(This started in the "First PAX, then I, now......'Ion'?? thread, but I started this one so the original wouldn't be swayed more off topic than it's been! Yeah, I guess I'm a hypocrite to a degree.....)



Author: Semoochie
Monday, February 19, 2007 - 5:52 pm


This is the first time I've heard of a network changing names before anyone knew what the old one was called! It sort of reminds me of the "Magnavox Decision": Oh, just kidding.

-------------------------------------------------
Author: Motozak
Monday, February 19, 2007 - 6:16 pm


Whuuhhhh????

-------------------------------------------------
Author: Motozak
Tuesday, February 20, 2007 - 12:24 pm


No, seriously--what do you mean by the "Magnavox Decision"?

Was this something to do with their merger with Philips a number of years ago, or what?

-------------------------------------------------
Author: Semoochie
Tuesday, February 20, 2007 - 2:18 pm


In 1980, the FCC chose Magnavox as the approved system for AM stereo. Soonafter, there were claims of "pops and ticks" and certain people threatened to sue. The FCC quickly backed down and after a 2 year delay, "decided not to decide" and went with the "marketplace decision" instead. In retrospect, if the FCC had stayed with the original decision at a time when AM still enjoyed nearly half of the radio audience, it may have encouraged receiver manufacturers to make better sounding AM radios when there was still plenty of music on the band and 2nd and 3rd generation improvements to the Magnavox system would probably have solved the "pops and ticks" problem or greatly reduced it.

.........but no, the FCC instead insisted that we listen to an AM stereo system that "platforms" so badly, people have been known to get sick to their stomach while listening over earphones!!

Wasn't the Magnavox system a sideband system similar to Kahn's?

The FCC didn't insist on anything until long after it had become a moot point. Belar, Harris and Magnavox had long since bailed out, leaving only Kahn and Motorola, the latter of which had far and away more receivers and stations using their system. The FCC realized this and tried to make them the ad hoc standard by protecting their system from interference but it didn't help. It was too late. Many years later, the FCC finally declared C-Quam as the standard. I have heard that the platform motion problem has been solved in later generations or is at least not bad enough to be very objectionable. I don't believe the Kahn system is similar to any of the others. On radios that received all 5 systems, there was a switch for either Kahn or the rest.

True, I listen to 1060 from Calgary (a soft-rock station....can't remember the call off the top of my head despite listening to them occasionally......CVMX?) sometimes out in my truck if it's *really* late at night, using a 1998 GM factory-stock radio with AM stereo, and have never heard it platform, or at least very slightly.

Listening on the Chrysler radio in my Gran'ma's 86 Eagle Premiere (still the same factory radio that shipped with the car, incidentally) proves otherwise!

So why did the FCC choose a technically-limited system (CQuam, referring to its drift and occasional platforming) over Kahn's system which reportedly had better fidelity and immunity to platforming, being a sideband carrier? Cost, licensing??

(Side query: I understand the Cam-D system is actually a re-branded Kahn Stereo rig, with a few enhancements and changed to enable it to broadcast digitally instead of analogue, using the same sidebands his stereo system used. Is thus true, and if the FCC supposedly outlawed his stereo system, how can he legally be doing this?)

1060 is now country.
You might also try 880 at night, although there is more interference on 880.

I never got sick from any platform motion. I think that was overblown scapegoat for people looking for excuses to abandon AM stereo.

Which local AM stations had listeners complaining of platform motion?

I do get sick from IBOC hash.

"So why did the FCC choose a technically-limited system (CQuam, referring to its drift and occasional platforming) over Kahn's system which reportedly had better fidelity and immunity to platforming, being a sideband carrier? Cost, licensing?? "

Politics. Lobbying. Money. World wide penetration of C-Quam.
Here is a good backgrounder:

http://ourworld.compuserve.com/homepages/kevtronics/history.htm

As I said, the FCC didn't choose until long after the marketplace had decided. They merely confirmed and I believe it took well over a decade for them to do so. I believe it's possible to use Kahn's "Powerside" system without interfering with C-Quam.

From what I understand, having actually spoken with Leonard, the CAM-D systems on air currently are not broadcasting the digital signal component.

Analog only at this time.

CAM-D ready gear will be able to transmit the digital component, should that become a more ready option.

Kahn claims his signal fits entirely within the old NRSC mask for AM broadcasts as well.

