DAB Digital Radio radio reception.

[KAZ12MAR12]

I do hope that this subject doesn't "Rub anyone up the wrong way"! Would it be useful for members to quote their experiences of this "Wonderful New method of receiving wireless signals" and what equipment they use?
When (November 2005) Roberts introduced their first "Proper mains DAB model RD-22" SWMBO volunteered to have one in our dining room: it is the one that comes with a 17 minute pause facility as well as credit card size remote control and FM reception.
All in all we are very satisfied with its sound quality and versatility: it's been in regular use for nearly SIX years with not a sign of "Bubbling chip fat noise"
using its own telescopic aerial.
Since its first introduction my children (Well the youngest is 29 and the oldest 50) have got hold of the one with a "Docking station" for their must have devices and apparently it does a good job with their favorite genre of "Music".
I realize that we are fortunate in having good reception here in North Bucks.
I should mention that I have lobbied my MP and Jeremy Hunt to slow down the cessation of analogue transmissions but my limited experience of this media is good in terms of quality and signal strength.

[Joe]

Agreed.

I've got a Bush PSDA2014MP3. I got this cheap off e-Bay as its battery was shot. Sorting that was a simple matter and I've no complaints at all. It meant to be used with head-phones but I often plug it into something else with speakers; at this moment it's connected to my Ferguson 104A.

Like you I don't have any problems with bubbling mud, or at least far less than I am troubled by hiss on FM. Where I live analogue reception is quite poor and I got this cheap DAB radio as I was far from sure that it would work.

The main thing I like about it is the extra stations available. I would certainly prefer to see it remain s an adjutant to rather than a replacement for conventional broadcasting.

- Joe

[DODGERN]

Yes, it has it's place alongside FM and AM but not as a replacement.
It must only be complimentary to analogue because of reception problems in some areas, especially on motorways. Digital transmissions do seem to have signal break-up problems. You have only to listen to football live reports to witness this. Sometimes mush or hiss is preferable to no sound at all. The signal search on radios without pre-sets is also annoying. No doubt these problems will be overcome in time.

Roger.

[Joe]

This thread seemed to make more sense here. Besides that it gave me a chance to practise moving one!

Joe-

[Mark Hennessy]

I frequently swap from DAB to FM on the same station on my Philips radio and you can hear that DAB lacks bass, mind you the station I listen to (The Beach) it's FM is 320KB/s+ DAB is 128KB/s so in numbers it's lower quality.

Hello,

First, what do you mean by "it's FM is 320KB/s+"?

Next, much as I agree that DAB isn't a suitable replacement to FM, you can't say that it lacks bass. Far from it. The most likely conclusion is that your DAB radio lacks bass, but that's not the fault of the DAB transmission system.

You need to compare apples with apples. Let's start at the broadcast end - hopefully this is vaguely interesting...

The signal from the mixing desk in the studio might well go through routers and other desks before they reach the output end of the station, where they split for FM and DAB. But once split, they might be handled slightly differently - in the BBC, there are separate compressors for FM and DAB. Just to avoid doubt, when I say "compressor", I mean a dynamic range processor. Optimod are a big player in this field. Of course, these processors might well be set slightly differently for each feed, depending on the target audience. But while these are differences, they don't remove or attenuate bass for the DAB feed.

I can't speak for the commercial broadcasters, but I found a document a while back that detailed Classic FM's operation. They don't do any dynamic range processing on the DAB feed, which I thought was interesting.

Next, the FM signal goes to an FM transmitter. These neither boost nor attenuate the bass end.

Meanwhile, the DAB signal needs to be compressed. When I say "compressed", I mean data-rate reduced. In other words, the signal is MP2 encoded. MP2 encoding is often maligned, but it's actually very good when used at its design bit-rate of 256kb/s or above. It's less good at the 112kb/s that Absolute 80s uses, but I'll return to that in a moment...

Either way, bass is not affected by this process. Indeed, the first sub-band*, which covers 0 to 750Hz, is treated with the most "respect".

*A full explanation of MUSICAM is beyond the scope of this post, but suffice to say, it starts by dividing the band up into 32 sub-bands, each 750Hz wide, sampled at 1.5KHz. The higher sub-bands are treated "less well"

Finally, we're down to comparing differences in receiver design. The signal appearing at the FM detector, or the DAB DAC output ought to be pretty good. What happens next is the problem. There are many ways to build audio amplifiers and loudspeakers, and not all of them are good.

