I remember on Penn and Teller's show "Bullshit" where they explained the concept of Perceptual subitizing, and it sounds like you're describing the audible version of that. I think I remember them saying the average person can "see" what number of objects there are without counting up to 5, but some can go way higher than the average person, assuming there isn't a clear pattern to help us recognize it, like on dice.
I've always had a keen ability to empty my mind, ever since I was a kid. I have to initially focus to do it, but I remember doing it regularly when I was around 4 and accidentally discovered meditation. It was extremely trippy to me. Ironically, I have ADHD, so typically my mind has at least 3 different layers of topics floating around, but if I consciously want to dump those thoughts, I can usually do it. Helps me fall asleep, but otherwise I don't really do it anymore. So I suppose it's useless until I decide to maybe make meditation a habit.