It’s all about the music.
Gill and Purves. “A biological rationale for musical scales” PLoS ONE, 2009
So you might think that music like this:
(HOT STUFF. Go to 0:35 for the real hotness. It’s Victoria’s O Magnum Mysterium)
(Also some killer hot stuff, 3:50 has the real chills. The Lauridsen version)
Don’t have much in common with THIS hot stuff:
(That’ll wake you up! No idea who this guy is, but he’s hilarious, and the dancers wearing body suits under skimpy outfits are the best!)
Or even much in common with this:
(That never gets old. MWAH HA HA HA!!!)
But you would be wrong. They have a lot in common. Most songs in both eastern (including Indian, Chinese, and Middle Eastern music) and western music are based on a limited series of musical scales (there are lots of exceptions, but the most popular songs tend to be based on common musical scales). And the question for years has been: why? These scientists have put together a new theory, which Sci will allow you to judge on yourself.
Humans can, all told, distinguish about 240 different pitches over a single octave. That’s a LOT of pitches, over a pretty small range. Our hearing may not extend very far into ultrasonic or anything, but we’ve got a good bit where it counts. Here’s an octave:
This person is playing from G to G on a standard piano. In a major scale like this one, there will be 8 tones from the lower G to the higher G. But in this same octave, a human can DISTINGUISH up to 240 different tones. Cool, huh?
So we’re pretty sensitive to changes in pitch (except those who are truly tone deaf). Some trained singers can even be trained to SING quarter tone pitches (we usually work in whole and half tones, but some middle eastern music requires quarter tones). But in a good part of the world, most music is based on a limited series of scale types, shown below:
Those are the 14 most commonly used scales in music. But we can distinguish THOUSANDS of tones. So why are we using these specific tone combinations for most of our music? Even if you narrow it down to an organization of scales based around an octave, there are still thousands of possible 5-7 note tone combinations. Not only that, but eastern and western tone scales are both often organized around the chromatic scale, a 12 note tone combination of half steps that are equally spaced (and is one of the major training things, along with the circle of fifths, that you learn to play very fast when you’re learning to play an instrument) So why do we just use these 14? And why do we organize scales along a chromatic tone structure?
Several theories have been put forward as to why. One theory states that we are attracted to the “lower harmonics” or the undertones (and presumably also the overtones) that occur in a harmonic series. If you play (or sing) a REALLY well tuned major or minor chord, you can hear overtones and undertones that resonate under and over the pitches you are singing. It’s a really chilling thing to hear and very cool, but unfortunately I can’t find any examples (send some if you have ’em!). But this theory doesn’t account for things like a minor second, which won’t result in overtones or undertones, meaning that minor scales might not be included.
Often, approaches as to why we use specific tone scales have used mathematical algorithms to predict scale structure, the idea being that we would use a specific mathematical formula because we’re totally parsimonious like that. In this evaluation, the scientists looked at similarities between tone scales and harmonic tone series, which merely evaluates the degree of tone similarities between tones in a scale (how far apart the tones are from one another).
Using this approach, they found that the scale that came out closest was the minor pentatonic scale, which is one of the most widely used scales in music. Appears to be a pretty close match. The second highest match was a scale used in Chinese and Indian music known as Ritusen (on the far right of the figure up there). Overall, most of the scales used most often came out well when compared to harmonic tone series. These all have similar ratios between the notes, making for a certain amount of equal spacing between the tones in the scale (ok, except the major 7th, that one never seems to come out well).
But what is the REASON for this preference? The authors put forth two reasons that are rather compelling. First, these harmonic tones are ones that are easily distinguished, and thus pleasant to us (if you have two tones that are too close together played at the same time, it created a “throbbing” kind of noise which isn’t fun to listen to at all, try hearing badly tuned instruments some time). The scales that we prefer are the ones with the highest harmonic overlap, which means they are spaced far enough apart that the “throbbing” sound is reduced as much as possible when the tones are played at the same time. This makes the tone combinations in a scale sound more pleasant.
Second, the authors came up with a biological rationale. Why do we prefer (and studies have shown that we clearly DO prefer) tones with high harmonic overlap and low “throb”? Well, it turns out that human speech has a characteristic series of harmonics associated with it, though these are changed by things like vowel tones. Human speech is often determined as much by its tone as it is by the consonants coming out. So the authors hypothesize that humans prefer harmonic vocal series because it is the most similar to the speech patterns of our conspecifics. Presumably we are best adapted to hearing those harmonic frequency (the human ear is optimized for sounds in the human vocal range) and also adapted to find them pleasurable. Interestingly, other studies have shown that humans respond best to music that is similar to their own vocalizations, preferring music from instruments which are tuned near the range of the human voice (like the guitar), and some of which even have a timbre which is similar to the human voice (like a violin or flute).
As to why the tone combinations we write down are between 5 and 7 tones (technically a full octave is 8, but one tone is repeated, so 7), the authors note that the 7 tone series provides the full range of options for musical combination. Go higher than 7 tones and the combinations become less pleasant, while once you get all the way up to two octaves, you’re going to be repeating yourself. So it’s possible that 5-7 tone scales produce the most pleasant tone combinations. It would be interesting to test this, though very hard to do it in humans, because you would have to control for the fact that most humans will be familiar with the 5-7 tone scales and could thus find them more pleasant.
Sci thinks this is a pretty interesting hypothesis, and not entirely unlikely. It would also be really interesting to see if you could find a similar effect in animals, say monkeys or birds, where you make “music” out of similar or dissimilar harmonics to those found in their vocalizations, and see how they feel about them. In highly communicative species, it might be possible that similar mechanisms have evolved making them prefer similar sounds. An interesting way to test the hypothesis. And as Sci loves her 5-7 tone scales, she thinks this is something to sing about.
(Someone ought to write a modern oratorio based around L337-speak. Instead of the “Hallelujah chorus” we would have something based on “w00t”. It would probably have musical references to Mario…)
Gill KZ, & Purves D (2009). A biological rationale for musical scales. PloS one, 4 (12) PMID: 19997506