Isolate audio frequencies

Hi there, i’m currently trying to figure out how to isolate frequencies from an audio file to use as audiodriven visuals.
I assume that the audio spectrum analyzer creates a matrix of frequencies based on the spectrum width so how can I isolate 1 of them ? (i’m quite new to all this but kinda thrown into learning so bare with me :)) So far i managed to get an equalizer but i want for example to be able to just pick the bass to drive the intensity of a lightsource.

kind regards,