1. Music Since 1950

2. Electric Music
Technological advances in the 20th century enabled composers to use electronic means of producing sound.
After the Second World War, magnetic tape became available for the creation of music by recording sounds and then manipulating them in some way.
When the source material was acoustical sounds from the everyday world, the term musique concrète was used; when the sounds were produced by electronic generators, it was designated electronic music.
After the 1950s, the term "electronic music" came to be used for both types.
Examples: Sometimes such electronic music was combined with more conventional instruments, Stockhausen's Hymnen, Edgard Varèse's Déserts, and Mario Davidovsky's series of Synchronisms

3. The term Electroacoustic music was later coined to include all forms of music involving magnetic tape, computers, synthesizers, multimedia, and other electronic devices and techniques.
Live electronic music uses live electronic sounds within a performance (as opposed to preprocessed sounds that are overdubbed during a performance)
Cage's Cartridge Music being an early example.
Spectral music (Gerard Grisey and Tristan Murail) is a further development of electroacoustic music that uses analyses of sound spectra to create music.
Cage, Berio, Boulez, Milton Babbitt, Luigi Nono and Edgard Varèse all wrote Electroacoustic music, often promoted in "happenings".

4. From the early 1950s onwards, John Cage introduced elements of chance into his music.
This has resulted in various musical techniques such as indeterminacy, aleatoric music, stochastic music, intuitive music, and free improvisation.
Process music (Karlheinz Stockhausen Prozession, Aus den sieben Tagen; and Steve Reich Piano Phase, Clapping Music) explores a particular process which is essentially laid bare in the work.
The term Experimental music seems to have been coined by Cage who was interested in writing complete works that performed an unpredictable action, according to the definition "an experimental action is one the outcome of which is not foreseen”. The term is also used to describe music within specific genres that pushes against their boundaries or definitions, or else whose approach is a hybrid of disparate styles, or incorporates unorthodox, new, distinctly unique ingredients.

5. John Cage
A pioneer of chance music, electronic music and non-standard use of musical instruments, Cage was one of the leading figures of the post-war avant-garde. Critics have lauded him as one of the most influential American composers of the 20th century.
Cage is perhaps best known for his 1952 composition 4’33’’, the three movements of which are performed without a single note being played. The content of the composition is meant to be perceived as the sounds of the environment that the listeners hear while it is performed, rather than merely as four minutes and thirty three seconds of silence,and the piece became one of the most controversial compositions of the twentieth century.
Another famous creation of Cage's is the prepared piano (a piano with its sound altered by placing various objects in the strings), for which he wrote numerous dance-related works and a few concert pieces, the best known of which is Sonatas and Interludes (1946–48).

6. Minimalism
In the later 20th century, composers such as La Monte Young, Philip Glass, Terry Riley, Steve Reich, and John Adams began to explore what is now called minimalism, in which the work is stripped down to its most fundamental features; the music often features repetition and iteration.
An early example is Terry Riley's In C (1964), an aleatoric work in which short phrases are chosen by the musicians from a set list and played an arbitrary number of times, while the note C is repeated in eighth notes (quavers) behind them.
Steve Reich's works Piano Phase (1967, for two pianos), and Drumming (1970–71, for percussion, female voices and piccolo) employ the technique called phasing in which a phrase played by one player maintaining a constant pace is played simultaneously by another but at a slightly quicker pace. This causes the players to go "out of phase" with each other and the performance may continue until they come back in phase.
Philip Glass's (1968) employs the additive process in which short phrases are slowly expanded.
La Monte Young's Compositions 1960 employes very long tones, exceptionally high volumes and extra-musical techniques such as "draw a straight line and follow it" or "build a fire".