Comment by mrob | Hacker News Reader

Comment by mrob | Hacker News Reader

Although the article talks about pitch ratios, there's no evidence that the human brain contains any hardware for pitch ratio detection. Consonance of simple ratios is a result of a simpler underlying rule, explained by William Sethares here:

http://sethares.engr.wisc.edu/consemi.html

Note that this only happens with musical instruments featuring overtones based around the harmonic series, which usually means instruments based on vibrating strings or vibrating columns of air. These are by far the most common instruments in Western music, but this is not the case for cultures that heavily use tuned percussion. Tuned percussion can easily have enharmonic timbres, which require different tuning systems for control of consonance and dissonance.

Note that Sethares' theory says nothing about dissonance being good or bad, and this new study says nothing about whether Tsimane people are capable of detecting dissonance or not. As the vast majority of humans can detect consonance and dissonance, including babies (see https://www.researchgate.net/publication/222455086_'Infants'... ), I would personally be surprised if they were incapable of perceiving it. I think it's more likely that their culture simply does not value consonance. The same is true of some Western subcultures. Atonal composition is high status with many music academics, and it's genuinely enjoyable to many of them. I've enjoyed listening to atonal compositions myself.

There is definitive evidence the brain contains multiple mechanisms for pitch ratio detection.[1] Spectral theories of dissonance like Sethares', meanwhile, fail to explain some very basic phenomena.[2]

It should also be noted that people have reported trouble reproducing Sethares' dissonance curves which Sethares has, to my knowledge (we've corresponded on the subject for almost 20 years), never addressed.[3]

Lastly, there are serious problems with the ethnomusicology in Sethares' book. The scales derived from timbres, e.g. of Indonesian instruments, are designed to match the dissonance curve of the timbre only in a single mode. Intervals not measured from the chosen tonic will in general not be present as minima in the corresponding dissonance curve (except in the case of highly symmetrical scales like the diatonic scale).

[1] e.g. http://dx.doi.org/10.1152/jn.00271.2001

[2] Spectral models are all based on pairwise interactions between partials and therefore predict roughly equal dissonance scores for harmonic and subharmonic chords (including the major and minor triads). But subharmonic chords are dramatically more dissonant, as you can hear for yourself

http://lumma.org/music/theory/demo/majmin/

(files beginning "o" are harmonic; "u" subharmonic)

This is a consequence of chords larger than dyads being almost completely ignored for the entire history of psychoacoustics. A strangely analogous situation may exist in economics, where the theory of comparative advantage is thought to be settled by most economists despite that there is no consensus on how to extend it beyond Ricardo's 2-country, 2-goods model of 1817.

[3] Briefly, the shape of the dissonance curves is unrealistically sensitive to the relative amplitudes of the input partials.

> no evidence that the human brain contains any hardware for pitch ratio detection. Consonance of simple ratios is a result of a simpler underlying rule,

My reading of your link is that it doesnt argue against pitch ratios being fundamental - what it does do is say that ratios are not only happening in chords but also in the sound of a single note, in different ways for different instruments.

This is very interesting work though and to me at least much more interesting than the headline post here which just points out the blindingly obvious (people raised in different musical cultures hear things differently)

The most fundamental aspect of dissonance is the empirically measured Plomp and Levelt curve. This is approximated as: d(x)=e^(-3.5x)-e^(-5.75x), where x is the difference in frequency between two pure sine tones. (see http://sethares.engr.wisc.edu/paperspdf/consonance.pdf)

If we decompose sounds into sine waves, and sum the values on the Plomp and Levelt curve for all the pairs of sines, weighted by amplitude, then for the specific case of timbres based around the harmonic series, the minima for the dissonance curve happen to fall at simple ratios. This does not mean the brain is actually counting cycles! It's only a coincidence, and for other timbres the minima fall at different places.

The curve describes the (approximate) outcome. It doesnt prove or disprove how brain processes work. What we do know is that the outcomes are related to both these curves and simple ratios.

For me it seems logical that the brain (as a well established pattern matching machine) is probably doing something far more primative than calculating exponential curves. But if thats your view i cant disprove it.

The disconnect here is because the basic function of acoustic dissonance takes places in the hair cells of the ear. Harmonic ratios simply resonate hair cells in steady patterns rather than fast beat frequencies. (Slow beat frequencies are generally non-dissonant).

Studies like the OP's turn up every few years and are massively flawed due to oversimplification. Acoustic dissonance is waaaay more than a single-dimensional binary function... and then cultural layers are added.

Your comment makes me think of playing catch. Do we really calculate parabolas in our brain when choosing how to catch a ball?

What I've read is that the brain learns what the sight picture of a ball coming right to you should look like. When we run to catch a ball, what we're trying to do is line up with that sight picture.

Do you have some sources maybe? I find it very interesting, because it doesn't agree with my experiences.

I've never played baseball, but lots of basketball and soccer, and I get this "virtual trajectory of ball" overlay, so that I can adjust my body position, jump at the right time if needed.

Also often you look at ball, memorize where it will fall, then run to get there without looking at the ball. It can take seconds if it's a long ball in soccer, so it can't possibly be just adjusting to the sight picture.

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