Rate scaling on a DX7 operator makes higher keyboard notes sweep faster, mimicking acoustic brightness-by-register

Rate Scaling on the DX7 causes EG rates — attack, decay, release speeds — to vary proportionally with keyboard position: the higher the note played, the faster the EG rates. Applied to the modulator’s amplitude EG, this makes the timbral sweep (brightness change) happen faster in the upper register and slower in the lower register. This mirrors a characteristic of many acoustic instruments — strings and winds tend to have faster transients in their upper range. Rate scaling is a separate parameter from velocity sensitivity: velocity responds to how hard you strike, rate scaling responds to where you strike. Settings from 0 (no scaling) to 7 (maximum) control the intensity of the effect.

Examples

FM Demo 1-C: Op. 2 EG with rate scaling ‘5’. The same chord played on the lower keyboard opens slowly and darkly; the same chord played high opens quickly and brightly, despite identical envelope settings.

Assessment

Distinguish between rate scaling and velocity sensitivity on a DX7 modulator: what input does each respond to, and what aspect of the sound does each control?