Where is the beef? Not on AM HD Radio.
One of the supposed advantages of HD Radio is improved fidelity over analog. As I observed in my listening test of HD on FM, there’s almost no real improvement for HD over the analog signal. The advantage for HD on FM, then, is the addition of one or two more channels of audio. However, due to the more limited sonics of analog AM radio, we are led to expect HD AM stations to offer significantly better fidelity; they don’t offer any additional channels.
But compared to FM, there are much fewer HD stations on AM. This is largely due to the fact that the AM band is seriously congested, with quite a bit of interference. Adding an HD Radio IBOC side-channel to a station greatly increases the potential for interference to adjoining analog stations. A secondary reason is that the AM band is dominated by talk radio formats where fidelity improvement is less important.
In Chicago iBiquity (owner of HD Radio technology) says there are seven HD stations on AM. Over the course of several days throughout the last few weeks I was only able to tune in the HD signal for three of these stations, WSCR, WBBM and WGRB. My Sony receiver detected an HD signal on two–WRDZ and WVON–but could not tune it in. The receiver detected no HD signal for two stations, WMVP and WRTO.
Two of the three stations with an HD signal I could receive are primarily talk stations, WSCR and WBBM. The HD signals of both had a modestly extended frequency range than the analog signal, but with clearly audible digital artifacting on the high end, similar to a medium bitrate MP3 (say about 96 kbps stereo or 48 kbps mono). However, wider frequency range is of negligible use for talk programming. For these stations the primary benefit of HD is the loss of background noise and interference, which can be distracting even on a strong AM signal.
One HD signal, WGRB, features both talk and gospel music programming. Depending on the source–some programs are recorded live in churches–there is a perceptible improvement in fidelity with music due to the extended frequency response. However, the high end artifacting and distortion due to the low bitrate is sometimes too distracting to my ear, leading me to prefer the analog signal, even if the compromise is less high end.
On the whole the only real benefit I can see for HD Radio on AM is the significant reduction in background noise. On FM this is a limited benefit, since background analog background noise is already very low by comparison. But on AM it’s quite noticeable and losing it is mostly welcome. At the same time, I can’t say it’s worth the trouble.
Of the three HD stations I could receive, the only one I’m likely to listen to regularly is news/talk WBBM, where I also heard the least sonic improvement. I chalk this up to the likelihood that the station’s airchain has been optimized for AM. Because the HD signal is broadcast as a lower power level than the analog, I have to work, moving the antenna around, to tune in the HD signal. When I’m not specifically trying to test HD reception, it’s unlikely I’d bother with the effort to get the HD signal.
Much more so than with FM, I consider HD Radio on AM to be mostly useless and not worth the effort. It’s especially not worth the loud digital hash noise I receive on my analog-only radios on the frequencies adjacent to the HD stations. It’s like a line of digital litter strewn across the AM radio highway.
After the jump are my technical details and listening notes for each station.
I did my AM listening test with a Sony XDRF1HD receiver connected to a Terk Advantage tunable AM loop antenna. For every station I attempted to optimize reception both by tuning the antenna for the corresponding frequency and rotating it. I placed the antenna in an open window and connected it to the receiver’s AM antenna terminals.
While I’m willing to work a little to optimize reception, I’m not really willing to go to great lengths for the purpose of the test. I’m looking at HD Radio not from the standpoint of an average radio listener, who I believe is generally not willing to work too hard to receive an HD signal.
These are the HD stations in Chicago according to iBiquity, and my listening notes:
670 WSCR – Sports/Talk – improved fidelity, with less compression than analog signal.
780 WBBM – News/Talk – modestly improved fidelity, still very compressed with strongly audible digital artifacting.
1000 WMVP – Sports/Talk – No HD signal detected.
1200 WRTO – Spanish Talk – No HD signal detected.
1300 WRDZ – Radio Disney – HD signal detected, but would not tune in.
1390 WGRB – Gospel – modestly improved fidelity, depending on source material.
1690 WVON – Talk – HD signal detected, but would not tune in.
What’s the point in HD Radio, in any case? If more channels were wanted, then FMeXtra could have been used, along with AM Stereo. A good site to check the situation for AM-HD stations (not always up to date) is:
http://topazdesigns.com/iboc/station-list.html
I don’t know why it constantly needs to be pointed out that IBOC was originally designed to cause severe adjacent-channel interference on both AM and FM, in order to destroy the smaller, community radio stations, and to “localize” the coverage of remaining HD Radio stations. IBOC destroys our ability to receive weaker, more distant radio stations.
@Greg, thanks for the pointer to the station list. It indicates that 1000 AM WMVP and 1200 WRTO are both no longer broadcasting in HD. So that means there are only five AM stations in Chicago broadcasting HD.
My point in doing this review is to judge the merits of HD on its face, from the eyes (ears?) of an average listener who is not aware of the technical or political problems of the technology. So far, it is failing on that count, which therefore offers little to redeem it’s other problems.
The Swiss just abandoned HD Radio:
http://www.microsofttranslator.com/bv.aspx?ref=Internal&from=&to=en&a=http%3a%2f%2fwww.infosat.de%2fMeldungen%2f%3fmsgID%3d59896
Does anyone know why FM HD2/3′s broadcast at 10% of the
HD1 and Analog?
@Joe, what do you mean by 10%?
If you mean power, then, yes, the digital signal broadcasts at 10% of the analog signal power because at higher levels the digital signal can interfere with adjoining stations. But this 10% applies to the HD1 signal as much as 2 and 3.
I can be in the parking lot of our church at night and see the tower 24 miles away that has an FM transmitting antenna at the top emitting 110,000 watts (analog). I have trouble receiving a consistent HD2 signal.
I can consistently hold the HD1 signal and other HD1′s on the 3 neighboring towers with 100,000 analog watts but it’s only the HD2′s that I have the problem receiving.
@Joe, I can’t speak to your problem with HD2/3, but it isn’t due to power differences. The digital signal contains all HD channels and therefore they’re all at the same power level; HD2 and 3 are at the same power as HD1. This sounds like an antenna or equipment issue, but I can’t say for sure.
Most stations are still operating at 1/100th the power of their analog signal; many stations are still evaluating the overhead cost of an upgrade. So, Joe, in your case a 100 kilowatt station is, most realistically, only pushing out 1,000 watts in HD.
Check to see if your radio flips back and forth from digital to blend-to-analog mode. Given the fidelity characteristics, you may not even be aware this is happening.
When in hell is FCC going to kill analog radio, this is FCC problem is causing on all of us. Digital AM is useless until they kill analog. This so called ‘hybrid’ radio is not working, screw it, either kill digital radio or kill analog radio, make up your damn mind up FCC.
Forget about it working well while driving. The AM IBOC flips back and forth between the analog AM and the HD channel. In Los Angeles, KNX 1070 is simulcast on 94.7 HD3. Radio sometimes takes forever to link. When direct selecting the channel it holds it own for awhile and will drop out when driving thru a freeway underpass or tunnel or is clipped by a mountaintop.
It sounds great, but I’ll live fine with my satellite radio.