Until the 1980s most popular music had come into homes in the form of records. But traditional sound recording had been done in analog, a continuous waveform which is theoretically capable of producing an exact replica of the sound recorded, but which loses fidelity when it is sonically "compressed" onto a record. In addition, analog records are prone to high levels of noise from dust or scratches in the record groove, which are reproduced by the needle as sound. Records also lose their quality of sound over years of use, as the needle gradually wears the playing surface away. With digital recording, instantaneous "samples" of an analog wave are taken at set intervals; the resulting information is stored as binary code (a system of 1s and 0s). Such binary code is then replayed from a disc using a laser beam, which never touches the...