I am trying to roughly interpolate a smooth curve of this shape for an audio synthesis project:

For example, a y=1/x curve yields an okay approximation but it's a bit too steep at the left and/or doesn't flatten out enough on the right:
Is there any other simple way to get this approximate shape you can think of?
The article this comes from is using these two equations:
They state: "A linear regression of Eq. (21) with ssyn instead of spick gives the “synthesized T30.”"
However, I don't need the exact equations. Just a rough approximation of the general shape. Any thoughts?
Edit: Someone suggested exp which looks nice:
I think that's probably the most right simple answer. But still open to further suggestions.



