So let’s talk about flow.
When we’re making sounds with all this articulatory business up here, things can get pretty dicey.
We block the air from getting out of our mouths in precisely calibrated ways, stopping it
right here or letting just a hiss through there.
We’re like acoustic chefs, cutting and chopping so we can serve up a gourmet meal of sounds.
And part of that sonic expertise is knowing how to let some consonants go humming freely
on a path out of our heads.
So what do those smoother sounds look like?
I’m Moti Lieberman, and this is the Ling Space.
When we’re talking, we generally press air up from our lungs, and then as it goes out through
our vocal tract, we change where we put our tongue and lips to shape the sound wave we’re producing.
For consonants, we can do things like stopping the air flow completely, like with [t] or [k],
or reducing it to a noisy, turbulent stream, like with [f] or [ʃ].
In contrast to vowels, where the airflow is smooth and easy, these consonants, known as
obstruents, stick out like a cranky diner owner at a fancy dinner party.
But there’s another set of consonants we can listen to, an intermediate zone between
the abrupt fits and starts of the obstruents, and the total fluidity and flow of vowels.
These free-spirited sounds are known as sonorants, and we can generally split them into two groups,
nasals and approximants.
Both kinds of sonorants share a property: in the vast majority of cases, they come automatically voiced.
Your vocal folds are set to vibrating, and that creates a stable, periodic sound wave
for the rest of your vocal tract to play with.
And so unlike stops and fricatives, nasals and approximants have their own predictable
acoustic formant structure.
As we discussed back in our episode about formants, the way our vocal folds vibrate
is more or less set biologically.
We create different sonorous sounds by changing the way we configure our vocal tracts, which
makes different frequencies within the sound wave resonate more than others.
The resonant bands we see on our spectrogram represent these frequencies, and are called formants.
And just like with vowels, we get a lot of information about what sonorant consonant
we’re hearing from how the formants look.
Let’s start with nasals.
These are sounds like the [m] you have in Emily, or the [n] at the end of Logan.
And if you try making a [m] like you just sipped some good coffee, you’ll get a feel for how they work.
[mmmm]!
They get made by closing off the airflow through the mouth, but lowering the soft palate
at the back of the mouth, and letting the air go out through your nose, instead.
But what does that mean for the wave itself?
How do we tell when we’re hearing a nasal consonant?
Well, they tend to be less loud than vowels, since there is less free flow.
And they tend to come on suddenly – all it takes is for the velum to open after a
vowel, and then fwoosh, the wave can travel through a whole new area.
But it’s not just the sudden change – the trip through the nose changes the quality
of the sound, too.
We see a pretty low first formant, or F1, which is just the resonance of the nasal cavity itself.
There’s another sure sign you’re hearing a nasal, too: the energy of the sound wave drops off fast.
Compare these two sounds, [n] vs. [l].
Now, for oral sounds like [l], we can find meaningful information in the sound wave going
up way into the several thousands of Hz.
And part of that is because our mouths do a good job at keeping the wave dancing along
and propagating it out into the world.
But our nasal cavities aren’t all calm and smooth on the inside.
Instead, they’re fluffy and rippled and soft, and that texture dampens and absorbs
some of the energy from the wave.
Those higher frequencies just don’t make it out in one piece.
So okay, that tells you how to identify that the sound you heard was a nasal.
But how do you tell which one?
Well, there are a couple of main pieces of information.
The first is the influence that the closure in the mouth has on the vowel sounds before or after it.
These formant transitions are similar to those of oral stops – so when you look at the
first sounds of each word in Miss Patty, the dark formant bands rise up into the following
vowel, because in each case, they’re bilabial stops.
And that’s what bilabial stops do: they tail up.
But another source is actually really cool, and really specific to the nasal manner of articulation.
And that’s anti-formants, zeroed out spaces in the energy spectrum of the wave.
How does that happen?
Well, just look at how we make these sounds again.
Sure, the wave is blocked from going out through the mouth, and so it flows out through the nose instead.
But that doesn’t mean it can just totally skip going into your mouth entirely!
No, some of it’s got to travel in there and hit your huge lip or tongue obstacle to
know that there’s no escape.
But traveling in there doesn’t stop that wave – it bounces back.
And it smacks into the rest of the wave that’s going out through your nose.
And where it hits, well, it matches up with and blanks out that part of the spectrum of
the wave that’s escaping.
So now you have these nasal anti-formants that show up in your words.
But depending on what the nasal was, different parts of the wave will get blanked out!
