This term, technically used, covers wind instr. formerly made of that metal, some of which, however, are now sometimes made of other metals; it does not incl. instr. formerly of wood but now sometimes of metal, e.g. fl., nor does it incl. metal instr. with reed mouthpieces, e.g. sax. and sarrusophone. Each instr. possesses a mouthpiece of the nature of a cup or funnel to be pressed against the player's lips, which vibrate within it something like the double reed of the ob. family. The shape of this mouthpiece affects the quality of the tone, a deep funnel‐shaped mouthpiece (e.g. hn.) giving more smoothness, and a cup‐shaped mouthpiece (e.g. tpt.) more brilliance. The shape of the bell with which the tube ends also affects the character of the tone as does the nature of the tube's bore, i.e. cylindrical or conical.
‘Natural’ brass instr., playing merely the notes of the harmonic series of their ‘fundamental’ note, are no longer in artistic use, a system of valves having been introduced which makes it possible instantaneously to change the fundamental note of the instr. and so to have at command the notes of another whole harmonic series. However, composers sometimes ask for a ‘natural’ sound, e.g. Vaughan Williams in his Pastoral Symphony (2nd movement) and Britten in his Serenade. And the ‘natural’ hn. is often used today for 18th‐cent. mus. The tbs. have always formed a class apart, as they possess a sliding arrangement by which the length of the tube can be changed and a fresh fundamental, with its series of harmonics, quickly obtained. Usual brass section of orch. comprises 4 hn., 3 tpt., 2 ten. and 1 bass tb., 1 tuba, with additions as specified.