HD Radio Time & Level Alignment

[k6sti]

I've just updated my HD Radio time & level alignment page, which covers a number of L.A. stations:

http://ham-radio.com/k6sti/roster.htm

Brian

 

[ajc_trw]

I've just updated my HD Radio time & level alignment page, which covers a number of L.A. stations:

http://ham-radio.com/k6sti/roster.htm

Brian

I've often wondered if doing the following would eliminate the delay problem.

Run the board audio out to the HD transmitter. For the analog signal pick up the audio from an HD monitor. Because you're symalcasting the HD signal in analog and analog has no delay both signals should stay in sync (though there may be a phase issue which shouldn't be that hard to fix).

Although I may be wrong.

If I am please correct me, but no flames please.

 

[davideduardo]

Run the board audio out to the HD transmitter. For the analog signal pick up the audio from an HD monitor. Because you're symalcasting the HD signal in analog and analog has no delay both signals should stay in sync (though there may be a phase issue which shouldn't be that hard to fix).

In most cases, the HD and analog transmitter is the same... think of it as a water faucet through which a mix of hot and cold are output. Even when a separate HD transmitter and/or is used, they are co-located.

The reason for the dealy is so that HD listeners who lose the digital signal/audio will be treated to the analog audio till the HD comes back. That means the analog is delayed in an amount equal to the system delay in the generation of the HD signal. Generally, the audio going to the HD exciter is processed differently than the analog audio. Using HD off-the-monitor audio would require additional processing, which would not improve the sound. In any case, a station would not want a failure point in the analog system to be the HD gear... the analog signal is the one with 99% or more of the listeners.

 

[Tom Wells]

There'd really need to be a built-in "analog output" "internally" so a combination analog/digital xmtr could do this.

It's interesting that no manfacturer designed one this way, which would have also needed an audio chain loss bypass with zero delay when the whole HD exciter crashes.

Biggest problem with using the HD decoded audio as the feed for an analog is that it would result in unavoidable artifacting.
I'd rather have the hiss and what's left of "full" analog resolution than have hiss AND an artifacted clumpy "analog" reproduction.

 

[oldiesfan6479]

...the analog signal is the one with 99% or more of the listeners.

I think the Old Gringo was spot on with that statement. If the analog signal has all but 1%
of the listeners, why even bother with I-CRAP on AM?

I can give FMs a qualified pass on this, as there are HD2 and HD3 possibilities, but I-CRAP
on AM is, well, crap. :

 

[ajc_trw]

There'd really need to be a built-in "analog output" "internally" so a combination analog/digital xmtr could do this.

It's interesting that no manfacturer designed one this way, which would have also needed an audio chain loss bypass with zero delay when the whole HD exciter crashes.

Biggest problem with using the HD decoded audio as the feed for an analog is that it would result in unavoidable artifacting.
I'd rather have the hiss and what's left of "full" analog resolution than have hiss AND an artifacted clumpy "analog" reproduction.

Thanks Tom, I had often thought that was it. Why use HD audio when board audio is artifact free and superior. And it's bad enough HD radio owners have to put up with it (unless there is an analog-only mode) much less subject 99% of our listeners to low bitrate audio.

IMHO this is definitely a rethink if the HD sound isn't good enough to use as a source for analog FM. Sad indeed.

 

[Jay Walker]

Generally speaking there is no reason for HD and Analog to be mistimed and/or have level changes.
All current state of the art FM processors have separate FM and HD outputs that are timed within the processor.

The same applies with level changes. In the beginning of FM HD, I tested a separate less aggressive processing algorithm on HD but after in the field listening I gave up on the idea. The reason? When blending between Analog and HD was in progress the texture and RMS level difference was too distracting in my opinion.

With a single processor I get a nice clean transition to and from HD without level and texture changes.
The HD even aggressively processed sounds better because I do not hear the 75us pre-emphasis artifacts that are heard on the FM carrier. Plus the processor allows me a little wiggle room to fine tune the EQ for the HD receiver.

I manage to keep the signals synced within one or two frames even though I am running separate high power analog transmitters separate exciters, and a stand alone HD. However unlike my fellow engineers on the west coast, I do not have any on channel boasters to deal with. Adding that to the mix brings in a slew of additional timing issues which thankfully I have not had to deal with here in North Texas where a full "C" is 100kw ERP at 550 meters.

And of course sound is subjective...

Happy Holidays
Jay Walker

 

[davideduardo]

However unlike my fellow engineers on the west coast, I do not have any on channel boasters to deal with. Adding that to the mix brings in a slew of additional timing issues which thankfully I have not had to deal with here in North Texas where a full "C" is 100kw ERP at 550 meters.

I agree that there is little reason to be far off on synchronization, even with separate transmitters.

The suggestion that the HD mod monitor audio be used to feed the analog exciter is a separate issue, as it puts a critical failure point of little value in the middle of the analog audio chain... and additional processing would likely have to be done, degrading the analog further.

I don't think there are as many on channel boosters as you imagine. Most stations don´t have them unless they are either rimshots (Las Vegas is littered with them) or shadow-filling propolsitions. If I had a rimshot, I would not do HD as it's unlikely anyplace in the metro I am shooting at could get a usable HD signal. And in the case of "canyon fillers" the spillage outside the dead area is minimal, and the invasion of the originating station is limited... most canyons in the western Rockies are natural Faraday shields.

 

[davideduardo]

IMHO this is definitely a rethink if the HD sound isn't good enough to use as a source for analog FM. Sad indeed.

The HD audio is not processed in most cases the same way analog audio is... meaning the HD output would have to be reprocessed, adding processing artifacts. While current processing like the 8600 is amazingly clean, nobody (except maybe a NYC FM) stacks processors.

 

[Jay Walker]

However unlike my fellow engineers on the west coast, I do not have any on channel boasters to deal with. Adding that to the mix brings in a slew of additional timing issues which thankfully I have not had to deal with here in North Texas where a full "C" is 100kw ERP at 550 meters.

I agree that there is little reason to be far off on synchronization, even with separate transmitters.

The suggestion that the HD mod monitor audio be used to feed the analog exciter is a separate issue, as it puts a critical failure point of little value in the middle of the analog audio chain... and additional processing would likely have to be done, degrading the analog further.

I agree 100 percent. The primary reason I went with a dual output processor was to remove the fail point of the HD signal generator from the FM audio path. As you know the HD signal generator is a computer and is prone to the associated failures of computers. No mater the operating system (in my case Linux)

Nothing worse than having to re-boot the HD generator to get the analog back on the air. And the idea of using HD air monitor to feed the FM leads to the same point of failure plus compromised audio quality from trans-coding errors as well...
Sorry for the lack of clarity in my earlier post.

PS...Love your website. I can't tear my eyes off of  it. So much radio history in one spot boggles the mind.
Thank you for your obvious labor of love of the medium.
Best regards
Jay Walker

 

[davideduardo]

PS...Love your website. I can't tear my eyes off of it. So much radio history in one spot boggles the mind.
Thank you for your obvious labor of love of the medium.
Best regards
Jay Walker

Thanks!!! You may not have noticed that the Broadcasting Magazines are now searchable, and I finally got a bug out of the cgi script for that function. Hope that is of value... I'm always trying to find something new to add, proving I have no life. :