by Géry Dumoulin
What is a wind instrument? Also called aerophones, wind instruments are characterized by the fact that their sound results from the vibration of air. In most cases, a column of air inside a tube is made to vibrate by a musician blowing, but there are also aerophones that vibrate ambient air around the instrument (a few examples: the whip, a displacement free aerophone, the rhombus (or "bullroarer"), a whirling aerophone, and the pistol, a plosive aerophone).
Most aerophones considered to be "wind instruments proper" have a tube (in various forms) in which air is vibrated by diverse methods. These methods define the different categories of wind instrument. Even if terminologies differ according to systematic classifications, we can distinguish three broad categories of wind instrument: "flute" style instruments - air is vibrated by being blown against an edge - "reed" instruments - air is vibrated by means of a single or double reed - and "trumpet" style instruments - air is vibrated by the player's lips on a mouthpiece. It's worth mentioning here that Victor-Charles Mahillon, the first curator of the mim, played an important role in the classification of musical instruments. In simple terms, the first two categories belong to the woodwind family and the third to the brass family. It is the method of sound production that decides which family an instrument belongs to and not the material the instrument is made of: so the saxophone, although made of metal, belongs to the woodwind family because it uses a reed, whilst the cornett, although made of wood, belongs to the brass family because it has a mouthpiece like a trumpet.
We know that the length of the column of vibrated air determines the pitch: a shorter tube produces higher pitched sounds than a longer tube. In addition, the method of air vibration is the main factor that decides the timbre and allows us to distinguish one instrument from another. The proportions of the air column (the bore) also change the timbre of an instrument. In order to make music and play melodies, it is necessary to be able to freely modify the pitch. A variety of methods are used in wind instruments. One of them is natural harmonics, the physical components of a sound. This is particularly the case for brass instruments before the invention of the piston valve: playing a natural trumpet or a natural horn is based solely on the use of harmonics, which the musician achieves mainly by varying the speed of vibration of his lips. The number of playable notes is often limited, and depends on the length of the instrument and the ability of the musician. Natural notes can then be modified in various ways to multiply the number of notes available in order to render the instrument partially or totally chromatic: stopped sounds (obtained by hand-stopping the instrument's bell to a greater or lesser extent), the slide, the finger holes or the keys (which obscure or expose holes placed in precise locations) and the piston valves (which add additional tubing to the main tube). In the woodwind family, it is mainly finger holes placed laterally along the body of the instrument that enable the musician to modify the height of a column of blown air. Closed by the musician's fingers, these holes can also be covered with rings or keys to facilitate playing.