CAM-D enhances ordinary AM analog broadcasts in a manner similar to his earlier systems, but with less overall distortion. This is on air at KYDL, samples are on his site.

He's finally got lab stereo signals up now. I've not had a chance to listen, but probably will in the next day or so.

I was most interested in the technical aspects of his system. For obvious reasons, he lets very little slip. I do know he made different tradeoffs where compression is concerned. Lowered the number of bits for higher frequency sounds. This trades accuracy for overall dynamic range and harmonic content. IMHO, an interesting tradeoff that is likely competetive to the spectral profiling and reproduction at the receiver end found in the IBOC system.

I know nothing of the actual encoding method used, nor could I confirm it being a hybrid system (lower frequencies analog, higher ones digital), but I strongly suspect this is the case, given it fits within the mask.

Interestingly you can give him a call and he will engage you in some very interesting conversation. For me, it was worth it to gain some perspective from a very passionate AM proponent.

Visit wrathofkahn.org for the details on that.

I did this while researching HD Radio / AM Stereo and the various tradeoffs early on.

Say what you want about Kahn, but I learned a ton from that guy in only 1/2 hour!

Re: Platform motion

The older radios did do this. I personally found it to be no big deal. Members of my family did though, so it's a concern.

The newer radios I own have almost none of this. IMHO, it's below the tolerance of the average person and no longer a significant concern.

What I don't get is the whole wide bandwidth discussion. Of course we like it as wide as we can get it, but when push comes to shove, even a 5Khz wide stereo broadcast is significantly more listenable than a monophonic one is, for a very large subset of available program material.

The stations, who have decided to turn their AM Stereo broadcasts back on, have only positives to report. Nobody loses significant coverage, and nobody hears reports of listener quality problems.

The only reports that come in are from those who have quality car radios and hear the difference!

Compared to the IBOC mess, this seems to be a no-brainer overall.

Doing any kind of stereo will provide a venue for more AM stereo programming to be produced. AM Stereo or IBOC, it's all the same. Better food for the xmitter and more potential listeners overall.

IMHO, the biggest excuse today happens to be those currently having invested in IBOC on AM, not wanting multiple standards killing it the way it happened to AM Stereo.

The difference between today and then is software defined radios. Honestly, it really does not matter if more than one modulation scheme is present or not. Either one has a newer radio, or they don't.

At the end of the day, we will either all be interested enough to buy new radios, or we won't.

If we have them, they will be software defined, and can then reproduce anything the broadcaster chooses to actually broadcast. It's actually in everyones best interest to encourage both techniques as they both have strengths that play to different program materials, topologies and antennas, etc...

Maybe someday more people will grok this and we will see more stereo on AM period.

My money is on AM becoming extinct within 20 years.

A new band will result in broadcasters handing back their AM licenses. Just like what lies ahead in TV. Owners will be given a slot on the new band and the rest of the channels will be auctioned off.

At an as yet undisclosed chunk of the electromagnetic spectrum to be announced.

The existing AM spectrum will be used for transporter beams.

Analog AM reception is horrendous on many radios! There are just too many that aren't wired correctly to override all the interference that takes place. A simple flip to FM and it's gone completely! AM IBOC is supposed to be completely free from these problems when received on a digital receiver. Simply broadcasting the analog signal in stereo won't do the trick. On the other hand, I don't think the hybrid method will pan out on AM either.

Maybe you guys are right.

All I know is I have a great AM experience every day. Maybe I've just not stumbled into the poor radios, but I don't buy expensive radios, so...

What gives?

"A new band will result in broadcasters handing back their AM licenses."

KNBR's frequency is MINE!

I'm not saying that AM radios can't be hooked up properly but when they aren't, the results can be an audio disaster and most people won't bother to fix the problem; they'll just switch to FM.

A lot of them new out of the box, are just terrible.
I has a sony home stereo receiver a few years ago, the design was just horrible. Even the strongest signals were FULL of noise, not to mention the 3 khz filtering.
Switch to FM, perfect. Even if there was no noise, the 3khz is a "would rather turn it off" problem. Use another better radio in same loction, AM is no problem. ITS THE RADIOS, for the most part.

I am having trouble agreeing that 5khz stereo is better than 10, 7 or 8 knz mono. I think I would pick the wide mono almost every time. But why do we need to make that choice?

Missing, did you have chance to re-read that report a couple weeks ago about AM bandwidth? Were their conclusions based on the data, or was the conclusions based on other influences? I think they should have sampled more radios.

