The basic idea of group-additive synthesis [130,69] is to employ a set of wavetables, each modeling a harmonic subset of the tonal components making up the overall spectrum of the synthesized tone. Since each wavetable oscillator is independent, inharmonic sounds can be synthesized to some degree of approximation, and the amplitude envelopes are not completely locked together. It is important to be aware that human audio perception cannot tell the difference between harmonic and inharmonic partials at high frequencies (where ``high'' depends on the fundamental frequency and timbre to some extent). Thus, group-additive synthesis provides a set of intermediate points between wavetable synthesis and all-out additive synthesis.
Further Reading about FM Synthesis