The difference isn't HD vs SD per se, but HD where AC3 is used as the codec. Certainly the BBC seem to adhere to some sort of AC3 movie standard meaning that to watch a normal programme, say Strictly, you have to increase the listening volume to 70, where 55-60 would suffice for non-AC3 encoded channels. It is a little irritating but not too tricky to deal with.

Chris
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