I think their sample was good enough to establish solid bandwidth and noise study points.

The conclusions of that report strongly reinforce the AMAX standard as being the right thing to do. Either we commit to that, or we don't. If we do, then higher quality radios will be produced. If we don't, then we get the status quo.

Radio, in general, is only as dead as the industry thinks it is. AM, in particular, suffers from this problem more than FM does.

IMHO, 20 years seems like a stretch long enough to see radio depart, but I doubt it. The newest gear being installed has that lifetime, plus. The simple utility of it, plus the existing body of listeners will easily carry it past that.

I've not seen a tech introduced yet that is actually a radio killer. Compressed audio downloads and portable media players are close. Wi-fi streaming is also close, but both have a long way to go yet.

All depend on recurring daily content to really compete with radio at it's strongest.

Some efforts to cultivate that will go a long way toward keeping radio relevant.

Put the newest generation on the radio --even the HD2's and watch them connect with one another just as everyone else did. If that happens, add another 20 to the radio lifetime.

This focus on technology and quality is good in that it expands what radio is capable of, particularly on FM where we've got more than one stream per station. That's infrastructure though, not content innovation.

So, the first part of the build out is done.

When do we see the second?

Regarding the question above about how the different AM Stereo systems worked, Magnavox and Belar were the two simplest of all. Belar transmitted the left-right difference channel as narrowband FM. Magnavox used phase modulation.

The Belar approach traces its roots as early as 1959, when some over-the-air tests were done on a very similar system. If Belar or Magnavox had become the standard systems, you could have very easily kluged together a good AM stereo decoder using a narrowband FM chip (like what would have been used by cordless phones and 2-way radios of the day) and a few op amps. You would just need a 6db/octave high frequency rolloff after the FM detector for Magnavox reception.

There were a few multistandard radios made, but such solutions proved too expensive, too difficult for consumers, and the audio quality was poor because these radios were not real C-QUAM or Harris receivers; they were hacks. Software defined (DSP-based) receivers make it less painful to add reception capabilities for more transmission formats. However, if we had a similiar scenario to competing AM Stereo standards today, I think that multistandard software radios would compromise performance just like their analog ancestors. The reason for this is that the radio manufacturers would want to do whatever they could to avoid paying royalties to the various companies that developed the competing transmission technologies.

Here's a question, particularly for Andy: Do you think that 20-30 years from now, any parts of the radio spectrum are going to be completely vacant?

"vacant?"

No. The propagation value of LW will always make it valuable for covering long distances, whatever and however the modulation.
The FM band is surrounded by the TV bands which are beginning the transition to higher frequencies. If the FCC crumbles to industry desire, the VHF low channels will take years to become reassigned, a chunk at a time. If the military ever gets off L Band, then digital radio could prosper there like it does everywhere else in the world. TV will eventually be all UHF but only in the near term if other wireless services can outlobby the NAB, but in the long term it's anybody's guess.

BTW, there are no vacant bands, only bands that have been unimplemented. The government calls them "reserved."

I don't believe digital radio has "prospered" anywhere thus far except in Britain. There seems to be a good argument for HDTV to abandon low VHF but it will take some doing to convince the high Vs from leaving.

Especially with the proposed merger of XM and Sirius, I will continue to stay "out on a limb" and predict a future convergence of AM, FM, HD radio and satellite (i.e. - Pay Radio) into some sort of high frequency terrestrial service that can all be received on the same receiver, with the Pay stuff locked if you don't pay for it.

Using similar (or whatever it evolves into in the future) technology to what CHUM-Toronto proposed as a competitor to satellite radio in Canada. But pulled the plug on in 2005 when the CRTC (FCC equiv.) approved both Sirius and XM for Canada.

That kind of technology should allow reception inside a vehicle or building, without an external antenna. After all, if I can get excellent cell phone reception inside a vehicle idling in a 3rd floor underground parkade, why would I want to use a technology that requires an antenna outside a vehicle or building with a clear line of sight to a satellite in space? (To the best of my knowledge, we don't have ground repeaters for satellite radio in Canada)

Of course, just to make things interesting, we now have FM Extra, which uses subcarriers for all digital information, interferes with absolultely nothing and requires technology that has been approved for decades! It's a real shame it wasn't ready 5 years ago.

