Yamaha TG500 Owner's Manual page 138

VOICE EDIT MODE / 3: Full Edit. 3-3: Filter
RS (Rate scaling)
126 3-3-02: LEVEL / 3-3-03: RATE
Allows the overall cutoff envelope generator rate for the selected filter to
be varied across the entire pitch range (i.e. keyboard range). This function is
only available if the "Ctrl" parameter (page 123) is set to "EG."
Plus ("+") settings produce a longer overall envelope time for the low notes
and a shorter envelope time for the high notes. The maximum "+7" setting
produces the greatest envelope length variation across the pitch range. Minus
("–") settings produce the opposite effect — a shorter low-note envelope and
longer high-note envelope. A setting of "+0" results in no envelope length
variation.