AM Digital NPRM

AM Radio discussion. Directional arrays are FUN!
ncradioeng
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Re: AM Digital NPRM

Post by ncradioeng »

They can do it because the audio is digitized and processed (i.e. compressed) down to a bit rate that fits in the 10 kHz wide slot. Just like OTA HDTV and mp3's.
COMMENG
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Re: AM Digital NPRM

Post by COMMENG »

ncradioeng wrote: Fri Dec 13, 2019 10:11 am They can do it because the audio is digitized and processed (i.e. compressed) down to a bit rate that fits in the 10 kHz wide slot. Just like OTA HDTV and mp3's.
I may have missed it, but I haven't seen anywhere in the NRSC or IBOC documents that any audio compression is being done.

Now in footnote 20 on page 4 of the NPRM:
20 NRSC-5-D Standard at 14, n.3. We note that NRSC-5 does not include specifications for audio source coding and compression (i.e., the means by which the audio data to be transmitted on a radio wave is encoded or compressed prior to transmission). In the iBiquity system, audio source coding and compression are handled by iBiquity’s HD codec (encoding software). iBiquity has committed to license all patents necessary to implement NRSC-5, either with or without the HD codec. It is also possible within the NRSC-5 standard to use audio source coding and compression schemes other than iBiquity’s HD codec. See Letter from Michael Petricone (Consumer Electronics Association) and Valerie Schulte (NAB) to Marlene Dortch, Secretary, FCC, dated May 18, 2005, in MM Docket No. 99-325.
If I am interpreting this correctly, Xperi does a an HD codec package that "could" compress audio and that others could use "...audio source coding and compression schemes other than iBiquity’s HD codec..."

But audio compression encoding at low bit sampling rates results in sterile sounding audio and more complexity in the audio chain.


The "Idealized" All-digital bandwidth for "service mode" MA3 is defined as having a digital bandwidth of 20khz.
12.2.2.2 All Digital Waveform
In the All Digital waveform, the secondary and tertiary interleaver matrices are mapped to 64-QAM
constellations while the PIDS interleaver matrix is mapped to 16-QAM constellations. S and T have
dimensions of 256x25 and each element contains a six-bit word. The PIDS matrix has elements consisting
of four-bit words and has dimensions 32x2.
Anyone who has seen the actual waveform of a system using convolutional coding and OFDM subcarriers being mapped onto 64-QAM, 16-QAM, and BPSK constellations knows the actual bandwidth is not the idealized bandwidth shown in the documents.

The All-digital data rate is approx. 40kHz with Layer Protocols P1 and P2.

See Table 4.1 Approximate Information Rate of AM Logical Channels, Page 12 of the IBOC HD document, SY_IDD_1012s.

See also 11.2.4, of the IBOC HD document, SY_IDD_1012s, for the Analog Audio Bandwidth Indicator (AABI) definition on Page 52.

https://www.nrscstandards.org/standards ... /1012s.pdf

So, we're occupying at least 20kHz of bandwidth using a bit rate of 40kHz and getting an audio bandwidth of 5 kHz? I hope that is not the case.


COMMENG
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COMMENG
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Re: AM Digital NPRM

Post by COMMENG »

ncradioeng wrote: Fri Dec 13, 2019 10:11 am They can do it because the audio is digitized and processed (i.e. compressed) down to a bit rate that fits in the 10 kHz wide slot. Just like OTA HDTV and mp3's.
I am surprised the Xperi and Nautel people haven't come on here to explain or to at least answer technical questions.

According to an acquaintance on another website:
Apparently HD Radio uses a proprietary CODEC called HDC (High Definition Coding) CODEC.
In the CBR bitrate table [from a non-HD website], the low-pass filter is set to 9640 Hz for 20 to 28 kbps, 13050 Hz for 28 to 40 kbps and 14260 Hz for 40 to 56 kbps.

Figure 5.4 [of the SY_IDD_1012S document] provides 40 kbps in 20 kHz of RF bandwidth and Figure 5.5 provides 20 kbps in 10 kHz of RF bandwidth. For a station sending the full 20 kHz of RF bandwidth, it's possible that the digital audio frequency response is 14.26 kHz. For a station sending the reduced bandwidth 10 kHz, it's possible that the digital audio frequency response is 9.64 kHz.
It was never stated in the testing that I read what the CODEC filter was set for but it appears that, depending on the bitrate used, the maximum analog audio bandpass that can be reproduced is around say 14.25 kHz for a high bitrate.

So, depending on how the CODEC was set up, about 9.5 kHz to 14.25 kHz of analog audio can be encoded.

