ENCODER

摘要

PURPOSE: To eliminate necessity for optimizing a delta modulator in a wide frequency band and to attain high secrecy by setting up the start point of a superframe consisting of the prescribed number of frames by up dispersion or down dispersion in accordance with the succeeding digit of a pseudo random binary number. CONSTITUTION: The order of up or down dispersion is switched after the prescribed number of frames in response to a pseudo random binary sequence. At the time of starting each superframe, whether a pseudo random binary number is up dispersion or down dispersion is determined independently of the direction of dispersion generated by a preceding sub-frame. A 6-bit feedback shift register 50 generates a pseudo random binary sequence. A logic decoding circuit 53 applies a control signal to a change-over switch 21 to switch the output of the delta modulator 10 to a state for inputting a synchronizing signal generated from the circuit 53 to a register 20. Consequently a sound frame is erased in each super-frame and a synchronizing signal is inserted to execute synchronization.