Odd Harmonics Sounds Great

I've never found good principles for making tuned chords that use high-prime-limit frequency ratios, but I recently heard of a cool trick that seems to work.

A tuned chord can be written "otonally" as a sequence of integers, like [4, 5, 6]. Divide all the list elements through by the first list entry to get the frequency ratios, e.g. [4, 5, 6] -> (1/1, 5/4, 3/2). That's a major chord and it sounds great.

You can generate random sequences of integers all day to make chords, and some will be okay, some will be bad, some will be good. But it's not easy to listen to 500 random chords, pick your favorites, try to remember how they sounds based on a name that is a list of integers, and then try to use them to compose. It would be nicer if we had some principles for finding tuned chords that sounded good almost surely.

I heard about such a method from Kite Giedraitis; you just use sequences of odd integers. I find that things sound better if you also keep all your integers within an octave, i.e. the largest integer in your list is smaller than twice the first integer in your list.

These chords almost all sound good to my ear. Or maybe I was just in a very-open-to-weirdness headspace when I played with them last night. But I think it's the former. And that's very exciting, because you can get very high prime limit chords.

Here's a list of frequency ratios between 1/1 and 2/2 that show up in such chords, with numerators up to 31: [1/1, 5/3, 7/5, 9/5, 9/7, 11/7, 11/9, 13/7, 13/9, 13/11, 15/11, 15/13, 17/9, 17/11, 17/13, 17/15, 19/11, 19/13, 19/15, 19/17, 21/11, 21/13, 21/17, 21/19, 23/13, 23/15, 23/17, 23/19, 23/21, 25/13, 25/17, 25/19, 25/21, 25/23, 27/17, 27/19, 27/23, 27/25, 29/15, 29/17, 29/19, 29/21, 29/23, 29/25, 29/27, 31/17, 31/19, 31/21, 31/23, 31/25, 31/27, 31/29].

Here they are sorted by increasing size: [1/1, 31/29, 29/27, 27/25, 25/23, 23/21, 21/19, 19/17, 17/15, 31/27, 15/13, 29/25, 27/23, 13/11, 25/21, 23/19, 11/9, 21/17, 31/25, 29/23, 19/15, 9/7, 9/7, 17/13, 25/19, 31/23, 23/17, 15/11, 29/21, 7/5, 27/19, 13/9, 19/13, 25/17, 31/21, 29/19, 23/15, 17/11, 11/7, 27/17, 21/13, 31/19, 5/3, 5/3, 5/3, 29/17, 19/11, 23/13, 9/5, 9/5, 31/17, 13/7, 17/9, 21/11, 25/13, 29/15].

If you sounds those in order against 1/1, you'll notice some elements are very close to each other. Like right at the start,

(29/27) / (31/29) = 841/837 @ 8 cents

is a fairly small comma, and

(25/23) / (27/25) = 625/621 @ 11 cents

is similarly small.

They're not unnoticeable commas, but if you want very-high-prime-limit temperaments, then I've heard of worse methods to generate very-high-prime-limit tuned commas.

The Bohlen-Pierce scale also doesn't use any even harmonics, but it limits things to 7-limit frequency ratios. I think it's cool that this extends Bohlen-Pierce.

I have no idea why this works. But let's figure it out. 

I've forgotten almost everything I've written about otonality and utonality. I haven't written much. Time to redo it, and better.

Chords made of frequency ratios are called tuned chords. They differ from chords made of intervals. Those are intervallic chords, like [P1, M3, P5]. We'll be looking at tuned chords in this post.

Here are the just frequency ratios for a 5-limit major chord: [1/1, 5/4, 3/2]. We can multiply through by the least common multiple of the denominators to get a sequence of integers: [4, 5, 6]. This is the otonal representation. To get back to the ratios, divide everything through by the first element of the otonal list.

We can find "inversions" of tuned chords, by which I  mean cyclic permutations modulo the octave. Pop the first element off of the list, multiply by 2, and stick it at the end of the list. Divide all the list elements by the new first element. Multiply through by the least common multiple of the denominators if you want that chordal inversion to be represented otonally.

The otonal major chord [4, 5, 6] has cyclic inversions of [5, 6, 8] and [3, 4, 5].

We can also find the elementwise inverse of chords. For each element {e} in a list, take {1/e} for the new element in that position. Sort by size and multiply through by the least common multiple of denominators. We'll call this the utonal inverse of the chord. Optionally you can divide through by the first element if you want frequency ratios. Cyclic inversions versus utonal inverses.

