Digital synthesizer
A digital synthesizer is a synthesizer that uses digital signal processing (DSP) techniques to make musical sounds.
A number of the techniques used by digital synthesizers are adaptations of processes developed for analog synthesizers, such as additive synthesis and FM synthesis. Other techniques, such as wavetable synthesis and physical modeling only became possible with the advent of digital technology.
Some digital synthesizers now exist in the form of 'softsynth' software that synthesizes sound using conventional PC hardware. Others typically use specialized DSP hardware.
They are generally speaking more flexible than an analog synthesizer, though they require substantial hardware to get the same response time as an analog synthesizer.
Relevant links.
There are also a Mpeg-standard for synthesizing sounds, Mpeg4-SA. http://sound.media.mit.edu/mpeg4/
An Mpeg4-SA community page: