In wind instruments, the air contained in a dedicated tube is made to vibrate directly by the musician's breath or a mechanical device (as with the organ). These instruments are usually divided into distinct families based on the material used to build the tube. From a physical point of view, however, the distinction between woodwinds and brass depends more on the way the air is set into vibration than on the material: the flute is made of metal and the saxophone of brass, but both are woodwinds. In woodwinds a reed, or an air jet striking an edge as in the flute, excites the air column, and the note is changed by opening and closing holes along the tube; in brass instruments the player's lips vibrate, and the note is changed by selecting a different resonance of the tube or by lengthening it with valves or a slide.

Wood instruments

The family of wood instruments includes the piccolo, oboe, English horn, bassoon and contrabassoon. The oboe and the bassoon are excellently characterised in Peter and the Wolf by S. S. Prokofiev, where the oboe is the duck and the bassoon is the grandfather: oboe, bassoon. The family also includes the clarinet, which is exemplified in this nostalgic theme taken from the second movement of W. A. Mozart's Concerto for Clarinet and Orchestra K. 622 that was used in several breathtaking scenes in the film “Out of Africa”. Moreover, it includes all wind instruments (i.e. those based on the principle of injection of air in a tube open at one end) built of wood (except the traverse flute). Sound is produced by a (single or double) reed that, thanks to the stimulus of the musician's lips and breath, makes an air column vibrate inside a resonance tube that usually ends with a bell (a slightly cone-shaped flaring). The traverse flute, which belongs to this family even though it is not made of wood and has no reed, is perhaps one of the instruments that offers the greatest variety of articulations and timbres (e.g. the famous solo by Ian Anderson of Jethro Tull, which is a jazz revisitation of a Bourrée by J. S. Bach with "staccato", flutter tonguing and other percussive effects). Sound pitch changes thanks to the multiple effect of air pressure changes, lip position changes and special keys moved by the fingers.

Brass instruments

The family of brass instruments includes the trumpet, trombone, horn, tuba and all instruments based on the principle of injection of air through a mouthpiece in a brass bore. In this case, the vibrating reed (which excites the air column) is replaced by the lips themselves that do the same work. Sound pitch changes thanks to the double effect of the lip tension, which together with the breath pressure selects which resonance of the tube sounds, and of pistons or cylinders controlled by the fingers, which lengthen the tube (in the trombone, the tube is lengthened with the slide). Brass instruments (especially in large ensembles) often play “fanfares” or evocative musical motifs (as we can hear in this passage from the first movement of J. Brahms' Symphony no. 4). However, sometimes when playing solos, they can be employed in unusual ways (including: the long horn “solo” in the second movement of P. I. Tchaikovsky's Symphony no. 5; the saxophone melody (the saxophone is in fact a woodwind, since it has a reed) in the famous Bolero by M. Ravel; or the majestic use of the trumpet by E. Morricone in his many western film soundtracks, such as Once upon a Time in the West).

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Further reading and links

• Related questions and answers:
  • Why do the flute, clarinet and oboe play in completely different registers even though they are almost the exact same length (about 60 cm)?
  • How important is the material with which a wind instrument is made?
  • Is it possible to play two notes simultaneously with one wind instrument?
  • If a free reed, like that of an accordion, is fitted in place of the head joint of a recorder, why does the note not change when the holes are opened and closed?