I am new to this site so have no idea if anyone has posted anything about this already. However, forgive me if they have but this struck me as an interesting insight into Benedict as an actor, not to mention how the music is worked on in the series. This is Eos Chater's blog concerning her work as a violinist and member of the classical music girl group Bond. She was brought in as Benedict's violin tutor and has written her musings on her time with the series. It's a very revealing article and actually makes me like Benedict all the more.
http://earthobservingsystem.tumblr.com/post/15188532235/sherlock-on-the-fiddle
She worked on set to sync her playing with his but he had to acheive the appearance of an expert player. Look her up on you tube as well. Bond is a great group to listen to.