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TABLE OF CONTENTS
Intended Audience for this Guide ........................................................................................................5
About the 2013 Edition............................................................................................................................5
Additional Resources ..............................................................................................................................5
About iZotope ...........................................................................................................................................5
1: INTRODUCTION ............................................................................................................6
2: WHAT IS AUDIO REPAIR AND RESTORATION? ................................................... 7
3: AUDIO REPAIR AND RESTORATION BASICS ........................................................8
Defining the Outcome .............................................................................................................................8
Repair and Restoration Tools ................................................................................................................8
General Recommendations when Repairing or Restoring Audio .............................................. 10
Restoration Quick Tips ......................................................................................................................... 10
The Tools of the Trade ........................................................................................................................... 11
4: UNDERSTANDING SPECTROGRAMS / IDENTIFYING AUDIO PROBLEMS . 12
What’s the Goal of Using a Spectrogram? .......................................................................................12
Principles of Spectrogram Displays ................................................................................................... 13
Spectrogram Types ................................................................................................................................16
Using a Spectrogram to Identify Audio Problems ......................................................................... 17
5: WHAT IS RX 3? .......................................................................................................... 23
What Can RX 3 Do? ...............................................................................................................................23
Where Can I Use RX 3? ....................................................................................................................... 23
6: DENOISING ................................................................................................................. 24
What’s the Goal of Denoising? ........................................................................................................... 24
Principles of Denoising ........................................................................................................................ 24
Using the Denoiser and Hum Removal in RX 3 ............................................................................. 26
Broadband Noise Reduction ..............................................................................................................26
Hum and Tonal Noise Reduction ........................................................................................................ 31
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Tonal Noise ............................................................................................................................................. 39
Dialogue Denoising .............................................................................................................................. 42
General Denoising Tips ....................................................................................................................... 46
7: REMOVING INTERMITTENT NOISES AND GAPS ...............................................47
What’s the Goal of Audio Repair? ..................................................................................................... 47
Principles of Audio Repair ................................................................................................................... 47
Using the Spectral Repair in RX 3 ...................................................................................................... 51
Intermittent Noises ................................................................................................................................ 54
Audio Dropouts ...................................................................................................................................... 58
General Audio Repair Tips ..................................................................................................................62
8: REMOVING CLICKS AND POPS ............................................................................. 63
What’s the Goal of Removing Clicks and Pops? ............................................................................ 63
Principles of Removing Clicks and Pops ......................................................................................... 64
Using Declick & Decrackle in RX 3 ................................................................................................... 65
Analog Clicks .......................................................................................................................................... 67
Digital Clicks ........................................................................................................................................... 68
General Tips for Removing Clicks and Pops ..................................................................................69
9: REMOVING CLIPPING ............................................................................................... 70
What’s the Goal of Removing Clipping? .......................................................................................... 70
Principles of Removing Clipping ........................................................................................................ 70
Using Declip in RX 3 ............................................................................................................................ 72
General Tips for Removing Clipping ................................................................................................ 75
10: REMOVING REVERB ................................................................................................ 76
What’s the Goal of Removing Reverb?............................................................................................. 76
Principles of Removing Reverb ...........................................................................................................77
Using Dereverb in RX 3 ....................................................................................................................... 78
General Tips for Removing Reverb ...................................................................................................80
11: EXPORTING AND DELIVERING AUDIO ................................................................ 81
What’s the Goal of Exporting and Delivering Audio? .................................................................... 81
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Principles of Exporting and Delivering Audio ................................................................................. 81
Exporting and Delivering Audio in RX 3 ........................................................................................... 81
GENERAL TIPS FOR EXPORTING AND DELIVERING AUDIO ....................................................83
12: SUMMARY ................................................................................................................ 87
About the Authors ................................................................................................................................. 88
APPENDIX A: GETTING SET UP TO REPAIR AND RESTORE AUDIO ............... 89
Equipment ...............................................................................................................................................89
Monitoring Audio ...................................................................................................................................90
Transferring Media to the Computer ................................................................................................. 91
Recording from Analog Formats ........................................................................................................91
APPENDIX B: GENERAL RX 3 TOOLS ....................................................................... 94
Comparing Settings .............................................................................................................................. 94
Batch Processing ................................................................................................................................... 95
Waveform Statistics ...............................................................................................................................96
EQ .............................................................................................................................................................. 96
Presets ...................................................................................................................................................... 97
Keyboard Shortcuts .............................................................................................................................. 97
APPENDIX C: REPAIRING EXAMPLE AUDIO ........................................................... 98
Example 1: Removing Broadband Noise from a Concert Recording .......................................98
Example 2: Restoring an Historical Speech: Making Voice More Intelligible ..................... 100
Example 3: Cleaning up a Phone Interview with Declick and Spectral Repair ................... 102
Example 4: Removing Clicks and Pops from a Concert on Record ....................................... 105
Example 5: Removing Clipping from a Phone Interview ............................................................107
Example 6: Removing Guitar String Squeaks with Spectral Repair ....................................... 108
APPENDIX D: TIPS FROM THE PROS ..................................................................... 109
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INTENDED AUDIENCE FOR THIS GUIDE
If you don’t know anything about audio repair and restoration, this guide is a great place to start. It will help
you develop practical and eective methods to remove noise and fix audio problems. Sure, we think you
should use iZotope RX 3® (www.izotope.com/rx) to repair and/or restore your audio… you certainly could.
But we’ve learned so much from the audio community over the past 10+ years that we’re happy to give
something back in return: a guide that’s useful for anyone that wants to learn more about audio repair and
restoration. As a result, this guide can be freely copied or distributed for non-commercial purposes.
If you own RX 3 but don’t fully understand audio repair and restoration, this guide will help you better
understand the powerful tools at your disposal. Each chapter demonstrates many useful concepts that you
can apply to your next piece of problematic audio.
If you own RX 3 and already know the basics of audio repair and restoration, this guide will show you new
tricks and techniques that are possible in RX 3’s modules. Just read through and say, “Yeah, I knew that”
when appropriate for the other parts.
You can also follow along by downloading the free 10-day trial of RX 3 at www.izotope.com/rx.
ABOUT THE 2013 EDITION
The 2013 edition of this guide has been revised and updated by the experts at iZotope HQ, based on years
of research and consultation.
ADDITIONAL RESOURCES
If you’re interested in exploring audio repair and restoration in greater depth, there are plenty of resources
available. The iZotope YouTube channel (www.youtube.com/izotopeinc) has a number of audio repair-
and restoration-centric tutorial videos aimed at anyone from the beginner to the advanced audio expert.
Additionally, third party training is available via the iZotope website. Learn more at www.izotope.com/store/
tutorials.asp
ABOUT IZOTOPE
iZotope makes innovative products that inspire and enable people to be creative. Based in Cambridge,
Massachusetts, iZotope has spent over a decade developing award-winning products and audio technol-
ogies for professionals and hobbyists alike. Learn more at www.izotope.com.
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1: INTRODUCTION
In today’s world, audio and video recordings can be made by almost anyone. From smartphones to
sophisticated studios and sound stages, large amounts of media content are created daily. And as our
world becomes increasingly and audibly congested, the rate of ruined recordings is rising in tandem.
Human error, unexpected electrical or mechanical interference and unwelcome intrusions from aircraft,
cell phones, pets, people and Mother Nature regularly impact even the most seasoned professional. Many
times, it just isn’t possible to record that “perfect take” over again, particularly when editing coverage of a
live event, or working to meet budgets and deadlines.
Whether you’re a professional or just getting started, you’ve probably ran into dicult audio situations like
those mentioned above, and wished you could correct what seemed like an impossible dilemma. We hope
this guide will help you understand the basics (and beyond) of audio repair and restoration and enable you
to fix previously unusable audio.
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2: WHAT IS AUDIO REPAIR AND RESTORATION?
When you hear the words “repair” and “restoration,” you might be inclined to think of dusty vaults filled with
aging master tapes and records. Some audio repair and restoration projects may indeed involve taking old
recordings and reviving them, but the methods used are useful for a wider range of scenarios. Every time
you record audio—whether at home, in the studio, or on location—there’s always the chance of encoun-
tering unexpected and unwelcome audio “guests.”
“Audio repair and restoration” is a phrase used to describe the various processes and techniques one can
use to remove noise and other imperfections from sound recordings. When used correctly, these tech-
niques can alleviate problems including:
• Ambient background noise
• Tape hiss
• Electronic interference such as hum and buzz
• Sudden background noises (coughs, ringing cell phones, etc.)
• Clicks and pops from older vinyl, shellac or phonograph recordings
• Clipping in both the analog and digital domain
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3: AUDIO REPAIR AND RESTORATION BASICS
DEFINING THE OUTCOME
The goal of good audio repair and restoration is to render the best possible sonic result with the least
audible human intrusion. In essence, your intervention in the original recording should be transparent and
not introduce new artifacts that distract the listener. Sometimes it’s possible to solve an audio problem
entirely, and other times it’s about finding the right balance between reducing the problem and preserving
the original audio.
It’s useful to remember that no recording is truly perfect, and any statement as such is purely subjective.
In the early 1980’s for instance, when CD players became readily available and aordable, commercial tape
vaults and archives turned into gold mines. But strangely, during the early days of CD restoration, whole
armies of purists became outraged when record companies sought to change the character of certain,
reverenced recordings (no matter how old) from their original, boxy-quality and dull, wooly ambience.
Today, we have fresher ears that seem to be more objective.
Whatever your tastes, and even as times and nostalgic aesthetics change, the basic intention of restoration
should remain the same: render the best possible sound with the least obvious interference.
REPAIR AND RESTORATION TOOLS
Repairing and restoring audio typically involves working with the following types of processors:
• Denoisers are used to reduce and remove steady state background noise. “Steady state” means
slowly changing noise. It might include constant ambient noise or tape hiss (referred to as “broad-
band” or “noisy” noise), or electrical buzz and hum (referred to as “tonal” noise because it typically
exhibits recognizable pitches or harmonics). Denoisers can be spectral or multiband, software or
hardware (such as iZotope ANR-B), and are sometimes designed for a specic use case, such as
vocals.
RX 3 TIP • RX 3 includes a single band Denoiser with independent control for both tonal and noisy
problems (it includes an envelope that may be used to shape the noise reduction curve). RX 3 Ad-
vanced also includes a multiband Dialogue Denoiser, which is more suited for real-time noise reduc-
tion on spoken word or sung vocals within a mix.
