A method of encoding a digital signal so that it takes up less memory. In delta modulation, each signal word after the first is stored as the difference between the current word and the previous one. In general, this takes up less memory because the delta values are usually fairly small and require fewer digital bits to encode. However, depending on how it is implemented, the detla modulation may not be able to encode an abrupt change or transient in the waveform, resulting in aliasing .
Delta modulation was used by some early digital delay lines in the 1980s, and variants of the technque were used to store pre-computed wavetables in some early sample playback synths. It had the advantage of saving memory at a time when memory was expensive. However, as the price of memory came down, the motivation to use delta modulation disappeared. Interestingly, one of the last remaining uses of it anywhere was that it was used to encode air-to-ground voice transmission on the Space Shuttle.