A cello trio is a musical group or specific type of string trio comprised of three cello players. The ensemble may play by itself, but it also can be accompanied. These trios play primarily classical music, but may extend into other genres such as jazz depending on the tastes of the ensemble members and the techniques they know how to use. More generally, the term also can refer to the music a group of three cellists perform.
Cello trios involve the use of three cellos. These are low-pitched members of the violin family that are between the viola and double bass in range. During a performance, although all performers use the same type of instrument, one cellist usually has the melodic line, the second carries the bass line, and the third cello fills in chords and adds counterpoint. This functional structure is similar to that found in other musical trios. It is not a hard rule, however, as what each player does depends on the composer's intent.
Musicologists and music librarians may separate cello trios into unaccompanied and accompanied categories. Unaccompanied means the three cellists are the only performers and that they can create the music without additional support. Accompanied means the cellists are supported by at least one other instrument that is not a cello, with some works calling for accompaniment by an entire orchestra.
The development of the cello trio is a fairly recent phenomenon from the music history point of view. Early string ensembles more commonly were string quartets because the leanness of the trio form presented more compositional challenges. When the string trio form did begin to appear out of the baroque trio sonata, the orchestration called for two violins and a cello, which later adapted to a violin, viola and cello. The baryton, a cello-like instrument of the viol family, frequently was paired with a cello and viola to form baryton trios up to the 19th century, and eventually musicians arranged some of these trios for three cellos and abandoned conventional string trio orchestrations to write new cello trio music.
Members of a cello trio traditionally performed classical music in homes as chamber entertainment, moving to settings such as churches and concert halls. As music advanced, however, different genres emerged, such as jazz and pop. Cellists learned new techniques to accommodate these styles and break away from the classical mold, aided by the development of the electric cello. A cello trio that perform outside of the classical realm typically works with arrangements, performing music by a range of artists.