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• Declickers are used to reduce and remove intrusive clicks and pops. These can be caused by any-
thing from dust and scratches on an old record, a CD skipping on playback, or even mouth clicks
and lip smacks from a voiceover.
• Decracklers are closely related to Declickers, but are optimized to help reduce and remove a more
continuous, quieter stream of clicks that blend together to cause what the human ear perceives as
a general crackle.
TIP • Using a Decrackler before using a Denoiser is often a very eective way of dealing with surface
noise recorded from vinyl or shellac records.
• Declippers are used to repair digital and analog clipping artifacts. These artifacts occur when over-
loading an A/D converter or over-saturating magnetic tape.
• Visual Editing Tools vary by manufacturer, but the basic premise combines visual representations
of audio, via a waveform or a spectrogram, with tools allowing you to select and edit certain audio
events rather than the entire le.
TIP • Chapter 4, Understanding Spectrograms / Identifying Audio Problems, will help outline the
fundamentals of working with audio in this new, visual way, before we dive in to the various tools in
depth.
• Dereverbs are a new, cutting edge technology, and are designed to remove or reduce reverbera-
tions from audio. They are particularly useful for dialogue editing and ADR matching, and allow the
engineer to remove unwanted or distracting reverberations from dialogue recordings.
RX 3 TIP • RX 3 Advanced has a proprietary Dereverb tool developed by iZotope.
With all of these tools available, you might wonder where to begin. There isn’t a single “correct” order
in which to use them—it all depends on the audio material you’re restoring. Always begin with the most
obvious or obnoxious audio problem that you can hear and identify. Then, depending on the audio, it may
make sense to perform some processing tasks before others. For example, a loud hum, a heavy crackle, or
severe clipping might at first prevent you from hearing and dealing with additional audio problems. Peeling
away that first layer may make the next step more obvious to you. Don’t be afraid to try out dierent combi-
nations of the tools to get the result you want.
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GENERAL RECOMMENDATIONS WHEN REPAIRING OR RESTORING AUDIO
We highly recommend that you educate yourself about the function of individual tools in your toolbox.
Dedicated audio repair and restoration tools can do a fantastic and fairly autonomous job, but learning
when, where, and to what degree of strength to use a specific tool can yield better, faster, and more trans-
parent results.
It’s also beneficial to establish your aim before setting out. Do you want to treat each file with individual
care and attention, or would you rather define the most appropriate settings with which to batch process
hundreds of files quickly?
RESTORATION QUICK TIPS
1. Back up your work. Always make a backup of the original audio file before you begin
attempting to restore it. Depending on the tool, some edits become permanent once the file
is saved, so it’s always advisable to maintain a prior backup.
RX 3 TIP • RX 3 allows you to save your work and unlimited undo history as an RX 3 document, which
can prevent losing or overwriting work.
2. Keep the ears rested and the mind open. While doing audio restoration work, you’ll likely
spend a lot of time focusing on subtle details. Taking breaks will help you return with a fresh
mind and see and hear the bigger picture.
3. Make multiple versions. Sometimes it helps to try doing the same audio repair more than
once with dierent settings and then compare the results.
RX 3 TIP • RX 3 has a great Compare Settings tool that helps A/B results as you go. Also, you may
come back to a version you tried a few days earlier when you were tired, and now find it sounding
worse than ever. This happens to all of us! See suggestion #2.
4. Keep detailed notes. This is invaluable, particularly when there are so many dierent
methods for dealing with dierent audio problems. For forensics work, documentation is
often a required deliverable.
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RX 3 TIP • Using RX 3 document files and saving module-specific presets can save you the trouble of
writing out all of the parameters on a recall sheet as you would in the analog domain.
5. Back up your work. The first and last rule of any audio editing project! You never know when
a hard drive, backup device or original master might fail. Again, always back up your work!
THE TOOLS OF THE TRADE
In the following chapters, we’ll briefly examine some of the essential audio repair and restoration tools.
This isn’t meant to be a comprehensive guide, but will hopefully give you some focused thoughts about the
tools and their uses.
Every noise is dierent, so a certain element of trial and error will always remain. As you continue to learn
by experimenting with dierent tools and processes, you’ll be able to refine and optimize your techniques
over time.
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4: UNDERSTANDING SPECTROGRAMS / IDENTIFYING AUDIO PROBLEMS
As with medical diagnostics, the key to successful audio restoration lies in your ability to correctly analyze
the subject’s condition. This can be a life-long, never-ending quest—constantly honing the ear to distin-
guish the noises and audio events that need to be corrected.
To get started, it’s important to identify the problems with your file and identify which tool(s) will give you
the results you want. Let’s briefly look at how to examine your audio using the spectrogram and waveform
display tools, then consider how to identify audio problems using these displays.
WHAT’S THE GOAL OF USING A SPECTROGRAM?
The aim of any good visualization tool for audio repair and restoration is to provide you with more infor-
mation about an audible problem. This not only helps inform your editing decisions, but, in the case of a
spectrogram display, can provide new, exciting ways to edit audio—especially when used in tandem with a
waveform display.
RX 3 TIP • Use this special
slider in RX 3 to blend
between detailed spectro-
gram and waveform views.
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PRINCIPLES OF SPECTROGRAM DISPLAYS
So what’s a spectrogram? A spectrogram is a very detailed, accurate image of your audio, displayed in
either 2D or 3D. Audio is shown on a graph according to time and frequency, with brightness or height (3D)
indicating amplitude. Whereas a waveform shows how your signal’s amplitude changes over time, the
spectrogram shows this change for every frequency component in the signal.
If you’re used to using the waveform display, it may take a while to get your head around this unique way
to “see” the audio. As a start, let’s look at a few simple pieces of audio.
Here’s a picture of a sine wave moving up in pitch from 60 to 12,000 Hz as seen using a waveform view.
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One thing you’ll notice when looking at the waveform display is that it’s good at showing audio amplitude,
but less eective at showing what’s happening at dierent frequencies. For example, we can easily see
here that the sine wave is the same loudness for the entire duration of the file. However, we can’t tell much
about how the pitch or frequency changes over time. Now let’s look at this same audio file using a spec-
trogram.
Now it’s very obvious that the
pitch of the audio is moving
up! The horizontal axis shows
time, just like the waveform
display. But now, the vertical
axis shows us frequency in
Hz—the pitch of the event
that’s happening. We can see
how loud events are by how
bright the image is. The black
background is silence, while
the bright orange curve is the
sine wave moving up in pitch.
RX 3 TIP • The blue/
orange color map is
optimized for easy sound
identification, and is the
default spectrogram color
map in RX 3. In the
spectrogram settings, you
may change the color
map based on personal
preference.
RX 3 TIP • Using this color map slider, you can increase the brightness of the Spectrogram to
make certain things easier to see.
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Now let’s look at something more complex: the human voice. Here’s a short, spoken phrase as seen in with
a waveform display:
What we’re seeing here is the amplitude of the spoken words over time. If we switch to the spectrogram
view, we’ll see many things we can’t see in the waveform view:
The human voice is much more complex than it might seem from looking at the waveform view. Each word
is made up of a fundamental frequency (at the bottom of the spectrogram), harmonics that extend above
that frequency, sibilance (“S” sounds) that begin or end words, and more. And of course, you can now see
more clearly the noise that is surrounding the voice.
This is why having a detailed spectrogram display is so important to doing audio restoration. It helps you
clearly see the problems that you’re trying to fix.
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SPECTROGRAM TYPES
Not all spectrograms are created equal. An algorithm known as the “Fast Fourier Transform”, or FFT for
short, is used to compute this visual display. Many products that feature a spectrogram display allow you to
adjust the size of the FFT, but what does this mean for audio repair and restoration? Changing the FFT size
will change the way the algorithm computes the spectrogram, causing it to look dierent. Depending on
the type of audio you’re working with and visualizing, this may help. As a rule, higher FFT sizes more
accurately display low frequency information, while lower FFT sizes more accurately display transient
information.
If you’re trying to identify a plosive, mic handling noise, or other
muddy low-frequency information, a higher FFT size in your
spectrogram settings will help. If you’re trying to identify a high
frequency event, or working with a transient signal (such as a
percussion or drum loop) choose a lower FFT size.
The following image is of a drum loop in a live concert setting, with
a member of the audience whistling. You can see how the dierent
FFT sizes aect the way we see high vs. low frequencies, as well
as transients vs. sustained notes.
RX 3 TIP • RX 3 has an Auto-adjustable STFT mode that automatically selects FFT size according to
your zoom ratio, so it’s always easy to see everything that’s going on.
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Now we’ll move on to some specific examples of how to visually identify noise and other audio problems.
Learning to identify these problems by sight will greatly help you—it means you’ll be able to use any
software that includes spectrogram technology.
USING A SPECTROGRAM TO IDENTIFY AUDIO PROBLEMS
Hum
Hum is usually the result of electrical noise somewhere in the recorded signal chain. It’s normally heard as
a low-frequency tone based at either 50Hz or 60Hz depending on whether the recording was made in
North America or Europe. If you zoom in to the low frequencies, you’ll be able to see hum as a series of
horizontal lines, usually with a bright line at 50Hz or 60Hz and several less intense lines above it at
harmonics. See below:
RX 3 TIP • To zoom in on the spectrogram with RX 3, you can scroll the mouse wheel, or use the
magnifying glass tool.
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TIP • In situations like this example, which only exhibits a few harmonics, a hum removal tool is an
ideal choice for getting the job done.
Buzz
In some cases, electrical noise will extend up to higher frequencies and manifest itself as a background
buzz. See the example below:
TIP • Hum removal tools usually focus on low-end hum, so when the harmonics extend to higher
frequencies, a denoiser is more eective at removing the problem.
Hiss and other Broadband Noise
Unlike hum and buzz, broadband noise is spread throughout the frequency spectrum and isn’t concen-
trated at specific frequencies. Tape hiss and noise from fans and air conditioners are good examples of
broadband noise. In a spectrogram display, broadband noise usually appears as speckles that surround the
program material. See image below:
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TIP • Denoisers are very eective at dealing with this type of broadband noise.
Clicks, Pops and Other Short Impulse Noises
Clicks and pops are common on recordings made from vinyl—but can also be introduced by digital errors,
including recording into a DAW with improper buer settings, or making a bad audio edit that missed a
zero crossing. Even mouth noises such as tongue clicks and lip smacks fall into the clicks category. These
short impulse noises appear in a spectrogram as vertical lines. The louder the click or pop, the brighter the
line will appear. The example below shows clicks and pops appearing in an audio recording transferred
from vinyl:
TIP • Declicking tools can recognize, isolate, then reduce and remove clicks such as these.
