i mean like flashing pictures. different flash rates will produce different alpha waves n stuff. or if the flash rates are irregular it can produce even more emotions. now how do u apply this stuff to music
also me and my cousin downloaded a frequency producer one day. we discovered certain frequency intervals that were extremely calming and others that were jarring. so this involves the timbre of an instrument, except the instrument we were using was basically a simple beep (i think you could make it sine or something.) so even though u may have two instruments playing the same note, you can still drastically alter the mood by changing the instruments frequency.