Interesting, indeed!

http://www.dreinc.com/products/technical.html

Drop your SCAs and RDS and add a little digital...But I would question if many broadcasters would want to do this instead of grabbing additional bandwidth from adjacent channels ?

Well, it's got a bandwidth of about 128Kbps!

That's enough to send an mp3 type of encode right over the digital channel. This is not quite the bitrate IBOC has available to it, but it's plenty good enough for two digital channels.

If IBOC can violate the traditional xmitter mask (and approval has been granted), then this scheme could also do that as well, bringing more bandwidth to the table.

This effort would be worth it to bring a higher quality dual stream capability within reach. The secondary streams are perhaps the biggest advantage that digital has on FM and are totally worth keeping.

How often are the SCA's used and what revenue do they bring in? That's the biggie on this system --that and receivers / adapters.

The simpler modulation scheme probably means easier design and manufacture of these units.

One other piece of good news is the encoding part of this appears to be open in that they suggest combining the system with whatever codec makes sense.

This will never happen, but I would combine this with the Ogg Vorbis open codec. That codec is open source currently and carries no royalties. It performs very well at mid to high bandwidths.

At the 128Kbps it would be competetive with the IBOC prorietary one. Radio could form a small co-op, and instead of paying royalties to Ibiquity, could simply invest in the Obb Vorbis codec to bring it's bandwidth consumption in line with industry expectations, if necessary.

The beauty of this would be no end-receiver royalties for receiver manufacturers --at least for the codec. There might be one for the core modulation scheme however.

There is another significant advantage that comes with Ogg Vorbis and that is repurposing the streams would essentialy be royalty free as well, thus limiting streaming royalties to the trade organizations responsible for the content streamed.

If software, such as Shoutcast were to be used, per stream royalties would be avoided as well.

There is hardware support in many portable media players today, and some effort on the part of the radio industry would only increase that, particulary if the two were cross-promoted!

Browser plugins have been available for a long time, as is an integer codec engine for portable media and receiver DSP operation.

All in all, the landscape for this system is considerably more friendly than the Ibiquity one is.

Having one common codec for all repurposing of content means, podcast type downloads could be done from the actual broadcast atream, as can editing, commercial insertion, etc...

Finally, this unified open codec potential means building aggragation facilities to distribute content from high-bandwidth, load sharing servers would only require an investment in time, people and gear to accomplish.

(actually that's not final!)

Instead of Ibiquity owning the industry on it's own dime, radio could be leveraging that investment for content aggragation and cultivation purposes.

VT talent operating from home studios could easily run the codec there and send transmit ready digital streams. They could operate via regular internet, sending their content to the regional aggragation facilities I mentioned above.

Additionally, stations wanting to repurpose their content could do the same things, royalty free.

(why do you think the BBC is investing in open codecs? --this is why!)

Station podcasts, etc.. could come from where ever it makes sense.

IMHO, IBOC exhibits this same potential as the modulation scheme does not technically require their proprietary codec, but I see zero potential for this as the revenue incentive is just not there.

Nice to dream though. I like this system for a lot of reasons, but the clear lack of codec dependance is a biggie for me.

FMeXtra is compatible with hybrid mode IBOC.

Missed this!

The implication is that receiver manufacturers could easily incorporated this system in with their existing IBOC capable designs.

How much you wanna bet Ibiquity has contractual agreements preventing exactly that from happening?

But to get the 128 kbs, the broadcaster would have to give up Stereo on the main analog channel. I would guess that few would be willing to do this during a transition period to digital. 64 kbs would be the max without giving up Stereo, or "borrowing bandwidth" from adjacent channels.
Since the SCA channels are touted to be compatible with hybrid mode IBOC (and some now carry digital info) it is possible Ibiquity could have missed this loophole.

it's supposed to cost stations about $10K and I believe there's already one receiver available for $150. If it catches on, AM stations will have to find something else because it's just for FM.

Interestingly, Ibiquity has just announced a 10K licensing plan for those who have yet to sign on.

I believe this is the total cost.

Of the FM Extra system?

The Ibiquity stuff is recurring.

Am I missing something? it looks like the Ibiquity fee is a one time expense for the main channel:

http://www.ibiquity.com/i/Licensing_Fact_Sheet2007.pdf

Secondary channels are a different matter, however.

Another advantage, not yet mentioned here, of the FMExtra system is that it is compatible with existing analog FM transmitters. The FMExtra subcarriers go into the transmitter's composite input just like SCA or RDS would.

