Amazing birdsong in Provence - but who was singing?

I've just come back from a short stay in the Luberon district of Provence.  I kept hearing this amazingly rich unfamiliar bird song which projected a long way.  It contained many different elements, from a very high weezing note, a sound like 'pretty, pretty, pretty, and much lower richer sounds.  Frustratingly, after standing for 20 minutes with binoculars near the hedgerow from which it appeared to be coming, I didn't catch a single glimpse of the bird!  I heard others in different places during my trip and the vocabulary was much the same in each case.  Any ideas?