The number of listening hours registered by Rajar's diary system fell from 1.076 billion in the third quarter of 2011, to 1.023 billion.
The Rajar period ran from 25 June to 16 September, including the Olympics and the Paralympics.
As in TV, commercial radio stations were shut out of the Olympics by the BBC's host broadcaster status.
Commercial radio was not especially impacted by the BBC's performance, with its share of hours holding steady at 43.3%.
But as it and the BBC had a smaller cake to divide between them, commercial's hours dropped from 466 million last year, to 443 million, and the BBC's hours dropped from 586 million to 554 million.
The movement of radio consumption to digital platforms unexpectedly took a backwards step. Having reached a record 31.5% in the second quarter, digital's share dropped back to 31.3% in the third.
While DAB and digital television listening increased from the last quarter, online listening (which includes apps) dropped from 4.6% to 4.2%.
However, digital's share is still up year on year, from 28.2% in the third quarter of 2011.
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