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Clipping
Clipping is an all-too-common problem. It can occur when a loud signal distorts on input to a sound card/
converter, mixing console, field recorder or other sound capture device. A spectrogram is not particularly
useful for identifying clipped audio—for this you’ll want to work with a waveform display.
RX 3 TIP • Move the slider below the spectrogram to the left to superimpose the waveform display.
As you’ll see in the image below, the clipping appears as “squared o ” sections of the waveform.
Many software programs allow you to zoom in on a waveform and see in detail where the waveform has
been truncated.
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TIP • Declipping tools can intelligently redraw the waveform to where it might naturally have been if
the signal hadn’t clipped.
TIP • Sometimes, heavily limited audio will also appear “squared o” when zoomed out, but this
doesn’t necessarily mean it will sound as heavily distorted. You can zoom in to see if individual wave-
form tops are clipped.
Intermittent Noises
Intermittent noises are dierent than hiss and hum—they may appear infrequently and may not be
consistent in pitch or duration. Common examples include coughs, sneezes, footsteps, car horns, ringing
cell phones, etc. The images below represent two dierent examples of these noises:
RINGING
COUGH
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Gaps and Drop Outs
Sometimes a recording may have short sections of missing or corrupted audio. These are usually very
obvious to both the eye and the ear! See below:
TIP • Noises and dropouts like the example above are often unpredictable, and usually need to be
removed or patched manually using a visual/spectral editing tool.
RX 3 TIP • The Spectral Repair module in RX 3 is one of the most revolutionary and eective ways of
repairing noises and dropouts.
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5: WHAT IS RX 3?
As we explore the various ways one can approach audio repair and restoration, we’ll be using iZotope RX
3 to demonstrate key concepts and showcase some unique tips and tricks.
RX 3 is a complete audio repair and restoration suite, consisting of both a standalone audio editor and
software plug-ins for use within a DAW. RX 3 oers advanced visual representations of your audio and
innovative new processing technology that removes noise and repairs audio. It’s unique workflow features
are designed to help you get great-sounding, ecient results even when working on challenging projects.
WHAT CAN RX 3 DO?
RX 3 combines Photoshop™-style selection tools with a visual spectrogram display and advanced audio
processing, enabling you to perform powerful audio edits. For example:
• Reduce both ambient and signal-based background noises such as hiss, hum and buzz—without
sacricing the delity and clarity of the original audio
• Isolate and then reduce or accentuate specic audio events, such as sudden background noises
• Replace damaged or missing sections of an audio le with seamless, natural-sounding patches
• Eliminate pops, clicks, and mouth noises without audible artifacts
• Repair audible analog and digital clipping with perfect precision
WHERE CAN I USE RX 3?
As a standalone software editor and plug-in suite, RX 3 is ideal for performing both real-time processing
and oine editing in various audio workflow situations. Such use cases include post-production mixing
for broadcast (TV, radio, web), audio mixing and mastering, audio restoration and archiving, digital audio
forensics and any other scenario that demands flawless audio delivered in a timely manner.
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6: DENOISING
“Denoising” in the context of audio typically refers to the reduction or removal of steady state background
noise. As explained in Chapter 3, steady state noise might include constant ambient noise, tape hiss or
electrical buzz and hum.
WHAT’S THE GOAL OF DENOISING?
There are many situations where removing steady state background noise can greatly improve the quality
of the material.
Removing steady state noise can improve the overall listening experience, increase intelligibility in
dialogue tracks, remove interferences like electrical hum from a musical performance, and make it easier to
combine dierent audio files into one scenario when mixing sound for picture.
However, there are other considerations too. If the noise carries a lot of low frequency information (often
described as rumble, hum etc.), reducing this can improve headroom and open up a musical or post-
production mix to greater dynamic range and mixing possibilities.
PRINCIPLES OF DENOISING
Denoisers are one of the most commonly used tools in audio repair and restoration. They work by first
taking a sample of the noise’s frequency spectrum, either manually or automatically, referred to as a
“noise profile.” This noise profile is then used to distinguish between the desirable (and usually much more
variable) audio, and the steady, undesirable background noise. As the algorithm identifies and separates
the noise from the desired signal, the level of noise is then intelligently suppressed. The user is able to
control the level of noise reduction applied, as well as certain parameters aecting how the noise reduction
works.
TIP • These additional parameters will vary by product and by manufacturer. Try downloading a trial
or listening to demonstrations online to find the best fit for you! For instance, more information on
iZotope RX 3 can be found at izotope.com/rx, or via our YouTube channel, youtube.com/izotopeinc
There are a number of denoising tools available, both software (such as iZotope RX 3’s Denoiser and
Dialogue Denoiser) and hardware (such as iZotope’s ANR-B).
When denoising, there are some universal home truths that apply regardless of the type of background
noise or the tool you’re using:
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1. Reduce > Remove. Often, if the goal is to improve the listening experience or increase
headroom, the best result isn’t necessarily obtained by attempting to remove the noise
entirely. Rather, reducing the noise to an acceptable or indistinguishable level often yields
better results.
2. Doing multiple, gentle processes will often yield a more natural result than one harsh
process of denoising. Though you do need to relearn the new noise before each processing
pass, this softly-softly approach allows the Denoising tool to more easily reduce noise
without aecting the desirable signal.
3. You can often reduce tonal noise more heavily, and with fewer artifacts, than you can reduce
broadband noise. Identify the type of noise(s) present in your signal, and keep this in mind
when treating them.
RX 3 TIP • The iZotope RX 3 Denoiser provides separate control over the tonal and noisy compo-
nents in your noise profile. They are linked by default, which usually delivers the best results. There
are use cases for delinking, however—like when trying to remove low-end amp buzz without reducing
the high-end noisy shine the amp gives the guitar signal.
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4. Applying dierent levels of noise reduction to dierent areas of the frequency spectrum can
help reduce artifacts. For example, try applying more gentle processing to the high-mids
than you would to the low-end, which usually contains less important audio information.
TIP • Multiband denoisers, or denoisers with enveloping capabilities, are designed to accommodate
this workflow. RX 3 Advanced makes both options available should you need them.
USING THE DENOISER AND HUM REMOVAL IN RX 3
There are some slight dierences in the tools you may use to treat tonal versus broadband noise, which
we’ll now investigate.
BROADBAND NOISE REDUCTION
In Chapter 4, we learned how to use a spectrogram to visually understand what’s happening in our audio.
Broadband noise appears as random speckles or a haze over the audio file—similar to the static you see
on your TV when there is no signal.
Below are screenshots of a noisy voiceover sound recording:
FIG. 1
Fig. 1 demonstrates the audio file via a waveform view, and we can see the blocks of noise between the transient audio events that
make up our voiceover.
Fig. 2 demonstrates the same audio file via a spectrogram view, and there are visible speckles. It’s important to use a spectrogram
when working with noise. As we see in the this view, the block of noise on the left is a better point to learn the noise profile from than
the block of noise on the right, which has some other audio elements mixed in that could confuse the noise learning process.
FIG. 2
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Step 1:
For broadband noise problems, always use a Denoiser. The first step is always to create a noise profile.
This may be done manually by isolating the noise, or automatically. A good denoiser oers both manual
and automatic modes.
Automatic modes—such as Adaptive in the RX 3 Advanced Spectral Denoiser—listen to the audio and learn
the noise profile on your behalf. These modes are useful when there is no easy-to-identify area of noise
from which to learn, or for when the noise profile changes slowly over time.
Some dedicated Dialogue Denoisers (such as RX 3 Advanced’s aptly named Dialogue Denoiser) typically
work in automatic mode, and may sound better when used on dialogue. For now, we’ll focus on manual
learning, as it’s the best solution for a wider variety of audio, including music. We’ll also be using the
Spectral Denoiser in RX 3.
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Select an area of the signal that contains nothing but noise, and click Learn (or the equivalent in your
Denoising software). As a general rule, a selection of 100ms should be long enough, but the longer your
selection of noise, the more accurately the computer can reduce the noise. We recommend a selection of
at least 1s, preferably 2–4s or longer if possible.
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Step 2:
Begin to adjust the level of noise reduction and listen closely to the changes that occur in the audio. Some
people prefer to slowly increase the amount of noise reduction until it sounds right, and stop once they
start hearing artifacts. Other engineers prefer to go hard, and then dial it back until it sounds appropriate.
Do whatever works best for you!
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RX 3 TIP • Use the Output Noise Only feature in RX 3’s Spectral Denoiser to listen to just the noise. If
you hear any desirable signal bleeding through, like low-level bursts of dialogue or music, you should
reduce the amount of noise reduction.
Levels of between -5 and -15dB of noise reduction are common. If you find yourself approaching -15dB
of noise reduction and you aren’t satisfied, consider doing a gentler pass of around -7dB. Relearn the
noise profile, and perform a second gentle pass of -8dB. You’ll end up with around the same level of noise
reduction and hopefully less artifacts.
Play close attention to your original audio. The peaks of your waveforms should still be intact, and it should
sound untouched. If you hear dulling or artifacts, it’s a sign you’ve gone too far.
RX 3 TIP • Algorithm D in RX 3 utilizes advanced high-frequency synthesis to avoid dulling. In RX 3
Advanced, you can access additional advanced-level controls to further tweak this functionality.
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Step 3:
Once your noise reduction is beginning to sound eective, direct your attention to any smoothing filters
your tool may oer, such as the RX 3 Spectral Denoiser’s Artifact Control slider. Adjusting these smoothing
tools can help eliminate any artifacts and preserve the main goal of improving the listening experience. We
certainly don’t want to make it worse by taking out some noise but adding in artifacts!
HUM AND TONAL NOISE REDUCTION
Hum and tonal noise are usually visible as bright, steady, horizontal lines. Hum and tonal noise look
dierent from each other, and there are dierent methods available for treating them. Let’s begin with hum:
Hum
Below is a screenshot of a recording with hum.
TIP • In order to see which frequencies make up the tonal noise, you must use a spectrogram to view
the audio. This can be much more accurate and easy to read than a spectrum analyzer.
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It’s usually easy to identify the fundamental base frequency, as it’s usually the most visible. Often, the
fundamental frequency will be 50Hz (Europe) or 60Hz (North America) due to those regions’ dierence in
electrical delivery. This audible hum originates from bad ground connections or inducted power sources
such as AC mains or transformers.
