Page "Speech coding" Paragraph 16

Much of the later work in speech compression was motivated by military research into digital communications for secure military radios, where very low data rates were required to allow effective operation in a hostile radio environment.

At the same time, far more processing power was available, in the form of VLSI integrated circuits, than was available for earlier compression techniques.

As a result, modern speech compression algorithms could use far more complex techniques than were available in the 1960s to achieve far higher compression ratios.