Audio and speech processing systems have steadily risen in importance in the everyday lives of most people in developed countries. From ‘Hi-Fi’ music systems, through radio to portable music players, audio processing is firmly entrenched in providing entertainment to consumers. Digital audio techniques in particular have now achieved a domination in audio delivery, with CD players, Internet radio, MP3 players and Pods being the systems of choice in many cases. Even within television and film studios, and in mixing desks for ‘live’ events, digital processing now predominates. Music and sound effects are even becoming more prominent within computer games.

Speech processing has equally seen an upward worldwide trend, with the rise of cellular communications, particularly the European GSM (Global System for Mobile communications) standard. GSM is now virtually ubiquitous worldwide, and has seen tremendous adoption even in the world's poorest regions.

Of course, speech has been conveyed digitally over long distance, especially satellite communications links, for many years, but even the legacy telephone network (named POTS for ‘Plain Old Telephone Services’) is now succumbing to digitisation in many countries. The last mile, the several hundred metres of twisted pair copper wire running to a customer's home, was never designed or deployed with digital technology in mind, and has resisted many attempts over the years to be replaced with optical fiber, Ethernet or wireless links. However with DSL (digital subscriber line – normally asymmetric so it is faster in one direction than the other, hence ADSL), even this analogue twisted pair will convey reasonably high-speed digital signals.