Hardware based MIDI decoding / synthesizing

I have a lot of old MIDI equipment that was recently given to me by a retired music teacher. I have a lot of interest in it, and would like to make a MIDI synth. It does not need to be high quality or sample based, but I want to know how to implement a MIDI decoder in hardware.
I know that MIDI is just digital signals representing instruments, so I’m thinking something like this.

Yeah, it’s not a technical diagram. But basically, I want a really excellent guide to how MIDI works. What the signal contains and so on. I have an arduino ready to act as a PWM generator and I have tested it. It just needs to generate simple waves (like square waves, NES/Famicom style).
Does anyone know a concise, easy to understand documentation for the MIDI standard? Something like what would be in “The Art of Electronics” (the textbook) if it talked about MIDI at all. Something that a beginner could understand, preferably. I mainly work in analog technology, so this has been a new experience for me.
Thank you. (By the way, I’m not asking you to build it for me; I just want to know where a good document is. I want to do this project on my own. Nothing more complex than simple logic IC’s, so don’t tell me about those MIDI generating IC’s.)