Earl, who ever told you that you can only hear two sounds at once has absolutely no idea what they are talking about. Anyone that has studied human anatomy and physiology knows that humans and most other mammals can hear thousands of sounds at the same time. When you hear a hissing sound of air leaking from an punctured tire, you are hearing thousands upon thousands of sound all a the same time, and thousands of individual frequencies. Same when you hear white noise. I do remember a few things from my A&P classes at University of Maryland.

All the best,

Gary 8)