How Human Voice Works + SoundToys Little AlterBoy

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How Human Voice Works + SoundToys Little AlterBoy

Hey, guys.

This is Eric Tarr for

I’ve been inspired by this plug-in released
by SoundToys called “The Little Alterboy.”

Now, for awhile, this plug-in was a free download,
so I hope you all had the chance to pick it

up during that timeframe.

If not, stay tuned for the future, because
SoundToys almost always releases full versions

of these smaller plug-ins at a later date,
so you can pick it up then.

What I’d like to do in this video is demonstrate
and talk about the features of this plug-in,

and discuss the signal processing of what’s
going on behind the scenes, and how an incoming

signal actually gets manipulated by this plugin.

You see on here that it’s listed as a monophonic
voice manipulation plug-in.

What exactly does that mean?

In order to understand how it’s going to process
a signal, you have to understand some characteristics

about the human voice.

That’s not to say, though, you couldn’t send
all other kinds of signals through it and

create some cool, unique effects as well,
but to understand how it works, you have to

understand those characteristics that are
unique to the voice, different from all other

kinds of percussive, or even melodic and harmonic
sounds that we normally work with in audio.

So, the voice is cool and unique and different
from all those other kinds of things.

This plug-in is very good at manipulating
those special characteristics of the voice.

So, what I’d like to do is provide some of
that background to you as part of this video,

and also demonstrate along the way, the different
controls of this plugin.

So, when a signal is created by a singer or
by someone talking, it starts out as air in

a person’s lungs, and that air exits the lungs,
and goes through their vocal box, also called

the larynx.

There, you’re going to find the vocal cords,
or also called the vocal folds.

The air passes through those vocal cords are
going to vibrate back and forth, and that’s

going to create our acoustic signal.

That’s going to be the source of our signal
– where it originates from.

Now, there are some muscles attached to the
vocal cords that are going to determine how

fast they can vibrate.

This is happening very quickly, relatively

So, for a male singer or talker, we’re in
the ballpark of about 100Hz.

100 times per second, these things are going
to vibrate back and forth.

Now, for a female singer, we’re closer to
150-200, for a child, maybe 200-250.

Those things are happening very, very quickly.

Nonetheless, we have these muscles attached
to the vocal cords that are going to determine

how the vocal folds open and close.

Now, one thing that’s kind of cool about it
is that the vocal folds open relatively slowly,

and close much much faster.

This is going to happen that many times per

This is going to create a signal that’s actually
similar in some ways to, like, a test signal

we use all the time in audio, and that’s a
sawtooth signal, where what you have is the

amplitude of the sawtooth signal is either
going to increase slowly, and then decrease

very quickly, or the opposite as well.

So, what I’m going to do to simulate the synthesis
of a voice signal is I’m going to use my sawtooth

here – my signal generator at 100Hz for
my male talker, and I’m going to create this

sawtooth signal.

I’m going to send it then into a spectrum
analyzer that I’ve got right here.

This one is from FabFilter Pro-Q. You can
see the harmonics that are created then with

my sawtooth signal.

The one is at 100hz, and then even and odd
harmonics all the way up the spectrum.

So, it’s going to sound like this.

[sawtooth plays]

In some ways, this is a good simulation of
the signal that’s created as air passes through

the larynx and causes those vocal cords to

But that’s only part of the story when a singer
creates a sound.

So, that signal as it exits the larynx is
going to go through a singers vocal tract

that consists of the mouth, the nasal cavity,
and then also the tongue is a very important

factor as well.

This vocal tract acts as our resonant tube.

There’s going to be some frequencies that
are actually going to resonate by going through

that system.

So, in many ways, talk about this tract as
being a spectral filter.

So, you have the source, then you have the

Now, what happens is as the singer or the
talker changes the configuration of their

mouth, whether the jaw is open, or the jaw
is closed, whether the tongue is forward in

the mouth, or whether the tongue is back,
it’s going to change where these resonances

occur across the spectrum.

So, you have some of the harmonics being accentuated,
and increased in amplitude, and you have some

of them being decreased, and no matter how
you put your mouth, your vocal tract is going

to change what kind of frequencies are enhanced.

