Musique Concrete
One of the most prominent experimental tendentions since electronic devices appeared, is to make music starting from concrete sounds themselves, rather than from abstract melodic ideas (pitches, harmonies, rhythms etc.) The idea of music of concrete sounds was clearly articulated and pursued for the first time by Pierre Schaeffer and his concept of ‘Musique Concrete’. He was bored with ‘do-re-mi-fa-sol’ music as he called it, realizing, while he was working on the radio, that sounds around us hold great power.
Music has to do with sounds," explains Schaeffer, "so we need to find them somewhere and it is preferred to find musical ones. You have two sources for sounds: noises, which always tell you something-a door cracking, a dog barking, the thunder, the storm; and then you have instruments. An instrument tells you, la-la-la-la (sings a scale). Music has to find a passage between noises and instruments. It has to escape. It has to find a compromise and an evasion at the same time; something that would not be dramatic because that has no interest to us, but something that would be more interesting than sounds like Do-Re-Mi-Fa... Pierre Schaeffer
Wikipedia:
Musique concrète (French; literally, "concrete music"), is a style of avant-garde music that relies on natural environmental sounds and other non-inherently-musical noises to create music. This genre starts to raise questions about electronic music and its composition. /…/ Much like electroacoustic music, musique concrète has been subject to conflicting perceptions about its character. The term is often understood as a practice of simply making music out of "real world" sounds, or sounds other than those made by musical instruments. Rather, it is a wider attempt to afford a new way of musical production and expression. Traditionally, classical or serious music begins as an abstraction, as musical notation on paper or other medium, which is then produced into audible music. Musique concrète strives to begin with the "concrete" sounds, experiment with them, and abstract them into musical compositions.
Schaeffer thought of composing as treatment of sounds instead of abstract notes, and composition as symphony of different sounds. Music is understood as a sort of language of sounds, possessing a grammar of sounds, where sounds impact us on certain way, often very concrete, meaning something concrete to us (that is where the name of the concept was derived). One can take Ennio Morricone's piece that opens movie “The Bad, The Good and The Ugly” as an example of this approach.
We could also depict music concrete by starting from the other end: if we start from melodic, rhythmic and harmonic aspect, then we could say that by adding words, or pictures, we can add something to music, ‘complete’ it. But even closer to the spirit of music, music telling can be completed with sounds. This second approach is more common, since it is certainly easier to apply. Methods of concrete music are now usually applied on this less ambitious way, environmental sounds like the rain falling, sound of airplane or trains being used to help in setting the atmosphere.