General characteristics

The horn is the second highest instrument in the brass family. The single horn is usually pitched in the key of F, although smaller instruments (for children or for specific professional uses) may be pitched in B-flat. Compared to the other brass instruments in the orchestra, it has a very different mouthpiece, but has the widest usable range - approximately four octaves, depending on the ability of the player. To produce different notes on the horn, one must do many things - the four most important are pressing the valves, holding the appropriate amount of lip tension, blowing air into the instrument, and placing the hand in the bell. More lip tension and faster air produces higher notes. Less lip tension and slower air produces lower notes. The right hand, usually cupped at a "three o-clock" position in the bell, can lower the pitch, depending on how far into the bell the player puts it, by as much as a semitone. The horn plays in a higher portion of its overtone series compared to most brass instruments. Its conical bore (as opposed to the cylindrical bore of the trumpet or trombone) is largely responsible for its characteristic tone, often described as "mellow".
Today, music for the horn is typically written in F (or sometimes, notably in British bands, in E-flat), and sounds a perfect fifth lower than written (or a major sixth lower for the E-flat horn). The limitations on the range of the instrument are primarily governed by the available valve combinations for the first four octaves of the overtone series and after that by the ability of the player to control the pitch through their air supply and embouchure. The typical written ranges for the horn start at either the F-sharp immediately below the bass clef or the C an octave below middle C.