So, how you hear someone’s – when they’re
talking, how you understand them saying different

vowels or consonants, depends on where these
resonances occur.

So, what I’ve done here is pulled up on the
internet a chart that shows you where these

resonances occur in the spectrum for different

So these are for vowels, here what you’re

The consonants are here just to provide context.

So you have the vowels like heed, hid, head,
had, and so on.

You can see where the frequencies are going
to occur of resonances from the vocal tract.

The lower frequency is called the first formant.

So, another name for these resonances in general
is just formants.

The lower one is called F1 for formant one,
the upper one is called F2 for formant two.

So, what happens is these resonances are kind
of paired together here for these simplified

for these first two lower formants.

You can come up with all kinds of different
vowel sounds.

What I’m going to do here is just use one
like from hit.

The “ih” sound around 320 and 2,500.

So what I’m going to do then is make use of
the equalization as part of this plug-in to

apply these spectral resonances, these formants
to my incoming sawtooth signal.

Again, this sawtooth sounds like this.

[sawtooth plays]

What I’m going to do is turn on these resonances
and simulate as if this sawtooth wave from

the source is now passing through a vocal
tract that now has some resonances around

315 and 2,500.

[sawtooth plays]

So, even though I’m using a very metallic
sounding synthesized signal and an equalizer,

you can almost get the impression then of
an actual human sound.

A vowel sound from a hit – so this is “ih.”

[sawtooth plays]

And in many ways, synthesizing a human voice
is done by doing a similar kind of thing,

where you have some sawtooth signal going
through an equalizer.

So, I’ve done just that.

What I’m going to use this for then is a signal
that’s going to be sent through Alterboy and

look at how Alterboy is going to process this
specific signal.

So, let me pull this one way up over here.

Next, pull up Alterboy.

I’m going to send this as my input signal
into Alterboy, and I’m going to use another

spectrum analyzer down here so we can look
at how this spectrum changes below, and you

can also listen to it, and see what each of
these controls is going to manipulate in my

incoming signal.

So, I start out with my sawtooth that has
harmonics at 100, 200, 300, even and odd harmonics

all the way up.

Applied a spectral filter that has resonances
for my formants at 315 and 2,500.

I see the same thing right now for the output
before I change anything.

First up, let me demonstrate the pitch knob
right here.

What this one is going to do, as long as I’m
in this transpose setting right here, is allow

me to change the pitch in semitones all the
way up to twelve semitones and down twelve


So, let me turn the signal back on and just
manipulate this control.

[sawtooth plays]


There are several things I want to point out

First up, I’m increasing it.

I can go up to a maximum of twelve semitones.

What that’s going to do is double my frequency
so my harmonics were at 100Hz.

Now I’m going up an octave at twelve semitones,
so now my fundamental has been moved to 200Hz,

my second harmonic has been moved up to 400Hz,
and so on.

So, I’m altering the frequency by using the
pitch control, such that the frequencies and

all my harmonics are changed relative to the
fundamental frequency.

So, I’ve doubled the frequency, or gone up
by twelve, doubled the frequency there.

I can do the opposite.

I can go down to minus twelve.

Now, my fundamental has been shifted down
to 50Hz, and then I have harmonics at 100,

150, 200, and so on up the spectrum.

Now, another thing that’s important to understand
about this specific kind of pitch shifting

processing is that it’s different in some
ways, even more powerful than just your conventional

kind of time compression, time expansion sort
of pitch effects, because if you’ve ever played

around with maybe playing back tape at the
wrong speed, where you speed it up or slow

it down, and do all that kind of stuff, or
you can even do it digitally – similar kind

of thing – if you do pitch shifting effects
with typical time compression or expansion,

not only do you shift the harmonics, but you
also end up with these kinds of Alvin and

the Chipmunks effects, because when you increase
the frequency of the harmonics, you also end

up shifting the spectral filter as well, where
these resonances occur.

That’s what causes Alvin and the Chipmunks
to happen.