If you make an [m], then that wave had to travel all the way from the back of your mouth
to your lips and then back.
That huge distance means that the relevant wavelength is going to be longer for what
gets amplified by that space, and so the frequency that gets blanked out will be pretty low.
For a sound like [ɴ], where the closure is at the uvula instead, the distance that the wave
has to travel before bouncing back is really short, and so the anti-formant’s pretty
high in the spectrum, instead.
Where those blank spaces are tells you a lot about what sound you’re hearing.
On the other hand, the other type of sonorant consonants, approximants?
They don’t have these weird open spaces in their spectrograms, because they just go
straight out your mouth.
And they flow really freely, too: they have formant structures that can look really similar to vowels.
In fact, some of them basically are vowels!
These kind of approximants, like [j] or [w], are sometimes known as semi-vowels, although
more often they’re called glides.
So just take a look at sounds like the [j] at the beginning of “Yale”, or the [w]
at the beginning of “wish”.
There’s no clear spot between where the glide ends and the vowel begins.
One sound just smoothly spills into the next.
And when we compare the acoustics of [j] to [i], or [w] to [u], they look, well, pretty
much the same: the first and second formants more or less line up.
They’re pronounced in the same parts of the mouth.
The glide versions may be shorter, and there may be slightly more constricted in the airflow,
but acoustically, they’re basically just faster, softer versions of the vowels that they line up with.
That’s not true of all approximants, though: some of them have their own formant structure that's unique.
Let’s take a look at [l] and [ɫ].
These are lateral approximants: the airflow is blocked through the center of the mouth
by raising the tongue tip to the alveolar ridge, but we curl down the sides of the tongue
instead, and so the air can escape that way.
Because there’s some blockage, they’re not as loud as vowels, but they’re still pretty free.
If you’re an English speaker, you probably think of [l] and [ɫ] as part of the same
phoneme, but acoustically, they look really different!
If we look at a word like “Luke”, and focus in on the first sound, we can see the
first two formants are pretty distinct, around 300 Hz and 1600 Hz, respectively, and then
the third formant up between 2500 to 3000 Hz.
But with an [ɫ], like the last sound in “wall”, the first and second formants are right on
top of each other, around 400 and 600 Hz, even if the third formant is still in the same place.
Really different, but we still usually group them together in English.
And then finally for today, there’s the other approximant, r.
There’s actually a whole class of r-ish sounds, known as rhotics, that can get produced,
with trilling or tapping or bunching your tongue in different ways.
We’ll talk about some of the other ones back on our website, but for here, let’s look
at the English [ɹ].
When we stick a [ɹ] after a vowel, it has a huge influence on that sound, to the point
where sometimes, they just meld together.
Take a look at “Richard”.
That final [ɹ] combined with the [ə] sound just before it makes a big old rhoticized
schwa thing, [ɚ].
There’s no separating them anymore.
But at the beginning of a syllable, [ɹ] is good with standing on its own.
Look at the beginning of “Richard” now.
That [ɹ] has pretty similar acoustics to the plain [l] we saw before for its first
and second formants, right?
Let’s stick an [l] here to compare.
The main difference is that the third formant, or F3 is much lower, closer to 2000 Hz instead of 3000.
And this gap in F3 is the main driving force behind why telling [l] and [ɹ] apart is so
challenging for many L2 English learners – their ears are really mostly picking out the first
two formants, and for those, there’s no real way to differentiate the sounds.
That F3 difference is what you need.
So sonorants are in this fascinating middle ground between hardcore blocking consonants
like stops and fricatives, and the free-spirited ease of vowels.
They let out air easily enough, but there’s still a lot of special stuff going on.
When it comes to laterals and approximants, you should just let everything flow.
So we’ve reached the end of the Ling Space for this week.
If you weren’t just going “la-la-la-la” while I talked, you learned that sonorant
consonants have a strong acoustic structure with formants; that nasals have a characteristic
sound that comes from traveling through your nose and getting part of their spectrum zeroed
out; and that approximants can look just like vowels, or have their own distinct structure
that allows us to pick them out.
The Ling Space is produced by me, Moti Lieberman.
It’s directed by Adèle-Elise Prévost, and it’s written by both of us.
Our editor is Georges Coulombe, our production assistant is Stephan Hurtubise, our music
is by Shane Turner, and our graphics team is atelierMUSE.
We’re down in the comments below, or you can bring the discussion back over to our
website, where we have some extra material on this topic.
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And we’ll see you in two weeks. Veloma!