Woodwind instruments are a subcategory of wind instruments that produce sound by blowing air on to a sharp edge, usually a single or double reed, and thus causing it to vibrate. Woodwinds differ from brass instruments in that the latter do not use reeds or sharp edges and are lip-vibrated, with the different pitches produced by alterations of both the air flow and the lip tension. Another difference is that woodwinds are non-directional, with their sound having approximately equal volume in all directions, whereas brass instruments are highly directional, with most of their sound traveling straight outward from their bell.
Despite their name, woodwinds can be made of any material, not only wood but also brass and other metal alloys, cane, and even ceramics, whereas brass instruments are made entirely of metal, usually brass, except for some small parts. Examples of single-reed woodwinds are clarinets and saxophones. Examples of double-reed woodwinds are oboes, English horns, and bassoons. Flutes differ from other woodwinds in that they do not use a reed, but instead produce sound with a flow of air blowing across an opening.