Re: SAPI 5 and One Core voices volume comparison?
The number of factors that come in to how humans perceive volume is just immense, as are the number of factors that can come in to how Windows (or any OS) deals with volumes when multiple programs are involved.
The easiest way to "even things out" across programs is to use volume equalization under Windows if your hardware supports it (mine doesn't). See the search results from:
for more tutorials on this subject than I could ever plow through in a lifetime. If your hardware supports it, consider going that route.
Brian - Windows 10 Home, 64-Bit, Version 1809, Build 17763
A great deal of intelligence can be invested in ignorance when the need for illusion is deep.
~ Saul Bellow, To Jerusalem and Back