I can get DAB, digital terrestrial, Sky, the iPlayer and FM. Which one of these gives the best quality sound from, say, a Radio 3 concert?
The BBC's online iPlayer gives the best quality with Radio 3 for two reasons. First, it uses a higher-quality codec than the other digital systems. Second, it and does not have any dynamic range compression (DRC), which means the loud parts are louder while the quiet parts are quieter.
Radio 3 is currently broadcast at 192kbps on Freeview, Sky, and DAB using the MP2 codec, which should have been pensioned off by now. Radio 3 on the iPlayer is 192kbps using the much more advanced AAC codec, and has better stereo. Not many listeners will be able to distinguish this from a CD. (Note: bit-rates may vary.)
On FM, Radio 3 uses DRC to reduce the dynamic range. AM and FM radio stations do this to make the quiet parts of the music sound louder, otherwise you would not be able to hear them over the background noise of your car tyres and engine. If you turned the sound up to compensate, of course, you'd be deafened by the loud parts. FM also has some low-level hiss and may suffer from interference.People vary in their sensitivity to the digital artefacts produced by compression, and to the effects of DRC, so I'm sympathetic to those who prefer FM to iPlayer, or vinyl to CD, or vice versa. However, an iPlayer signal should sound better if reproduced via the same hi-fi system. One day, I'll try it.