Six FM operators let a voice split its spectrum into three independently-enveloped bands

The source (quoting Rob Hordijk) gives the design logic of the DX7’s six operators: three pairs of sine operators can generate three spectral ‘bands’ — a fundamental band for pitch identity, a mid ‘formant’ region for instrumental character, and a bright/noisy top for attack brilliance — each with its own amplitude envelope. Because each band evolves on its own envelope, the voice can produce the kind of complex, time-varying timbre that acoustic instruments have (percussive attack, sustaining body, fading brightness). Four-operator FM synths cannot separate these three bands independently, which is why some DX7 voices cannot be reproduced convincingly on them. The 32 algorithms are the fixed routings that assign which operators act as carriers versus modulators.

Examples

A DX7 tuned-percussion voice can devote one operator pair to the deep fundamental, one to a woody mid character that peaks then fades, and one to a sharp transient top — each on its own decay. A four-operator synth must share fewer envelope slots and compromises one of these bands.

Assessment

Explain why six operators help simulate acoustic instruments better than four. Given a six-operator algorithm diagram, identify which carriers likely serve the (a) fundamental, (b) mid-formant, and (c) brightness bands.