Music is an art form whose medium is sound and silence. Its common elements are pitch (which governs melody and harmony), rhythm (and its associated concepts tempo, meter, and articulation), dynamics, and the sonic qualities of timbre and texture.
Sound design is the process of specifying, acquiring, manipulating or generating audio elements. It is employed in a variety of disciplines including filmmaking, television production, theatre, sound recording and reproduction, live performance, sound art, post-production, and video game software development.
There is an infinite range of applications in multimedia (web sites, GPS navigation systems, e-learning, etc.). That's why a voice and an audio comment are the best guides to interactively find the way through the vast combination of media provided (including video, still images, audio, text) to the exact information required.