Range is -144.6 to 6 in the specification, but some SFZ players can utilize values above 6.
volume=-24 volume=0 volume=3.5 gain_cc1=12
This will play the sample at unchanged volume when CC1 is at 0, and apply a 12 dB boost when CC1 is at maximum.
gain_ccN is useful for creating volume controls, an alias for the ARIA extension
Also see the ARIA extension amplitude_onccN for another way to do a simple volume control.