Here are the three inversions of the otonal major chord and the utonal inverse for each after a double colon:

    [4, 5, 6] :: [10, 12, 15]

    [5, 6, 8] :: [15, 20, 24]

    [3, 4, 5] :: [12, 15, 20]

The utonal inverses are also inversions of each other, i.e. the set is closed under cyclic permutation modulo the octave. They happen to also be justly-tuned minor chords. 

What if we space things out more, beyond the octave? If we remove factors of two, i.e. raise and lower things by octaves until the factors of two are gone from the utonal integer list, then the major chord has only one all-odd voicing: [1, 3, 5] and its utonal inverse has only one all-odd voicing, [3, 5, 15].

And.... all-odd voicings usually sound good, at least within an octave, not that these necessarily are within an octave. So can we take a bad sounding chord and make it sound better by spacing it out in an all-odd voicing? Are there chords that sound better when compressed into an octave than when expanded to the all-odd voicing?

I think a normally voiced harmonic seventh chord, [4, 5, 6, 7], sounds way better than its all-odd voicing, [1, 3, 5, 7]. So there's one.

...

Defective Portuguese

In Portuguese, a few verbs are missing some conjugations. They're called "defective verbs". The standard example is "colorir", to color, which has no first person singular forms. You might say, "Obviously the simple present tense form should just be coloro?" and your language teacher will say that word is forbidden.

Wiktionary has a list of which verbs are defective in continental versus Brazilian, and there's... no overlap. So basically all the verbs have obvious forms, but different countries have different taboos?

To be fair, I have heard that "colorir" is defective in both Continental and Brazilian Portuguese, even though it isn't on both lists. But it's still pretty suspicious pair of lists. And it's pretty weird to have defective verbs at all, regardless of whether they're agreed on.

The weird spells to summon leather

I was reading about different tanning methods and I'm fairly confused about what they're achieving.

Like, some cultures would soak hides in poop... for proteolytic enzymes? And others just wouldn't and that seemed to work fine. Or you can use chromium III sulfate to change the spacing between collagen threads, but also you can just cover the thing in astringent bark water (or other sources of tannic acid, but why would you gather small rare parasitic oak galls if you could just use waste tree bark or leaves), and wouldn't it be nice if your nice-smelling leather products that children might want to chew on weren't impregnated with poisonous heavy metals?

Or I saw a buckskin recipe that covered the hide in egg wash, or a mix of grated bar soap and vegetable oil, or you can rub the deer's brain on its skin, and supposedly these methods all soften the leather in equivalent ways, with emulsions of triglycerides in water, but they don't even mention a protein changing step to finish. It's just: 1) take off the fur and fat with alkali and then 2) soften with brain grease or eggs.

And then I see references to "tawing", meaning treating the hide with alum and something else, like eggs or flour, as an alternative to proteolytic enzymes or protein-complexing chromium or protein-binding tannins, so maybe the alum does something like tanning but you need to soften the hide at the same time to prevent the alum from over-drying the hide?

It feels like there are 20 different ways to make leather, so it shouldn't be a finicky process, but all of the processes require some highly specific bullshit like green papaya latex or deer brains or fermented pigeon droppings.

Chitosan Fiber

The Thought Emporium on youtube made a video about weaving fibers made from the chitin, obtained from waste arthropod exoskeletons, e.g. shrimp and crab shells. I shared it with a friend and they didn't like the presenter's style, so here is a text summary. It's also a summary for me, because I don't remember all that many exact process details after watching a 16 minute video.

To make chitosan: reduce crustacean shells to very small pieces, perhaps powder, and cover with 10% solution of HCl. Stir for several hours (with heat?). Filter out solids and rinse. Cover solids in 10% solution of NaOH. Heat at 90 C for 2 hours. Filter out solids and rinse. Cover in 45% NaOH. Boil vigorously for 3 hours, topping off with water to maintain coverage. Strain and rinse. Now you have chitosan.

To make chitosan threads: Dissolve in vinegar. The mixture thickens a lot and will need to be stirred for a day for full incorporation. You'll only get about 3% chitosan by weight into your solvent, but you need more like an 11% solution for making threads. Heat the dilute solution to 65 C with stirring overnight (for 16 hours? until the solution reduces to a 1/4 of its initial volume?) to drive off water. You'll have a thick brown jelly now. Chitosan is soluble in the vinegar (and other acids), but not in bases, so to form fibers, extrude the jelly solution into NaOH and you get coagulation or some similar effect. Pull the coagulated thread from the extrusion syringe, through te NaOH bath, and then through a water bath to rinse, then hang to dry. Thinner extrusions will be less brittle. You might be able to loop the thread around a sequence of rollers with gradually increasing speeds to pull the thread thinner.

The lab hopes to put acetyl groups back on the chitosan threads at some point, turning the chitosan back into chitin, to make the threads more generally insoluble.