Digital Audio Broadcasting

Or DAB for short. I heard it was great in the home but doesn't work
well at all in cars due to multipath. The system uses OFDM I think. Can
anybody confirm?


Naebad

naebad wrote:

> Or DAB for short. I heard it was great in the home but doesn't work
> well at all in cars due to multipath. The system uses OFDM I think. Can
> anybody confirm?
> 
> 
> Naebad
> 
Dunno.  OFDM is supposed to be particularly resistant to multipath 
because of the length of the symbols, but I don't know how robust the 
decode algorithms are to rapidly changing multipath.

-- 

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

See

http://www.ibiquity.com/hdradio/index.htm

I saw a demo there (in Columbia, MD) in late 1996 that handled
multipath very well (don't know if demo was representive of actual
performance or not). Also, don't know if things have changed since
then.

It is pretty cool that the digital radio spectrum overlays the analog
radio spectrum for the same channel so both analog and digital signals
are accessible.

Dirk

Hello Naebad,

> Or DAB for short. I heard it was great in the home but doesn't work
> well at all in cars due to multipath. The system uses OFDM I think. Can
> anybody confirm?
> 

Ok, maybe I shouldn't ask this from an EE point of view but I'll do it 
anyway: Who really needs DAB?

IMHO AM and FM are working quite well. Considering the rather bland 
content of many of the stations that are owned by large enterprises I 
also wonder what would improve from a listener's point of view.

Regards, Joerg

http://www.analogconsultants.com

Hello Tim,

>> Or DAB for short. I heard it was great in the home but doesn't work
>> well at all in cars due to multipath. The system uses OFDM I think. Can
>> anybody confirm?
>>
> Dunno.  OFDM is supposed to be particularly resistant to multipath 
> because of the length of the symbols, but I don't know how robust the 
> decode algorithms are to rapidly changing multipath.
> 

There'll also be drop outs. If there is enough data redundancy a 
buffering scheme like it is used for web casting can work. But even 
there it often doesn't. For listening to overseas broadcast I went back 
to the trusty old shortwave receiver. It's right here on my desks and 
works much better.

I have listened to a few digital transmissions. When analog gets close 
to the noise you can still make out what is said. In digital it goes 
like "And the latest from P   is  tha  ning   cars   e  co  zard  the  ic".

The real multipath disappointment might hit all those local terrestrial 
TV stations when the FCC order the analog plug pulled. I can already 
smell major layoffs when the ad revenues tank because of that.

Regards, Joerg

http://www.analogconsultants.com

Joerg wrote:

>> Or DAB for short. I heard it was great in the home but doesn't work
>> well at all in cars due to multipath. The system uses OFDM I think. Can
>> anybody confirm?
> 
> Ok, maybe I shouldn't ask this from an EE point of view but I'll do it
> anyway: Who really needs DAB?

Who? All the EEs to design new gear. All the stores to sell new
DAB gear to people who think they need it. All the installers
who can put the gear in cars and houses for people.

Good formats are replaced every 20 years or so to keep
the engine of commerce working.


-- 
Pat

Hello Pat,

>>Ok, maybe I shouldn't ask this from an EE point of view but I'll do it
>>anyway: Who really needs DAB?
> 
> Who? All the EEs to design new gear. All the stores to sell new
> DAB gear to people who think they need it. All the installers
> who can put the gear in cars and houses for people.
> 
> Good formats are replaced every 20 years or so to keep
> the engine of commerce working.
> 

That's kind of my thinking as well. But it won't create many jobs in the 
US. It'll all come from China, engineered in India.

Radio has a rather low appeal factor these days with consumers. So what 
if hardly anyone makes the move and buys the new DAB gear? Buys iPods 
and X-boxes instead? Right now I think that's kind of happening with 
terrestrial DTV. No takers. And I am not going to be one of the takers 
either unless there is a substantial increase in worthwhile content 
(which I do not see).

Regards, Joerg

http://www.analogconsultants.com

The sound quality is better.  Quoted results are CD quality for FM
stations and near FM quality (stereo IRCC) for AM stations.  If people
will pay a large premium to put a Bose or more expensive sound system
in their car, I think there is some interest.

Dirk

Hello Dirk,

> The sound quality is better.  Quoted results are CD quality for FM
> stations and near FM quality (stereo IRCC) for AM stations.  If people
> will pay a large premium to put a Bose or more expensive sound system
> in their car, I think there is some interest.
> 

But let's face it. The majority of people who put Bose systems in their 
cars are kids and they aren't listening to radio. You can hear them 
coming when they are still two miles away. First the boom sequence of 
the rap song, then the exhaust roar of their Honda low rider. One 
neighbor owns the coolest: He built air suspension into his low rider 
truck and when he arrives at home, phsssssst, his truck lays down onto 
the road for the night.

Adults seem to be similar, except that they usually don't listen to wrap 
music. Whenever I carpool with someone I find that hardly anyone has the 
radio on. It's mostly CD, with some going to iPod.

Regards, Joerg

http://www.analogconsultants.com

dbell wrote:
> The sound quality is better.  Quoted results are CD quality for FM
> stations and near FM quality (stereo IRCC) for AM stations.  If people
> will pay a large premium to put a Bose or more expensive sound system
> in their car, I think there is some interest.

Expense is often more important than sound quality. (Monster cables, 
etc.) Years ago, my wife and I were driving home a long way and heard a 
familiar piano concerto that we couldn't immediately recognize as 
Chopin's 1st. We listened intently, hoping for clues. The mono radio had 
a 3x10" speaker with an open back facing up in the dash ( bouncing the 
highs off the slanted windshield). After a few minutes, we said almost 
simultaneously, "It sounds like Emanuel Ax" (me) and "It sounds like the 
Philadelphia orchestra" (wife; Ormandy's free bowing is distinctive). We 
were both right.

There's a minimum amount of sound quality needed to make those 
judgments, but it's evidently not as high as vendors would like us to 
think. A great deal less quality suffices to identify the work, but that 
came only later. I'll not subscribe to DAB any time soon.

Jerry
-- 
Engineering is the art of making what you want from things you can get.
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