This dissertation introduces a physically-informed, abstract synthesis method that applies loopback frequency modulation (FM) to real-time parametric synthesis of percussive sounds. Loopback FM is a variant of FM whereby the output ``loops back'' to modulate its frequency by an amount determined by a feedback coefficient which, when made time-varying, results in pitch glides. Here, loopback FM is used to parametrically synthesize this effect in struck percussion instruments, known to exhibit this characteristic due to nonlinearities in modal coupling. Inspired by the sonic potential of physics-based nonlinear percussion synthesis models, the loopback FM synthesis method uses an abstract synthesis approach in order to create a wide variety of percussive sounds in real-time. A linear, modal synthesis percussion model is modified to use loopback FM oscillators, which allows the model to create unique, eclectic, and experimental sounding percussive hits in real-time. Musically intuitive parameters are emphasized resulting in a usable percussion sound synthesis method.