What is the purpose of a key signature in music?

The purpose of a key signature is to show the performer the key of the music. It is a crucial element found at the beginning of a piece of sheet music that indicates which notes are sharp or flat throughout the piece. By understanding the key signature, musicians can grasp the tonal center of the music, which is essential for interpreting the work accurately. The key signature directly informs the performer about the scale and harmony being used, allowing them to play in the correct pitch and maintain the intended sound of the composition.

In contrast, the other options do not align with the primary function of a key signature. The tempo of a piece is indicated through markings or metronome settings, while dynamics are expressed with specific symbols written into the score. Furthermore, while a key signature relates to the scale, it does not itself define the type; it serves more to dictate the particular tonal framework within which the music resides.