Hiya, welcome back,
OPen the main Fraps window,
Click the "Movies' Tab.
TICK the "Record external input" tickbox
If you have multiple external inputs, select your micrphone from the dropdown list.
If you have a Nvidia GPU, GTX6XX or GTX7XX, I suggest swapping over to using the Nvidia ShadowPlay utility in the newest Nvidia drivers. It's absolutely amazing bit of software that does NOT lower FPS during recording. Some info here to get started:
https://www.realitymod.com/forum/f112-p ... 8-2-a.html