Arduino sound equalizer
Use a MSGEQ7. This IC is a "Seven Band Graphic Equalizer".

Here is its datasheet:

https://www.sparkfun.com/datasheets/Components/General/MSGEQ7.pdf

This method is more efficient, accurate and easier then pulsein() or analogRead(). The IC is fairly cheap and there are many libraries for it.

https://github.com/NicoHood/MSGEQ7

Here is a nice project that I found and that uses that IC. It can be a good souce of inspiration for both your code and your electronics.

https://www.youtube.com/watch?v=InrQvtUuS2w