Abstract: An apparatus and circuit is disclosed for the generation of a masking sound noise by which unwanted noise may be overcome without undue and unwanted sound levels. The apparatus and circuits have at least two multi-stage shift registers in which the last register sends an input signal to a first exclusive OR gate and to this same OR gate an intermediate connection to the shift register is made. The output from this first OR gate is sent to the first stage of the register and this same signal is sent as an output to a second exclusive OR gate. Each shift of each register is pulsed by an asynchronous clock. A second exclusive OR gate receives the output signals from each of the first OR gates and sends the output signal to a divide-by-counter and the output therefrom is sent to amplifying means and one or more speakers.

Abstract: A matrix printer and method for printing characters so as to reduce the likelihood of forgery by printing both the desired character and its complement on the same medium.