Controlling filters with MIDI note input

Hello. I am new to JUCE and programming in general and am in a university course for audio programming. For my final I am creating a filter/eq band effect that can be controlled by midi note input, essentially allowing the user to create peak filters at the frequency of the notes being played.
I have been hard pressed to find any tutorials or explainers online to help send midi note input to something that isn’t a synth. I started building a synth thinking I could just route that to the filters instead of an osciallator but then I watched this tutorial about building a midi processor ()Juce Tutorial 60 - Create your first MIDI Plug-in with Eyal Amir (Xfer Records) - YouTube) and it seemed like the way to go, but I’m so confused by what’s happening in the process.
Does anyone have any insight that might be helpful? Thanks in advance.