But physics is not everything. Our brains are plastic and our perceptions push back against the physical world all the time. We think we hear reality, but we don't. Just consider the fact that we forget about constant unchanging sounds all the time, but when they stopped suddenly like when the refrigerator compressor suddenly stops its hum. The environment suddenly seams very loud. That's called habituation. They're good evolutionary reasons for its existence in our brains. For example, if the forest suddenly gets quiet, there might just be a bear nearby. Habituation is one example of how we really don't perceive reality evenly and there are many others. This plasticity of our perceptions can be shaped by our environment. If you grow up in a swamp or you grow up in a desert, that swamp or that desert, they'll always seem like home. If you grew up hearing wild and physically dissonant sounds, those sounds will always sound beautifully emotionally consonant to you. Because they're what you're used to, they sound together naturally. Not according to the natural physical world, but according to your natural cultural world. My favorite example of this phenomenon is music from the Balkans. Here is an anonymous harvest song from Bulgaria. Listen for awhile, and notice that although the vertical combinations of sounds are objectively shrill, they're truly beautiful. Well, okay, if you don't think they're beautiful, at least notice that they can be beautiful. There are lots of non Pythagorean half steps whole steps and I don't know what they are steps, but that physical dissonance, it's just a flavor. It's the flavor of home if you like sheep. But seriously, the singers here do not think this is dissonant, they think it is colorful and fun. In any case, notice that after you listen for a while, the sound world does become normalized. What sounds together, sounds together and is therefore by definition consonant, which is of course, tautological. But only because it's tautological. Anyway, here's music from a completely different culture. It's from the Indonesian island of Bali. At first, this also might sound dissonantly clangorous. The overtones are clashing. Each metallic instrument is out of tune with itself. This is because a round bell often has two different fundamental pitches and the overtones of each of those pitches gloriously clash with the others, and the flutes, they are not quite playing the same pitches as the bells. But after a very short while, the clanging just becomes the color. It becomes the beauty of the sound. It just goes. It's the way it should be. It sounds consonant because the sounds just go together and the flutes variations on the pitches, they are not dissonant. They constantly expressive. That self-contained inevitability is cultural and very learnable. In fact, each individual piece of music can generate it's own culture. Beyond a cultural context, an individual composer or an individual piece can define its own world of consonance and dissonance. Take this Webern piece for example. If you're not used to listening to Webern, his music can sound strange and dissonance. My father who loved classical music, just to complain that it was all way too dissonant to him. Just listened to the- Mozart would never. I would try to explain to my father that what he didn't like about the piece was maybe that there was no dissonance in it at all. In terms of the sound world created by this piece, almost anything can go with anything else and therefore everything is consonant. In the contextual sense, the definition of consonance is expanded so inclusively that it wouldn't make sense to listeners from previous cultural eras like my father, who were just used to narrower definitions of what could and couldn't be sounded together at the same time. In that way, the Webern news closer to other forms of modal music where what counts is the mode or the limited choice of pitches and how it's used melodically. In that sense, maybe the Webern is much closer to traditional Indonesian Gamelan music. Gamelan music is wonderfully clingy and with different limited modes, everything and anything can sound together as long as the horizontal melody seems right. Now, yes Webern is more complicated than that. But then again, so as Gamelan music. For now, we're just trying to develop a general language of how to talk about all these wonderful, joyful complications. Hey, speaking of complications, here's another one. We've just noted that when you play all the notes, they all seem consonant. Some people of course, except that you can play any combination of pitches. But those people might still yearn for that sense, the feeling of dissonance. How did you get it? Here's a famous example from Stravinsky's Rite of Spring. It's much more dissonant than the Webern. Because the inner structure of this iconic thumping chord has a real structure. In fact, after listening to Stravinsky, well does the favorite example feel astia even elegant, almost not dissident. Stravinsky actually designs a chord. He wants to always sound dissonant. No matter how used to it you become. Let's take a look at this chord that you just listened to and see what I'm talking about. You can think of the chord as two normally consonant chords, a half step apart. In other words, instead of having just two pitches in physical distance with one another, Stravinsky get two entire chords in physical dissonance. Here is half the cord, and here's the other half. They sound so innocent. So sweet. Put together though, the Thelma and Louise each other off the cliff and sound like this. Is a great example of pumping the stakes, mirror pairs of notes that are dissonant, that is so ordinary these days. In fact, it is so ordinary that by the early 20th century, it doesn't even seem dissonant anymore. Here, I give you pairs of entire chords that are dissonant. Just a little more physics. Stravinsky also places that dissonant combo chord, actually quite low in the orchestra which means that all those juicy 1D interference patterns end up right in the middle of our optimal hearing range. Anyway, while we are muddying the waters to show how plastic and fluid these rules and terms are, let's return to the building block analogy where physical consonants is like smaller blocks fitting in very evenly to larger blocks. If you build out of blocks where the lengths aren't quite even divisions of larger units, you might build something that looks long with edges sticking out all over. But if you really mean it and you study and think and pay your dues, you might just build something that looks beautiful and write rules. In other words, they're not so much rules per se, but rather guidelines. If you do this one thing, it might affect your music, in this one particular way. But that's not saying you have to do that. Now, rules can be very important guidelines to be used as you see best. For instance, in the worlds of consonance and dissonance, who's to say that you can't actually mix entirely disparate styles. Check out this one song by Charles Ives. It's called Down east. In this song, the mystique dissonant present where anything can be played against anything, suddenly clears into a sharp, nostalgic, and consonant picture of the way things used to be. It's okay not to like the song. If anything, I'd rather you hated it then you are ambivalent. But whatever your reaction, can you hear the abrupt change of system of consonance and dissonance that Ives uses and do you get that he's at least trying to use that change for a very expressive effect. Let's try to apply some of these principles ourselves in a more personal way.
