> There are some subtle differences. For example, (very oversimplified), if you were made to listen to a waveform containing the frequencies of 60 Hz and 90 Hz,

> There are some subtle differences. For example, (very oversimplified), if you were made to listen to a waveform containing the frequencies of 60 Hz and 90 Hz, your auditory system would "hear" a pitch corresponding to a fundamental frequency of 30 Hz, since 60 Hz and 90 Hz are integer multiples of 30 Hz. Eh, so if you add 60hz and 90hz you get a wave that repeats every 33ish milliseconds. You don't "hear a 30hz sine wave" that your brain is inventing, that's a very common misconception. You just hear a 30hz "thing" that is not a sine wave because there's a 30hz thing that is not a sine wave playing. Just try adding an actual 30hz sine wave to the 60+90 thing and you'll see it sounds very different to what you hear when you add those two sine waves. If you keep on adding waves spaced 30hz adding the 30hz or 15hz one wouldn't make much of a difference because what you are listening to is something very similar to a low pass filtered 30hz pulse wave.