In 1964, he attended summer courses at Darmstadt taught by Karlheinz Stockhausen, and took composition lessons with Richard Rodney Bennett the following year.

[3][2] Before the end of 1965, Souster was a producer with the BBC Third Programme, and put on many performances of contemporary music by composers such as Boulez, Berio, Barraqué, Cardew, Feldman, Henze and Stockhausen.

His first acknowledged composition involving electronic techniques was Titus Groan Music (1969) for wind quintet, ring modulator, amplifiers and tape.

In August of the same year he moved to King's College, Cambridge and formed a live-electronic group with Roger Smalley, Andrew Powell and Robin Thompson called Intermodulation.

[3] As well as compositions by Souster and Smalley, the group performed contemporary music by Cardew, Riley, Rzewski, Stockhausen and Wolff.