Well yes, there are, the sensors for wind instruments or bowed string instruments are really hard to get right. Never mind bowing, look at plucked string instr

Well yes, there are, the sensors for wind instruments or bowed string instruments are really hard to get right. Never mind bowing, look at plucked string instruments - there aren't any really successful guitar synths that are actually playable to any real degree. The old Roland analogues in the 80s did the best job using a hexaphonic pickup and six PLLs to track the string frequency but they still didn't track well on lower notes, which is why Pat Metheny plays so far up the neck.