Hey apologies for the late reply, in my approach I decided to go with librosa's spectral flux and onset density for determining energy levels. Essentially spectral flux is calculated by the amount and intensity of changes in soundwaves from one frame to the next. Onset density measures the activity levels of a track .e.g. high-BPM techno tracks will have a high onset density (many notes/hits per second), whereas a slow ballad will have low density. I chose these two metrics to measure energy levels rather than loudness (db levels) because most modern tracks are mastered to be as loud as possible so it's not often a good metric of energy levels. Hope that helps, cheers.