HD Reception in New England

[tomservo]

Show me just ONE analog MW signal that sounds so crisp and bright. If you are unable to detect the superiority of the HD over the analog in your audio clip, I seriously suggest that you consult an ear specialist. Just a tap of the treble control can adjust that audio brilliance to any acceptable level. I'm glad that they punch the highs on the HD eq. It showcases the quality and capabilities of HD quite nicely. HD is saying to analog, " I can hit these high notes, how's about you?"

Someone already gave us that excellent Canadian wideband audio AM YouTube link, but I've got another example with a much more local, and therefore, much more clear signal. Check out this (14 MB) aircheck of my local hometown station, WHEP.

Now, it IS an aircheck so it's mostly commercials and DJ banter, but there's some snippets of music. It's not as rich as that Canadian station, but the noise floor is about as low as you'll hear on AM, and it's very crisp and clear. Also, it's like a window into small town radio, which makes it worth a listen for that factor alone.

I didn't dislike the WBZ audio at all, surprisingly. I found it to be much nicer than the detractors here claim. BUT, it isn't that much of an improvement over what AM is capable of, especially when you hear clips like the one I linked above.

 

[pianoplayer88key]

Here's a couple more youtube AM Stereo links (am I the only one in the habit of capitalizing that phrase as if it were a deity?) that I think sound pretty good...

http://www.youtube.com/watch?v=cq6KSavcVMI
http://www.youtube.com/watch?v=7XgM99C4lrg&feature=plcp

I wouldn't be surprised if some AM Stereo airchecks exist that would make those sound like an 8 kbps mp3 that was improperly encoded (forced stereo, lowpass filter disabled, etc), I just haven't come across them myself yet. I'd also like to hear some actual off-the-air HD airchecks that sound at least that good on an ipod-shuffle-sized Insignia-or-Coby-or-equivalent portable using only the built-in antenna (no external wiring including disqualifying using headphones as an antenna) ... preferably where the equivalent (same transmitter power & antenna system) analog signal would be barely detectable (as in so weak that using a high-end SDR and beverage antenna, only the carrier might barely be detectable - even a PSK31 or QRSS CW transmission that took 2 full solar cycles to send the letter "E" would be too weak to identify). Bonus points for doing it on a graveyard frequency at night in the eastern US.

Also here are some mono airchecks I recorded in winter last year on some local stations...

1700 XEPE
1470 XERCN
1170 KCBQ
760 KFMB
And, with the same radio as in the 4 links above, one station running IBOC: 600 KOGO

Hey I was wondering ... if analog AM was allowed to open its bandwidth as wide as IBOC is permitted (I'm thinking average levels from 10-15 kHz permitted on analog would be the same as the levels used for IBOC), how good could it possibly sound?

Now what I'd like to be able to do is pull in that previously-linked 1242 JOLF in San Diego at the quality in those videos ... even though we have a local station on 1240, and regularly (at least during the day, maybe also at night) get one from Santa Barbara on 1250, whose transmitter is right on the beach. I've pulled in 594 JOAK out from between KOGO and its IBOC (I'm not quite 8 miles east of their transmitter) a couple years ago (skip ahead about a minute to dodge the IBOC splash & hear some weak audio) using a Tecsun PL-380, set to its narrowest bandwidth, and a Select-A-Tenna.

Also, I'll save it for another post sometime/somewhere (if I ever get around to it), but I have quite a few AM Stereo recordings from 1110 KDIS using the Sony SRF-42. They range in strength from very weak (barely receivable, like maybe <3 dB S/N ratio, but they still had stereo separation(!)) to quite strong (driving by the transmitter and overloading the radio). I still have the radio, but it's currently dismantled, and IIRC has something wrong with it.

