Originally, the French horn ( the third highest in pitch behind the trumpet and cornet) was a simple development of a hunting horn made from the horn of some animal. Concerns rose as the complexity of music increased regarding the accuracy of the instruments in the higher registers... and a bloke by the name of Kruspe developed the double, or German horn... a clever idea that uses a 4th valve to control the length of the horn allowing the hornist to alternate between the deeper, warmer sound of the French and the more hysterical, higher notes of the German horns. In essence, that cuz made the sound crusper.
