Cherry Surreal MG-1 Plus User Manual page 12

Tone Sources mode- This defines the behavior of the internal voltage-controlled amplifier,
which acts as something of an automatic volume control and on/off switch for the final
sound.

Contoured- Rise Time, Sustain, and Fall Time parameters are applied to amplitude.

Keyed- Rise Time, Sustain, and Fall Time parameters have no effect on amplitude -
notes play in simple on/off fashion. This is useful when using using the Contour
section for controlling filter envelope sweeps via the Filter Contoured Cutoff slider.

Continuous- Notes sound continuously. This is useful for drones and exceptionally
lazy keyboardists.
Cherry Audio: Surreal MG-1 Plus User Manual
Page 12