Why can't the brain place a dyad in two different ways simultaneously?

This is a serious question.

When the signal from your ears first reaches your brain, it's in the
form of an entire wash of sound coming in. Somehow, this wash gets
separated into different "sources," harmonic spectra consolidated into
single timbres, etc.

The different sources that the brain picks out of this wash are often
not 100% discrete, but tend to blend into each other. For example, if
you play a perfect fifth, not only are you aware of the individual
notes as consolidated spectra or individual "sources" themselves, but
you are also aware of them as a fragment of the harmonic series
originating from an octave below the root. You can also hear the
entire fifth as one whole "note," if you give it enough elbow grease.

Here's another example that everyone is familiar with: the 5-limit
minor chord. This chord simultaneously contains sonorities of a 3/2
interval over the root, a 5/4 over the minor third, and a 6/5 over the
root - as well as a single 10:12:15 chunk of the harmonic series. This
means that the possible modalities existing in this chord involve a
fundamental an octave below the root, two octaves below the minor
third, three octaves below the minor sixth, and four octaves below the
sixth, respectively. Clearly this isn't a "multistable" perception
like the neutral third that can flip back and forth between being 6/5
and 5/4 - all of these modalities, I believe are present
simultaneously to some extent, although which one is "dominant"
becomes a matter of musical context (and inversion).

However, why doesn't this apply to single dyads that are maximally
"out of tune"? Take, for instance, again, the neutral third: you can
easily flip your perception of this interval back and forth between it
being a "very flat 5/4" or a "very sharp 6/5." But why can't the brain
simply hear it as two sources at the same time - a very flat 5/4 AND a
very flat 6/5? Why can't the brain simply assign two harmonic spectra
to the same dyad?

We can hear the fifth in a 4:5:6 triad as its own 3:2 AND
simultaneously hear it as a 4:6 (with the fundamental an octave lower)
because of the 5-- why we can't easily do the same thing with just a
3:2 by itself?

I'm trying to piece this "theory of multiple consonances of chords" I
have together, but this one has me stumped. Do any of you auditory
scene analysis guys have the insight here?

-Mike

--- In tuning@yahoogroups.com, Mike Battaglia <battaglia01@...> wrote:

> However, why doesn't this apply to single dyads that are maximally
> "out of tune"? Take, for instance, again, the neutral third: you can
> easily flip your perception of this interval back and forth between
> it being a "very flat 5/4" or a "very sharp 6/5." But why can't the
> brain simply hear it as two sources at the same time - a very flat
> 5/4 AND a very flat 6/5? Why can't the brain simply assign two
> harmonic spectra to the same dyad?

Hi Mike,

I think this can be explained if we distinguish intervals and dyads.
An interval is just the distance in pitch between two tones and a
dyad is a chord formed by two tones. I speculate that the two tones
that are maximally out of tune don't evoke any root pitch and that
means that the brain doesn't assign even one harmonic spectrum to the
dyad. It is the category of the interval that is ambiguous, not the
root of the dyad since there is no root.

Kalle Aho

Hi Kalle,
> Hi Mike,
>
> I think this can be explained if we distinguish intervals and dyads.
> An interval is just the distance in pitch between two tones and a
> dyad is a chord formed by two tones.

OK, so you're saying that the "interval" term refers to how wide a dyad is?

> I speculate that the two tones
> that are maximally out of tune don't evoke any root pitch and that
> means that the brain doesn't assign even one harmonic spectrum to the
> dyad. It is the category of the interval that is ambiguous, not the
> root of the dyad since there is no root.

Well, I don't know about you, but if I listen to a neutral third...
it's hard for me to get away from hearing it as SOME kind of third.
That's why it's such an irritating interval for me, because it flips
back and forth between 5/4 and 6/5 constantly, with no end in sight,
ever, for the rest of my life.

But then again I tend to hear harmonic structures in all sorts of
stuff, transient fragments of tonality in atonal music, etc. It could
be that my AP has something to do with that, I don't know if that's
universal.

-Mike

--- In tuning@yahoogroups.com, Mike Battaglia <battaglia01@...> wrote:
>
> Hi Kalle,
> > Hi Mike,
> >
> > I think this can be explained if we distinguish intervals and
> > dyads. An interval is just the distance in pitch between two
> > tones and a dyad is a chord formed by two tones.
>
> OK, so you're saying that the "interval" term refers to how wide a
> dyad is?

Not really. Interval is the distance in pitch between two tones even
when they don't form a dyad. There is an interval between the first
and the last note of a piece of music for example.

> > I speculate that the two tones that are maximally out of tune
> > don't evoke any root pitch and that means that the brain doesn't
> > assign even one harmonic spectrum to the dyad. It is the category
> > of the interval that is ambiguous, not the root of the dyad since
> > there is no root.
>
> Well, I don't know about you, but if I listen to a neutral third...
> it's hard for me to get away from hearing it as SOME kind of third.

But you DO hear it as some kind of third! Intervals are heard
categorically, I just don't think that a major third is necessarily
the same thing as 4:5 or heard as such.

Kalle Aho

> Not really. Interval is the distance in pitch between two tones even
> when they don't form a dyad. There is an interval between the first
> and the last note of a piece of music for example.

OK, well then I'm talking about a "dyad" here - two notes being played
simultaneously.

> > > I speculate that the two tones that are maximally out of tune
> > > don't evoke any root pitch and that means that the brain doesn't
> > > assign even one harmonic spectrum to the dyad. It is the category
> > > of the interval that is ambiguous, not the root of the dyad since
> > > there is no root.
> >
> > Well, I don't know about you, but if I listen to a neutral third...
> > it's hard for me to get away from hearing it as SOME kind of third.
>
> But you DO hear it as some kind of third! Intervals are heard
> categorically, I just don't think that a major third is necessarily
> the same thing as 4:5 or heard as such.

Perhaps, but this applies even if I'm just playing the note itself, in
a drone, without any kind of scale built around it or anything. I will
tend to hear a neutral third as either a messed up 5/4 or a messed up
6/5, and it'll just keep flip flopping back and forth until I
eventually get fed up and just turn it off.

-Mike

> Kalle Aho
>
>

--- In tuning@yahoogroups.com, Mike Battaglia <battaglia01@...> wrote:
>
> > Not really. Interval is the distance in pitch between two tones
> > even when they don't form a dyad. There is an interval between
> > the first and the last note of a piece of music for example.
>
> OK, well then I'm talking about a "dyad" here - two notes being
> played simultaneously.

Two notes played simultaneously is not necessarily a dyad. There
might accidentally be two simultaneous notes when for example two
songs are played simultaneously. These would generally segregate into
two separate auditory streams. Dyad is two tones heard as a unit,
there is a difference between a mere simultaneity and a chord.

> > But you DO hear it as some kind of third! Intervals are heard
> > categorically, I just don't think that a major third is
> > necessarily the same thing as 4:5 or heard as such.
>
> Perhaps, but this applies even if I'm just playing the note itself,
> in a drone, without any kind of scale built around it or anything.
> I will tend to hear a neutral third as either a messed up 5/4 or a
> messed up 6/5, and it'll just keep flip flopping back and forth
> until I eventually get fed up and just turn it off.

I speculate that this doesn't matter because you have learned certain
interval categories by being a member of your musical culture.
Neutral thirds don't form a separate category for you so your brain
is trying to put it in existing categories, hence the flip flopping.

Kalle Aho