 

[iyiyi]

C-QUAM can hold a very low signal - in full stereo, until the signal is unlistenable. Assuming no co-channel or other QRM. AM is capable of broadcasting a quality frequency response well into the megaHz range. TV is a perfect example. All analog TV picture information is AM. FM is not usable for pix info in analog TV. The number of significant sidebands required to FM video data would exceed the 6 mHz channel. So... Analog AM is not limited to audio frequencies.

Several audio clips have been presented in this thread that exhibit excellent C-QUAM separation and demonstrating very good frequency response for both C-QUAM and mono stations. These clips were recorded under ideal conditions. Example: Run WCTC's signal 3 1/2 miles from their xmtr - at night - and let's see how things sound then. Let's hear WCTC's daytime signal from 8 miles out and see how well 1450 jumps out at you from there. Add a little co-channel and or skywave and... Voila!

Some of the audio clips demonstrated decent audio response out to 10kHz or so, which is practical, reasonable and acceptable for ANY MW station. Listen closely to those "bright" clips and I believe that you will hear the exact same high end "equalization" on those as the WBZ HD has. Main difference being the IF roll-off in the analog receiver "masks" some raspiness.

FWIW: C-QUAM only increases noise by 3dB. Analog FM stereo, OTOH, raises noise levels 23dB.

Analog: Background, mixer and static noise all increase rapidly with distance from xmtr.
Digital: Signal solid and clean right out to the end of HD's usable range.
Analog: Dynamic range very compressed and limited. Obvious in all the above analog airchecks.
Digital: Wide dynamic range. Clearly noticeable in HD-to-analog shift on WBZ aircheck.
Analog: 30dB stereo separation. There is no need to blend mono (for noise). Full separation until signal loss.
Digital: Better than 70dB stereo separation. No blend to mono required.

Observations: The WBZ aircheck was talk. You want heavy compression with talk because it is very important that the audience can loudly and clearly hear every word. Large dynamic range can be very frustrating for talk listeners trying to follow a conversation. Music would really showcase HD's forte.

Lightning? If you live in Tampa, you might have a legitimate complaint. If you live in LA, who are you kidding? Also, if lightning causes HD to briefly lose lock, what do people think C-QUAM does with lightning?

Analog is to HD what phonograph records are to CD's.

-

 

[satech]

Several audio clips have been presented in this thread that exhibit excellent C-QUAM separation and demonstrating very good frequency response for both C-QUAM and mono stations. These clips were recorded under ideal conditions. Example: Run WCTC's signal 3 1/2 miles from their xmtr - at night - and let's see how things sound then. Let's hear WCTC's daytime signal from 8 miles out and see how well 1450 jumps out at you from there. Add a little co-channel and or skywave and... Voila!

The video of WCTC was made about 10 miles away from the transmitter.

Here is hi-fi C-Quam AM Stereo over 500-mile nighttime skywave reception in Japan:
http://www.youtube.com/watch?v=YMAPKTnJtnA

 

[spunker88]

Couple of other HD/analog comparisons in the WBZ aircheck. Far superior signal/noise ratio in HD.

The only reason the anslog has a lot of noise in the background is because the HD dropped during skywave fade so when it fell back to analog when the signal was weak.

Analog: Background, mixer and static noise all increase rapidly with distance from xmtr.
Digital: Signal solid and clean right out to the end of HD's usable range.
Analog: Dynamic range very compressed and limited. Obvious in all the above analog airchecks.
Digital: Wide dynamic range. Clearly noticeable in HD-to-analog shift on WBZ aircheck.
Analog: 30dB stereo separation. There is no need to blend mono (for noise). Full separation until signal loss.
Digital: Better than 70dB stereo separation. No blend to mono required.

Observations: The WBZ aircheck was talk. You want heavy compression with talk because it is very important that the audience can loudly and clearly hear every word. Large dynamic range can be very frustrating for talk listeners trying to follow a conversation. Music would really showcase HD's forte.

Lightning? If you live in Tampa, you might have a legitimate complaint. If you live in LA, who are you kidding? Also, if lightning causes HD to briefly lose lock, what do people think C-QUAM does with lightning?

