Sight-reading is the reading and performing of a piece of music or song in music notation that the performer has not seen before, also called a prima vista. Sight-singing is used to describe a singer who is sight-reading. Both activities require the musician to play or sing the notated rhythms and pitches. While both sight-reading and sight-singing can be significantly challenging, in comparison to the normal way that notated music is learned–practicing the melodies and passages individually–sight-singing is more challenging, because the musician does not have any keys, frets or valves (on keyboard instruments, guitars, and valved brass instruments, respectively) to help them obtain the correct pitches.