The key signature refers to the symbol used to indicate the pitch and rise of notes in the staff. These symbols are usually marked at the beginning of the staff and are used to indicate the pitch and key at which each note should be played.

In music, the key signature is one of the basic tools used to represent the pitch and tone of music. By using different key signatures, musicians can easily change the tone and timbre of music to express different emotions and atmospheres.

The key signature usually consists of a series of rising and falling marks. These notations indicate the number of semitones by which each note should be raised or lowered. For example, a sharp (#) means raising the note one semitone, and a flat (b) means lowering the note one semitone.

In staff notation, the key signature is usually located at the beginning of each line of music, immediately after the clef. The key signature usually includes the name of the key (such as C, D, E, etc.) and the sharp and flat marks. If a note is preceded by a sharp or flat, then the note should be raised or lowered according to the key signature. By using different key signatures, musicians can express different emotions and atmospheres and hit each note accurately during their performance.

The importance of the key signature:

1. The key signature can affect the pitch and tone of the music. Each key signature has its own specific sharp and flat notations, which tell the player how to adjust the pitch to achieve the correct tone. By using different key signatures, musicians can create different timbres and tones to express different emotions and atmospheres.

2. The key signature can also affect the emotional expression of music. Different key signatures have different emotional colors. For example, when using the major key signature, the music will usually convey a cheerful and bright mood; while when using the minor key signature, the music may express sad and tender emotions. Therefore, choosing the right key signature allows the music to better express its emotions.

3. The key signature can also help musicians avoid errors during performance. If the key signature is ignored during performance, the notes may not be played accurately. This will not only affect the pitch and timbre of the music, but also destroy the harmony of the entire musical work.