Structure in jazz and math

Last night I went to a concert by the Branford Marsalis Quartet. One of the things that impressed me about the quartet was how creative they are while also being squarely within a tradition. People who are not familiar with jazz may not realize how structured it is and how much it respects tradition. The spontaneous and creative aspects of jazz are more obvious than the structure. In some ways jazz is more tightly structured than classical music. To use Francis Schaeffer’s phrase, there is form and freedom, freedom within form.

Every field has its own structure, its tropes, its traditions. Someone unfamiliar with the field can be overwhelmed, not having the framework that an insider has to understand things. They may think something is completely original when in fact the original portion is small.

In college I used to browse the journals in the math library and be completely overwhelmed. I didn’t learn until later that usually very little in a journal article is original, and even the original part isn’t that original. There’s a typical structure for a paper in PDEs, for example, just as there are typical structures for romantic comedies, symphonies, or space operas. A paper in partial differential equations might look like this:

  1. Motivation / previous work
  2. Weak formulation of PDE
  3. Craft function spaces and PDE as operator
  4. A priori estimates imply operator properties
  5. Well posedness results
  6. Regularity

An expert knows these structures. They know what’s boilerplate, what’s new, and just how new the new part is. When I wrote something up for my PhD advisor I remember him saying “You know what I find most interesting?” and pointing to one inequality. The part he found interesting, the only part he found interesting, was not that special from my perspective. It was all hard work for me, but only one part of it stood out as slightly original to him. An expert in partial differential equations sees a PDE paper the way a professional musician listens to another or the way a chess master sees a chess board.

While a math journal article may look totally incomprehensible, an expert in that specialization might see 10% of it as somewhat new. An interesting contrast to this is the “abc conjecture.” Three and a half years ago Shinichi Mochizuki proposed a proof of this conjecture. But his approach is so entirely idiosyncratic that nobody has been able to understand it. Even after a recent conference held for the sole purpose of penetrating this proof, nobody but Mochizuki really understands it. So even though most original research is not that original, once in a while something really new comes out.

Related posts

Electrical hum

If you hear electrical equipment humming, it’s probably at a pitch of about 60 Hz since that’s the frequency of AC power, at least in North America. In Europe and most of Asia it’s a little lower at 50 Hz. Here’s an audio clip in a couple formats: wav, mp3.

The screen shot above comes from a tuner app taken when I was around some electrical equipment. The pitch sometimes registered at A# and sometimes as B, and for good reason. In a previous post I derived the formula for converting frequencies to musical pitches:

h = 12 log(P / C) / log 2.

Here C is the pitch of middle C, 261.626 Hz, P is the frequency of your tone, and h is the number of half steps your tone is above middle C. When we stick P = 60 Hz into this formula, we get h = -25.49, so our electrical hum is half way between 25 and 26 half-steps below middle C. So that’s between a A# and a B two octaves below middle C.

For 50 Hz hum, h = -28.65. That would be between a G and a G#, a little closer to G.

Update: So why would the frequency of the sound match the frequency of the electricity? The magnetic fields generated by the current would push and pull parts, driving mechanical vibrations at the same frequency.

Related: Acoustics consulting

What key has 30 sharps?

Musical keys typically have 0 to 7 sharps or flats, but we can imagine adding any number of sharps or flats.

When you go up a fifth (seven half steps) you add a sharp. For example, the key of C has no sharps or flats, G has one sharp, D has two, etc. Starting from C and adding 30 sharps means going up 30*7 half-steps. Musical notes operate modulo 12 since there are 12 half-steps in an octave. 30*7 is congruent to 6 modulo 12, and six half-steps up from C is F#. So the key with 30 sharps would be the same pitches as F#.

But the key wouldn’t be called F#. It would be D quadruple sharp! I’ll explain below.

Sharps are added in the order F, C, G, D, A, E, B, and the name of key is a half step higher than the last sharp. For example, the key with three sharps is A, and the notes that are sharp are F#, C#, and G#.

In the key of C#, all seven notes are sharp. Now what happens if we add one more sharp? We start over and start adding more sharps in the same order. F was already sharp, and now it would be double sharp. So the key with eight sharps is G#. Everything is sharp except F, which is double sharp.

In a key with 28 sharps, we’ve cycled through F, C, G, D, A, E, and B four times. Everything is quadruple sharp. To add two more sharps, we sharpen F and C one more time, making them quintuple sharp. The note one half-step higher than C quintuple sharp is D quadruple sharp, which is enharmonic with F#.

