A while back, I linked to this page on, among other things, sound waves and how they relate to music. If you scroll down to the section titled “Musical Beats and Intervals” you see three diagrams showing three different pairs of overlaid wave forms. One is a very consonant octave set (something like a low C played over a high C), one is a relatively consonant 5th interval and the final one is a dissonant, ugly sounding interval. The point these diagrams make is that consonance and dissonance are not abstract properties of music, they are related to how two or more sound waves overlay on top of each other. Waves where the peaks and valleys generally line up sound good; waves where the peaks and valleys don’t consistently line up are weird.

The same is true with rhythms. If I take a drum groove played at 100 beats per minute and lay it on top of a drum groove at 200 beats per minute, everything should sound all right since the hits in the 100 beats per minute groove will correspond with every other hit in the 200 beats per minute groove. But if I overlay a groove at 157 beats per minute over a groove at 100, not much will line up and it will sound chaotic.

Now, this is no different in the first example using notes. Notes are really sound waves vibrating at certain frequencies. You could think of the peaks of sound waves as the “hits” in a drum rhythm. If you take two sound waves and the peaks line up most of the time you have something consonant. But the less they line up, the more dissonant they get.

So basically, when you hear consonant sound waves (or drum rhythms) your brain is comparing the peaks or hits and determining that they match and delivering a pleasant sound to your mind. But this comparison, this brain processing, is something we are unaware of. With two dissonant notes, we aren’t aware that the sound wave frequency rates are out of sync, we are just aware they sound bad.

And I suspect this is true with a lot of things. Our brain looks for patterns, for synchronicity. When it finds the pattern, it says, “yay, I like this.” When it doesn’t find the pattern it gets frustrated. But much of this processing goes on “under the hood;” we aren’t consciously aware we are doing it.