Delta modulation

Delta modulation (DM): Analog-to-digital signal conversion in which (a) the analog signal is approximated with a series of segments, (b) each segment of the approximated signal is compared to the original analog wave to determine the increase or decrease in relative amplitude, (c) the decision process for establishing the state of successive bits is determined by this comparison, and (d) only the change of information is sent, i.e., only an increase or decrease of the signal amplitude from the previous sample is sent whereas a no-change condition causes the modulated signal to remain at the same 0 or 1 state of the previous sample.

Note: Examples of delta modulation are continuously variable slope delta modulation[?], delta-sigma modulation[?], and differential modulation[?].

Source: from Federal Standard 1037C and from MIL-STD-188