Technological Obsolescence
Dolby's analogue noise reduction systems, though still used in some professional applications, as well as in the large installed base of consumer tape decks, are becoming increasingly obsolete due to the widespread adoption of digital audio (in the form of compact discs, MP3s, MiniDiscs, and to a lesser extent DAT) in the home for entertainment and professional studios for recording. In other words, Dolby NR is not becoming obsolete for analog recording, but analog recording itself is becoming obsolete as digital recording replaces it.
Read more about this topic: Dolby Noise-reduction System