The horn blends with all the instrument groups in the orchestra better than any other instrument.
Horn + brass instruments
If the horn is used in combination with other brass instruments the sound becomes thicker: cup and funnel-shaped mouthpieces mutually cancel out their characteristic sounds.
Horn + horn
Because four horns are usually used in the orchestra, chords are often written for four horn parts.
Horn + tuba
The sound of the tuba as the median between the sounds of the cup and funnel-shaped mouthpieces blends very well with the horn.
Horn + trumpet, trombone
In unison with the trumpet the horn loses its mellow euphony, the composite sound assumes a little of the trumpet’s metallic edginess and becomes more sober as a result.
In chord combinations of horns with trumpets and trombones the instruments’ dynamics must be carefully balanced: Played piano all brass instruments sound at more or less the same volume; but a horn played forte has only about half the volume of a trumpet or trombone played forte. These discrepancies can be compensated for by using proportionate dynamic instructions: trombones or trumpets pp = horn p. A trumpet or trombone played forte corresponds roughly to two horns played forte.
Horn + woodwinds
Horn + oboe
The combination of horn and oboe only produces a homogeneous sound if the horn is stopped or muted.
Horn + clarinet, bassoon
Horns, clarinets and bassoons played in unison blend very well.
The horn/bassoon combination is very effective when the bassoon plays the bass part. Blending is also very good with the bass clarinet when the latter plays pp or p.
Framing the woodwinds with horns is not recommended, because the latter smother the former.
Horn + strings
Strings combined with horns blend into a homogeneous overall sound. The cello is particularly suitable for playing in unison with the horn, since both have more or less the same pitch. This combination increases the intensity of the sound of both instruments.
A particularly pleasing effect is achieved when the muted horn is played with muted strings, as in Richard Strauss’s opera Salome.
The horn is allocated a wide variety of functions thanks to its numerous possibilities of expression:
In closed chord groups, for the playing of melodic, harmonic or rhythmical passages, or as a solo instrument, in unison with several other horns for the evocation of distinct, dominant themes; the horn section can be assigned a number of specific tasks (performance of filling-in parts, counterpoint parts or sections of these, bass parts, tremolos or trills, figurations etc.).
The horn frequently carries the main musical theme.