Yamaha MODX6 Supplementary Manual page 33

 Normal Part (FM-X)
Mod/Control (Modulation/Control)
2nd LFO
[EDIT]  Select the Part from [Common]  Operator [Common]  [Mod/Control]  [2nd LFO]
Operation
Speed (2nd LFO Speed)
Adjusts the speed of LFO variation. The parameter range has been increased from 0 – 99 to 0 – 415.
Range:
0 – 415
Extended LFO
This lets you select between the old parameter range (Off: 0 – 99) or the new parameter range (On: 0 – 415). If you want to
maintain compatibility with settings made in the old parameter, set this to Off.
Settings:
Off, On
MODX Supplementary Manual
33