Singers also learn to work with solo Accompanists, or accompany themselves on an instrument. They learn all about how music is put together, so they can have input into the arrangement, figure out the best key for a song they will sing, and work with other Singers, musicians, and Producers. Most Singers will specialize in a specific style of music, such as Pop, Jazz, Rock, Musical Theater, or Opera. Some Singers cover many styles, or work in the studio singing jingles (music for advertising). Other Singers specialize in singing background parts, which is actually more difficult than singing lead, since they must be able to blend their voice in a group of Singers.