What are Ledger lines used for in music notation?

Ledger lines are utilized in music notation to extend the range of notes beyond the staff. When a note falls above or below the standard five lines and four spaces that make up the staff, ledger lines are added to provide a visual reference for those notes. These short lines allow musicians to read pitches that are either higher or lower than what the staff can accommodate. For example, notes that are just slightly above the staff might be notated with one or two ledger lines above it, while notes that are significantly lower than the staff can be depicted with ledger lines below. This method preserves the clarity of the notation and ensures that musicians can accurately identify and play the desired pitches without confusion.

Other options relate to different aspects of music notation. Changing the key signature involves distinct symbols at the beginning of a staff, indicating alterations in the scale. Tempo changes are marked by specific terms or symbols (like "allegro" or metronome markings), while dynamics are indicated using terms such as "piano" or "forte," or through specific symbols in the score. Each of these roles is separate from the function of ledger lines, which is solely to expand the pitch range expressible in written music.