What’s cool about this pitch processor is
that – I’ll demonstrate it again – as

you change the frequency of the harmonics,
the resonances do not change.

So the formants – right?

These are being controlled independently of
the harmonics here in the signal.

So, let me show you this again.

[sawtooth plays]

So, it doesn’t matter whether I’m up here
at one, two, three, four, five, six, my sixth

harmonic is at 315Hz, and whatever harmonic
this is way up here at 2,500, the resonances

are still at the same exact place.

I can shift all the way through, and the resonances
stay in the exact same place.

So this allows me to do pitch shifting on
the source signal of my voice without actually

changing the resonances that are normally
thought of independently as part of the vocal


Well, then that leads me to the formant control,
because this is going to allow me to change

the frequency of these resonances without
changing the frequency of these harmonics.

So, I can go all the way up to twelve here…

The harmonics are all in the same place, but
now where this resonance has been shifted.

It used to be at 325, now its up here around

We can go the opposite.

Harmonics are still the same, it’s the resonance
that’s now been shifted.

The thing to know about it here is the maximum
of twelve is shifting up the resonance by

a factor of two, just like before.

Pitch was shifted up by doubling it in frequency.

Before, we had 325 here, 315.

Now it’s going up to maybe 630 for one resonance,
and 2,500 is now being shifted up to around

5kHz, where the opposite is true here.

We’re bringing the resonance down here around
175, the other one is around 1,200, around

that range too.

So, you have a similar kind of processing
or relative processing for the formant, but

the main thing about this is the very powerful
way to independently control the spectral

curve of your signal, and also the pitch of
your signal independent of the spectral curve.

So, you can avoid all this Alvin and the Chipmunks
kind of effects, and it’s a cool way because

when a singer actually creates a sound, or
when a talker speaks, the vocal tract in many

ways can create resonances that are independent
of the frequencies that are contained in the

source signal.

So now, we can manipulate those kinds of things
as well by using this kind of plug-in processor.

Those are the main controls to understand
about the plug-in, or kind of the cool things

or complicated things about it.

The last things I’ll show you with Quantize,
what it’s going to do is just shift the signal

relative to a chromatic scale, so it actually
has to fit notes C, C#, D, and so on.

So you’ll hear…

[sawtooth plays, adjusting pitch]

If I was at 100Hz before, it ends up getting
moved down to an actual musical scale.

Also, the robot is a little bit different.

Watch this.

If I start out with my sawtooth wave that
has harmonics at even and odd frequencies.

So, I go to robot, I no longer have that consistent
kind of spectrum here where it’s no longer

just 100, 200, and so on.

So, it sounds like this.

[sawtooth plays]

The last thing to know about this is the drive

This is a harmonic algorithm that’s taken
out of the SoundToys Decapitator.

The Decapitator has a bunch of different distortion
effects, and they just pulled one of them

out is my understanding, and put them here
just to have some extra kind of tricks up

your sleeve when you’re playing around with
this plug-in.

Last, you have the wet/dry knob to mix between
unprocessed and processed in this plug-in.

Other than that, though, that really takes
care of everything.

Hopefully by seeing what’s going on here with
the plug-in, how you can manipulate that harmonics,

the frequency of the harmonics without changing
the spectral curve, or how you can change

the spectral curve without changing the harmonics.

You can see that this plug-in is pretty cool.

It’s very powerful, and you can do all kinds
of cool effects with it, so go and see what

you can come up with, see what kind of unique
things you can apply this for.

Maybe with voice, or maybe not with voice,
and let us know what you end up doing with


We love to hear those kinds of things, so
until next time, take care guys, and I’ll

catch you then.

How Human Voice Works + SoundToys Little AlterBoy // how the human voice works and a breakdown of SoundToys Little Alterboy.

About The Pro Audio Files

Tutorials on mixing, mastering and producing music in Pro Tools with plugins from Waves, FabFilter, SoundToys, Softube, Sonnox, PSP, Slate Digital and more. Learn how to mix using EQ, compression and effects like reverb, delay, saturation and distortion on vocals, drums, guitar, bass and more.

How Human Voice Works + SoundToys Little AlterBoy

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