Detecting Frequency of a Audio/IR LED signal

Hello everyone. For a group project, one of the small parts I am stuck on is detecting the frequency of a Sound and IR pulsating LED. What happens after detecting these signals is not relevant.

Basically, there will be an external source of either a 3Khz or 7khz signal of both Sound and IR (LED). If both Sound and IR LED are on at 3khz, decision x will be carried out and decision y for 7khz.

So far, we've built bandpass filters and amplication circuits with some success (we are only using the Sound, less chances of interference). However, I was wondering if there was a direct way to use the Arduino to directly sample the rate of any of these signals.

I'm very new to robotics and Arduino in general and have found some examples quite confusing. From what I've read, It may be possible to detect the Peaks and Troughs somehow. Either way, could someone please detail out any feasible ideas, any guidance is much appreciated!

What happened if you feed a google with "arduino frequency measurement library"?