iPods will soon be introduced. An iPod can do many things and at less cost than most single-purpose HD Radios. Streaming audio can have much better quality than even the best HD signal. Instead of HD1 and HD2, it is possible to have unlimited streams. The formats that can be streamed by a station are limited only by their resources and imagination, not some technical limit of their transmission medium. Reception of a stream is possible anywhere there's an internet connection, not limited to the coverage radius of a single transmitter. It literally is global. Power costs to run a stream are insignificant compared to a transmitter. No large towers, or arrays of towers are needed. Streaming is far more "green" than IBOC, if you care to look from that perspective. In terms of quality, variety and environment, HD Radio is obsolete right out of the box.
From a business angle, having the FCC mandate a proprietary system is unprecedented. All previous systems for anything were all open source. The technology to create a piece of equipment was there, every parameter. With HD Radio, none of these parameters are public, at least not enough that some clever engineer could roll their own. This is very unfair, and smacks of a monopoly. The whole HD Radio specifications should have been in the public domain. Were someone to reverse engineer this method, no doubt they would be hauled before a judge and significantly fined. All because some company has convinced the federal government that it has the only way to do the job. The parallel would be if the government decided that to drive on the interstate you had to buy a new Buick.
Recently it was announced that there may be pay-to-listen encrypted HD broadcasts. Could this be why they want the system proprietary? So nobody can legally write a decoder to bypass their pay scheme?
In conclusion, I'll relate a conversation I had with someone who has an extensive non-technical radio background. A local Clear Channel GM gave this person an HD Radio. It was tried, and shut off. Decoding the signal was very problematic even within the city grade contour of several stations. This person related to me that HD Radio was a bad joke and a complete waste of time. This was said without me even bringing up the subject. It seems to be a common "joe average" result when a non-radio person tries HD Radio. Too much effort to get a signal. They want to turn it on and get flawless audio, just like their iPod. It doesn't happen, so they simply return the radio for a refund saying it "doesn't work".
Well, I have had a fair bit of feedback on this article. Here are some samples.
* I agree 100% on this. The noise is horrible.
Reply: Unless everything is exactly right, that noise also intrudes onto the analog audio. Background hiss.
* Are you some sort of Luddite? Do you want radio to die? I cannot believe you would attack radio when it is only tryeing (sic) to survive.
Reply: No, not a Luddite, at least not in most things. My objection is entirely from them trying to force signals onto an inappropriate band. The AM band is completely wrong for digital signals when overlaid onto the existing analog content. There is insufficient station assigned bandwidth to do it right. There is way too much noise from too many sources. The night propagation absolutely insures that interference from other stations will be a problem. This band does not get into modern concrete and steel buildings. Many of the existing facilities may never be able to be engineered for sufficient bandwidth for the digital carriers. Finally, going all digital will make a half billion (with a B) radios useless. This should have been in another frequency band. Period.
* Have you ever listened to HD Radio? Don't you think it is worth the cost?
Reply: Yes, I have indeed listened extensively. I have bought two different radios out of my own pocket to check it out. The primary content on AM is voice. The current analog receivers do sound muddy and sometimes distorted. However, I do clearly remember the great sounding radios such as Zenith and others built. I adapted a Belar RF amplifier once with a great linear detector on the output. It sounded amazing! As do most of the modulation monitors used. I would put the analog audio from one of those against the AM HD audio any day. Dymek-McKay also built some excellent HiFi type radios. Given the relatively low digital audio rate of AM HD Radio, I think these analog examples might even sound better. So, what's the advantage? Being able to see Artist/Title info? Hardly worth it. In fact, I bet I could figure a frequency shift keying method for existing analog stations to add the Artist/Title and associated info.
* You will never work for my company.
Reply: Probably not. If your company cannot accept a critical view, then I would not want to work there anyhow. I have stated on several occasions that my personal views in no way affect my work performance. If someone wanted to pay me to put AM HD Radio on, I would do my best to make it happen. So far only one of my clients has any interest in HD. And the timeline for that is at least a year away.