Audio Dithering 101 — What is Dither?

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Audio Dithering 101 — What is Dither?

Hey, guys.

This is Eric Tarr for theproaudiofiles.com.

I’ve been going through a series of videos
where I’m demonstrating techniques that you

can use to analyze your effects plug-ins.

My approach has been to try to come up with
some creative visualizations to help you see

and understand the processing that’s taking
place.

I’ve already looked at spectral processors,
distortion or saturation processors, and also

dynamic range processors.

In this video, I’d like to change it up a
little bit.

I’d like to look at dithering.

Now, I know what you’re going to say.

That’s not a very exciting or as cool as looking
at those other kinds of creative effects,

but what I want to argue is that dithering
is a very important and necessary part of

working with audio; especially if you’re working
inside of a digital audio workstation as a

mastering or mixing engineer.

You should absolutely understand what is dithering
and how does it work?

I’d like to show you these things with this
video.

Now, I’ll be the first to admit that dithering
can be kind of confusing for a couple of reasons.

First off, I think that it seems counter intuitive
to a lot of audio engineers, because typically,

when you think about working with signals
and noise, what you would like to do is reduce

the amplitude of the noise relative to the
signal as much as possible.

But with dithering, we do the exact opposite.

We actually intentionally add in noise, which
seems backwards.

But the thing to understand is that when we
add in this noise, it’s actually going to

have a perceptually pleasing end result.

Another thing that makes dithering kind of
confusing is if we’re using it properly, we

don’t even notice that it’s there, and in
fact, the whole point of dithering is to make

it very difficult to see something called
“quantization noise,” or hear something

called “quantization noise” that shows
up anytime we change the resolution of a signal

from a higher resolution to a lower resolution.

So, what I’m actually going to do in this
video is kind of over-exaggerate the concept

of dither noise to help you really understand
how it’s going to work, even if we normally

can’t hear it.

As an example of this, throughout this whole
video, I’ve actually had 16-bit dither noise

going on in the background.

If you’re listening over computer speakers
or your laptop speakers, or headphones, it’s

probably pretty difficult to hear relative
to the amplitude of my voice.

Here, when I’m working inside of Ozone 6,
I can change the amplitude of the dither noise

that’s going to be added in.

Right now, I’ve just got it on 16-bit, which
is the standard you’d want to use for CD if

you’re mixing down to 16-bit, or you could
use 24-bit if you’re working with DVD audio,

but here, I can actually increase the amplitude
of the noise up to 8-bit.

Probably at this point, you’re able to hear
that there is some noise being mixed in with

the background – in the background relative
to my voice.

I can also increase the amplitude of this
noise.

[dither noise increases]

Make it easier for you to hear.

[dither noise lowers]

So what I’m going to have to do in this video
to help you understand it is to exaggerate,

or show you the concept of dither noise, not
at 16 bits, but at lower bits.

Well, what is the whole purpose of dither
then?

Well, one thing you need to understand is
when you’re working inside of a digital audio

workstation, your computer is going to be
processing audio at a very high resolution,

at 32-bit floating point.

Now, whenever you want to listen to that audio
back, either play it back on a CD, or on a

movie like I was talking about before, you
half to reduce the resolution from 32-bit

floating point down to 16-bit or 24.

Anytime you reduce the resolution of a signal,
you have quantization error that comes in,

or also called quantization noise.

So just by doing that change in resolution,
you have noise that gets added in.

So what we’re going to do is pick and choose
the noise that’s going to get added in, so

you need to understand that noise is inevitable
whenever you change resolution, but we’re

going to use dither noise in order to be very
intentional about the noise that’s going to

get added in.

So, as the example of this to further illustrate
it, visually, here I’ve got three tracks side-by-side.

I’ve got an original sine wave track that’s
been printed here at full resolution.

This is 16 bits.

Then what I did was I performed bit reduction
on it down to 2-bits.

