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.