RX 3 TIP • The Magic Wand tool in RX 3 can automatically select the fundamental frequency, and
double clicking will automatically select all the additional harmonics.
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We’ll start by using the Hum Removal tool. Hum removal tools, such as the one in RX 3, are extremely
precise filters, designed to notch out very specific frequencies. For basic hum with anywhere from 2 to 7
harmonics, this is an eective tool.
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Step 1:
To begin, identify the frequency of your hum. Your ears and the spectrum analyzer module may help. Set
the base frequency to 50Hz or 60Hz, depending on where the audio was recorded. If the hum isn’t located
at 50Hz or 60Hz, you may use Free mode, which unlocks the filters and allows you to set the base
frequency yourself.
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RX 3 TIP • Use the time selection tool to select an area of hum and click Learn. This automatically
sets the filters to the correct frequencies based on your selection.
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Step 2:
Next, adjust how aggressively Hum Removal attacks the primary frequency by pulling down the first
frequency node. The deeper the cut, the more hum will be removed—but you may also adversely aect
wanted audio in that frequency range, so tread carefully.
RX 3 TIP • Try selecting
the Linear-phase filters
check box when you’re
making very deep filter
cuts in full frequency
range content. This helps
preserve surrounding
audio due to the filter’s
exceptional steepness.
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Step 3:
If you can see and hear additional harmonics, start reducing the gain of these as well.
RX 3 TIP • Use the Number of harmonics control to select up to 7 harmonics above the primary
frequency. The spectrogram display makes it easy to identify the number of hum harmonics in your
project.
Step 4:
As you start reducing the additional harmonics, it’s a good idea to ensure you aren’t removing any
desirable audio. A good hum removal tool allows you to adjust the “Q”, or width value of the filters.
Generally speaking, narrower filters will provide a better result, as they can more accurately notch out
frequencies without aecting the surrounding audio.
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RX 3 TIP • Use the Output hum only control to isolate and hear
the audio that will be attenuated. If you hear any desirable audio
creeping in, narrow the filter Q.
RX 3 TIP • Filter DC oset removes the DC (direct current) oset
caused by the imbalance that sometimes occurs in A/D convert-
ers. DC oset is exhibited by the waveform appearing above or
below the zero line, and is undesirable because it prevents you
from achieving maximum audio levels. DC oset may also cause
audible artifacts depending how the signal is being processed.
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TONAL NOISE
Tonal noise, such as buzz from fluorescent lighting, is more dicult to trace back to a primary frequency
and may extend up into high frequencies that are out of the scope of what RX 3’s Hum Removal module
can handle.
Tonal noise is dierent from the broadband noise discussed previously in that it tends to be concentrated
at certain frequencies. For this, we can use the RX 3 Denoiser module, which gives us separate control
over the tonal and broadband noise elements in a noise profile.
Below is a screenshot of a recording with tonal noise. As you can see, there are a lot of harmonics present:
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To remove Tonal Noise using the Denoiser, follow the steps for dealing with broadband noise outlined
earlier in this Chapter, but with the following additions:
• When adjusting the level of noise reduction in Step 2, de-link the sliders by clicking on the Chain-
link icon. Then, increase the amount of tonal noise reduction using the now de-linked Tonal slider.
This will start to clamp down more heavily on the tonal elements of your noise prole.
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• Make sure the Reduction curve is showing on the noise prole graph. Click the toggle box to show
it. Now you may use this reduction curve as an envelope to notch certain areas of the noise prole
to be aected more heavily. Where you see tonal peaks, you can direct the Denoiser to be more
aggressive in those areas.
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DIALOGUE DENOISING
Recorded dialogue may have broadband or tonal noise problems, so why not just treat dialogue with the
aforementioned methods? Well, you can—and would likely get a good result!
However, as mentioned in Chapter 3, some denoisers are designed specifically for use on dialogue and
vocals. Because of the unique nature of voice recordings—plus our innate ability to hear the minute
subtleties of the human voice—regular denoisers that might sound fantastic on music or other audio may
not deliver the best possible results on dialogue and vocals. Dialogue-specific denoisers use custom algo-
rithms better suited for vocals.
RX 3 TIP • iZotope RX 3 Advanced includes a dialogue denoiser. We’ll take a look at using it shortly.
Another reason for using a dialogue-specific denoiser has to do with workflow. In post-production projects,
there might be tens or hundreds of dialogue regions in any given session. It’s much quicker and more
ecient to use a denoising plug-in in real-time than to destructively edit and then reimport so many
files. Dialogue-specific denoisers are low latency and can run in real-time with minimal impact on system
resources.
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Step 1:
You can use the Dialogue mode in the RX 3 standalone application’s Denoiser module, or use the dedi-
cated plug-in in your DAW.
Insert your dialogue-specific denoiser on your audio track, and allow the audio to begin playing. iZotope’s
Dialogue Denoiser has two modes, Manual and Auto. Make sure you start with Auto.
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A good dialogue-specific denoiser will oer multiband functionality, allowing you to quickly adjust the
amount of noise reduction applied to dierent areas of the frequency spectrum. In the Dialogue Denoiser
Manual mode, you can adjust these multibands.
This is useful if your audio has a lot of hiss or low-end rumble, for instance.
TIP • Apply gentler pro-
cessing to the high-mid
frequencies, as this tends
to be where vocal arti-
facts are more audible.
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Step 2:
Increase the amount of reduction until you hear the noise begin to disappear. Listen closely, as you’ll want
to set the amount of reduction slightly below the level at which it begins to aect the voice.
TIP • Remember that a higher value for the denoiser’s reduction parameter doesn’t mean more noise,
it means more reduction (and therefore less noise).
If your denoiser has a threshold control (as the Spectral and Dialogue Denoisers in RX 3 do), adjusting it
can help remove more noise with fewer artifacts.
A higher threshold value will reduce more noise, but suppress low-level signal components, so if you go
too far, you may start to hear the ends of words being truncated slightly. A lower threshold value helps
preserve these low-level signal components, but if you go too low, you may cause noise modulation. It’s all
about finding the right balance!
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GENERAL DENOISING TIPS
1. Softly, softly. Be gentle and do multiple passes if necessary. This will often lead to a better sonic
result than one harsh denoising pass.
2. Reduce with caution. The amount of reduction is the most important control, so listen very closely
as you adjust it. It’s possible to over-compress or over-saturate an audio signal using conventional
mixing tools, and it’s also possible to overuse a denoising tool.
3. Know your noise. Using the tips outlined above, identify the components of your noisy signal.
Broadband noise and tonal noise require dierent approaches, so treat them accordingly.
4. Learning is good. If time permits and the noise prole is constant throughout, using Manual mode
on a carefully learned noise prole can produce better results than Auto.
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7: REMOVING INTERMITTENT NOISES AND GAPS
Intermittent noises can include a wide range of intrusive sounds that don’t fall into the broadband or tonal
noise categories. These can include a cell phone ringing at a violin recital, a door hinge squeaking during
an interview, or trac noise interrupting the dialogue being recorded for a film.
Gaps, dropouts and short sections of corrupted audio are also common audio problems. These can be
caused by everything from a loose audio cable to digital errors.
These audio problems tend to occur suddenly and last for a short duration—that’s what dierentiates them
from the conventional noises we dealt with in Chapter 6. We’ll refer to the process of repairing these inter-
mittent problems as audio repair.
WHAT’S THE GOAL OF AUDIO REPAIR?
Repairing audio involves carefully patching over troublesome areas and performing precise audio edits—all
without causing audible artifacts that listeners may detect.
Audio repair might be performed for an obvious benefit, such as salvaging a live recording that suers
from an audio dropout or sudden and distracting audio event. However, the principles of audio repair can
also be used for more subtle edits and enhancements. For example, removing springtime birdsongs from
an audio recording intended to be set in the depths of winter, eliminating vocal plosives, and smoothing
abrupt transitions in certain frequency areas are all ways in which audio can be polished in the post-
production stage.
PRINCIPLES OF AUDIO REPAIR
No matter what software you choose, the audio repair process will require using some sort of visual editing
tool(s).
Perhaps the most important is the spectrogram display, which is used to make precise selections of iden-
tifiable audio events. These precise selections can then be patched or repaired. If you didn’t know how to
read a spectrogram display when you started reading this guide, you probably now have a better sense of
what they can be used for.
The tools that allow you to interact with the spectrogram are also important. Good audio repair and resto-
ration software should include a number of selection tools, which you can use to draw or highlight specific
audio events and frequencies that you observe on a spectrogram.
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RX 3 TIP • In addition to the common horizon-
tal and vertical time/frequency selection tools,
RX 3 includes several advanced selection
tools, such as Lasso, Brush and Magic Wand.
These provide much more control over
selecting sudden audio events that change
frequency and move about.
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Terms such as brush and lasso are common across visual editing platforms such as Adobe Photoshop™.
Here’s what they mean in the context of audio repair:
• Lasso: A lasso tool lets you use your mouse to outline a freeform selection of an image.
• Brush: A brush tool lets you use your mouse to outline a freeform selection with a dened brush
size. The brush size is usually adjustable.
• Magic Wand: A magic wand tool lets you automatically and intelligently select a specic audio
event within a spectrogram (or certain pixels making up part of an image).
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Once you’ve highlighted certain events, the final step to audio repair will be audio processing.
There are several things that make intermittent noises especially hard to fix:
• They can be wildly unpredictable in frequency and timing.
• Unlike broadband noise, hum, clicks and crackles, noises like this can’t be removed with an auto-
mated process and can be time consuming to x.
• Most traditional audio editing tools cannot eectively remove them without leaving many artifacts
or damaged audio.
• There’s a lot of diversity between the audio repair methods and tools available, so it’s worth check-
ing out audio examples and downloading demos to nd the right solution for your needs.
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USING THE SPECTRAL REPAIR IN RX 3
In this Chapter, we’ll explore using the RX 3 Spectral Repair module to remove intermittent noises and
fill in unwanted gaps. We’ll begin with these algorithms as they work in particularly unique ways. Please
note that other audio repair and restoration solutions may not include the following functionality, or might
achieve the intended results dierently.
The process of using Spectral Repair requires making precise selections using either the basic or advanced
tools. If you’re using Spectral Repair as a plug-in inside a DAW, note that it includes a built in spectral editor
window that works in a similar way to RX 3’s interface.
