Just Intonation, Part 3: A (Very) Brief History of European Tuning
Most European and American musicians (and increasingly, those in the rest of the world as well) take the 12-tone equal-tempered scale for granted. But in fact, it's a fairly recent invention, and is highly artificial -- not a natural system at all. The fact that it's also extremely versatile and serviceable for certain types of music made its triumph historically inevitable. Only with the introduction of electronic instruments has it become practical to overthrow the tyranny of 12-tone equal temperament and work, if we choose to, in other tuning systems.
We don't know what ancient European music sounded like, but the rather sketchy information we have suggests that, like the music of many cultures around the world in more recent times, it was primarily monodic. That is, there were melodies, but the melodies were probably sung over a fixed harmonic underpinning of some sort -- perhaps a drone like that provided by the Indian tamboura. Chord progressions and counterpoint were unknown.
During the Middle Ages, the first period for which we have written records, church choirs started singing music (which later came to be accompanied by simple pipe organs) in which two or more voices sang complementary melodies at the same time. This practice was called counterpoint. As the centuries passed, the counterpoint became more complex. Listeners got comfortable with the sound of three or more voices singing different notes at the same time. In our terms, they had discovered chords. And as the voices moved, one chord was followed by another. Chord progressions came into being.
When the singers were unaccompanied, they could adjust their intonation to one another (consciously or unconsciously) so that the chords all had the sweet sound of pure intervals. (For an explanation of why pure intervals sound good, read the page on Acoustics.) Barbershop quartets still make these minute adjustments in pitch to produce more consonant chords.
But when you press a given key on an organ keyboard, the pipe connected to it always produces the same pitch. If you're singing with an organ and try to adjust your pitch to fit with the other singers, you'll just sound out of tune with respect to the organ. Some organs were in fact built with split black keys, to allow them to play either a G-sharp or an A-flat, for example, since those two notes did not have the same pitch.
As composers started using more complex chord voicings (vertical sonorities) and chord progressions (horizontal movement from chord to chord), a problem arose. The problem was that some of the chords didn't sound quite right. That is, they didn't sound the way composers and listeners wanted them to. For instance, the C major triad (C-E-G) might sound pure, while the D major triad (D-F#-A) sounded a lot less pleasant. And if the organ was built with pipes of the correct lengths to make both the C and D major triads sound good, some other chord or chords would sound bad. (I'm using the word "bad" here to mean what listeners probably meant at the time. In fact, those "bad"-sounding chords can be quite interesting.)
In order to be able to play music that used complex chord progressions, the musicians of the time needed either to build keyboards with lots of split keys (which would have been impractical to play) or to have instruments built with compromise tuning systems that would sound good no matter what chord they played. That is, the tuning system would have to fudge a little here and there. One of the pitches would be raised slightly, another lowered slightly. In such a system, some of the chords would sound a little less pure than they had before, but none of them would sound too bad.
The general term for tuning systems is "temperaments." This is because the process of adjusting certain pitches is called "tempering," by analogy with the process of tempering a piece of iron to make steel. A number of temperaments were developed in the 16th, 17th, and 18th Centuries. (Here's a link to a site that has some discussion of the temperaments used during this period.)
This process of evolution culminated, in the early 18th Century, in the development of 12-tone equal temperament. This scale, the one we use today, is absolutely uniform. You can move a chord voicing up or down in half-steps without hearing the slightest change in the quality of the voicing. All chord roots and all keys are interchangeable.
The advantages of 12-tone equal temperament are undeniable. For instance, if a singer finds that a melody is too high in the key of D, the accompanist can lower the accompaniment to the key of B or B-flat without having to worry about sonic changes. Well, that's not strictly true. Changing the key can force the player to re-voice chords on some instruments, such as guitar. But the intervals of the chords will have the same quality no matter what key the song is played in.
The development of 12-tone equal temperament gave composers a great deal of freedom. For the first time, they could modulate (change the tonal center) to any key in the course of a piece of music. This possibility existed from the mid-18th Century onwards, but Beethoven, writing at the beginning of the 19th Century, was the first composer to take full advantage of it.
As the 19th Century unfolded, composers (most of them heavily influenced by Beethoven) explored the harmonic resources of the 12-tone equal-tempered scale. Increasingly, their music had a restless, unsettled quality. This reflected the social ferment of the Industrial Revolution, but it also reflected the fact that 12-tone equal temperament provides no real resting place, harmonically speaking. Even a straight major triad simply doesn't sound very good.
By the beginning of the 20th Century, the bonds of traditional harmony had been entirely broken, and the atonal era was ushered in. Functional harmony, it seemed, was a dead issue in classical music, though it was still used -- is still used -- in pop music. Not coincidentally, jazz underwent a similar harmonic evolution, from simple triads and 7th chords to almost complete atonality, in the period between 1910 and 1960.
Pop music has resisted the move toward harmonic complexity. In pop music, the underground revolution against equal temperament has taken a slightly different form. Although you'll hear a fair amount of harmonic ambiguity (bitonalism) in mainstream pop arrangements, harmonic content has been replaced more and more by raw rhythm and timbral sophistication -- sampling, synthesis, and effects, in other words. The trend seems clear: In spite of all the wonderful music that uses 12-tone equal temperament, everybody is trying to get away from it.
Since the 1960s, classical composers have returned increasingly to tonal composition. Partly this shift is due to the influence of minimalism. Two of the pioneers of minimalism, Terry Riley and LaMonte Young, have experimented extensively with just intonation. Arguably, an even more important reason for the resurgence of tonal composition has been the realization that the sound of tonal harmonic relationships is simply pleasing. This sound communicates with listeners in a way that atonal music only rarely did.
Because the 19th Century system of functional chord progressions is no longer used, however, composers are free to explore alternate sonorities, such as those provided by other tunings.
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