Abstract: An adaptive delta modulator must produce at its output a periodic 0-1 sequence when the input signal (w) to be coded assumes zero value. The delta modulator of the present invention is provided with a generator (GE) to produce a periodic 0-1 sequence which is transmitted to the receiver instead of the delta coded signal when the input signal to be coded assumes zero value. This generator (GE) is switched to the output line of the delta modulator at the instant at which the output voltage (Us) of a filter (IN) in the feedback path of the delta modulator, for determining the instantaneous quantizing unit of the delta modulator, assumes zero value. If this filter (IN) is implemented with digital components, the generator (GE) is triggered by the output pulses of a gate (G1) whose inputs are connected to the respective locations of the input signal storing means of the filter (IN). A delay line (V) prevents triggering of the generator (GE) at extremely short pauses in the input signal (w) to be coded.