COMMENG
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Re: AM Digital NPRM

Post by PID_Stop »

ncradioeng wrote: Fri Dec 13, 2019 10:11 am They can do it because the audio is digitized and processed (i.e. compressed) down to a bit rate that fits in the 10 kHz wide slot. Just like OTA HDTV and mp3's.
OTA HDTV (that is, ATSC) uses Dolby AC3 encoding that provides 20-20kHz on every channel except LFE, which runs 20-120Hz. A typical 5.1 encoder outputs 192kb/s, which is pretty much a drop in the bucket compared to the channel's total 19.39Mb/s. As for MP3s, there are too many variables to generalize. The upper limit of frequency response is dependent on bitrate, among other things, and at 320k CBR, the high end can easily reach 19kHz.

Jeff
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Re: AM Digital NPRM

Post by Kelly »

COMMENG wrote: Wed Dec 18, 2019 1:21 pm
So, depending on how the CODEC was set up, about 9.5 kHz to 14.25 kHz of analog audio can be encoded.

COMMENG
That sounds about right (pardon the pun). The claim is that AM MA3 digital would have about the same frequency response as analog FM, without the need for preemphasis/deemphasis. Considering even good FM tuners roll off at around 13kHz, 9.5-14.25 seems right in the ballpark.
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ncradioeng
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Re: AM Digital NPRM

Post by ncradioeng »

Does all-digital do stereo?
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Re: AM Digital NPRM

Post by Kelly »

ncradioeng wrote: Fri Dec 20, 2019 8:55 am Does all-digital do stereo?
Yes it will. When the receiver first locks-on audio may be mono for a few seconds until enough bits are captured.
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Re: AM Digital NPRM

Post by w9wi »

My experience with WWFD was that capture was pretty quick. Roughly half to a third the time of a hybrid-mode station.
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COMMENG
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Re: AM Digital NPRM

Post by COMMENG »

Kelly wrote: Fri Dec 20, 2019 9:15 am
ncradioeng wrote: Fri Dec 20, 2019 8:55 am Does all-digital do stereo?
Yes it will. When the receiver first locks-on audio may be mono for a few seconds until enough bits are captured.
It can do stereo depending on the CODEC used.

But here is that catch.

Since there is a maximum bitrate for a specified RF bandwidth (maximum bitrate is defined by channel bandwidth), in some CODECS Stereo requires that the audio bandpass of each channel be reduced.

So let's say in mono you can transmit audio up to 14.5 kHz within the 20 kHz digital channel.

However, in Stereo, and in order to not exceed the same bitrate or bandwidth, you may only be able to transmit audio up to 9.5 kHz.

So has anyone measured the reproduced analog bandwidth in both mono and Stereo?

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dd92251
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Re: AM Digital NPRM

Post by dd92251 »

I don't know about the rest of you but I'm an Old Fart with reduced hearing. My belief is that most AM listeners are somewhat that same category. So having a "wide" audio response in this proposed AM Digital Mode isn't a necessity. Anything above 7.5K is wasted.

FWIW: I've listened to Analog AM stations along the east coast that play 60's and 70's songs and they sound fine in my car radio. The fact that the audio bandwidth of that radio is about 4khz doesn't seem to matter. Somehow my brain gets used to it and I enjoy hearing songs that others don't play.
Kelly
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Re: AM Digital NPRM

Post by Kelly »

dd92251 wrote: Sun Dec 22, 2019 12:32 pm I don't know about the rest of you but I'm an Old Fart with reduced hearing. My belief is that most AM listeners are somewhat that same category. So having a "wide" audio response in this proposed AM Digital Mode isn't a necessity. Anything above 7.5K is wasted.
I suspect that most self-described "Old Farts" won't bother trying to receive an MA3 AM station. Anymore, AM has their chosen forms of programming anyway; usually right wing talk, news, or some other form of spoken word programming. If you'd prefer the AM band die with you, then I guess it's okay to leave it as is. Ultimately it may happen anyway. Nothing lasts forever. That said; for those groups or owners who own AM stations with an FM translator, what harm is it to let them go full digital/MA3? It's not like there aren't other analog AM stations playing that sort of programming.
dd92251 wrote: Sun Dec 22, 2019 12:32 pm FWIW: I've listened to Analog AM stations along the east coast that play 60's and 70's songs and they sound fine in my car radio. The fact that the audio bandwidth of that radio is about 4khz doesn't seem to matter. Somehow my brain gets used to it and I enjoy hearing songs that others don't play.
That's fine for people who don't care about signal to noise, whether the audio is stereo or mono, or rolls off at 4kHz. Those folks are in the vast minority and are aging-out. There is so much more competition for ears than there was in the 50's-80's, starting with phones. Station owners can either take a chance and try something new, or risk facing eventual business extinction. The question really is: Is it too late for AM? And will someone come up with compelling programming to cause listeners younger than 60 to want to tune it in? I'm hopeful the Commission won't listen to the: 'AM isn't broken, so don't fix it'-curmudgeons, and at least give the station owners an option to try and build a future. Not stay stuck in the past.
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COMMENG
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Re: AM Digital NPRM

