Venice, February 4th, 1715. … Towards the end [of the opera], Vivaldi played an admirable solo to accompany an aria, at the conclusion of which he added an improvisation that really frightened me, for I doubt anything like it was ever done before, or ever will be again: he came to within a hairsbreadth of the bridge, leaving no room for the bow, and this on all 4 strings, with imitations and at an incredible speed. He astonished everyone with this, although to say it touched me would not be true, because it was not as agreeable to listen to as it was cunningly contrived.
Wednesday, March 6th, 1715. Vivaldi, the famous composer and violin player, came to see me, for I had repeatedly left word at this house requesting him to do so. I had spoken of certain concerti grossi which I wished to obtain and had ordered them from him; and I had also sent him (since he belongs to the musical tribe) several bottles of wine. And so he let me hear his very difficult and quite inimitable improvisations on the violin; and I was compelled to admire his dexterity the more at close quarters, although I saw quite clearly that, while he played extra difficult and colourful things, he did so with no great charm or tunefulness.