You could repeat this exercise with flats. Going up a forth (five half-steps) adds a flat. Or you could think of a flat as a negative sharp.

More music posts

How to convert frequency to pitch

I saw somewhere that James Earl Jones’ speaking voice is around 85 Hz. What musical pitch is that?

Let P be the frequency of some pitch you’re interested in and let C = 261.626 be the frequency of middle C. If h is the number of half steps from C to P then

P / C = 2h/12.

Taking logs,

h = 12 log(P / C) / log 2.

If P = 85, then h = -19.46. That is, James Earl Jones’ voice is about 19 half-steps below middle C, around the F an octave and a half below middle C.

More details on the derivation above here.

There’s a page to do this calculation for you here. You can type in frequency or pitch and get the other back.

(The page also gives pitch on a Bark scale, something you may not care about that is important in psychoacoustics.)

 

Photo credit Wikipedia
Music image created using Lilypod.

New Twitter accounts for DSP and music theory

I’ve started two new Twitter accounts this week: @DSP_fact and @MusicTheoryTip.

DSP_fact is for DSP, digital signal processing: filters, Fourier analysis, convolution, sampling, wavelets, etc.

MusicTheoryTip is for basic music theory with a little bias toward jazz. It’ll tweet about harmony, scales, tuning, notation, etc.

Here’s a full list of my 15 daily tip twitter accounts.

If you’re interested in one of these accounts but don’t use Twitter, you can subscribe to a Twitter account via RSS just as you’d subscribe to a blog.

If you’re using Google Reader to subscribe to RSS feeds, you’ll need to switch to something else by July 1. Here are 18 alternatives.

Mars, magic squares, and music

About a year ago I wrote about Jupiter’s magic square. Then yesterday I was listening to the New Sounds podcast that mentioned a magic square associated with Mars. I hadn’t heard of this, so I looked into it and found there were magic squares associated with each of solar system bodies known to antiquity (i.e. Sun, Mercury, Venus, Moon, Mars, Jupiter, and Saturn).

Here is the magic square of Mars:

The podcast featured Secret Pulse by Zack Browning. From the liner notes:

Magic squares provide structure to the music. Structure provides direction to the composer. Direction provides restrictions for the focused inspiration and interpretation of musical materials. The effect of this process? Freedom to compose.

The compositions on this CD use the 5×5 Magic Square of Mars (Secret Pulse), the 9×9 Magic Square of the Moon (Moon Thrust), and the ancient Chinese 3×3 Lo Shu Square found in the Flying Star System of Feng Shui (Hakka Fusion, String Quartet, Flying Tones, and Moon Thrust) as compositional models.  The musical structure created from these magic squares is dramatically articulated by the collision of different musical worlds …

I don’t know how the composer used these magic squares, but you can listen to the title track (Secret Pulse) on the podcast.

More chess-related math posts

All day long I’d bidi-bidi-bum

This evening I watched my daughter in Fiddler on the Roof. I thought I knew the play pretty well, but I learned something tonight.

Before the play started, someone told me that the phrase “bidi-bidi-bum” in “If I Were a Rich Man” is a Yiddish term for prayer. I thought “All day long I’d bidi-bidi-bum” was a way of saying “All day long I’d piddle around.” That completely changes the meaning of that part of the song.

When I got home I did a quick search to see whether what I’d heard was correct. According to Wikipedia,

A repeated phrase throughout the song, “all day long I’d bidi-bidi-bum,” is often misunderstood to refer to Tevye’s desire not to have to work. However, the phrase “bidi-bidi-bum” is a reference to the practice of Jewish prayer, in particular davening.

Unfortunately, Wikipedia adds a footnote saying “citation needed,” so I still have some doubt whether this explanation is correct. I searched a little more, but haven’t found anything more authoritative.

Now I wonder whether there’s any significance to other parts of the song that I thought were just a form of Klezmer scat singing, e.g. “yubba dibby dibby dibby dibby dibby dibby dum.” I assumed those were nonsense syllables, but is there some significance to them?

Update: At Jason Fruit’s suggestion in the comments, I asked about this on judaism.stackexchange.com. Isaac Moses replied that the answer is somewhere in between. The specific syllables are not meaningful, but they are intended to be reminiscent of the kind of improvisation a cantor might do in singing a prayer.