After studying an original piece of music, orchestrators and arrangers experiment with it and choose various combinations of instruments to produce desired effects. Arrangers also may add vocal parts. The difference between orchestrators and arrangers is in the degree to which they change the original music. Orchestrators and arrangers use music notation software to copy their music and prepare performance scores and parts.
Orchestrators assign specific passages of a score to particular instruments to produce the desired tonal colour (variation of sound) but often do not make other changes to the original composition. Then they create each individual musical part on score paper. Often the composer of the piece is also the orchestrator, or the composer provides an orchestral sketch and the orchestrator uses music notation software to prepare all of the instrumental parts in detail.
Arrangers make changes in the original piece of music to accommodate the requirements of a particular medium (band, orchestra, choral group, solo artist, film score, radio jingle). They may work on new arrangements of old hits (for example, arrange an old gospel tune in a jazz style) or arrange new compositions for different mediums or in different styles.
Arrangers often use synthesizers and computers to experiment with musical sounds. During recording sessions, arrangers may act as musical directors, selecting songs, scoring charts, rehearsing musicians and conducting the performance.
Many orchestrators and arrangers notate their own scores, although they may hire music copyists to copy musical parts.