Abstract: 1. In a key pulse generating circuit for producing key pulses varying in amplitude in highly irregular manner, said pulses occurring at a given rate, means to generate high speed off-on pulses at a rate many times higher than said given rate in a plurality of separate paths, means to hold over certain of said off-on pulses into subsequent of said high speed pulse times, means to combine the pulses so held over with pulses subsequently generated in certain of said paths to form combination of said high speed pulses, and means to select and combine with one another to form one of the final key pulses occurring at said given rate, individual ones of said last-mentioned high speed pulses occurring at instants of time separated from one another by several of said high speed pulses while discarding the intervening high speed pulses.6.