So, you can see that the resulting signal
looks a little bit different, and in a second,

we’ll listen to it, and analyze it to see
what’s the difference.

So, this is what happens to a signal when
you go from a higher resolution down to a

lower resolution.

Now, I’ve also got down here when I took the
original signal and printed it down to 4-bit,

you can see that the signal, when it’s at
a lower resolution, it doesn’t look as smooth.

Now, when it’s at 16-bit audio, it still looks
really smooth, but this is kind of the concept

of going from higher resolution down to lower
resolution.

What is the end result to that signal?Well,
another good thing to do is hear – let’s

play back the signals – the various signals
– and analyze what the signal sounds like.

So what I can do here, for the example, is
I’m going to use a sine wave generator here

at 300Hz.

This is the stock Pro Tools plug-in.

Then what I’m going to do is I’m going to
buss this signal from this auxiliary track

here of “tone.”

I’m going to buss it over here to another
auxiliary track that I’m going to call “Sum.”

On this summing track, I’ve got another plug-in
up here that I can use to change the bit-depth.

So I can go from full resolution of 16-bit,
I can go down to 2-bit, 4-bit, 6-bit, and

see, what is the end result when we change
the resolution of a signal?

When we go from a higher resolution down to
a lower resolution.

Then I’ve also got iZotope Insight here that
I can use.

It’s a spectrum analyzer to see the end result
after the signal gets reduced in resolution.

So what I’m going to do – let me go ahead
and bypass Ozone 6 – I’ll bring in the tone

and we can look at what it is at full resolution.

We’ll see the 300Hz tone here.

Then we’ll see what happens when I reduce
the resolution of the signal down to 2-bits

and 4-bits and so on.

Here’s 300Hz.

[sine wave plays, getting bit-reduced]

I’m going to mute this, but we can still look
at the result.

So, we still have our 300Hz signal, but when
I reduce the signal down to 2-bits, you can

see that there is a sequence of harmonics
that are also created.

This is the distortion that comes in when
you go from then higher resolution down to

a lower resolution.

The thing to know about it is that these harmonics
are all related to the fundamental, or the

original signal.

So we’ve got the 300Hz signal originally,
then we’ve got harmonics at 600, 900, 1200,

every 300Hz or so.

The thing to understand about this is that
without any other kind of processing, or dithering,

taking place, the noise that’s essentially
added in, these harmonics we call “quantization

noise,” the distortion that comes in, these
harmonics are all related, or another term

for it is “correlated,” with the original
signal, and that’s a problem, because these

harmonics will actually be easier to hear
than if the noise was random, and so what

we would like to do is add in noise in such
a way that the distortion that occurs, or

the noise that occurs, is uncorrelated with
the original signal.

So, the approach to this is going to be to
mix in noise.

So, another thing that I’ve done here is I’ve
got a second auxiliary track called my “noise”

track over here.

I’ve got white noise on this track, and then
what I’m going to do is blend in this noise

along with my tone, and see the end result
up here.

What we would like to have is the 300Hz tone,
and then try and remove, or make the rest

of the signal uncorrelated with this signal.

So I can blend in the noise here, and we’ll
even listen to it at least initially so that

you can hear that this is happening, and watch
the end result over here on the spectrogram.

[sine wave plays]

Alright, so you can see, I still have my 300Hz
tone, but then what I’ve done is I’ve blended

in noise so that the harmonics that are created
from the distortion are no longer there.

They’re being masked by this noise.

That’s a good thing.

Now, certainly at 2-bits, this is an example
where you can hear the level of the noise

that needs to be blended in to de-correlate
that distortion from the original signal.

But, what I’m going to do then – let me
turn down this noise – let me go through

some more examples where I go up to about
4-bit.

You can still see I’ve got harmonics at the
same frequencies.

They’re related to the original signal, but
I can still blend in some noise here, and

now, they disappear.

Alright, we can listen to this.

[sine wave plays with noise, then without
noise]

Now the relative level of the noise is much
quieter.

