The creative design of all sound except music and dialogue.
Creates different layers of sound and cuts them according to the needs of the story and the ideas of the director. These sound may come from existing sound recordings in a sound archive, as well as audio specially created for a film.
An element that is included specifically for each film are noises augmented by Foley (see Foly Artists). In other cases, special atmospheric or sound effects are recorded especially for a film.
These can be achieved by various processes (slow, reverse, etc.). These noise in a way are sometimes musical, but are not necessarily perceived as music.
In general good sound design happens under the radar the viewer who does not consciously perceived the sound effects, but rather feels them. In this regard, good sound design, though often much less conspicuous than music, can produce a similar effect.
Today refers to the actual creation of new, original sounds and sound F/X, in contrast to sound design in regards to the entire film audio track. See also Sound Effects (F/X)