Intermodulation Distortion Analysis of a Guitar Distortion Pedal With a Starving Circuit

Despite the recent trend of digital transformation in the music industry, the popularity of guitar effects pedals (GEPs) designed with analog components has not declined. This paper describes the complexity of the nonlinear characteristics of the analog circuitry in a distortion pedal, which originates not only from clipping diodes but also from the integrated operational amplifier itself. It is well known that variation in the supply voltage of a distortion pedal influences its sound. Based on this phenomenon, we have designed a voltage-starving circuit to control various distorted transfer functions depending on the frequency. Particular attention is given to the difference between odd and even nonlinearity in the mechanism of generating intermodulation distortion (IMD) for two-tone dissonance and consonance. These transfer functions are analyzed in detail using a 9th-order polynomial approximation. As a result, all peaks of the intermodulation frequencies are successfully identified in a complex spectrum. Furthermore the spectral shape of the measured IMD peaks is reproduced with an error of less than 50 dB by the simulation of their approximate formula.