THE SOUND THE FRENCH HORN MAKES can be modified in several ways. One of these involves pushing the hand that is not playing the valves into the bell of the horn so that it changes the pitch of the note that is coming out.
Another way to alter the pitch is to use a mute. Just as with all other brass and stringed instruments this makes the instrument sound more softly - but it can also produce some remarkable results.
A professional player will have several mutes for different effects.
Debussy used muted horns in the last five bars of his tone-poem L’Après-midi d’un faune which he completed in 1894. The result is quite magical, and suggests a sound that is coming from a long way away.
Steve Bell talks about some of the mutes he owns and how he uses them.