controlling all sounds from their volume point

hi i have a sfx volume control which changes all sfx volume between 0 and 1, but im trying to work out the best way to control all their volumes from their current volume point.

because the sfx change on each level im using an array to find all the sfx tagged when the menu is first opened, but how do i say to each one that 1 is their maximun volume relative to their current number so 1 may = 0.75 on another one

any ideas

Just use Math.

Your max volume is the 1 value.
Your min is 0 value.
Your average is your 0.5 value.

Instead of changing with direct values, just multiply by the actual volume.

If the sfx volume in that point is 0.3, so its max would be

0.3 * 1 = 0.3

and its average would be

0.3 * 0.5 = 0.15