Abstract: This is an electronic organ which economically simulates long duration aperiodic musical waveforms, such as the clash of cymbals. It employs the digital waveform generation technique, in which successive instructions are read out of a memory to determine the amplitude of the waveform at successive sample points. To save memory capacity, the memory addresses are rescanned; and to avoid audible discontinuities the scan direction recirculates numerically back and forth across the address field. Despite the bidirectionality of the scan, monotonic decreases in amplitude and in higher harmonic content are achieved. The monotonic decrease in amplitude is accomplished by impressing an exponentially declining envelope upon the digitally generated amplitudes. The monotonic decrease in higher harmonic content is accomplished by preventing the rescan from returning to a memory region of greater harmonic content after it has once entered a region of lesser harmonic content.

Abstract: An envelope is imposed on a sequence of binary waveform samples representing a musical waveform signal by repetitively summing selected ones of a group of scaled representations of each of the waveform samples of the form A/2.sup.m, A/2.sup.m+1 . . . A/2.sup.m+p, where A represents the magnitude of the waveform sample, p is a predetermined integer, and m is an integer changing by a factor of unity each time a predetermined number of the groups have been developed. The sum of each group of scaled representations differs from the sum of the preceding group by the factor A/2.sup.m+p whereby a staircase signal is produced amplitude modulating the musical waveform signal, the step size of the staircase signal charging each time said predetermined number of groups have been developed.

Abstract: In order to tune the frequency characteristics of a filter or oscillator as an exponential function of the position of a note on a musical scale, a pulse stream with an exponentially scaled duty cycle is used to gate an on-off switch which controls an electronic tuning signal for the first or second stage of the filter or oscillator. The pulse stream source can be a pulse code generator responsive to a priority note generator, or it can be an oscillator-driven one-shot with an exponentially scaled power supply governing the charging rate of a reactive component which determines the one-shot cycle time. There are also pitch offset and pitch modulation features in the circuit, the latter being usable in a constant deviation or a constant interval mode.

Abstract: A time-shared electronic musical instrument is provided with programmable wave-form generating and tone coloring circuits in order to maintain the musical characteristics regardless of pitch. The circuits comprise programmable keyers and wave-shapers, programmable envelope generators, programmable filters, and a programmable voicing selection circuit, in all of which certain characteristics of the output signal are tailored to the frequency of the musical tone.