Re: [IRCA] DRM vs IBOC

[Scott Fybush <scott@xxxxxxxxxx>]

Patrick Martin wrote:
> I have also heard that DRM is much better than IBOC, but the possible
> profits to be made with higher fees are better with IBOC. DRM also does
> not cause as much QRM as IBOC does. Plus the audio quality with DRM is
> better. Anyone ever compare the two?

Right now, it's something of an apples-to-oranges comparison, 
particularly because there's no such thing as "the" DRM system, any more 
than there's "the" Ibiquity system. Both organizations are developing a 
variety of systems to meet different needs.

DRM's main offerings are non-hybrid systems for use on MW, SW and up in 
the 26 MHz region. For these systems to work, broadcasters have to 
either use separate spectrum from their analog transmissions (not an 
option for US MW broadcasters, but easy enough to do on SW) or be 
willing to shut off their analog in favor of going digital-only. That's 
something some European MW broadcasters are willing to consider; it's 
not yet something most US MW broadcasters want to do.

Because there are a variety of choices that broadcasters using DRM can 
make with respect to the bit rate they transmit at and the amount of 
error correction they use, it's impossible to make any kind of blanket 
generalization about "DRM sounds better" or "DRM sounds worse." It all 
depends on the tradeoffs that the broadcaster using DRM wants to make - 
to get the bit rate you need for better audio, you sacrifice some of the 
robust error-correction needed to make DRM work over skywave. The DRM 
systems, unlike Ibiquity's, include a choice of three different audio 
codecs as well, and the audio quality varies dramatically depending on 
which codec is used.

There's no free lunch: there's only so much bandwidth in a channel on MW 
or SW, and once you start taking up the amount of data needed for robust 
error correction, you just don't get that many bits for audio, whether 
it's Ibiquity's system or DRM's. I've heard some samples of DRM over 
shortwave that sound like so-so webcasts...which is about where the 
state of the art for Ibiquity's MW system is, too. I've also heard 
samples of DRM at 26 MHz that sound much better.

I believe DRM has done some work on a hybrid system similar to the 
Ibiquity MW "in-band, on-channel" (really IBAC, as we know) system, but 
absent much demand for a system like that anywhere outside North 
America, it's not a priority.

Unlike Ibiquity, DRM doesn't currently have a working system for use at 
VHF frequencies. It's been promising an "FM" system for a few years now, 
but at last check it was still vaporware, as are most of the physical 
radios that have been promised thus far.

The big advantage DRM has over the Ibiquity system, to my mind, is that 
it's an open system. Its technical specifications are public, and 
there's no licensing fee to build transmitters or receivers for the 
system, which means you can build a software-based receiver for DRM 
without having to pay any fees to anyone.

That's great for experimenters and hobbyists, which may be why there's 
this myth that's evolved (the "I have also heard..." that seems to 
accompany so much talk about digital radio on these lists) that DRM is 
far superior to Ibiquity's system.

 From a philosophical standpoint, that may be true, especially if you 
are (as I am) a strong proponent of open-source as a way of doing 
business. But from a technical standpoint, DRM has many of the same 
"features" that are so often cited by DXers as failings in the Ibiquity 
IBOC system. It's still essentially a buzzsaw across the band when heard 
on an analog receiver, albeit on-channel instead of adjacent-channel. It 
still requires new receivers, few if any of which are currently on the 
market (unless you have the technical know-how to experiment with a 
software-based receiver, which limits the audience to DXers). It's still 
pretty limited in audio quality at MW and SW frequencies, and there's 
some evidence to suggest its useful range is limited, compared to an 
analog signal at the same power and frequency.

And because it's not a hybrid system, it's politically a non-starter in 
the US unless stations are willing to go digital-only or the FCC opens 
up new spectrum at 26 MHz. If THAT ever comes to pass (and I think the 
former scenario is somewhat more likely than the latter, though not by 
much), there is - at least in theory - an Ibiquity all-digital system 
that would be technically comparable to DRM, albeit still proprietary.

Bottom line: DRM is not a magic bullet. In the context for which it was 
designed - high-powered MW facilities in Europe/Asia/Africa on 
relatively uncongested channels - it has some promise of moderate 
success, IF analog MW more or less goes away in the process. It may also 
find moderate success on SW.

On the much more crowded North American MW band, with absolutely zero 
political support from anyone to abandon analog, I think it's likely a 
non-starter. Even if DRM does develop a workable hybrid system, it's a 
few years too late; much as many broadcasters would welcome an 
open-source system, the horse is pretty much already out of the barn (or 
perhaps locked up tightly within the barn, depending on how you see it.)

And of course such a hybrid DRM system would be an "IBAC" system just 
like Ibiquity's, with all the interference issues that go with it.

It's too bad; I certainly like the approach of the DRM contingent more 
than the proprietary Ibiquity way of doing business.

s
_______________________________________________
IRCA mailing list
IRCA@xxxxxxxxxxxxxxxx
http://montreal.kotalampi.com/mailman/listinfo/irca

Opinions expressed in messages on this mailing list are those of the original contributors and do not necessarily reflect the opinion of the IRCA, its editors, publishing staff, or officers

For more information: http://www.ircaonline.org

To Post a message: irca@xxxxxxxxxxxxxxxx