The tuba is the largest of the low-brass instruments and is one of the most recent additions to the modern symphony orchestra, first appearing in the mid 19th century where it largely replaced the ophicleide. There is usually only one tuba in an orchestra, and is used as the bass of the brass section, though its versatility means that it can be used to reinforce the strings and woodwind, or increasingly as a solo instrument.
Tubas are also used in wind and concert bands and in brass bands, although they are referred to as Eb and Bb basses, there being 2 of each.
In the hands of a skilled player, it has the largest range (some 4 1/2 octaves) of any brass instrument, and can be remarkably agile.
Tubas are found in various pitches, most commonly in F, Eb, C, or Bb. They can have rotary or piston valves, numbering up to 6, although 4 is by far the most common number. Most piston valved tubas have a compensating system to allow accurate tuning when using several valves in combination to play low notes.