What instrument has the highest pitch?

The highest note written for any instrument in the symphonic repertoire is a Db, just over four octaves above Middle C, for a piccolo in Mahler's second symphony. Few piccolists actually manage to produce the note. A violin can, in extreme contidions and using special techniques, reach notes that are higher still, but it is still impractical for any performance purposes. Any modern day synthesizer can electronically produce pitches above and beyond the average human hearing limit of 20,000 Hertz.