Post by COMMENG »

Kelly wrote: Sun Dec 22, 2019 3:47 pm
I suspect that most self-described "Old Farts" won't bother trying to receive an MA3 AM station. Anymore, AM has their chosen forms of programming anyway; usually right wing talk, news, or some other form of spoken word programming. If you'd prefer the AM band die with you, then I guess it's okay to leave it as is. Ultimately it may happen anyway. Nothing lasts forever.
I thought we were going to keep this technical and not inject politics.

I think the FCC will allow a voluntary switch to all-digital for those corporate stations who choose to do so and can afford it with higher power transmitters, say maybe > 2.5kW.
Kelly wrote: Sun Dec 22, 2019 3:47 pmThat said; for those groups or owners who own AM stations with an FM translator, what harm is it to let them go full digital/MA3? It's not like there aren't other analog AM stations playing that sort of programming.
For those stations that do go all-digital it has been suggested they relinquish any FM translator license they hold and I happen to agree, because this All-Digital system is being advertised as having FM quality audio so the FM translator license should not be further needed. They can't have it both ways.
Kelly wrote: Sun Dec 22, 2019 3:47 pm...Station owners can either take a chance and try something new, or risk facing eventual business extinction. The question really is: Is it too late for AM? And will someone come up with compelling programming to cause listeners younger than 60 to want to tune it in? I'm hopeful the Commission won't listen to the: 'AM isn't broken, so don't fix it'-curmudgeons, and at least give the station owners an option to try and build a future. Not stay stuck in the past.
Or they can take a risk and lose the audience that doesn't have digital radios. Most Small-to-medium town community-involved analog AM stations are doing well financially. Does something new really mean it is a good approach for "ALL" stations?

We could have had AM improvement back in the 2014 and earlier timeframe had the industry followed these recommendations: (See first PDF).

Maybe Kelly can give us a non-political (technical) explanation as to why DRM wasn't also tested as a digital engine/medium for AM?

COMMENG
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Kelly
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Re: AM Digital NPRM

Post by Kelly »

COMMENG wrote: Mon Dec 23, 2019 7:53 pm I thought we were going to keep this technical and not inject politics.
Not sure where you see politics in my comment. Right Wing talk? Since Air America isn't on the radio, let alone any AM stations anymore, there is no Left Wing Talk that I'm aware of to balance out labeling the format. The label wasn't intended to be political.
COMMENG wrote: Mon Dec 23, 2019 7:53 pm For those stations that do go all-digital it has been suggested they relinquish any FM translator license they hold and I happen to agree, because this All-Digital system is being advertised as having FM quality audio so the FM translator license should not be further needed. They can't have it both ways.
I don't agree with that option. Many FM translators don't replicate the city-grade coverage of an AM station anyway. Many AM stations no longer provide even their original city grade coverage, mainly because of the continued increase in terrestrial noise from consumer devices. I attribute any comments like that to; 'sour grapes' thinking.. 'Okay fine, you want to take a risk and change the way you modulate your station? Then you give up one that most people can listen to.' The purpose is to potentially help survivor-ability the MW band, not punish licensees for wanting to try something different.
COMMENG wrote: Mon Dec 23, 2019 7:53 pm
Or they can take a risk and lose the audience that doesn't have digital radios. Most Small-to-medium town community-involved analog AM stations are doing well financially. Does something new really mean it is a good approach for "ALL" stations?
Hey, at least it would be the licensee's choice. Nobody is talking about "ALL" AM stations switching to MA3.
COMMENG wrote: Mon Dec 23, 2019 7:53 pm