RX 3 TIP • The Spectral Repair plug-in only works with DAWs that support a technology called oine
processing. Pro Tools is one such example.
TIP • We strongly recommend that you try the Spectral Repair examples included in the Appendix, as
well as the audio demo files that accompany this guide.
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Spectral Repair oers four dierent algorithms that you can use for audio repair:
1. Attenuate is an intelligent gain adjustment. It can be used to push unwanted audio events
into the background—particularly useful if the unwanted audio events don’t completely
obscure the desired signal.
2. Replace is used to replace damaged audio, including entire gaps and dropouts. It can
resynthesize audio using the audio information surrounding the damaged area.
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3. Pattern is suited to patching badly damaged audio that contains repeated components, such
as instrumental vibrato. It’s an intelligent copy and paste function that incorporates advanced
blending techniques.
4. Partials+Noise is a more advanced version of Replace. It’s more eective on heavily
harmonic content, and focuses on detecting and resynthesizing harmonics.
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INTERMITTENT NOISES
Step 1:
Begin with identifying unwanted noise in the spectrogram. See Chapter 4 for more details on using the
spectrogram to hone in on dierent types of problematic audio.
Using the selection tools, isolate the noise as precisely as possible. You can either draw a freehand
selection around the edges of the unwanted audio, or use the Magic Wand tool in RX 3 to make the
selection automatically.
RX 3 TIP • Use the Play Frequency Selection tool to play back the selection of audio in the spectro-
gram. This helps to determine whether you’ve correctly set the boundaries for the selection.
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Step 2:
Once you’ve isolated the unwanted noise, open Spectral Repair and ask yourself the following questions:
• Do you want to push the noise gently into the background? If so, use Attenuate to process the
selection.
• Do you want to completely remove the noise? If so, use Replace or Partials+Noise to process the
selection.
As a general rule, Replace is a good starting point for removing sounds entirely. Partials+Noise might be a
better choice if the surrounding audio is heavily harmonic—like a chair squeak from a live orchestral
recording.
RX 3 TIP • Using the Compare function will let you quickly A/B the results of your chosen modes and
settings whilst experimenting with audio treatments.
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Step 3:
Now that you’ve identified, isolated, and treated unwanted noise, it’s time to play back your audio. Listen
out for any changes that may have been made to the desirable audio, such as the introduction of artifacts.
Remember that listeners will only hear what you’ve left in the mix, and not what you’ve taken out. If you fail
to identify and treat leftover artifacts, they may distract the listener. It’s important to make an edit sound as
seamless as possible!
Step 4:
Removing the noise can usually be done in one pass.
In other cases, you might need to do a couple of patch repairs to remove the problem entirely.
In this image, the unwanted noise is a bicycle bell. You can use one pass to remove the ring of the bell,
which is visible as a collection of horizontal frequencies.
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In this second pass, you can select and patch the initial attack of the bell, which is a more mechanical
sound.
Understanding the dierent components that make up unwanted noise can help you identify how best to
treat it, and whether one or several passes would be most eective. This process is similar to how you
identified dierent types of noise and the ways to treat it in Chapter 6: Denoising.
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AUDIO DROPOUTS
Step 1:
Audio dropouts are easily spotted in either a waveform or a spectrogram view.
Working with a spectrogram view does make the repair process easier.
Firstly, you’ll want to make sure you have the gap highlighted. A full-bandwidth selection tool is most
preferred for this, and you should highlight a very small amount of audio to the left and the right of the gap.
TIP • It’s best to select a small amount of audio to the left and right of the gap as clicks will be present.
This is a result of the waveform being interrupted between zero crossings. This technique also helps
hone in on material that will later be replaced.
Step 2:
Once you have the audio gap highlighted, ask yourself these questions before processing:
• Is the audio fairly steady, with low harmonic content? If so, use Replace to process the gap.
• Does the audio have a repeating pattern, such as a vibrato? If so, use Pattern to process the gap.
• Does the audio seem suited for treatment with Replace, but is much more harmonically intense
(like music)? If so, use Partials+Noise to process the gap. Replace always connects harmonics from
two sides of the gap horizontally, while Partials+Noise can connect frequency-varying tones, more
common in music.
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Step 3:
As mentioned above, listening back is important—particularly when performing repair on full bandwidth
audio dropout.
Repairing the audio dropout may work the first time, but sometimes you’ll need to do a couple of passes.
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For instance, in the above image, we have an opera singer and an orchestra. Pattern was used to replace
the dropout, resulting in this:
Although this may sound good, we can see that the slowly evolving orchestral chord has been repaired
abruptly.
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In situations where a whole signal does not transition smoothly, it’s advisable to perform a second pass.
Target the specific frequency area and process it with the appropriate algorithm. In this case, you should
use Partials+Noise to replace the harmonic content.
In this image, the audio dropout has been repaired and some additional steps have been taken to ensure a
seamless edit.
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GENERAL AUDIO REPAIR TIPS
1. Trial and error is good. Although you’ll likely get great results the first time around, you’ll
become more eective at using Spectral Repair the more you experiment and work with it.
2. Provide more infor-
mation. If you fail to get
a perfect result the first
time, simple tricks like
extending the
surrounding region
length parameter may
help.
3. Look around you. If a
noise only takes up
a certain area of the
frequency spectrum
(between 5–8 kHz, for
instance), you might
get a more transparent
result performing
area-specific spectral
repair, rather than
full bandwidth repair.
This is because the
audio surrounding the
area being patched
(anything below 5kHz
and above 8kHz in
the above case) is left
unaected and will
help smooth over the transition.
4. Keep it simple. For example, you might find that plosives are better treated using the
Gain module by simply turning the gain down to zero. But most times, Spectral Repair is
the answer—its default parameters are well designed and are eective without too much
fiddling!
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8: REMOVING CLICKS AND POPS
Clicks and pops can occur at almost any stage of the recording process. They can be caused by surface
noise from mechanical media (especially discs), static electricity, power lines, cell phones, mouth noises,
inadvertent physical contact with a microphone and bad audio connector cables. Occasionally, digital
errors will result in unexpected clicks too.
WHAT’S THE GOAL OF REMOVING CLICKS AND POPS?
In the case of old analog playback mediums such as vinyl or shellac records, clicks and pops are under-
stood to be commonplace. It’s extremely dicult to obtain a perfect analog to digital transfer of an old
record without including clicks and pops. In this example, the goal is to remove the extraneous clicks and
pops that might distract the listener, and still retain the true character of the original audio.
TIP • Many are nostalgic about the sound of vinyl. For this reason, there exists dedicated software that
makes digital audio sound as if it were playing from an old record. iZotope Vinyl helps achieve this
sound, and was iZotope’s first ever plug-in—released in 2001. It’s available for free from the iZotope
website, at www.izotope.com/vinyl
Clicks and pops that are caused by digital errors or interferences have the potential to render audio
useless. Listeners are far less accepting of clicks and pops caused by such errors, as they not only sound
dierent, but are not expected in commonly pristine digital audio.
In the case of mouth noises, removing clicks helps improve the general sonics of a vocal recording. Profes-
sional vocal talents are often highly skilled at controlling mouth noises, but clicks from the mouth are
usually a perennial problem in dialogue editing.
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PRINCIPLES OF REMOVING CLICKS AND POPS
It’s not possible to remove clicks and pops eectively with conventional tools,, nor is it possible by notching
with a precise EQ. This is because clicks usually cover a wide frequency bandwidth and are extremely
momentary.
Declicking tools are designed to identify and recognize the sonic signature of a click, enabling the user to
then attenuate or remove it entirely, either one by one, or by processing the entire audio file at once. Some
declickers may have a single mode, but a good declicker should have several dierent modes optimized
for dealing with the variety of clicks mentioned above.
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USING DECLICK & DECRACKLE IN RX 3
Chapter 7 covers using Spectral Repair to eliminate certain clicks and pops, but for more troublesome
distractions, an even better tool is available for use. The Declick & Decrackle module in RX 3 repairs and
reduces clicks, pops and other impulse noises within the waveform. It has three modes: Declick, Decrackle,
and Interpolate.
RX 3 TIP • Declick
automatically reduces the
vast majority of clicks.
There are several options
in the RX 3 Declicker that
combat these, and we’ll
explore them all shortly.
RX 3 TIP • Decrackle re-
moves repeated, quieter
clicks that blend together
to form what we perceive
as crackle.
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RX 3 TIP • Interpolate
performs one-o
manual click repairs that
Declick is unable to
treat. Interpolate can
also be used to fix very
slight audio dropouts.
Clicks occurring in the analog domain, whether caused by the surface of a mechanical playback medium or
a mouth, are sonically and visually dierent to digital clicks.
The first image demonstrates a click that occurs during playback of a vinyl record. It’s a solid frequency
event on the spectrogram, and can be considered random.
The second image demonstrates a click caused by cell phone
interference. When zoomed out, it looks similar, but zoomed in, we
can see that the single click is actually a very short, periodic signal.
The RX 3 Declicker features both a Random and a Periodic mode
that you can use to tackle these problems respectively.
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ANALOG CLICKS
Step 1:
Open Declick & Decrackle.
Select the Declick tab, and
then select M-band (random
clicks) mode.
“Click” will be the click type
selected by default. If you
believe that the click is being
caused by a low-end thump,
you should select Thump as
your click mode instead. The
third option, Discontinuity, is
ideally suited to clicks caused
by bad audio cuts that have
missed a zero crossing.
Step 2:
Before adjusting the strength beyond the default settings, click Preview to hear the result of the processing
on your audio file. Many declickers will oer an appropriate level as a starting point.
As the audio plays back, you
can adjust the strength of the
declicker up or down. Higher
values will reduce more clicks.
If you’re working with single
clicks on a one by one basis,
process each and listen back
regularly. You can always
undo any processes that don’t
work eectively.
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Step 3:
After choosing an acceptable level of click reduction, listen carefully to ensure you aren’t unintentionally
harming any transients. Using a declicking tool on its highest settings can audibly soften transients. If you
can hear that the transients are losing their edge, turn the strength of the declicker down a little.
RX 3 TIP • Use the Clicks Only feature in RX 3 to listen out for the isolated
clicks. If you hear desirable audio creeping in, your settings are likely too
harsh.
DIGITAL CLICKS
Repeat the same steps used to treat the analog clicks, but instead
use M-band (periodic clicks) mode.
