In case you are still interested - and for the sake of completion in case people stumble upon this topic - I believe these are the corresponding formulas.
EDIT: I spoke a bit too soon. EmeraldSlash helped me find the correct formulas for each of the roll-off modes. He documented them in this post!
Old post
The formulas are a bit messy and could probably be simplified, but they should display the correct behavior. The formulas for ‘inverse’ and ‘linear’ were pulled from the fmod website’s documentation. Linear square should just be the linear formula, but squared. The only bit of doubt I have is the formula for ‘inverse tapered’. The Roblox documentation mentions it interpolates between ‘inverse’ and ‘linear square’, but there is no information on the kind of interpolation, so I assumed a simple linear interpolation was used.
I should also mention my graph for the ‘inverse’ fall-off slightly differs from Emily’s graph. Although I don’t know what Emily used, I followed the description from the fmod documentation:
When FMOD uses this model, ‘mindistance’ of a Sound / Channel, is the distance that the sound starts to attenuate from. This can simulate the sound being smaller or larger. By default, for every doubling of this mindistance, the sound volume will halve.
I interpreted this as ‘starting from the minimum distance, for every doubling of the distance, volume is halved’.