[BC] IBOC AM Quality

[Robert Orban]

At 04:22 PM 3/23/2007, Rich Wood wrote:
>------ At 04:52 PM 3/23/2007, Robert Orban wrote: -------
>
>>If you use exactly the same processing on the HD and FM analog channels 
>>and modulate each one to its permitted peak level, the HD will be 5 dB 
>>louder when the receiver crossfades. THAT would drive the listener nuts. 
>>Instead, you use 5 dB less limiting on the digital channel, the receiver 
>>fades smoothly from analog to digital, and the digital sounds much less 
>>grungy if the analog FM is heavily procesed.
>>
>>I keep explaining this but it doesn't seem to have sunk in :-(
>
>I think it has sunk in. The analog is heavily processed and the IBUZ 
>isn't. That means the "quality" keeps changing. That's annoying. In my 
>market there is absolutely no audible difference between analog and 
>digital. There's no change on my Accurian in the 8 seconds it takes to 
>switch to digital. I have to look for the HD icon to know I'm enjoying the 
>awesome sound of precision-processed IBUZ.

Assuming that the only difference between the analog and digital is that 
the digital has less peak limiting (and no high frequency limiting), the 
difference between the analog and digital will be less than when an analog 
FM receiver blends to mono and/or filters high frequencies in response to 
RF conditions (which is typical behavior for most car radios).  Yet people 
listen through that all the time without changing stations.

In the case of an HD radio crossfade with well set up processing, the 
loudness will stay the same, the spectral balance will be similar except 
that the HD has crisper high frequencies, the HD will sound less distorted 
than the analog, and the HD will have more transient punch. I don't know 
how they are processing the HD at the stations to which you listen, but 
here in the Bay Area, I hear this difference frequently.

A friend of mine was helping me with an interior paint job today and he 
wanted to listen to the radio while he worked. I brought up a very nice 
Sony world-band receiver (from my collection of radios that I use when 
developing processor presets) and tuned it to his favorite station. No 
matter how I oriented the whip antenna, I couldn't get rid of the 
multipath. You want to talk about annoying -- THAT was annoying. I realized 
that I had become spoiled by the Boston Acoustics radio and had forgotten 
how poorly FM analog works in many parts of the Bay Area.

Bob Orban