Another technique long known but rarely touched upon in print is horn chords, also referred to as vocalizations or multiphonics.
How and why
Barry Tuckwell in Playing the Horn presents how to play them and also why to play them.
The playing of chords on brass instruments used to be considered a cheap music-hall trick, although Weber uses the effect in the cadenza of his Concertino, even if the printed notes he asks for are not possible. Now, however, it is used by many serious modern composers and must be accepted as a part of the basic horn-playing technique.
To play chords the player must play a note and sing another note with the voice typically a fifth or sixth away. This produces as Tuckwell notes a chord “produced by resultant tones” if the two sounds “are well matched dynamically and are perfectly in tune.” He further notes that
It is for each individual to decide whether to sing above or below the played note; this will depend on the vocal ability and the register required. All intervals other than fifths and sixths produce overtones outside the limits of the tempered scale; third, quarter, there-quarter tones, and so on. If the sung and played notes are brought close together, a definite beat will be heard when the two sounds conflict.
Coordinating the buzz and the voice
Douglas Hill has a fairly extended discussion of vocalizations in Collected Thoughts on Teaching and Learning, Creativity, and Horn Performance, with exercises designed learn the effect. He suggests the key is “learning how to coordinate the aperture buzz with the voice.”
Traditionally I would also add that it was thought to be an effect more suited to the male voice. However, Hill notes in one of his exercises to “Try the following, either as is or up an octave for higher voices.” The effect can work for a hornist of any vocal range.
As his book is still available I will leave it to readers to track down his specific suggestions, but for those that would like to try to play a horn chord I would suggest one of the following as a first pair of notes to try, adjusting the voiced note up an octave as needed. A traditional approach would be to play a low C (an octave below the staff written) and sing the G above it. An alternate would be to play that same low C but sing the E on the bottom line. If you get either interval well in tune magic happens and you will begin to hear another note come in, the resultant tone.
As to a work to try, as Tuckwell indicated, the Weber Concertino is not written in a way that really works.
There are a few others to chose from. A favorite of mine being Sonorites II by Walter Hartley, from which this brief example was selected, with instructions by the composer. It is the same chord I suggested trying earlier, but down a half step and showing the resultant tone. The voicing of all the chords in this composition works well for me exactly as written. Composed in 1975 for the late Calvin Smith (“with special thanks to Frank Lloyd”) this short work is not heard often enough.
To conclude, horn chords are not an effect for everyone, but are still well worth experimenting with for any player.