We could have had AM improvement back in the 2014 and earlier timeframe had the industry followed these recommendations: (See first PDF).
That ship had sailed back in the 80's. The groundswell of music abandoning AM was almost complete by then. Even still, the Commission saw fit to squeeze-in too many allocations all around the country, causing over-congestion to the band. Listeners under 30 had already abandoned AM as a place to go for music, so the aging-out of the AM audience was well underway. A good example was the whole AM stereo debacle. The FCC decided to make the choice of stereo method a 'marketplace decision'. Problem was; besides Leonard Kahn suing everyone, there was no marketplace interest.
COMMENG wrote: Mon Dec 23, 2019 7:53 pm
Maybe Kelly can give us a non-political (technical) explanation as to why DRM wasn't also tested as a digital engine/medium for AM?
I observed some DRM installation and testing on a SW station. It seemed to work great. DRM was chosen as the European standard for digital replacement for SW and MW broadcasting. The reason DRM wasn't taken seriously in the U.S., and has pretty well been absent in Europe, is lack of commitment from receiver manufacturers. Since many MW/SW stations in Europe and MENA are government owned, there was no competitive appetite to make consumer electronics manufacturers build DRM receivers. Classic chicken-and-egg argument. Stations weren't willing to switch to digital broadcasting if nobody could hear them. Receiver manufacturers wouldn't build receivers if there was no commitment from stations to broadcast in that format.

In the U.S., Ibquity which purchased the IBOC engineering from AT&T, came to the table with financial and promotional backing from a couple large broadcast groups, Texas Instruments, and broadcast equipment manufacturers. DRM was a small alliance by comparison, with little financial commitment behind it. DRM wasn't charging a license fee to use their codec, so there was no business model to even get started. Not a technical reason DRM wasn't considered in the U.S., but certainly a business one.
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COMMENG
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Re: AM Digital NPRM

Post by COMMENG »

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COMMENG
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Re: AM Digital NPRM

Post by COMMENG »

COMMENG wrote: Tue Dec 24, 2019 5:50 pm
Kelly wrote:Even still, the Commission saw fit to squeeze-in too many allocations all around the country, causing over-congestion to the band. Listeners under 30 had already abandoned AM as a place to go for music, so the aging-out of the AM audience was well underway. A good example was the whole AM stereo debacle. The FCC decided to make the choice of stereo method a 'marketplace decision'. Problem was; besides Leonard Kahn suing everyone, there was no marketplace interest.
I couldn't agree more and the second file I posted is all about that but it seems you hadn't read either one. Had the FCC made a firm decision AND had mandated a receiver bandwidth commensurate with what should have been the selected Stereo system, we would have an existing AM stereo system specification. Secondly the FCC shoehorning additional stations only made it worse.
Kelly wrote:The groundswell of music abandoning AM was almost complete by then.
That is not true as there are many stations across the country today playing a music format with community news, local advertisements, local sports, and the like. I don't know what formats are being broadcast on the East Coast but don't assume the East Coast corporate broadcaster formats apply to local broadcasters across America. In addition, if you know how to set up an audio processing system with a good PWM transmitter audio delivery can be much improved.
Kelly wrote:...Many FM translators don't replicate the city-grade coverage of an AM station anyway. Many AM stations no longer provide even their original city grade coverage, mainly because of the continued increase in terrestrial noise from consumer devices...
From the IBOC/HD document Page 18, Section 5.4 it says:

In the All Digital waveform, the analog signal is replaced with higher power primary sidebands. The unmodulated AM carrier is retained. In addition, the secondary upper sideband moves to the higher frequencies above the primary upper sideband and the tertiary lower sideband moves to the lower frequencies below the primary lower sideband. The secondary lower and tertiary upper sidebands are no longer used. Furthermore, the power of both the secondary and tertiary sidebands is increased.


From the NPRM FCC-CIRC1911-05:

D. 26. Finally, we seek comment on how signal power should best be measured in all-digital broadcasting mode, for the purposes of compliance with sections 73.44, 73.51, 73.1590, and the HD Radio Emissions Mask.95 What procedures and equipment would give the most accurate results?96 The NRSC states that it anticipates that “instrument manufacturers may develop innovative methods for evaluating signals and achieving compliance.”97 Should the Commission specify what types of
measurements will be acceptable to demonstrate compliance with the Commission’s rules? Due to the
peak-to-average ratio of the MA3 mode, which is significantly higher than that of standard amplitude
modulation, the power level meter on some transmitters may not read accurately.98
Do the majority of
digital transmitters include measurement tools capable of accurately monitoring compliance with the
operating power and emissions mask limitations proposed herein?


The reason some have suggested the relinquishing of translator licenses for all-digital operation is because of the above engineering language which essentially says the city grade contour would be re-established because of the higher than peak-to-average power ratio (PAR) envelope of the digital signal and because of the error correcting codes built into the CODECs.

I think it would be educational for every BE to read and study both documents to see what is really involved in this technology, because it seems many are unaware of the engineering details and the advantages and disadvantages of this technology.

I don't think the question of why DRM wasn't also tested has been answered in engineering terms.


COMMENG


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