This paper describes an approach to nonlinear distortion synthesis, which uses Over-Threshold Power Function (OTPF) Feedback. The linear gain of an OTPF Feedback distortion synthesizer (using a high gain amplifier) is determined by a linear feedback element. When the output signal becomes greater than a positive threshold value, or less than a negative threshold value, additional OTPF feedback is applied to the distortion synthesizer. The action of this OTPF Feedback Distortion synthesis closely emulates the soft limiting input/output response characteristics of Vacuum tube triode grid limit distortion. An important feature of an OTPF feedback distortion synthesizer that it always behaves as an instantaneous soft limiter, and never results in clipping of the output signal peak levels (even at maximum allowable peak input signal levels), if its non-linear gain constants are set optimally. The paper also describes both circuit and software plug-in realizations of distortion synthesizers which employ Over-Threshold Cubic Function Feedback
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