HD Radio

My Tests

By Neil H. Schubert

The Test Setup:

I used a Sanyo ECD-HD1990M Car stereo reciever for these tests. I chose Sanyo, because of their history of making good analog radio receivers with excellent selectivity and sensitivity. See my “The Best Radios” for more information.

The antenna in all of these tests was placed on the top of a chevy Astro van, on the “CB MOUNT” flat spot, towards the rear of vehicle, and a braided and foil shield, high quality cable was run through the vehicle away from internal wiring to a PL259 “UHF” plug, where it was then screwed into a motorola plug adaptor and plugged into the radio.

This is the best example of what could happen if analog FM were ever dropped, and listeners were forced to go to digital. This recording begins while driving down Hwy 41 Near Lomira. In this case, the radio was set to play only digital, either because of a glitch, or because blending was disabled by the source. Note that the background squeal is from a ground loop that picked up my vehicle's alternator, and not a signal problem.

Thought you were irritated by static?

Which one is HD?

The one that is HD has less mid and more bass. The reason why this happens is because there is a mismatch between the emphasis at the transmitter and de-emphasis in the radio. The discrepency is most likely at the trasmitter end, you may notice a little “fuzz” sound, which is not caused by the signal itself, but by a high frequency rectifier (or digital emulation) in the audio processor.

The Mighty 92 like you never heard it before. HD goes away at sundown, however. At first, I was pretty impressed by the audio. Then, I turned it up a little bit, and it reminded me of XM radio. The audio has much work to be done yet! The audio sounds like an over-tensioned cartridge tape – kinda like windows media combined with mpeg 1 layer 2 at 128k. This format would work fine for Mono, but the stereo image is so distorted and broken up, it might as well be mono. It has the little “aliens” running in the background! C-Quam AM Stereo did not have this. As far as I'm concerned, this is “smoke and mirrors” to disguise the fact that the audio compression is not able to render stereo.

My First Listen to Music Via Digital on AM

The Stereo Image of the above recording – L+R reduced 85%

The L-R and L+R

After hearing this, I was quite digusted with the FCC. The audio on the analog portion of the broadcast lacked any high end. The “digital” audio is completely artifical- it lacks integrity, and is not at all faithful to the artist's work. Based on these tests, the audio has a Total Harmonic Distortion that is worse than a 45RPM record played 1000 times. And, based on the fcc rules of the previous 50 years of stereo sound on AM and FM, which state that “the stereo subcarrier must be in phase with the primary program channel”, I believe that iBiquity digital is violating FCC rules. C-Quam did not have this problem, and their THD was only about 5% with bad reception being a factor.

I personally think that radio listeners, and the artists and musicians being broadcast on these stations, should take legal action against the AM stations broadcasting iBiquity “HD Radio”, but more importantly, the FCC itself, for mandating this technology, as well as iBiquity Digital, itself. I believe that iBiquity Digital has greatly decieved consumers into thinking that HD Radio on AM is actually FM radio quality.

Ibiquity Digital's transport system (the actual transmission itself) will not function properly unless the bandwidth of the analog portion is limited to 8Khz. Therefore, when the radio switches to digital, OF COURSE IT WILL SOUND BETTER! I equate this deception to a stereo salesman that wants to sell the high-end model for more money. To make it sound better, simply turn the treble knob down on the other models, while re-aligning the marker so that it looks like it is at zero. When the buyer goes to listen to the different models, the more expensive one WILL sound better, even though in reality, they all probably sound pretty close to each other.

What is even worse is the fact that if you are like the many of us that have AM radios that have a 12Khz or higher receive bandwidth, the background eggs frying begins at sunrise, and finally ends at sunset. Again, OF COURSE DIGITAL HAS LESS NOISE – DIGITAL IS MAKING THE NOISE!

This recording is 79 minutes long. I started recording when leaving the parking lot (or what used to be the parking lot!) of Bayshore Mall in Glendale, and headed north. I have traveled this road since it became a freeway, when I was a baby. When I was much younger, my parents had a Pioneer “SuperTuner” stereo (digital, but the old two knob type), which was dealer-installed in our 1985 custom astro van. This radio could pick up WKTI “clear” to just short of Manitowoc, where blend would kick in to stage three, and the stereo symbol would finally flash. WKTI would finally fade just north of Manitowoc. This coverage has always been consistent, although the range is sometimes extended to just south of green bay on a good day. I have heard WKTI in northern wisconsin, as far as Crivitz, although the reception is not consistent on a day to day basis. Anyway, on most car radios I have tested recently, WKTI cuts out just north of Manitowoc. This pattern has been consistent for almost as long as I can remember.

Did HD Radio make the reception any better? NO, not at all! Digital came in fine, until I got to Sheboygan. From Milwaukee to Sheboygan is where WKTI is always pretty strong and has very little noise and audible interference, on analog. When you get just past the observatory telescope in Sheboygan, the signal gets choppy. Digital got jittery and then just dropped to analog. For a short period of time, the analog signal faded completely, also. The explanation is actually a design flaw in the radio itself. When I get near another FM broadcast tower, the radio looses AGC gain. The flaw is that the AGC is determined before the signal passes all three IF filter stages – the radio gains down because it is picking up overload from another frequency. The first time I found this type of problem was with DELCO GM radios made between 1991 and 1993. The same exact design in previous models had two extra IF filter coils on the the IC that determined the AGC voltage. When these two models were connected side by side, the one without the extra coils had more signal problems. Sanyo may have this problem also. The other issue may be the use of semiconductor packages that are too small for RF signals. I have found that RF leaks across the pins of those tiny 40 pin surface mount chips, causing all sorts of issues.

The big problem, is that when the analog signal came back....The digital did not....and there was blending and static. The analog signal got better, but the digital did not come back. It gradually got noisy until I got just north of Manitowoc. Then it got unlistenable, and I finally ended the experiment. So I guess my question is.....WHAT's THE POINT? There is usually no static or noise between Milwaukee and Sheboygan, anyway. Maybe one or to spots where there is a little fuzz, but not enough to change the channel. When the noise does happen, the digital goes away, and you hear...THE NOISE and STATIC. I would be much more willing to embrace this technology if it actually improved the sound and the length of time that I could listen to the signal. It does not do this, it is a concept like Dolby FM – it only improves the sound if the signal is not noisy already. Heck, even Dolby FM probably did more for reducing noise than iBiquity.

Digital does not have the coverage that conventional FM has. Because the broadcasts are the same over-compressed, over-processed audio that is fed to the analog, the digital isn't any better. I personally think that the solution is to iprove the sound quality of the Analog, not try to add a medium that is incompatible, and argueably, not better than what already exists.

NOTE: The impulse-like static and the “tunnel effect” are from a tip-ring-sleeve connector that I was using to toggle between analog and digital. I was unaware that this was affecting the recording, but found out later on. This does not affect the experiment, and it should not be implied that this noise was from the analog or the digital. The jitter and “doubling” was from the digital. Digital goes away at about 49 minutes into the recording.

I will try to make a better recording in the future. This should give you the idea.