Unit Four begins the general discussion of perhaps the most interesting achievement in the 20th Century in terms of instrument invention, the synthesizer. Initially a tools only found in the big experimental studios, eventually market forces, smart inventors and intrepid composers and musicians brought these instruments into live performance, personal studios and into many different genres of music. While tape music tended (until the present time at least), to be an avant-garde expression and the purview of the contemporary composer, synthesizer-based electoracoustic music quickly transcended genre boundaries and became, in time, firmly established. Music would be changed forever.