The current IBOC system is not as simple to implement. Somebody correct me if I'm wrong, but don't most FM stations that are broadcasting IBOC use a separate antenna and transmitter to put out the IBOC signal? I remember reading, years ago, that the other option is to combine the outputs of the analog FM and IBOC transmitters in a Wilkinson combiner and send them to a common antenna. However, this approach wastes half of each transmitter's output power in a big load resistor.

I don't think this method wastes much power:

http://www.shively.com/tb-llcat.pdf

Semoochie~
"Of course, just to make things interesting, we now have FM Extra, which uses subcarriers for all digital information, interferes with absolultely nothing and requires technology that has been approved for decades! It's a real shame it wasn't ready 5 years ago."

And now, reportedly, there are radios being produced that can receive the FMExtra signal (no, not a regular analogue FM with an SCA demuxer!!)

They were just announced and demoed at the National Radio Broadcaster's convention a couple weeks back. I read about it on the "HD Radio" board at Radio Info (and if I remember right, even commented there):

http://www.radio-info.com/smf/index.php/topic,63957.0.html

And the guy who wrote the initial post announcing the radios' introduction, "Chuck", also put up some pictures he took at the NRB:

http://www.chalkhillmedia.org/kzqx/fmextra.htm

My view:
If I should happen to be a participating listener in this whole mess called the "digital radio revolution" I certainly wouldn't throw money away on a closed-system Ibiquity IBAC. I'd get a radio that could do IBAC AND FMExtra AND possibly others! Might cost a bit more than a single-system rig but at this point in evolution, it could be a very intellegent move, as a listener, to avoid being locked down to one particular system whilst others are in development and battling it out. While there reportedly aren't any FM-X stations in Portland yet (I haven't heard anything buzzing my SCA rig outside of KBOO and 88.3) that's not to say there won't be any in the future (There may very well be, who knows.)

Kinda like AM Stereo years ago, only this time around it's on FM! What's that old adage about "the more things change"............. ;o)

I was gratified to see mention of LW here; I was beginning to wonder if my view of its potential for domestic broadcasting was shared by anyone else on this side of the pond, or was even sound/feasible/realistic.

Actually, MW and VHF have propo variabilities that required careful engineering of their allocations, which unfortunately has apparently gone out the window in the past decade or two, especially on the AM band, where I view tacking digital onto it like putting a silk purse on a sow. (No, more accurately--pardon my French--it's pissing in the soup.)

While I've lived most of my life here, a few years in New England (where I happened to work marine VHF--156-162MHz, plus 2182kHz, not yet sideband) made me acutely aware of the shortcomings of VHF and MW. While I'm relating communications experience here, the same problems apply more or less to broadcasting in those bands; please bear with me.

Tropo ducting and skip made VHF a nightmare in summers (the annual yachting explosion gave rise to the quasi-official term "SAR season"--for search and rescue). I'd turn on my car radio on the way to work, and if I could hear New York FM I knew I was in for a rough watch on noisy channels (sometimes several distress cases were simultaneously audible and being worked on one channel across a couple hundred miles).

Fishing boats didn't usually have HF then, and Georges Banks (where our main "clients" aside from summer yachters, the New Bedford fleet, fished) was beyond VHF and on the fringe of our daytime MW range from Cape Cod (in thunderstorms, snow or heavy rain, forget it), and its nighttime range of 1000+ miles (including the Great Lakes) made night working difficult due to congestion and interference. (We often heard Mayday Relay auto alarms from Lands End Radio in England in winter, with the rest of the broadcast inaudible, causing much consternation and interruption until we identified the source.) Toward the other end of MW, the roughly 300-mile daylight range of 500kHz required an extensive, elaborate system of stations and sea watches to ensure distress reception. (Although watching 500 at night, with its 1500-2000 mi range, particularly during the winter when it was much less noisy, was a delight which those who did it will always remember.)

And my upbringing in the West (plus a couple years in and out of Alaska) has made me sensitive to the needs of the outback, where I don't think a sat dish should become required to obtain broadcast information.

(I must note I greatly enjoyed being able to hear New York from Cape Cod on AM. Oh, for the mighty car radios of the sixties.)

While I hate to see bands moved, if the receiver base is going to be obsoleted by changes in mode of delivery anyway, we might as well get it right: UHF for urban areas, and LW for regional 'casts and "white area" service (no, not C&W, but the technical term for remote/underserved territory).