Analog is to HD what phonograph records are to CD's.

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On some of those analog AM youtube videos when I analyze the audio in Audacity they both acheive the same frequency response, both end around 15khz. The HD stays at a higher amplitude until its sharply cut down right before 15khz. The analog on the other hand has a slower decay rate which starts around 10khz. So the HD may do a better job at higher frequencies but highest frequency alone does not determine audio quality.

The "stereo" effect of HD sounds like a faux stereo effect to me. I have some audio from Radio Disney in HD and to me it sounds like stereo blended into mono. AM Stereo on the other had has great separation, better than some FM stations.

Lighting is a concern with HD Radio on AM, even here in upstate NY where thunderstorms are pretty common in the summer. Imagine listeners trying to rely on a local AM HD Radio station to give them important information with severe weather approaching, assuming this is sometime in the future where analog has been shut off. I'm surprised the FCC isn't concerned about this with EAS requirements. Granted for now there is analog fallback but I always thought the goal of HD was to eventually go pure digital.

 

[satech]

Also here are some mono airchecks I recorded in winter last year on some local stations...
1470 XERCN
Hey I was wondering ... if analog AM was allowed to open its bandwidth as wide as IBOC is permitted (I'm thinking average levels from 10-15 kHz permitted on analog would be the same as the levels used for IBOC), how good could it possibly sound?

XERCN is already an example of that, as according to a spectrum analysis of that recording, they are transmitting a 12.5 kHz audio bandwidth -- likely using an Optimod 9100 with the NRSC filter disabled, which results in that bandwidth (because even when you disable the NRSC filter, the 9100's 12 kHz audio input lowpass filter remains active).

 

[Tom Wells]

Couple of other HD/analog comparisons in the WBZ aircheck. Far superior signal/noise ratio in HD. Night and day difference between the spacious dynamic range of HD vs the compressed, flat audio of the analog. Continuous audio levels in HD vs the rise and fall of analog audio with signal strength variations. No limit on frequency response, up to the designed parameters, of HD. Analog OTOH, needs to equalize or otherwise process it's audio in an attempt to compensate for poor receiver IF response, transmitter and antenna system deficiencies, uses heavy compression to provide maximum S/N ratios - yet for all that, background noise increase is still a function of distance from the xmtr.

Oh yeah... Seems like nobody noticed the perfect, seamless segue from HD back to analog when the signal deteriorated. Also the fact that the aircheck was stopped just as soon as the analog audio went over the cliff into static...

One could get the impression that digital technology has improved just about everything except radio...

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It will be necessary to compare the HD result to an equivalent analog reciever...not the processed "analog" delivered by ANY reciever
designed for iboc decoding. This is smoke and miirrors and the worst sort of intentional mal-engineering.
It's very easy to brickwall analog upper end in processing.

May I suggest using something like a nice 1980s Sony to compare to.

The dynamic range compression you hear is a result of two steps of misunderstanding in engineering.
1. Square wave detection instead of sinewave mixing/detection distorting linear analog detection.
2. A/D detection sampling rates/filtering in the HD chip are another square wave detection/encoding step, resulting in further
gradient resolution loss.

It's no different from making copies of copies of photographs...each step loses gradient scale steps and usually loses "full scale"
"impact or contrast" data range.

I much prefer the heavy compression of heavily processed AM powerhouses ('70's style) when it's done well, over straight mp3 player tunes.
The trick is making such a compressed signal still sound huge, loud and satisfying when it's still turned down low.
That's why I prefer the "radio sound" of music presentation over all others.

Insert praise here for Breakaway Broadcast Processor in bringing the dream of perfect radio sound...
Nothing about the pure, "noiseless" AM HD decode signal is appealing to listen to.
If there's ANY audio signal that needs a capacitor "decade box" strapped across the line to tone down the shill response, it's HD AM audio.
Any difference in overall frequency response as presented between the analog vs the digital decode is pure huckster sham engineering work.