Equalizer from audio data

I have a mp3 file, so I need to play it, and display an equalizer (like in attached image).

So playing is not problem, but I have no idea how to measure power of current playing sample's dBs based on frequency.

By which steps I can get data for displaying dBs of current sample?

As I guess, I need to get some array of powers in different frequencies, am I right?