Sound is produced on all brass instruments by the performer’s lips, which vibrate together to make a buzz. The instrument becomes a resonating chamber when the column of air in the instrument is excited by this buzz. The tubing is made of brass, and the flared bell radiates the sound. Lip tension determines the pitch, greater lip tension producing higher harmonics based on the fundamental determined by the instrument’s length.
Before valves were commonly used with brass instruments, natural horns and trumpets were limited to pitches in the harmonic series, which explains how music was written for early brass. The length of the column of air could be altered by the use of "crooks," or additional short pieces of tubing inserted into the instrument. Some composers called for combinations of brass instruments pitched in different keys at once. Tuning slides were common on many brass instruments; these allowed the player to tune the fundamental down by a half-step on short notice. Parts were typically written in the key of C, and the length of the crook determined the sounding pitch. More information on the distance and direction of transposition for the various natural horns and trumpets can be found in the lesson on Transposition.
By the middle of the 18th century, horn players had adopted the practice of inserting their hand into the bell of the horn, lowering the pitch by a semitone or a whole tone to produce notes other than those available in a given overtone series. Varying the length of the tube by means of valves was introduced circa 1815, and modern valved brass became quite different from their predecessors. Most of the older trumpets were twice as long as their newer counterparts and sounded an octave lower.
The modern trumpet has penetrating power in its upper register, but in the middle to low registers it can be played softly and blends well. Having a wide dynamic range throughout its compass, the trombone can be an assertive voice or blend well with other instruments in any register. The horns, due to their conical bore, length of tubing, and shape of mouthpiece, are not as penetrating in their middle and lower range. A popular adage is that it requires a pair of horns at a moderate to loud volume level to balance with one trumpet and one trombone if all instruments are in their middle registers. Orchestrators should allow brass instruments to lead up to high pitches, rather than asking them to hit high notes without preparation. In this respect treating brass performers as one would treat vocalists is wise. Chords scored for trumpets and horns generally sound better in close spacing than in open position, as is also true of trombones together in their upper register. A wide interval between second and third (bass) trombone also produces a well-balanced sound from the section.
Vibrato: Alternate small variations in pitch above and below the actual center of a tone. This is not a normal aspect of traditional orchestral brass technique. Three types of vibrato are possible: diaphragm, jaw, and mechanical. The jaw vibrato is most commonly used.
Lip trill: Vacillate between two pitches by tightening and loosening the embouchure; no change in fingering or slide position is made. Lip trills are most effective in the upper register, where consecutive overtones are closer together.
Glissando: Slide smoothly between two pitches, sounding some or all of the pitches that lie between. It may move upwards or downwards.
Brassy tone (IT: metallizzare i suoni, FR: cuivre, GER: schmettern): Produce a strident, forced sound with metallic quality. This is used only at loud dynamic levels.
Bells up (It: campana in aria, Fr: pavillon en l’air, Ger: Schalltrichter auf): Raise the bell for better projection as well as the visual effect.
Multiphonics: Play one pitch and hum another.
Straight: Most common, made of metal or cardboard; produces a bright, pungent sound. This type is used when the term "muted" is indicated for orchestral brass.
Cup: Produces a colorless, nasal sound without any edge.
Mica: Similar to the cup mute, but mellower with a little more natural sustain.
Harmon: Metal mute with an adjustable stem; sound has a sharp edge.
Bucket: Also called Velvetone; used for mellow, soft sound with no edge.
Whispa: The softest mute; absorbs the sound.
Solotone: Rarely found; the tone is nasal with some bite.
Mutes make instruments more difficult to play. Conservative passages that avoid extremes of range work best when mutes are applied. Allow sufficient time to insert and remove the mute. Two measures at a moderate tempo is adequate, assuming the player is prepared. Brass instruments may also be muted by playing into the stand or by covering the bell with the hand, a hat, or a plunger.