Audio notes are scrolls that you find in various locations. You do not need to get 60 in one play-through. I noticed in new game plus finding audio notes you already have does count towards your 60. As I played naturally and finished the game around 50, I got this soon after starting new game plus and I'm pretty sure I picked up notes that I already had but it popped! You can check how many you have by checking the Lore section in the pause menu.