RX 3 TIP • Use Click widening to expand the click size if your
clicks are not being fully recognized and removed by the
Declicker.
RX 3 TIP • Using the Frequency skew can achieve better results if
a click is focused specifically towards the high or low end. Gener-
ally, however, this is best left in the middle.
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GENERAL TIPS FOR REMOVING CLICKS AND POPS
1. Two is better than one. As with denoising, there are scenarios where two processes of
any declicker are better than one, particularly if you’re dealing with an old recording full of
unwanted clicks. Performing one process of declicking will remove the most obvious clicks,
allowing the second process of declicking to remove the quieter ones.
2. When is a click not a click? The simple answer is: when it’s a transient. Overly harsh declick
settings can harm the attack of transients within your audio, particularly instruments such as
brass, acoustic guitar and percussion. It’s important to listen out carefully for this, and dial the
declicker back if it’s occurring.
3. Choose your battles. It’s easy to process an entire file with only one problematic click. But
there’s no need to risk the fidelity of good audio if it only contains a small number of clicks.
For infrequent click problems, treat them individually before moving on.
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9: REMOVING CLIPPING
Live concerts and on-location interviews frequently become victims of signal overload or clipping. This can
happen in both the analog and digital domain, as well as during the A/D process. This is often the result
of time constraints in setting up and sound checking. In music recording, overly enthusiastic singers and
drummers are frequently the worst oenders!
WHAT’S THE GOAL OF REMOVING CLIPPING?
The goal of removing clipping is to repair clipped sections while allowing the originalaudio to sound as
natural as possible.
Although a certain level of residual noise is often deemed acceptable by the human ear, clipped audio
causes actual destruction of the audio—something the human ear tends to be less forgiving with.
Some distortion cannot be fixed. For example, old records that have been over played may have groove
wall distortion from record wear—something that is virtually impossible to fix.
PRINCIPLES OF REMOVING CLIPPING
Declipping tools can help treat both analog and digital clipping or overload distortion.
Zoom in on a clipped waveform to clearly see where the audio has been truncated. The squaring o of the
waveform occurs when there isn’t enough dynamic range available to express the amplitude of the audio
signal.
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It’s technically possible to obtain moderately good results by using the mouse to slowly redraw each
sample—restoring it to what it might have been prior to clipping. Declipping tools, however, use more
advanced techniques to intelligently redraw the waveform. This saves the audio engineer lots of time, and
removes manual work.
In RX 3, you can use the Declip module. It uses advanced interpolation techniques to intelligently rebuild
the peaks of clipped audio.
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USING DECLIP IN RX 3
Step 1:
If you can actually see where the clipping
occurs, Declip is both easier to use and more
likely to succeed. Once you’ve identified
exactly where the clipping occurs, you can
open Declip in the RX 3 standalone appli-
cation and set a suitable threshold. There are
two ways you can do this:
1. Zoom in on the waveform and drag
the threshold down until it sits just
below the truncation.
2. Adjust the threshold so that it sits
just below the clipping as displayed
on the histogram display—this
automatically computes for you,
based on the selected audio.
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Step 2:
RX 3 TIP • The height of the histogram represents the high and low levels of the audio, whilst the
width of the bar indicates the most frequent levels. Here, a white line that covers the full width indi-
cates that clipping is present.
RX 3 TIP • Clicking on the Suggest button will cause Declip to automatically place the threshold. This
may save you some time and manual work.
Declipping tools redraw a truncated waveform. Therefore, if the waveform is
clipped at 0dB, redrawing it will cause the waveform to go above 0dB. Declipping
tools utilize makeup gain to counteract this, which allows you to recover the
natural sound without creating additional clipping. This facility accommodates the
increased peak levels caused by the declipping process.
Generally, makeup gain of around -3dB to -6dB is a good amount to begin with.
Try that, and click process.
RX 3 TIP • Using the Post-limiter in the Declip module will automatically limit
the audio to avoid creating additional clipping. This may be necessary in
some cases to avoid a drastic reduction in level, but you shouldn’t solely rely
on this. You can get a more natural sound with the right makeup gain settings applied.
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Step 3:
Occasionally the audio may have what’s called asymmetric clipping—a scenario where clipping occurs at a
dierent level on one side of the waveform.
When confronted with this scenario, click the linked icon to delink the two
thresholds. This will allow you to set dierent threshold values for the positive
and negative sides of the waveform, which oers the best sounding results
when removing clipping. This feature is exclusive to RX 3 Advanced.
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GENERAL TIPS FOR REMOVING CLIPPING
1. If your declipping tool does not work for you, you may be able to use RX 3’s Spectral Repair
tool to fix short corrupted segments. See Chapter 7 for more details.
2. To avoid volume fluctuations you may want to process the entire audio file rather than
specific sections.
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10: REMOVING REVERB
Reverb is used to add certain spatial characteristics to audio. It’s often used on vocals and instrumentation,
but can be used on sound design elements too.
It’s a relevant topic to discuss, even for audio repair. Technologies that are able to attenuate reverberations
in an audio signal aren’t very common, and there are only a few eective tools that do this job well.
RX 3 TIP • RX 3 includes brand new technology created by iZotope that reduces reverb. It’s oered
as part of the RX 3 Advanced Dereverb module.
WHAT’S THE GOAL OF REMOVING REVERB?
There are two main reasons why an audio engineer might seek to reduce reverb in an audio signal.
Reason #1
The presence of unwanted reverb is a common issue when editing automated dialogue replacement
(ADR), matching location recorded dialogue with studio dialogue and mixing dialogue recorded in larger
spaces.
Reverb can prevent an audio engineer from achieving a smooth, warm, and present dialogue mix. Particu-
larly if recorded in a large studio or space, reverberations might be so overwhelming that they prevent the
audio engineer from adding more reverb as an eect.
In this case, the goal is to remove as much unwanted reverb as possible, without impacting the original
audio.
Reason #2
Reducing unwanted reverb before doing heavy denoising is a helpful process when repairing and restoring
audio.
An overly enthusiastic denoising process may modulate reverb tails, which results in unwanted artifacts. If
you’re required to perform heavy denoising, reducing the reverb tails first may lead to a better result.
In this case, the goal is to reduce rather than remove entirely.
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PRINCIPLES OF REMOVING REVERB
The above images show a reverberant signal versus the same signal without reverb. The dierence
between the two is most obvious in the decay that follows the transient, known as the reverb tail.
Technologies that seek to attenuate reverb often look to these tails in order to identify and distinguish the
reverb. This is so that attempts can be made at reducing its eect.
Reverbs with short tails or heavy early reflections can be very hard to reduce, as it makes identifying rever-
beration more dicult for algorithms.
It isn’t always possible to remove early reflections, and you may have to settle for reverb reduction rather
than total removal.
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USING DEREVERB IN RX 3
Please note that reverb reduction tools are very few in number, and you may find that the controls
mentioned here are specific to RX 3 Dereverb.
Step 1:
Listen to your audio. Try and discern how long the reverb tail is, and then set the tail length accordingly.
Using an incorrect tail length setting can cause more harm than good.
RX 3 TIP • The Learn feature may help here, as this will automatically set the band thresholds for you.
For best results, learn from the entire audio file. Dereverb is not like Denoise, thus learning from a
selection of ‘just reverb’, as you would ‘just noise’, will not help the computer distinguish the reverber-
ant elements of the signal.
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Step 2:
RX 3’s Dereverb is multiband.
There are four sliders allowing
you to adjust the amount of
reverb reduction in dierent
areas of the frequency
spectrum.
If you used the Learn feature
in step 1, these sliders may
have been initially positioned
for you. Step 2 is all about
making sure.
Using the Solo function, listen
to each band and adjust the
slider until you’re happy with
the amount of reverb being
reduced.
Step 3:
Now that you’ve set the frequency-specific processing details, you can adjust the master Reduction slider
to control the overall amount of reverb reduction.
Now you should use the Output Reverb Only function to listen to the signal being removed. As with other
repair and restoration tools, it’s useful to check what you’re actually removing, in case it contains any
desirable audio. In this case, you should be hearing the reverb in isolation, and not the direct audio.
RX 3 TIP • Enhance Dry Signal is a useful additional control, designed to help clarify the audio being
left behind, and avoid dullness.
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GENERAL TIPS FOR REMOVING REVERB
1. Reverb is often centered in the mid range, and focusing your attention on the low and hi-mid
multiband sliders will help ensure a good result.
2. Use a gentle pass of 2-4dB of denoising before removing reverb and then doing some
heavier denoising. A slight, gentle pass can help remove the top ‘silky’ layer of noise in the
audio signal, allowing reverb removing algorithms a better peek at the reverb underneath.
You might find this gets better results even if not explicitly recommended by the reverb tool’s
manual.
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11: EXPORTING AND DELIVERING AUDIO
Once you’ve completed the repair and restoration process, you’ll want to take the necessary steps to
export and deliver your work.
This might be as simple as rendering/bouncing your mix from a DAW, or saving an audio file that you can
use elsewhere. But sometimes, particularly in the case of audio forensics or audio for TV and broadcast,
delivery requirements might be somewhat demanding.
WHAT’S THE GOAL OF EXPORTING AND DELIVERING AUDIO?
Much like the mastering process, the goal is to deliver high-fidelity audio in the correct medium—with the
right deliverables attached.
TIP • A deliverable could be something else that’s required of the audio engineer, such as the docu-
mentation of steps taken (often required in audio forensics), or a proof of loudness compliance (often
required for broadcast audio).
PRINCIPLES OF EXPORTING AND DELIVERING AUDIO
It may sound obvious, but knowing what the client requires is perhaps one of the most important principles
of exporting and delivering audio.
Establishing the deliverables at the beginning of a project, whether for personal or commercial purposes,
can save time and help avoid additional hours of prep work.
EXPORTING AND DELIVERING AUDIO IN RX 3
If you’ve been using the RX 3 plug-ins inside a DAW, you can simply render/bounce your mix session.
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RX 3 TIP • If any of the RX 3 plug-ins have been using a
lesser-quality setting for latency purposes (such as Low or
Medium in Declip), change this to High before bouncing.
When using the RX 3 standalone application, you have
several options at your disposal. Although these options are
described within the context of RX 3, the principles of maintaining
session data and multiple copies of your work still apply across any
form of audio repair and restoration work.
Step 1:
Click on File in the upper menu bar.
This provides several options.
• Save File As… allows you to save your work as an RX 3 document, which is a session le that saves
your processing history for later recall, or as a WAV or AIFF le.
