Overtone is a phenomenon that happens when a single note is sounded and then a series of higher notes are produced or naturally occur simultaneously. The most common manifestation of overtone is the singing traditions of musical cultures in Mongolia and Tuva. It is called throat singing and the performer uses the tongue relative to the roof of the mouth to encourage a number of higher notes over a drone which are then employed to play a melody.
Normally this technique is not used in instrumental playing though flute players have commented that the sound of the instrument may be enriched this way. Australian Aboriginal player Alan Dargin played overtones on his didgeridoo. It is also the case that overtones are designed into bells, particularly church bells which accounts for the rich complex ringing that a good bell will produce.
In the case of horns and trumpets from ancient Ireland and Britain, their design including the absence of a choke and a wide-open mouthpiece allow for the inclusion of overtones. This is achieved by using a similar method to that of throat singers. Whilst a note is being played small movements of the tongue relative to the roof of the mouth behind the upper teeth will create distinctive higher notes.
Throat singing works because the tone generator, the voice is behind the mouth so that the sound is passed through from the vocal chords and may then be manipulated. However, in the case of ancient horns and trumpets the sound is created by the lips of the player so that the note happens in front of the mouth cavity. This should mean that it would not be possible to alter the sound. The alteration occurs and is explained by including the mouth, throat and lungs with the instrument so that the air vibrates over the whole length of the cavity from the diaphragm along to the bell end of the horn or trumpet. This would mean that the tone generator in this case, the lips, are approximately half way along the whole air cavity. Thus, deliberate alteration of the mouth can allow for the production of overtones.
It is not known if tone enrichment of this kind was used on the Bronze Age or Iron Age instruments in antiquity. Yet, there is no doubt that the use of these overtone methods have a startling effect on the sounds that may be played and give a whole new aspect to the idea of lip reed musical instruments from antiquity and how they may have been used.
See ‘Overtone’ – Ancient Music of Ireland album for examples of overtone.