Abstract: The present invention relates to the D.C. supply for a subscriber control system, and consists essentially in supplying the control system from the exchange solely in response to a request, such request being emitted either by the exchange or by the control system, a preamble message being emitted in-line by the control system in order to initialize a communication in the latter case. The invention is applicable to the digitalization of the subscriber's telephone.

Abstract: A digit rate reducing system for PCM signals comprises a predictor stage, an automatic gain control stage, and a quantizer stage for adaptive quantizing. The predictor stage includes a predictor and a subtractor for subtracting from a sample x.sub.n of the PCM input signal a predicted signal x.sub.pn derived from preceding samples. The subtractor provides a difference signal d.sub.n representing prediction error to the automatic gain control (AGC) stage. A divider in the AGC stage divides the difference signal d.sub.n by m, providing a divided signal e.sub.n to the quantizer stage. In this last stage, a quantizer encodes the divided signal e.sub.n into a signal Y.sub.n of reduced rate. The predictor uses a first adder which receives the predicted signal x.sub.pn and a reconstituted signal d.sub.n derived from the reduced rate signal Y.sub.n ; a plurality of shift registers and associated multipliers; and a second adder connected to the outputs of the multiplier. Shift registers T.sub.1 . . . T.sub.

Abstract: The common return path of a circuit for applying pulses in alternating polarity to the balanced input transformer of a bipolar code signalling circuit is switched to block the first half and pass the last half of each pulse with a timing independent of polarity. The pulses supplied to the switched pulse-applying circuit have the same duration as the binary signal pulses from which they are derived, but these binary signal pulses are alternately supplied to the two sides of the pulse applying circuit by means of an AND-gate and a multivibrator. The same clock pulse generator times the multivibrator and the common path switching of the pulse-applying circuit. The circuit converts binary to bipolar signals free of asymmetric timing errors.