Routing the Mod Wheel to FM modulator amplitude gives the performer real-time control of brightness

Where an envelope makes an FM timbre brighten and darken automatically, the same modulator-amplitude lever can instead be routed to a physical controller so the player shapes brightness live. On the DX7, assigning the Mod Wheel to the modulating operator’s output level (via EG Bias) lets rotating the wheel away from the body raise modulation depth — brightening the tone like opening a low-pass filter — and rotating it back darken it. This is the FM analogue of hand-riding a filter cutoff on an analog synth: identical timbral result to an automatic EG sweep, but under continuous manual, expressive control rather than fixed per-note. The same routing can be assigned to Foot Pedal or Aftertouch.

Examples

MW-Demo 1: same two-operator patch as the automatic Demo 1-A, but Op. 2’s output is under Mod Wheel control. Rolling the wheel forward mid-note opens the sound; rolling back closes it, in real time.

Assessment

Explain how MW-Demo 1 differs from FM Demo 1-A in what controls the brightness sweep, and name one other DX7 controller that can be substituted for the Mod Wheel to achieve the same effect.