## Wednesday, July 11, 2012

### You can tune a piano...

You can tune a piano, but you can’t tuna fish.
Or so goes the title of the REO Speedwagon album. I have always disagreed. Both parts are wrong. You can tune a fish by going up and down the scales. And, contrary to popular belief, you can’t tune a piano. Read on, and I’ll explain why you can’t.
The circle of fifths
As a first example, we consider the circle of fifths. No, I don’t mean a circle of my buddies Jack Daniels, José Cuervo, Johnny Walker and Jim Beam.

I mean the circle of fifths on the piano. From C to G is an interval known as a fifth. From a G to a D is another fifth. This eventually winds up back at C, so the whole thing forms a circle with twelve notes. I suspect that many of those who have read this far are well aware of this.
C → G → D → A → E → B → F# → D→ A → E → B → F → C
Now for two facts putting these to facts to their logical conclusion will lead to a contradiction that will prove that you can’t tune a piano. First fact: The ratio of frequencies from a note to the note that is one octave higher is two. If the A below middle C is tuned to 440 Hertz (440 cycles per second), then the A above middle C is 880 Hertz.
If you count the octaves as you go through the circle of fifths, you will find that they span seven octaves. Put this together with the first fact, and you will see that the frequency of the last entry in the circle is exactly 128 times the frequency of the first C in the circle. 128. Remember that number.
Now for the second fact: The ratio of frequencies from a note to the note which is one fifth above that note (as in from C to the next G up), is 3/2. Thus, if we tune to A 440, the E just above middle C is 660 Hertz.
We’re coming up on the contradiction, so pay attention.
There are twelve steps in the circle of fifths1. If each of those steps is 3/2, then the ratio of frequencies from the C at the end of the circle to the C at the start should be (3/2)12, which is 531,441 divided by 4,096, which is about 129.746. The astute student of mathematics will note that 129.746 is not equal to 128.
The conclusion is that this set of three statements is not consistent: An octave is a ratio of two. A fifth is a ratio of three halves. The circle of fifths winds up back where it started.
A Hint from Pythagoras
As the story goes, Pythagoras happened to be walking by the blacksmith’s shop one day when he noticed the musical tones that were created by the different blacksmiths pounding on the iron with their hammers. As the story goes, Pythagoras was intrigued, and started experimenting to try to understand what caused the tones to be different. As the story goes, he found that the weight of the hammers was the important factor, and that the ratio of weights told what chord the hammers would make when they were pounded together.
He determined a very simple, yet powerful fact. Simple ratios make for consonant notes. The octave, with a ratio of two to one, is a simple ratio, and the two notes sound consonant. The fifth, with the simple ratio of three to two, is also consonant. The major third has a ratio of five to four, and this is also consonant.
This story comes to us by way of Iamblichus, who was born in the third century AD, about eight centuries after Pythagoras. The story was wrong2, but the conclusion was correct. The note that is produced when you hammer on a piece of iron depends on the piece of iron, and not the weight of the hammer. Pythagoras probably came to this conclusion by some other means, perhaps listening to the tone produced by a string held taught by differing amounts of weight, or perhaps by listening to the tone produced by a column of air of different lengths.
Defining a C major scale
Regardless of how the “simple ratios” rule was determined, it can be used to define all the notes in a C major scale. Much like early Rock and Roll, we just need three chords: the tonic, the dominant, and the subdominant, that is, C, G, and F.

