07-11-2012, 01:37 AM
(06-11-2012, 05:18 PM)Steve_P Wrote: Why give up good sounding FM for rather poor DAB radio. Mine hasn't been switched on for 4 years now because I'd rather listen to people speaking sense and decent music. All I get on DAB is bubbling mud and trashy music played in bubbling mud.
Steve,
If you are hearing bubbling mud, this is telling you that you have a reception problem.
When the standards were being agreed - roughly 20 years ago - it was decided that the listening public wouldn't like the "digital cliff" effect. So, rather than have an "all or nothing" scheme, it was decided to build an error detection and correction scheme that has a bit of a "soft" edge. In other words, with a good signal, the signal is perfect. With errors exceeding a certain rate, the error correction causes the "bubbling mud"effect. When the errors reach the next level, then the signal mutes completely.
In other words, the bubbling mud is a deliberate and intentional effect that informs listeners that they need to improve their aerial system.
Unfortunately, the public doesn't realise this. So they associate bubbling mud with MP2 compression. People knock DAB, saying it uses an outdated codec, and DAB+ (with AAC) will be much better. Not so!
Your Freeview box uses MP2. But do you ever hear bubbling mud when watching TV? Thought not...
MP2 is great. It's much better than most people give it credit for. The same could be said about DAB itself. Aside from the bubbling mud, the audible problems with DAB are caused by poor system design and poor operational practices - nothing to do with the DAB medium itself. Indeed, arguably, the DAB medium offers a more direct "window" into the transmission signal, so problems at the broadcast centre are easier to hear.
The biggest problem with radio in general is dynamic range compression. All stations use it; most use it excessively. The so-called "loudness war", that started back in the 1980s, is still all-pervasive today. If I listen to DAB radio, I don't hear problems caused by MP2 data-rate reduction. I hear problems with signals bouncing off the limiters because people are over-driving the desk. In local radio, operators use the faders as switches, with no regard to levels - the Optimod processors prevent the transmitters from over-modulating.
As an aside, I was in the basement of BH in London today, looking at the Optimod processors for the national services. They have bargraphs showing the incoming signal and the leaving signal. It's very dramatic, especially on R1. From the desk, a lot of dynamic range. Leaving the processor, almost none. Literally, you can hardly see the level meter move. Just a dB or two. I took pictures, but the battery in my camera went flat shortly afterwards...
Just to be clear, I don't advocate FM-switchoff. We have a long way to go first - not least with car stereos and portables. The public don't get DAB because they don't feel the need for more stations when all the commercial offerings are indistinguishable anyway. Long live FM, definitely.
But, DAB is fine. More bit-rate would be nice; more discrete-stereo services would also be an improvement, but where I live, DAB generally sounds much better than FM. I am much more sensitive to multipath distortion than MP2 artefacts. In careful tests, most people are much less able to perceive MP2 artefacts than you might imagine. Yes, AAC might be better, but if we moved to DAB+, just how long do you think it would be before they decide to wind the bit rates down to very low levels? And don't forget that a move to DAB+ would render the majority of existing sets obsolete...
My DAB listening is mostly on an Arcam Alpha 9 - very nice, and expensive back in the day. Mine was rescued from a skip, and just needed a new voltage regulator IC. I also have a Genus Type R portable, which sounds most unlike typical portables. If anything, it lacks treble. And it looks like a Hacker, which was the reason for buying it!
