How to compute key of a song? I'm looking for a precise way to compute the key of a song. BPM would be cool too. Analog is ok. I tried to approach it from the DFT angle, but got stuck and can't really put a finger on what's the issue. New perspective would allow me to get out of the mental hole I'm in.
Insert a tuner into the audio chain and take down the notes coming through. Use the circle of fifths to calculate the key as best as possible.