As I continue up, let’s try – let me turn
the noise down – let’s try 8-bits.

Alright, I’ve still got these harmonics, but
all I need to do now is blend in some noise,

such that these harmonics are going to disappear,
and we just have some low level noise.

[sine wave plays, layering in noise]

So again, the noise is very, very quiet.

I could continue this on all the way up.

Maybe I’ll increase this.

You’ll see the harmonics, they are being reduced
in amplitude, but they’re still there.

If I get up to 10-bits…

Now, at this point, I really just need a very,
very quiet level of noise in order to mask

those harmonics.

The same thing holds true when we go from
32-bit floating point down to 16-bit.

All that we end up doing with dither noise
is we add in a very, very low level of noise

to mask those correlated harmonics with the
original signal.

That way, we primarily just hear that original
signal, and then the distortion or noise that’s

left over is very difficult for our ears to
hear.

The last thing I’ll demonstrate when it comes
to dither is I’m going to pull back up here

my Ozone 6 plug-in.

We can look at this.

Within Ozone 6, you have the possibility to
do what’s called “noise shaping.”

So, here I’ve got 16-bit going.

I can turn on noise shaping.

What this is going to do is provide – or,
apply a spectral curve to the additive noise

that’s coming in.

So instead of having equal amplitude at all
frequencies where the possibility for – probability

of equal amplitude at all frequencies, we
can perform spectral shaping on it, such that

we still add in the same relative level of
noise, however, we focus the frequency content

into frequency regions that are very difficult
for our ear to perceive.

That way, we can still add in this random
noise to have the good perceptual effects,

but we’re actually making it even more difficult
for our ears to hear, because we bring in

high frequency around 15-20kHz, such that
our ears are not very sensitive to this region,

and we scoop out some of the mid-range around
2kHz, 5kHz, 10kHz.

In this range, we make the noise quieter.

So, to illustrate this, what I’m going to
do – let me go ahead and bypass this one

– I’ve got an EQ that I can bring up here,
and I’m going to do a similar kind of thing.

I’m going to send my noise through the EQ.

Maybe I’ll just turn off the tone now and
we can listen to how I’m going to shape this.

So, we’ve got the low level noise here…

Bring it up a little bit…

[noise plays]

Now, watch what I’m going to do.

I’m going to turn up, using the high shelf,
here I can bring it in.

Bring up the high shelf here.

Now I need to turn down the output so I match
the relative level.

Okay.

Then I’m also going to scoop out my mid-range.

This is just a conceptual example of what
I had before.

I’ll scoop out my mid-range so that I push
the content of the noise, you can see over

here, into the higher frequencies.

The mid-range frequencies that our ears are
going to be more sensitive to, I reduced the

amplitude there.

Next, I can go back and look at what happens
if I blend this noise in.

It will still have the same positive effect
of removing these harmonics – so I can bring

this down maybe to about 8-bit – now I can
bring in noise that’s very difficult for our

ears to hear, that’s going to de-correlate
these harmonics from the original tone.

[sine wave plays, adding in noise]

So, there you have it.

I’ve tried to demonstrate in a visual way
why dithering is helpful, and perceptually

important.

I’ve also discussed some of the parameters
– typical parameters you might find in a

plug-in like Ozone, where you need to understand
what bit-depth level to choose, and then if

you want to use some noise shaping to make
it more difficult in order to hear that dither

noise being added in.

Whether it’s at 16-bit or 24-bit.

That’s it, guys.

If you’ve got questions, post them below.

I’ll try my best to answer them.

Until next time, take care.

Audio Dithering 101 — What is Dither?

http://theproaudiofiles.com // An explanation and visual breakdown of dithering.

More videos on analyzing effects: https://www.youtube.com/playlist?list=PLe1lxu8fHox8aWwzqklc-fUvz2-UJMxRF

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.

Audio Dithering 101 — What is Dither?

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