Just intonation creates perfectly stable, consonant intervals by tuning notes to simple whole-number frequency ratios, producing no audible beating or pulsing when notes are in tune; however, this system only works optimally within a single key, causing severe tuning problems when modulating to other keys. In contrast, equal temperament distributes tuning compromises evenly across all twelve diatonic keys, allowing musicians to play in any key without significant tuning issues, though none of the intervals are perfectly just—the major third in equal temperament is approximately 13 cents sharper than its just intonation counterpart.
Just Intonation vs Equal Temperament: Visual Demonstration
Added:The image you see on the screen is from an app called Helix Tuner.
Here's a C major scale, played in equal temperament.
The image becomes stable when the pitch is in tune.
It rotates right when the note is sharp and left when it's flat.
Now I'm going to play the C major scale using just intonation.
Notice how much more stable the images are this time.
Let's see the equal tempered scale again for comparison.
We can also use Helix Tuner to look at chords and intervals, two or more notes together at the same time.
In the key of C major, here' the route on a middle C.
And if we add the note G, which is the fifth, it looks like this.
Now, if the C remains in tune, but the G become slightly flat, it will look like this.
And if the G is slightly sharp, it's like this.
When the G is out of tune with the route, we hear the volume pulsing up and down and the shape on the screen also pulses in and out in a similar way.
The image on the screen is like a oscilloscope graph that's twisted up into a circle.
It's displaying the actual sound waves in real time, so it's not just an animation.
If we put the tuner in automatic mode and we play a chromatic scale, it will automatically follow along with the scale, changing the tuning note to stay in equal temperament.
It looks like this.
However, if we want to see the tuning of just intervals, as opposed to equal temperament, we need to manually select the route note.
I'm switching the tuner from automatic to manual mode.
And I'm going to set the route note to C.
Now if we play the note E, which is a major third above C, we see that it's slightly sharp.
It's sharp because when we set the tuner to C, but play the note E instead, the tuner is showing us just intonation in the key of C.
But the E note that we are playing was generated using equal temperament.
Just intonation can be defined in different ways depending on the context, but as a starting point, we'll say that a pair of notes is tuned in a just interval when we don't hear any beating or pulsing due to the notes being out of tune.
To make this idea as clear as possible, let's start with two notes playing exactly the same note.
That's the trivial interval called unison.
When the two notes are exactly in tune they sound as one note.
We do not even hear them as separate tones.
When the tuning of the two notes is mismatched we clearly hear pulsing.
If the pulsing is slow, that means they're only slightly out of tune.
And when the pulsing is faster, it indicates that they're more out of tune.
At this point, you might be thinking, why don't we just tune all the intervals in the scale using just intonation so that the tuning will be perfect?
Well that does sound like a reasonable thing to do until we realize that an instrument tuned in C major just intonation sounds horribly out of tune when played in the key of B major.
If we were to tune an instrument in just C major, we would have to commit to playing every song in the key of C, or else we have to accept that songs played in some of the other keys would be very out of tune.
Obviously for most musicians, that's not an acceptable situation.
Do equal temperament is a compromise that assures that we can play equally well and tuned in all 12 diatonic keys.
The cost of this compromise is that none of the keys has perfectly just intervals.
Here's the major third C and E in equal temperament.
And here's the same major third in just intonation.
Here's the equal temperament major third again.
When we play the E by itself, we can see that it's more than 13 sense sharper than the just interval.
We'll now play through all of the intervals in the equal temperament C major scale one last time to see how they compare against the just intonation that Helix Tuner is visualizing.
And here's the scale in just intonation.
If you're interested in trying this for yourself, click the link in the description to download Helix Tuner.
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