Padding sounds and harmony are both expression techniques in music. They have differences in definitions, functions and forms of expression:

1. Definition: Pad sounds refer to the use of some kind of Instruments or timbres are used to fill the gaps in the music to enhance the stability and coherence of the music. Harmony refers to the combination and arrangement of different notes, and the harmonic effect formed can enhance the harmony and beauty of music.

2. Function: Pad sounds are mainly used to fill the gaps in the music to make the music sound smoother and more coherent, and at the same time to increase the layering and rhythm of the music. Harmony is mainly used to enhance the harmony and beauty of the music, to produce richer changes and transitions between different notes, and to enhance the expressiveness and appeal of the music.

3. Expression form: Pad sound is usually expressed through a certain instrument or timbre, such as piano arpeggios, guitar playing, etc. Harmony is expressed through the combination and arrangement of different notes, such as the arrangement of chords, the transformation of harmony, etc.