The alphorn is an instrument which uses natural harmonics. The player has to vary the pitch without help from fingerholes, which make it possible to raise the fundamental pitch of a wind instrument, or from valves with additional tubing which can be opened to lower the fundamental pitch. It is by adjusting the speed and force of the lip vibrations which are transferred via the mouthpiece to the air inside the cone that the breath entering the cone can be periodically interrupted. This produces so-called natural harmonics.
Originally it was the length of the particular tree used to make the horn that determined its fundamental pitch. Nowadays the measures required to achieve the desired pitch are known, which means that horns tuned to the same pitch can be played together, or with other musical instruments.
In the tempered tone system the octave is divided into 12 semitones. On the alphorn the chromatic scale can only be produced from the fourth octave on. In the lower octaves the natural harmonics are far apart: in the deepest register they are a whole octave apart. In the second, a fourth and a fifth can be heard, and in the third the thirds are also there.
An amateur player can play some 13 natural harmonics over a range of not quite four octaves. Virtuoso players, however, can achieve more than twenty harmonics over four and a half octaves.
In the selection of tones usually played on the alphorn, there are three which do not occur in the tempered tone system. The 7th natural harmonic is a slightly high B; the 11th sounds distinctly higher than F, but too deep for F sharp, and the 13th is somewhat higher than A flat. The easiest of these three "wrong" tones to recognise is the 11th natural harmonic. It is known as alphorn F.
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