Continuously variable slope delta modulation

Voice coding method. This is delta modulation with variable step size. Adaptation of step size allows to avoid slope slope overload (step of quantisation increases when signal rapidly changes) and decreases granular noise when signal is constant (decrease of step of quantisation). Change of step of quantisation in coder depends on previous N output bits of decoder (N = 3 or N = 4 is very common). CVSD is sometimes called a compromise between simplicity/low bitrate/quality. Bitrates are 64 to 9.6 kbit/sec.