古筝、钢琴、电子琴、小提琴、二胡等乐器演奏出的音，人们在唱歌时发出的音都属于乐音。音乐世界主要是由乐音组成的。
The sound produced by zither, piano, electronic organ, violin, erhu and other musical instruments, and the sound emitted by people when singing, all belong to musical sound. The music world is mainly composed of music.
半音与全音：
Semitone and whole tone:
音与音之间最小的音高距离叫半音，两个半音构成一个全音。在简谱中，7、1之间及3、4之间是半音。
The minimum pitch distance between tones is called a semitone, and two semitones form a whole tone. In the simplified score, the chromatic sound between 7 and 1, and between 3 and 4.
音符：
Note:
乐谱中表示音的长短的符号叫音符，在简谱中用1、2、3、4、5、6、7表示。
The symbols indicating the length of the sound in the music score are called notes, which are represented by 1, 2, 3, 4, 5, 6 and 7 in the simple score.