How did technological innovations in the music industry affect American popular music in the postwar era? The arrival of audio tape made the process of overdubbing far easier; by the late 1940s recording studios were using audio tape, rather than master discs, to produce most recordings, and some artists (notably Bing Crosby) had begun to use tape to pre-record their appearances on radio. In 1948 the Ampex Corporation, backed by Crosby, introduced its first tape recorder, a machine that soon became a mainstay of the recording industry. That year Crosby gave Les Paul the second reel-to-reel tape recorder ever produced for sale by Ampex, and Paul immediately began tinkering with the off-the-shelf model, creating the first multitrack recordings ever on tape by adding a second recording head and additional circuitry. The year 1949 saw the introduction of a two-track recorder, which could record simultaneous inputs from two microphones and thus produce stereo effects. While tape recorders were not initially successful as a home consumer item, the advantages of magnetic recording were felt immediately in the music industry