Time division multiplexed transmission systems for telephone or like signals with frequency band compression

A digital transmission system for efficient transmission of time division multiplexed digital telephone signals, wherein a plurality of telephone signals are cyclically sampled and quantized so that each sampled value may be encoded into a binary codeword of a preset number of bits and that a series of said codewords equal in number to said telephone signals may constitute a frame defined by a frame synchronization signal and a series of a predetermined number of said frames signal may in turn constitute a superframe defined by a superframe synchronization signal, thereby to provide said time division multiplexed telephone signals, wherein said system comprises:

• input means for receiving said time division multiplexed telephone signals;
• means coupled to said input means in parallel and responsive to a state-representing signal for successively converting each said binary codewords into a plurality of modified codewords, said modified codewords being variably assigned comparatively smaller and greater numbers of binary digits depending on said state-representing signal, said comparatively greater number being equal to or smaller than said preset number;
• selection means supplied in parallel with said modified codewords for selectively allowing in response to said state-representing signal one of said modified codewords to pass therethrough for each said binary codewords;
• means responsive to the output of said input means for detecting the level of each said digital telephone signals for each said codewords;
• means for producing said state-representing signal in response to the level detected by said detecting means, and for producing, for each said modified codewords, a bit-number-representing signal indicating the number of binary digits assigned to the binary codeword being transmitted;
• means coupled to said state-representing signal producing means for arranging in time domain the output of said selection means, bit-number-representing signal and said superframe synchronization signal, so that said time division multiplexed digital signals with said modified codewords are provided;
• and
• means for generating timing pulses for controlling the operation of all the foregoing means;
• and
• wherein said system comprises at the reception end:
• input means for receiving said time division multiplexed digital signals with said modified codewords;
• means responsive to said bit-number-representing signal for reproducing said binary codewords respectively from said modified codewords, thereby to reproduce said time division multiplexed digital signals of unmodified codewords suited for decoding.