• Export Selection allows you to export the audio you’ve highlighted, which is particularly useful if
you tend to break apart larger projects.
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Step 2:
Decide on your output format.
The file format options
available to you are WAVE,
AIFF and RX 3 document.
Should you choose WAVE or
AIFF, RX 3 allows you to save
in 32-bit floating point. Many
other audio editing and repair/
restoration suites allow this too.
If you are saving your audio in order to resume work later, you may wish to save it as an RX Document,
which retains your edit history.
For other contexts, choose 24-bit or 16-bit. 16-bit is preferred if you’re delivering media for an audio CD for
example.
GENERAL TIPS FOR EXPORTING AND DELIVERING AUDIO
Prior to exporting audio as outlined above, ensure you’ve at least considered the tips below, as they may
be relevant to a specific project or scenario:
1. When reducing bit depth, always dither. If the bit depth of the audio upon delivery is going to
be lower (a 24-bit digital audio file being reduced to 16-bit for a CD master, for example),
dither should always be applied as the final step before exporting.
RX 3 TIP • RX 3 includes
iZotope’s award win-
ning MBIT+ Dither (also
available in Ozone 5
and Ozone 5 Advanced),
which manages your dith-
ering process automati-
cally.
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TIP • If you’re interested in learning more about the concept of dithering, iZotope has produced this
informational video: youtu.be/vVNzylf9sGo. If you prefer to read, you can download iZotope’s free
dithering Guide at www.izotope.com/ozone/guides.
2. Deliverables. Whatever your audio repair and restoration solution, make sure you document
the steps you take. Keep copies of the original audio, save presets, and note as much
information as possible about the process. This is most useful for people working in audio
forensics who might be required to verify and authenticate work. It also applies to freelance
engineers who might need to clarify their time commitments.
RX 3 TIP • RX 3 saves your work as an RX 3 document, in addition to allowing you to export your edit
history via XML. The inclusion of iZotope Insight (mentioned below) also allows you to measure and
export graphs and spreadsheets of your audio loudness data—required by many large clients.
3. Ensure loudness compliance. If your audio repair and restoration work is part of a larger mix
that’s likely to be broadcast, you should ensure it complies with the latest loudness regula-
tions in your territory. This avoids costly remixes and adjustments once you’ve delivered your
audio.
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RX 3 TIP • RX 3 Advanced includes iZotope Insight, a comprehensive metering suite that monitors
and ensures loudness compliance. For more information, watch this useful video:
http://youtu.be/XpmOLjDSo0c.
And for more information on Insight, visit www.izotope.com/insight.
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4. Sample rate. Ensure everything is the correct sample rate, as required for delivery. A project
destined for CD would require a sample rate of 44.1kHz, whereas the audio for a video
project would typically require 48kHz. This may involve either downsampling or upsampling
your audio. Please note: upsampling audio does not enhance sonic quality.
RX 3 TIP • RX 3 includes iZotope’s Sample Rate Conversion (SRC) technology as part of the Resa-
mple module. It supports sample rates between 11.025kHz and 192kHz.
5. Control. Always retain a copy of your work that is of the highest quality. If your audio is going
to be delivered across multiple formats (such as MP3, AAC, WAV or FLAC) it’s a good idea to
handle these conversions yourself. This will allow you to maintain quality control, and avoid
a client taking your high fidelity work and using a bad encoder that will convert to these
formats.
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12: SUMMARY
We hope this guide has increased your knowledge of audio repair and restoration and, as a bonus, given
you some ideas of how to use RX 3 eectively. When conducting audio repair and restoration, it’s important
to understand that each noise problem is dierent. Learning the fundamentals, such as those outlined in
this guide, will allow you to quickly and eectively hone in on which tool you need for the job, and how
best to use it.
Ultimately, there are no right answers, no wrong answers, and no rules—audio repair and restoration is
about experimenting and having fun. To test what you’ve learned from this guide, be sure to download
our audio examples and move on to Appendix C, where you’ll find descriptions of how to repair real world
audio problems. Enjoy!
Thanks,
iZotope, Inc.
P.S. Aside from RX 3, we also invite you to try out our other products. Each one is available for download as
a free 10- day trial at www.izotope.com/trials.
Here’s a quick overview of several of our other products:
iZotope Ozone 5
Complete Mastering System
Ozone is a single, integrated plug-in that
includes eight essential mastering tools:
Maximizer, Equalizer, multiband Dynamics,
multiband Stereo Imaging, Post Equalizer,
multiband Harmonic Exciter, Reverb, and Dith-
ering. Become the master of your audio!
www.izotope.com/ozone
iZotope Nectar 2
Complete Vocal Suite
Make your vocals and dialogue sound
professional in a broad range of genres with
Nectar’s complete set of vocal production
eects. www.izotope.com/nectar
iZotope Insight
Essential Metering Suite
(Included with RX 3 Advanced)
Insight is an extensive set of audio analysis and
metering tools, perfect for visualizing changes
made during mixing and mastering, trouble-
shooting mixes, and ensuring compliance with
broadcast loudness standards.
www.izotope.com/insight
iZotope Alloy 2
Essential Mixing Tools
Alloy gives you futuristic tools, fast results
and—most importantly—fantastic sound. Bring
character and life to every element of your
mix with Alloy.
www.izotope.com/alloy
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ABOUT THE AUTHORS
In addition to the hard work of iZotope’s development, QA and content development teams, we also wish
to extend our thanks to Nat Johnson whose writing, restoration expertise and audio examples contributed
greatly to the original version of this guide published in 2008.
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APPENDIX A: GETTING SET UP TO REPAIR AND RESTORE AUDIO
EQUIPMENT
Software
iZotope RX 3 installs both the standalone audio editing application, and the separate plug-ins for use with a
DAW.
If you prefer working inside a DAW, you can load many of the RX 3 modules as plug-ins, provided it
supports one or more of the following formats in 32- or 64-bit: VST, VST3, AU, and AAX.
Spectral Repair only functions in DAWs that support oine processing, such as Avid’s Pro Tools 11. In a
DAW, you can open a spectrogram by using Spectral Repair as a plug-in.
iZotope audio repair and restoration technology is also licensed to a number of third party manufacturers.
Certain algorithms and parameters are accessible within software such as Sony’s Sound Forge—a good
way to get started with the basics, if you don’t yet own RX 3.
Many software solutions for audio repair and restoration, such as iZotope RX 3, have free trials. Taking
advantage of these trials is an eective way of establishing your preferred solution.
Computer Requirements
Audio repair and restoration tasks can be some of the most CPU-intensive audio processes to perform.
Therefore, powerful machines are preferred, as they will be faster at processing edits. Here are some
requirements to keep in mind:
• A fast, multi-core processor. You’ll need this kind of processor if you want to take advantage of RX
3’s optimized speeds.
RX 3 TIP • RX 3 is already fast, but is additionally optimized to take advantage of multi-core proces-
sors. Thus the faster your processor, the faster your performance will be when crunching advanced
audio algorithms.
• A large, high-resolution monitor. Spectrograms are incredibly visual by nature, so the more screen
real estate you can dedicate to this way of visualizing audio, the better.
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TIP • Dual monitor setups allow you to place a spectrogram on one screen, and your audio process-
ing modules on another.
• RAM. If you work on large les, and have several audio or video editing programs running at once,
a large amount of RAM is needed to cope with the load.
• A backup hard drive. With hard drive technology so aordable these days, the initial cost of a
backup hard drive is far outweighed by the benets of having everything backed up and retriev-
able—particularly useful if your audio repair or restoration project is for a big client!
Sound Card/Audio Interface
You can use the sound card that came with your computer to monitor audio when doing restoration work,
but we recommend investing in a high-quality sound card or audio interface designed for professional-level
audio recording and playback.
In most cases, this will let you monitor audio with less noise, and will give you higher quality A/D inputs for
transferring analog media to your computer. It will also include professional standard outputs such as XLR
or balanced quarter-inch phone jacks, which will let you connect to audio reference monitors with well-
shielded cables.
Visit your favorite audio retailer to check out a wide range of interfaces at a wide range of prices. Pick one
that suits your needs. If, for example, you’ll be transferring a lot of recordings from vinyl 33rpm or 45rpm
records, choose an interface that includes a ground screw and built in phono preamp.
MONITORING AUDIO
Reliable audio monitoring, as you might imagine, is essential to successful restoration. We suggest a full-
range speaker system that suits your needs, as well as your working space. It’s a good idea to frequently
check your work on other systems as well. As with mastering, the most important advice we can give you
when it comes to monitors is to learn the unique characteristics of your pair and how they sound in your
room. The best way to “learn” your monitors is to listen to lots of recordings that you know well. A good
pair of headphones can sometimes help, as you may want to listen to low-level details that may not be
obvious on loudspeakers.
Room Acoustics
You can have the best reference monitors money can buy, but if you’re working in a tiny square room
without acoustic treatment, you won’t accurately hear the flat representation of frequencies. Even small
details, such as where you place the speakers, will change their frequency response drastically. We
recommend researching room acoustics online. Even if you’re on a budget, there will always be a solution
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that will help improve the sound of your room.
Companies that make acoustic treatment typically have a large number of resources available, and these
resources are designed to help you determine what your space requires.
TRANSFERRING MEDIA TO THE COMPUTER
When you sit down and start restoring an audio project, you might be lucky enough to have a digital audio
file that has either already been digitized, or that began life as a digital format. However, many audio resto-
ration tasks require you to get an old recording from tape, vinyl or other source onto your computer. Here
are some tips for getting the most usable digital transfers of your audio.
Start with the Master Copy
This can’t be stressed enough: always utilize original, unprocessed source audio where possible. Files that
have already been copied from record to tape, or digital files that have been converted to MP3 or another
compressed format like lossy ATRAC, will be more dicult to repair. You’ll face more audible artifacts that
are introduced during the copying and compression process. Similarly, it may be much harder to get good
results from audio that has already had audio repair work done to it.
Input Levels
Whatever your source—tape, disc, analog or digital—it’s important to keep input signals at a moderate level
if you’re recording audio into a computer. A high level may result in inadvertent clipping at the soundcard
or audio interface level. Too low a level and you may not have adequate headroom to accommodate
changes in level as you apply certain processing functions during restoration. Since the noise floor of an
analog to digital converter is fixed, you’ll have a lower signal-to-noise ratio if you record at an unnecessarily
low level.
