I think we are looking at a short scale single strung archlute tone transposing. Ed astutely pegs the tuning. You could call it attiorbato I suppose....though that word may just mean theorbo.
Having played this piece quite often, that is the easiest solution (down a step), though I prefer the middle movement slightly in D on the archlute. Also works nice on 6 course mandolin, and archlute in mandolin tuning. On mandolin you have not the parallel octaves, and the modulating parts are easier with the open e string in the middle. Extensive slurring on the fast notes in this performance, which is fine but I prefer those notes plucked. Orchestra is way bigger than I like for this piece, that little spot mic near the bridge (schoeps cardiod maybe) is doing the heavy lifting. In the slow movement I personally use piombi for the fiddles--mutes made of lead. With organo chiuso (the shutters closed). Often referred to as Vivaldi's guitar concerto, Vivaldi wrote no works for guitar, but everything else including the clarinet. dt To get on or off this list see list information at http://www.cs.dartmouth.edu/~wbc/lute-admin/index.html
