Abstract: For imitating periodic signals occurring in digital transmission systems during some operating conditions in view of the multiplex structure a word generator is proposed which includes a read-only memory from which during a test signal cycle only 4116 permutations are successively read out of a total of 65,536 possible word sizes and permutations of e.g. a 16-bit word. The remaining 61,420 permutations are generated by shifting bit-by-bit the entire packet of continuous signals so that in case of a fixed 16 bit pattern the packet starts at a different bit position during each successive cycle and after 16 cycles all 16 bit positions occur as begin state. The shift is caused by a framing bit sequence which determines the test signal cycle and whose length is aliquant to n=16.