TIP: Some CD and DAT players feature digital outputs, and many sound cards/audio interfaces have their
own digital inputs. Taking advantage of this can be the perfect way to get digital audio directly into your
computer without having to go through conversion to analog and back to digital.
RECORDING FROM ANALOG FORMATS
Vinyl LPs and 45s
After transferring a record to a computer, you can do a lot to remove noise and improve the quality of the
recording. However, getting a good transfer from a vinyl record can be tricky. Keep these things in mind:
• The vast majority of turntables don’t output a line level signal. They usually require a phono pre-
amp. Phono preamps not only boost the level of audio coming in from the turntable, but they also
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apply special equalization—a part of the RIAA standard for creating vinyl records. Without this gain
and EQ stage, your transferred vinyl will likely sound bad.
• Most audio ampliers designed to work with turntables have phono preamps built in. So too do
professional DJ mixers (many of these also provide excellent balanced outputs suitable for con-
necting to your audio interface). As mentioned earlier, some audio interfaces even have built-in
phono preamps.
• Some turntables now include direct USB outputs, getting around the preamp problem. However,
keep in mind that many of these are very inexpensively made, and that the audio quality usually
suers during the A/D conversion process. Make sure you check the specs before you buy. A good
turntable/audio interface combination may give you better quality and value for money.
• Make sure your turntable is grounded! Mixers and ampliers with phono inputs will usually have a
thumbscrew, which allows you to connect the ground wire from your turntable. Use it! If you don’t,
you’ll probably be adding electrical hum to your transferred le.
• Clean your records! Removing dust with a vinyl brush and/or using a vinyl-cleaning product will
make a huge dierence in the quality of your vinyl transfer. Why spend hours removing dust pops
on the computer? You can get rid of most of them beforehand by simply cleaning your record.
• Use a good stylus. If your record player has had the same needle for 30 years, chances are it’s time
for a replacement. Using worn out needles can aect the audio quality and cause damage to your
records. Some turntables are now hard to nd replacement needles for. Nevertheless, there are
plenty of companies from whom you can purchase a replacement stylus.
• When you have a choice, choose a stylus that is made for archiving. Many available solutions are
tailored to scratch DJs and sacrice sound quality for tracking and other characteristics.
Shellacs, Cylinders and Older Phonograph Formats
There are a wide range of formats out there that preceded the modern vinyl LPs and 45 singles that are
so commonplace today. In general, use caution when trying to transfer these types of recordings yourself,
without the proper equipment. Many shellacs, for example, require dierent, non-standard stylus tips due
to the varying widths of their groove wall. Some formats, like the Edison Diamond discs, have grooves that
capture audio through vertical motion (called the hill and dale method) rather than lateral movement used
by modern vinyl records. If you don’t have the right equipment, consider finding someone that specializes
in formats like this to do the digital transfer for you.
While we could write an entire book on these formats, it’s simply out of the scope of this guide. If this is an
area you’re interested in, you’ll find numerous web sites oering useful information and good tips on 78
RPM history, availability and playback equipment, as well as storage and general care advice.
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Magnetic Tape
There are endless recordings out there made on cassette recorders and reel-to-reel machines. Whether
you’re trying to restore the Watergate tapes, working on reel-to-reel masters, or simply cleaning up old
four-track cassette recordings of your high school garage band, there are a few things to keep in mind
when transferring:
• The quality of your playback equipment will make a dierence. If you connect your old ghetto
blaster’s RCA outputs to your computer, you’ll not only introduce more noise into the transfer, you
might have other unwanted problems like speed uctuations.
• Slight changes in a tape’s speed (called wow and utter) can cause problems when you’re trying to
remove noise. This is because the noise can modulate along with the tape playback speed. It can
make tonal and broadband noise dicult to remove as it changes over time. Work with a well-built
and well-calibrated tape machine if possible.
RX 3 TIP • RX 3 Advanced has a Deconstruct module. You can use this to reduce noise that changes
sound as a result of wow and flutter, and also the time-variable wear found on older 33s, 45s and 78s.
• Tape heads can pick up debris and become magnetized over time, leading to poor playback qual-
ity. Cleaning your deck’s tape head, capstan and rollers can help ensure the upmost quality for
your recordings. You can nd deck cleaning and demagnetizing kits online, and in specialty stores.
• Old mylar/polyester tape can stick to itself over time, which causes tapes to self-destruct upon
playback. If you’re pulling an old reel-to-reel tape out of a dusty archive, you may want to consult
with an expert before trying to play it. Some tapes can be baked in an electric oven to remove
moisture and revitalize the tape’s adhesive, but we don’t recommend you try this at home.
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APPENDIX B: GENERAL RX 3 TOOLS
The following is a list of general RX 3 tools that are extremely useful for the workflow of the audio repair
and restoration engineer.
COMPARING SETTINGS
The ability to easily,
repeatedly and accurately
compare settings—visually
and aurally—with the RX 3
modules is a valuable tool and
timesaver for every project
you undertake. You’ll find the
Compare Settings feature
to be an extremely useful
reference when contrasting
a wide range of choices with
the original.
Using the Compare Settings Window
Find a setting in the module you feel works for a specific situation and then click on the Compare button.
RX 3 will automatically open the Compare Settings window while processing the result of your settings in
the background.
View and change your settings and click again on Compare. RX 3 will add a new item to the list for each
time you click on it. You’ll have an instant comparison with every setting listed in the window.
Notice that the Spectrogram display, as well as the sound, changes each time you select a setting in the
Compare Settings window.
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BATCH PROCESSING
RX 3 oers numerous time savers, and Batch Processing is one of its best. Simply defined, Batch
Processing enables the automation of processing on file groups.
If you have several files that need to be processed in the same way, you can use Batch Processing to
define the set of steps (e.g. denoise, then declick, then normalize), as well as the output format and naming
convention for each. RX 3 will then automatically process all of the files in the background.
Apply Batch Processing to Files
Click File from the upper menu bar, and then click Batch Processing. Click the Add Files button to add one
or more files for batch processing, then choose the processing module(s) you wish to use.
Select a preset for the module, or define your own settings. To view the settings for a particular batch-
processing job, click the View Settings button.
RX 3 TIP • It’s a good idea to use one file to manually establish the settings which can be applied to
the other files that share the same problem.
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Running a Batch Process
Once you’re satisfied with the batch processing jobs, click Process to run them all. You’ll see a progress
dialogue box while RX 3 runs each job. To cancel the current job and all subsequent jobs, click Cancel.
WAVEFORM STATISTICS
Waveform Statistics supplies the audio
engineer with useful information about the
peak, RMS and loudness levels of the audio,
as well as potential warnings about DC osets
and clipping.
It’s accessible via View in the upper menu bar.
EQ
RX 3 includes a 4-band parametric equalizer
module with adjustable notch filters and
low-pass/high-pass filters. This is a handy tool
for cutting or boosting certain frequencies, or
for quickly removing unwanted low- or high-
frequency sounds like rumble and hiss.
The EQ module comes in two EQ Types:
Analog EQ is a non-linear phase filter. The
Linear-phase EQ uses a FIR (finite response)
filter.
The analog filter applies a very dierent
(some say warmer) character compared to the
linear phase filter, which is very precise and
designed to minimize phase shifts in audio. You can easily switch between the two filters to hear which
best suits your project.
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PRESETS
Groups of settings in each of RX 3’s modules and plug-ins can be saved and recalled as presets. Once
you’ve made modifications to the settings in a module, you can name the preset and save it with a custom
filename. Moreover, you can easily export your presets as .XMLs and store them on your computer—
perfect for backup, or to share with other RX 3 users.
KEYBOARD SHORTCUTS
Similar to presets, RX 3 includes default
keyboard shortcuts. For greater flexibility,
you can customize these to better suit your
personal preferences. The keyboard shortcuts
menu is simple, and it will save you time and
increase your eciency.
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APPENDIX C: REPAIRING EXAMPLE AUDIO
Let’s take a look at some real world examples of audio problems and some tips and tricks to help go about
fixing these common problems. To try out these fixes for yourself, download the example les.
EXAMPLE 1: REMOVING BROADBAND NOISE FROM A CONCERT RECORDING
Details:
Player-organ recording in Boston: Vierne Organ Symphony No. 1- Allegro (STEREO). Originally recorded on
Ampex 440-B, ¼” analog tape, zero noise reduction used during session.
Comments:
The principal problem was a steady, low-level
background noise resembling tape hiss. The
challenge was to reduce the noise without
sacrificing upper register harmonics that appear
during quieter passages. The settings used in
Denoiser, particularly threshold, were conser-
vative.
The Spectral Denoiser has some tools that may
help:
• The ‘Broadband’ and ‘Tonal’ reduction slid-
ers can be delinked. There are not really
any tonal elements in the noisy signal, and
reducing them would perhaps aect the
low-level organ harmonics as they fall into
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the noise oor. The ‘Reduction Curve’ has been enabled, and it reducing the high and low ends
more harshly, since this is where the tape hiss is occurring. The curve is also being used to back o
the mid range, where the organ is centered.
• In RX 3 Advanced, you can see the ‘Enhancement’ slider. ‘Enhancement’ is being used to enhance
signal harmonics that fall below the noise oor.
TIP • Examining the waveform of a quiet passage, and checking your program aurally against the
original, helps verify that your material is not being compromised during processing.
Goals:
• Train RX 3’s Spectral Denoiser using a sample of pure noise. Use Denoiser to reduce background
hiss and low-level hum.
• Try not to damage the musical quality of the performance—sometimes leaving a little noise be-
hind is better than taking the life out of the recording! You may want to be conservative with the
noise reduction controls, and use the smoothing options to prevent artifacts.
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EXAMPLE 2:
RESTORING AN HISTORICAL SPEECH: MAKING VOICE MORE IN
TELLIGIBLE
Details:
This file contains the voice of famed philanthropist Andrew Carnegie, recorded in 1914 (Internet source)
(MONO).
Comments:
Some of the words in this speech, recorded by Carnegie in 1914, are somewhat dicult to decipher—owing
to a pronounced Scottish accent, made even more mued by someone’s rudimentary attempt at noise
reduction. In addition, there’s
a steady background noise
present. raise the voice out of
the mud using a slight boost—
roughly between 1K and
9K—and then using Denoiser.
The EQ compensation was
left intact following the use
of Denoiser, as this left the
speech a bit clearer.
Goals:
• Use gentle linear-phase
equalization to lift the
voice out of the back-
ground noise.
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