Programmable sound circuit for electronic games

Claim 1

A sound generator for game controlled by a microprocessor, comprising; first clocking means for providing a clock rate with a system cycle time period defining a system cycle, second clocking means for providing clock signals dividing each of said system cycle times into a sequence of at least two subcycles, the time duration of each subcycle in said sequence substantially conforming to a preselected sequence of time durations, sound generating means for generating electrical digital signals having fundamental frequencies in the audio range on each of a plurality of channels, a plurality of programmable filter means, each coupled to a respective channel, for independently filtering the respective signals on such channel with filter characteristics controlled by said microprocessor in accordance with the play of said game to produce a respective filtered output signal, wherein each of said programmable filter means comprises at least one duty-cycle-controlled resistor having an effective conductance proportional to said on-time, and filter control means for controlling the on-time of each duty-cycle-controlled resistor during the time duration of each system cycle so that said on-time is substantially equal to a sum of respective subcycles of said sequence of subcycles, said sum including at least one such subcycle, summing means for mixing and amplifying said filtered output signals to provide electrical analogue signals, and loudspeaker means for converting said electrical analoque signals into audible sound.