[BC] IBOC AM Quality

[James Kuzman]

Rich Wood said:

"You have to have a continual supply of very good weed to believe the
same grunge processing won't be used on the digital signals. It has
to be. Otherwise the constant mode switching in cars will drive the
listener nuts. Bad processing habits are very hard to break. The
minute the General Manager hears his signal softer than the
competition the order will go out to make it loud."

Hi Rich - We may be an exception here for a few reasons.

One, there's no competition for our audience from other AM stations in our 
area.

Two, no other AM station in town is running HD on a regular basis, so 
there's no one with whom to compare loudness.

Three, the fringe-area reception benefit that density provides on AM analog 
is a non-issue for AM HD - so there's no more coverage if you wind up the 
processing on the digital side.

Four, when our station mode switches from analog to digital, it is a little 
quieter - but you don't notice that so much as you notice the huge increase 
in quality and openness.  When it goes from digital to analog, you notice 
it's a bit louder - but you notice the drop in quality and bandwidth more 
than anything, and realize how bad 5KHz audio on a narrow band receiver 
sounds.

Five, the ear has a short memory.  When you can switch between two stations 
instantanously it will hear a difference in loudness (or perceived 
loudness).  But put a few seconds of time between "A" and "B" and it isn't 
going to remember that the first station was louder - and that's exactly 
what happens with IBOC because you have to step "through" the analog signal 
to get to the HD.

Let's say you're listening to station "A" in analog, then it gathers up the 
HD signal, and switches to digital.  Hit anothe preset on your radio and 
you're going to leave station "A's" digital signal, lock onto station "B's" 
analog, then get their digital a few seconds later again.  In that time, the 
ear will have little or no recollection of how loud the first station was.

Finally, with non-HD processing, you can obviously create audible 
distortion, but the average listener would be hard pressed to identify 
exactly what's "wrong" with the sound - espeically since they have come to 
accept it as "normal."  With AM IBOC, at least, the degradation of the 
audio, be it from poorly mastered source material, data-compressed source 
material, a compressed STL or satellite uplink, cascading algorhythms, and 
finally, poor or agressive processing is painfully obvious to even an 
untrained ear.  You can't miss that ringing sound or in extreme cases the 
underwater sound that IBOC can produce at low bit rates.

So I guess what I'm saying is that you're right, there is a small loudness 
difference - but I don't envision AM stations getting into loudness wars on 
the HD side anytime soon.  At least I hope not... the results won't be 
pretty :-)

Jim Kuzman
WDYZ AM 990, Orlando

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