Audio beat notes produced by sampling a square wave in a digital quadrature FM demodulator are reduced by adding filtered random noise, or dither, to the signal to be demodulated to randomly vary the width of successive pulses in the square wave. Filtration of the random noise prevents feedthrough of...http://www.google.co.uk/patents/US4772853?utm_source=gb-gplus-sharePatent US4772853 - Digital delay FM demodulator with filtered noise dither