Let us start by assuming that we have tuned our instrument so that middle C is equal to 240 Hz. This is a bit off, but it makes for easier calculations. With this definition of C, then G must be three halves of that (360 Hz), and E must be five fourths (300 Hz).
The G chord allows us to build from the definition of G (360 HZ) to ascertain that the fifth above that, D, is 540 Hz. This is in the next octave, so we can divide by two to bring it into this octave. Thus, the D above middle C is 270 Hz. From the G chord, we can also ascertain B, the third above the G. This makes B out to be 450 Hz.
The F below middle C is a fifth below C. That means that the frequency of F, when multiplied by three halves, gives you 240 Hz. Thus, F must be two thirds of the frequency of C, or 160 Hz. This is in the octave below middle C, so we multiply this by two to get 320 as the frequency of F above middle C.
The note A is the final note in the key of C major. This is five fourths the frequency of F, which gives us 400 Hz. Here is the full table for a C major scale, with C tuned to 240 Hz.
 Middle C 240 Hz D 270 Hz E 300 Hz F 320 Hz G 360 Hz A 400 Hz B 450 Hz C 480 Hz
Trouble brewing
This was all pretty simple. Given that the circle of fifths ran into trouble, it should come as no surprise that there might be problems underlying our simple C major scale as well. The trouble can be exemplified by asking a seemingly simple question, “what is the ratio for a minor third?” The C major scale gives us three opportunities to figure this out. D to F is a minor third, as is E to G, and A to C.
The ratio from E to G is six fifths (1.200), as is the ratio from A to C. But the other example of a minor third is D to F, with a ratio of 32 / 27, or 1.185. We have two problems here. The first is that we don’t know for sure what a minor third is. The second is that sometimes a minor third has a ratio that is simple (6/5) and sometimes it is not (32/27). What went wrong?
The difficulty is that we have implicitly accepted two different notes as being the same note. First, there is the F that is a fifth down from C. Second, there is the F that is a minor third up from D. The piano forces these two different notes into the same key. The keyboard of the piano is a lie. The two different notes are only 1.25% different, but they are different notes.
All we need to do to fix this up is to add a second F to the keyboard, defining it to be a minor third above D. And of course, we need to officially define a minor third to be the simple ratio 6 / 5. And all is well with the world.
Well, at least until someone wants to play a chord that has a sharp or a flat. Or until someone wants to play anything by Cole Porter. Then Debussy comes along and asks you to play in sixteen sharps. Pretty soon, your piano has exactly 4.76 gazillion keys. Every chord is perfectly in tune. Now, If your name is Ruben, then you could probably learn to play such a monster, or at least a toy version of it. All the rest of us mere mortals have learned to live with a piano tuning that is a compromise, where each key is tuned to be a compromise between all the frequencies that it is supposed to play.
Two halves don’t make a whole
Every choir director I have ever known has played a trick on us during warm ups. Maybe it’s been on purpose, or maybe they don’t realize that it’s just a cruel joke. A joke like asking a third grader to find an integer fraction that, when squared, gives you 2. Choir directors ask you to sing a chord, and then move down by a half step and then another. Then they ask you to go up a full step. The cruel task master will then chastise the choir for going flat. Cruel trick. There is a perfectly reasonable explanation for going flat that has absolutely nothing to do with the indolence or skill of the choir.
First, let’s consider what “going down a half step” means. If I am the lead voice, and I am singing a C, then a half step down is to B. That is, a half step is from do to ti. From the chart above, we can see that going down a half step means multiplying the frequency by 15 / 16. And the next half step, you just repeat that3. So, after two half steps, the frequency is now 225 / 256 times the original frequency.
Then the choir director commands to go up by a whole step. If you are singing the root of the chord, then you are going to be going from do to re. Looking at the chart above, do to re is the interval from C to D, which means multiplying the frequency by 9 / 8. This means that the final landing point is (225 / 256) X (9 / 8) = 2025 / 2048. This is about 0.98877, just over 1% short of returning back home.
The choir director, in tyrannical ignorance, will demand that two half steps be equal to a whole step, and accuse the choir of (God forbid) going flat. But the choir is just doing what it was told.
I hope this section has caused some choir directors to have a bit more humility. Maybe some of them will even find contrition in their hearts, and will be willing to apologize for their misguided despotism.
If any of my previous choir directors feel such a need, rest assured that apologies are not necessary. I have been blessed through the years with many, many choir directors who were inspirational magicians, and I want to thank them for the glorious moments of ethereal chords.

That is why I say that you can’t tune a piano.
1)      Any alcoholic will note a certain irony in that.
2)      This of course was not the only thing that history has gotten wrong about Pythagoras. See a previous blog for another example.
3)      Crucial point here: if the choir is doing their job right, they will mentally change keys when they drop a half step. The old ti will become the new do from which to move up or down.