I've always had a suspicion that the frequencies in music have an effect on our mental and/or emotional states that isn't really widely understood. Not anything necessarily audible but frequencies within the soundwaves. Kind of like how sand on a tuning plate forms different shapes depending on the frequencies running through it. Everything internally is waves, frequency, vibration. Brain waves, heart waves, electromagnetic pulses, right down to the vibrations of the atoms that make up our structure. How does the resonance/dissonance between all these things affect us physically. I've definitely heard of the better music producers using this knowledge to engage listeners on a more emotional level, not sure where exactly I read about this though.