French Horn Stopping Why the Pitch Shift?

The opening four points of this article point out the 4 special challenges of playing the modern French horn. When the player uses the "stopping mute", he/she must transpose the music down one semitone in order to play in the correct key. This inconvenience is discussed in the middle three paragraphs. The last section is more of a "physics" approach to producing music on the modern French horn. Using illustrations and a detailed explanation, the author explains how sound is produced on the instrument.