Amplitude generator for an electronic organ

摘要

An amplitude curve generator for use with an electronic organ or the like to control the musical shape of an audible tone. The generator utilizes a simple binary down counter driven from a clock source to produce a sequence of decreasing binary numbers that approximate the relative amplitudes of equally spaced points along an exponential decay curve. The count condition of the least significant bits of the counter correspond to the mantissa of number expressed in binary floating point notation. The most significant bits represent the power. The bits of the mantissa are transferred to a parallel shift circuit and shifted a number of times determined by the bits of the power to convert the number in the counter to fixed point notation. The output of the shift circuit is used to control the envelope amplitude of a musical tone. The output may be subtracted from one (2's complement) to produce a set of values that correspond to an exponential attack curve rather than a decay curve. The counter can be interrupted at any point for some period of time or counted at a different frequency to tailor the wave shape to a particular attack, decay, sustain and release pattern.