As for giving up stereo for FMeXtra, it would certainly be a significant marketing problem, but seriously, I doubt a majority of the audience knows the difference--just put a second speaker on it, or add a touch of reverb, and they think that's "stereo." I think for some formats and demos, the tradeoff of stereo for an alternate channel would be a favorable one.

Oh, I enjoy stereo immensely myself on my Walkmans (I anxiously awaited the ICF-40, a hundred bucks in 1981) and when listening in a quiet home, but find it distracting in the car (where it interferes with my identification/location of outside sounds). And FM stereo in many areas is iffy to the point of degradation; for many years, KINK's multipath was horrible in my SE suburb (caused, I was once told, by their 100kW signal reflecting off Mt. Hood).

And how many of you were guilty of or scolded for listening to program out instead of the air monitor because of its inferiority?

I know Long-wave has been used for decades as a broadcast band in the UK and Europe (and many other parts of the world) but wasn't it also tested as a BCB here in the US as well, later dropped in favour of its current band spectrum? Kind of like the situation when FM broadcasting was the latest thing in the '30s?

Also I would think if FMExtra was implemented into the system at KNRK I'd really go for that. (Unfortunately from what I have heard/tuned they are an IBAC station.....) I do enjoy hearing it in stereo but where I live (East Vancouver near 205, with a good view of Portland) and at home (East Vancouver, due south-west of the KVAN towers, but up on the hill) KNRK comes in great in mono (at times) but its stereo signal is nearly impossible to receive satisfactorily. I'm not certain if FMX runs at the same 10% overall modulation that analogue SCA runs at but reportedly (also from experience) if the main carrier is a bit scratchy, your SCA reception is doomed. (Try DXing Spokane's feed of the Evergreen Radio Reading Service sometime in certain areas of Pendleton, like the Shari's near the Red Lion, and you'll see!!)

I believe KINK used to run a small amount of power into about 18 bays and am not sure about the vertical power. I don't think they had a handle on using multiple bays in those days and think it hurt them. I know I found it noisy while driving around but there were several other stations that did the same thing. That may have been before "beam tilt".

"I believe KINK used to run a small amount of power into about 18 bays and am not sure about the vertical power. I don't think they had a handle on using multiple bays in those days and think it hurt them. I know I found it noisy while driving around but there were several other stations that did the same thing. That may have been before "beam tilt"."

I think it was 12 bays. I watched them replace that in the mid 80's when I worked at 2. Lee McCormick (dec. aka "Grid Leak"), long time KGW/KINK engineer, told me it was about KING not wanting to spend a lot on an FM when they got started since it was an unproven band, etc. Less power (cheaper xmtr) with more antenna gain is a good option in many places, just not in Portland's West Hills.

Mechanical beam tilt is ancient. Electrical beam tilt and null fill also goes back quite a way. It definitely was around in the 70's.
KINK's problems close in would not be solved by beam tilt alone, because the antenna is so high up above the close in city. Null fill is required, and even some of the newer antennae to be employed in the west hills over the last 20 years with beam tilt and null fill do not solve the lack of reception in certain areas close in and under these antennae.

Electrical beam tilt, which is a constant change in the
electrical phase along the antenna to tilt the pattern down, is done on most antennae to place the main lobe on the ground at the horizon for maximum coverage. In cases where the majority of audience is close in (less than 20 miles away) or the antenna is extreme high in relation to the city of coverage the beam tilt may be more to place the main lobe into the population center. Null fill, which is a variable manipulation of the electrical phase along the antenna, is used to fill in lower signal areas in the pattern in close to the stations (within 15 miles).

It is unfortunate that the IBOC Digital radio codec standards are not open and royalty free, unlike the analog radio and TV standards that have been in place for years. I like the ogg-vorbis suggestion.

The major disadvantage of FMExtra over HD Radio as I understand it is that, since it's broadcast on the main carrier, multipath will interfere with it just like it does with analog FM. HD Radio transmits indepdendent COFDM carriers which makes them more immune to multipath since the reflection of a carrier will only interfere with that carrier. With FMExtra all the carriers are subcarriers so they'll all get hit equally if multipath interference happens.

There's also a question of how robust the error correction is in FMExtra. 128 Kbps is a lot of data to pass through that bandwidth.

