Valves are used to change the length of tubing of a brass instrument allowing the player to reach the notes of various harmonic series. Each valve pressed diverts the air stream through additional tubing, individually or in conjunction with other valves. This lengthens the vibrating air column thus lowering the fundamental tone and associated harmonic series produced by the instrument. Designs exist, although rare, in which this behaviour is reversed, i.e., pressing a valve removes a length of tubing rather than adding one. One modern example of such an ascending valve is the Yamaha YSL-350C trombone, (this is entirely separate from the slight deficiencies between
Western music's dominant
equal (even) temperament system and the
just (not equal) temperament of the harmonic series itself). Since each lengthening of the tubing has an inversely proportional effect on pitch (
pitch of brass instruments), while pitch perception is logarithmic, there is no way for a simple, uncompensated addition of length to be correct in every combination when compared with the pitches of the open tubing and the other valves.
Absolute tube length For example, given a length of tubing equaling 100 units of length when open, one may obtain the following tuning discrepancies: Playing notes using valves (notably 1st + 3rd and 1st + 2nd + 3rd) requires
compensation to adjust the tuning appropriately, either by the player's lip-and-breath control, via mechanical assistance of some sort, or, in the case of horns, by the position of the stopping hand in the bell. 'T' stands for trigger on a trombone.
Relative tube length Traditionally, the valves lower the pitch of the instrument by adding extra lengths of tubing based on
just intonation: • 1st valve: of main tube, making an interval of 9:8, a
pythagorean major second • 2nd valve: of main tube, making an interval of 16:15, a
just minor second • 3rd valve: of main tube, making an interval of 6:5, a
just minor third Combining the valves and the harmonics of the instrument leads to the following ratios and comparisons to 12-tone equal tuning and to a common
five-limit tuning in C:
Tuning compensation The additional tubing for each valve usually features a short tuning slide of its own for fine adjustment of the valve's tuning, except when it is too short to make this practicable. For the first and third valves this is often designed to be adjusted as the instrument is played, to account for the deficiencies in the valve system. In most trumpets and cornets, the compensation must be provided by extending the third valve slide with the third or fourth finger, and the first valve slide with the left hand thumb (see
Trigger or throw below). This is used to lower the pitch of the 1–3 and 1–2–3 valve combinations. On the trumpet and cornet, these valve combinations correspond to low D, low C, low G, and low F, so chromatically, to stay in tune, one must use this method. In instruments with a fourth valve, such as tubas, euphoniums,
piccolo trumpets, etc. that valve lowers the pitch by a perfect fourth; this is used to compensate for the sharpness of the valve combinations 1–3 and 1–2–3 (4 replaces 1–3, 2–4 replaces 1–2–3). All three normal valves may be used in addition to the fourth to increase the instrument's range downwards by a perfect fourth, although with increasingly severe
intonation problems. When four-valved models without any kind of compensation play in the corresponding register, the sharpness becomes so severe that players must finger the note a half-step below the one they are trying to play. This eliminates the note a half-step above their open fundamental. Manufacturers of low brass instruments may choose one or a combination of four basic approaches to compensate for the tuning difficulties, whose respective merits are subject to debate:
Compensation system In the Compensation system, each of the first two (or three) valves has an additional set of tubing extending from the back of the valve. When the third (or fourth) valve is depressed in combination with another one, the air is routed through both the usual set of tubing plus the extra one, so that the pitch is lowered by an appropriate amount. This allows compensating instruments to play with accurate intonation in the octave below their open second partial, which is critical for tubas and euphoniums in much of their repertoire. The compensating system was applied to horns to serve a different purpose. It was used to allow a double horn in F and B to ease playing difficulties in the high register. In contrast to the system in use in tubas and euphoniums, the default 'side' of the horn is the longer F horn, with secondary lengths of tubing coming into play when the first, second or third valves are pressed; pressing the thumb valve takes these secondary valve slides and the extra length of main tubing out of play to produce a shorter B horn. A later "full double" design has completely separate valve section tubing for the two sides, and is considered superior, although rather heavier in weight.
Additional valves Initially, compensated instruments tended to sound stuffy and blow less freely due to the air being doubled back through the main valves. Early compensated designs had sharp bends in the tubing and other partial obstructions of the air-flow. Some manufacturers therefore preferred increasing the number of 'straight' (i.e. non-compensating) valves instead; these extra valves could for example be pitched a little lower than the 2nd and 1st valves, and were intended to be used instead of these in the respective valve combinations. While no longer featured in euphoniums for decades, many professional tubas are still built like this, with five valves being common on CC- and BB-tubas and five or six valves on F-tubas. Compensating double horns can also suffer from the stuffiness resulting from the air being passed through the valve section twice, but as this really only affects the longer F side, a compensating double can be very useful for a 1st or 3rd horn player, who uses the F side less.
Additional sets of slides on each valve Another approach was the addition of two sets of slides for different parts of the range. Some euphoniums and tubas were built like this, but today, this approach has become highly exotic for all instruments except horns, where it is the norm, usually in a double, sometimes even triple configuration.
Trigger or throw Some valved brass instruments provide
triggers or
throws that manually lengthen (or, less commonly, shorten) the main tuning slide, a valve slide, or the main tubing. These mechanisms alter the pitch of notes that are naturally sharp in a specific register of the instrument, or shift the instrument to another playing range. Triggers and throws permit speedy adjustment while playing. Trigger is used in two senses: • A trigger can be a mechanical lever that lengthens a slide when pressed in a contrary direction. Triggers are sprung in such a way that they return the slide to its original position when released. • The term "trigger" also describes a device engaging a valve to lengthen the main tubing, e.g. lowering the key of
certain trombones from B to F. A throw is a simple metal grip for the player's finger or thumb, attached to a valve slide. The general term "throw" can describe a u-hook, a saddle (u-shaped grips), or a ring (ring-shape grip) in which a player's finger or thumb rests. A player extends a finger or thumb to lengthen a slide, and retracts the finger to return the slide to its original position.
Examples of instruments that use triggers or throws Trumpet or cornet Triggers or throws are sometimes found on the first valve slide. They are operated by the player's thumb and are used to adjust a large range of notes using the first valve, most notably the player's written top line F, the A above directly above that, and the B above that. Other notes that require the first valve slide, but are not as problematic without it include the first line E, the F above that, the A above that, and the third line B. Triggers or throws are often found on the third valve slide. They are operated by the player's fourth finger, and are used to adjust the lower D and C. Trumpets typically use throws, whilst cornets may have a throw or trigger.
Trombone Trombone triggers are primarily but not exclusively installed on the F-trigger, bass, and contrabass trombones to alter the length of tubing, thus making certain ranges and pitches more accessible.
Euphoniums A euphonium occasionally has a trigger on valves other than 2 (especially 3), although many professional quality euphoniums, and indeed other brass band instruments, have a trigger for the main tuning slide.
Mechanism The two major types of valve mechanisms are
rotary valves and
piston valves. The first piston valve instruments were developed just after the start of the 19th century. The
Stölzel valve (invented by
Heinrich Stölzel in 1814) was an early variety. In the mid 19th century the
Vienna valve was an improved design. However many professional musicians preferred rotary valves for quicker, more reliable action, until better designs of piston valves were mass manufactured towards the end of the 19th century. Since the early decades of the 20th century, piston valves have been the most common on brass instruments except for the orchestral horn and the tuba. See also the article
Brass Instrument Valves. ==Sound production in brass instruments==