Sound delay - DAB and normal radio.WHY?

ampersand

Happily listening to new DAB radio this morning(see lucky John Lewis price match post elsewhere)but am working between two rooms and have normal mains radio on, too.
The ordinary mains one is about 2-3 seconds ahead of DAB.
I probably won't understand an explanation, but will someone try and enlighten me, please?

custardy

i get the same on cable TV vs freeview
i assume the signal goes through some digital conversion before transmission

vyseyboy

I guess at the transmission end, they must do a on-the-fly conversion from the analogue transmission signal to a digital stream (is it a 96kbps mp3 stream? I think it might be.) And then it must somehow be encoded into the digital transmission multiplex.

This'll all be done on-the-fly by some kind of always on high-end computer, but the encoding process will introduce a latency of a few seconds, as there'll be a "buffer" of analogue input while the machine is encoding sound from a few seconds earlier. If that makes sense...? I've confused myself a bit there.

john_s_2

I've seen this discussed on a different forum, and I'm sure I heard it discussed on R4 as well.

My understanding is it's the decoding at your end - didgy radios (and television tuners) need to decode the signal before it's played. Unlike analogue signals.

What's more, different tuners decode the same signal at different speeds, so you're unlikely to be able to sync them up. I have various radios dotted around my flat although the only didgy one is my Sky box. Very annoying, although the hourly pips are quite interesting to listen to :-\

Progress eh?