The only valid test is to use high quality FM and DAB tuners feeding a decent monitoring system, where the amplifiers and loudspeakers are common to both. Which is what I have downstairs. Where I have never noticed DAB lacking in bass

Unfortunately, people are quick to jump to conclusions, based on a lack of rigour. For example, I know people who think MP3 is rubbish, just because they don't like the sound of their iPods driving the standard headphones. But, what these people haven't done is to make a .WAV file of the same tracks, and listened to it on the same playback system as the .MP3 - thus using the same DAC, amplifier and headphones. Instead, they have formed an opinion of MP3 based on the crummy amplification and headphones that come with an iPod (and those "buds" are pretty bad!).

Back in the MiniDisc days, I did something similar. People were making recordings and doing playback via the analogue ports of their MD decks, so as well as the compression scheme (ATRAC), they were hearing the sound of the ADC and DAC converters. I solved this by using an external DAC that I could switch between the S/PDIF outputs from the CD player and MD deck. The optical output of my CD player went into the MD deck. So no ADC required, and the same DAC was used for both sources - i.e. the CODEC was isolated for all to hear. Not that anyone could hear a difference :D

Yet bizarrely, I could hear a difference with an old DAT recorder (remember those?). Despite it being 16 bit linear (no compression), it wasn't that nice to listen to. Why? A mis-aligned ADC...

At work, I have a number of demo CDs so that people can hear before/after samples. And they also contain difference tracks, which allow you to hear what was altered by the coding process. There is never any bass content in the difference tracks - but often a fair bit of HF, especially for sibilant speech.

I'm not saying these schemes are perfect, BTW. Just this weekend I heard MP2 coding artefacts on Radio 3, which surprised me because it's running at a reasonable bit-rate. But quickly switching to FM confirmed it. FYI, it was a Sarah Vaughan song, played just before midday on Sunday. The vocal was very "scratchy" on DAB - classic quantisation distortion caused by not allocating enough bits to the sub-bands concerned. Another way to upset MP2 is harpsichord music, BTW...

Back to Absolute 80s, when I listen to that, I rarely, if ever notice MP2 distortion. But what really irritates me is the overly heavy dynamic processing that causes the output to "pump". But this has nothing to do with DAB; this is a bad setting of the Optimod...

Hopefully this background is interesting to people with an interest in radio. It's all to easy to forget how the signal got on the airwaves

Mark

[Joe]

Not interesting, Mark. Fascinating would be a better word! Thanks for taking the trouble to post this.

I've got Absolute 80s on 247m on my Fergy at which is playing White Snake at present and sounding damned good.

- Joe

[KAZ12MAR12]

You're dead right Joe I will have to really study Mark's very interesting response so that I may be better educated; his profile describes him as a lecturer: wish I'd attended some of them!!
Best regards
John

Not interesting, Mark. Fascinating would be a better word! Thanks for taking the trouble to post this.

I've got Absolute 80s on 247m on my Fergy at which is playing White Snake at present and sounding damned good.

- Joe

[tiv48]

dab can sound good(if the broardcasters dont reduce the bit rate too much) but fm sounds better maily on live music from radio 3
rob t

[Yorkie]

Thanks for an informative posting Mark, from someone 'on the inside track' at the Beeb!

I've had a Pure Evoke-1 with a second speaker for some years now, which was a present, and I've been really pleased with it. DAB sounds fine to me, but you rightly make the point that many who listen to AM do so on higher end tuner-amps with much better speakers. If I compare my Evoke to a similar sized FM portable, any diffrences are to my ears, indiscernable. I'm inclued to the view that many who say DAB is rubbish, are in the audio-fool camp. who think that gold plated mains flex improved the quality of the audio from their hi-fi sets.

Unfortunately, some stations aren't good on the telescopic aerial on my Evoke-1 - Classic FM for example, which is fine of FM, but I guess that's due in part to the reception area I'm in.

You right about MP3 players and bud earpieces too. I've got a little i-pod nano, but I used a pair of Bose over-the-ear folding headphones that fit into a compact hard case. I find it quite astounding that so much misic can be stored and playbe back from such a tiny thing, at such quality.

Although I've reached the age at which I qualify to be called a 'coffin dodger' my hearing is good and I've always taken care of it by wearing ear defenders when using power tools, lawnmowing, and when riding a motor bike, which I did for many years until a couple of years ago. Ears are of course the one component in whatever audio system we use, that are the limiting factor, which no sound system, transmission mode, or any amount of money spent on gold plated flexes and plugs is going to alter!

As to the rate at which DAB is adopted as a replacement for FM, that will be determined by the point at which many millions of cars have DAB reception facility and country wide coverage with few 'not-spots'. That's going to take years, considering that most new cars being sold today still don't have DAB radios as standard - only as an expensive optional extra. High listerneship is essential for the survival of commercial broadcasting stations.

That's my take on things.

David