I was under the impression that the main carrier would continue to broadcast the standard analog and the digital simulcast would be on the subcarriers. Are you saying that the subcarriers would receive whatever multipath interference the main signal gets? Doesn't being digital help in that respect? If it doesn't, we may have to go back to the drawing board or wait for HD to improve. This may be why HD ended up as an IBAC system. It's not as if they didn't try to keep it within the allotted bandwidth.

I can see what "scowl" is talking about. With an IBAC system, the digital carriers above the center frequency (i.e. the analog carrier) can be independent from one another. However, in the FMExtra system, each digital subcarrier that is sent to the analog FM transmitter will generate a sideband above the center frequency and one an equal distance below the center frequency. There is no way around that because that is the way FM works. I imagine that trying to model how the two systems would hold up under various multipath conditions would be very difficult or maybe not even practical. It seems like the only way to compare the robustness of the two systems would be to get a station to simultaneoulsy broadcast IBOC and FMExtra and then outfit vehicles with FMExtra and IBOC receivers connected to common receiving antennas.

Agreed.

One other aspect of this, I believe favors IBOC, is the stream being sent across multiple carriers. Given some robust ability to degrade the signal, IBOC may well see a performance advantage in that data is sent in parallel streams, making such a capability more practical.

A single serial stream will do this, but with a greater degree of overall latency than multiple streams would exhibit.

From the description that I read earlier, I think that the FMExtra subcarriers are similar to IBOC in that the data is encoded onto all the carriers simultaneously. What I am saying is different with FMExtra is that if multipath causes the upper and lower sidebands to have different strengths at the receiver there could be distortion in the received composite signal. This distortion would "pollute" the received FMExtra signal with intermodulation products of the FMExtra sidebands, the main channel audio, and whatever else might be present in that station's composite signal.

IBOC, on the other hand would see a signal in which some of the carriers were stronger than others, but there wouldn't be a whole bunch of intermodulation products to degrade the signal.

What we don't know is how the error correction mechanisms of both of these systems would deal with signals that have been degraded in the ways described.

All the technical Bull$#!+ aside, IBOC still sucks as a digital platform for AM!

As I understand it, the subcarriers in FMeXtra are modulated by the main carrier, just like the L-R stereo signal and RDS and other SCA services. With HD Radio, each carrier is an independent RF signal with its own frequency so multipath would only cause that carrier to interfere with itself and not with other carriers.

FMeXtra has sort of acknowledged that multipath is problem with their system and they've designed a receiver that uses adaptive equalization to attempt to cancel it out. I don't know how successful this has been but it would probably make regular analog FM sound better too.

The last time it was determined that an FM system had additional trouble with multipath, they were never heard from again! I'm thinking FMX. Does that sound right?

Yes, it was FMX. I remember reading it was tested at one Bay Area station without the chief engineer's knowledge.

As I recall, it improved FM in some way, providing that there was no multipath interference. If there was, it made it much worse! I'm thinking it extended stereo coverage out to mono limits and if they had gotten past the multipath problem, it would have been a significant improvement!

I'm thinking FMX was a matrix scheme similar to what was done on some records at the time. It may have been deployed in conjunction with the recording industry version.

there was a madonna record and a janet jackson record done with the spatial enhancing technology.

Radio refused to play these versions as i remember because of some technical issues.

someone here surely remembers all the details.

I recall the issue resurfacing a few years ago during discussions of adding surround to FM.

One plan was said to be a "matrix" scheme similar to FMX to which a prominent audio processing guru highly protested. his protest had to do with the multipath issue caused by such matrix schemes.

> I recall the issue resurfacing a few years ago
> during discussions of adding surround to FM.

What I had read (in RW Online or some other industry trade journal) was that Dolby had refused to license its matrix surround system to autosound makers. The reason for this was that Dolby feared that running the output of an automotive FM tuner through their surround sound decoder would add emphasis to artifacts of multipath and of the action of the tuner's high blend circuitry, and that the public would associate these sonic flaws with Dolby's surround sound. In other words, Dolby wanted to avoid a possible marketing headache.

Does the amount of L-R correspond with the amount of mulitpath distortion? In other words, if you reduce the L-R below the correct amount, does the distortion go down? If you increase the L-R above the correct amount, does the multipath distortion go up? Some of the techiques for adding spacial enhancement, surround sound, etc. monkey with the amount of L-R, or add out of phase to the opposite channel? Does this increase distortion due to multipath? Wasn't the standard changed for recordings to restrict anything from being too far right or far left? Like maybe only 30 dB max seperation?