iZotope RX 4 vs 3 Feature Comparison

It seems like just a few months ago that I wrote an article comparing iZotope’s RX3 audio restoration software with its predecessor, RX2.

At that time, RX2 had been known as a respected tool for polishing troublesome audio. The software hadn’t seen a major update in years, however. So, last year’s announcement of RX3 was met with considerable excitement. It delivered a fresh coat of paint, new tools, and welcome workflow improvements.

iZotope didn’t wait as long to release RX4. It arrived roughly a year after RX3. Does that seem quick to you? You wouldn’t be the only one to think so. Many sound editors understandably wondered what could have changed so quickly to be worth hundreds of dollars in upgrade fees.

I’ve written this article to answer that question. What’s new in RX4? What’s changed? Is it worth your upgrade dollars? Today’s post takes a deep dive into RX4 to learn more about the cornerstone audio repair software.

Contents hide

What is RX?

RX Features and Sound Effects Work

What’s New

New General RX4 Features

New RX4 Repair Modules

New RX4 Production Modules

Changes Between RX3 and RX4

Differences Between RX4 Vanilla and RX4 Advanced

Should You Buy RX?

What is RX?

RX is software developer iZotope’s suite of audio repair tools.

Audio can be damanged in many ways. RX addresses this by focusing on repairing audio by type: crackles, noise, peaks, and so on. The software attacks each problem using modules designed to repair each type of flaw. Examples include Hum Removal, Dialogue Denoiser, Spectral Repair, and others. These modules can be stacked one after another to repair many problems at once, or they can be fixed just one at a time.

The RX software applies these changes in a standalone tool that’s a cross between a two-track editing app and a plug-in. RX also installs regular plug-ins compatible with most pro audio editing apps.

Read more about how RX works in the previous article.

RX Features and Sound Effects Work

I’ve used RX4 in a number of projects since its release in September 2014. I’ve spent dozens of hours buried inside noise profiles. Today I’ll share my observations of what’s changed. So, this post will introduce the features of RX4 and see how it has evolved from RX3.

I won’t focus on audio quality in particular. The point of this post is to help you decide if RX4’s new features are worth upgrading.

How do you decide? Well, it depends how you use RX. Do the changes improve your workflow? Are the features helpful to your craft? Many audio disciplines use RX. Certain tools will be more valuable to some sound pros than others. For example, film restoration pros, mixers, and dialogue editors may have their own opinion of the tools. I’ll explore RX4 from the perspective of sound effects pros: editors, mastering techs, and sound library curators. I’ll also contribute some observations and experiences of my own.

What’s New

So, what’s new?

There are many changes. I’ll focus on just the most significant ones that affect sound fx editors in the current version, v4.01 Advanced.

New General RX4 Features

Major Feature Changes

RX Connect. RX Connect allows clips to be exported and imported back and forth between your editing app (such as Pro Tools) and the RX4 standalone application.

The plug-in zips a selected audio clip out of your editing app and dumps it into RX. Regions, selections, and entire clips can all be transferred with RX Connect. Multiple clips can be exported as well as a single, merged file.

After the audio is transferred, the standalone RX app is automatically brought to the foreground. Any amount of processing or edits can be applied. Then, when fixes are complete, RX Connect sends the polished clip back to the editing app. In most cases, the source track will still be selected from before. RX Connect will replace it with the fixed version. It’s also possible to select a blank area on another track. This will simply dump the repaired clip there instead.

Here’s a video that shows the process:

Why would you do this? Why not just repair the audio in Pro Tools in the first place? Why use RX Connect to export damaged audio and fix it in the standalone RX app?

Well, this process, known as round tripping, offers three significant perks:
1. Improved control. RX’s plug-ins use the same repair algorithms as the standalone app. However, the standalone app offers far more control. It’s easier to compare the waveform with the spectrograph. The waveform is more detailed. The standalone app allows you to rubber-band frequencies as well as timelines, and much more.
2. More repair options. The standalone RX app offers modules not available as Pro Tools plug-ins. The Dereverb, EQ Match, and others simply don’t exist as Pro Tools plug-ins. Notably, as of RX4, the Spectral Repair module is no longer available as a plug-in either. So, if you want to use it in your editing process, you must use RX Connect.
3. Improved workflow. In the past, repairing audio with RX required one of two techniques:
  - Fix audio using the cramped editing app plug-ins.
  - Bounce temp files from Pro Tools to repair your audio in the standalone app after all DAW editing is complete.
  The first was clumsy, and the second was a laborsome two-stage process. RX Connect offers the best of both worlds: do your heavy editing in Pro Tools and clean the clips in RX without disturbing your Pro Tools editing session.
So, how does it work in practice?

I found it was fantastic. It saved a massive amount of time. It allowed me to keep elaborate editing sessions and workflow intact, yet dip out to repair a clip here and there from anywhere in the session timeline. RX Connect is a great way to take advantage of the detail and power of the standalone RX app on the fly.

It was also particularly helpful with de-noising. It’s hard to pluck out a good noise profile from a mastered sound effect. After all, all the good tone may have been trimmed away. However, using RX Connect, I was able to transfer loosely-cut clips with precious room tone on either end. That helped grab the tone and de-noise the clip in RX, then return the repaired file to Pro Tools for final trimming.

RX Connect does have some limitations. It grabs only the audio you select. It doesn’t automatically grab handles, or little bits of audio on either side of selections. Many sound pros find handles offer a lot of flexibility when editing.

Some quibbles: clips sent to RX don’t adopt their region or file name. They’re temporarily given a generic name instead. Also, the exchange process can become derailed if you shorten the clip duration in RX, or return the repaired clip to a different position in the timeline. That caused a few crashes. The transfer process also stumbled if RX wasn’t open already. It wasn’t as smooth sending the audio back to Pro Tools, either. While the revisions were indeed always sent back to the app, Pro Tools wasn’t always returned to the foreground. Again, most of these gripes are small and understandable.

Overall, I felt RX Connect was one of the most significant changes to RX4. It took a bit of time to get used to it, but I now find it indispensable. It’s particularly helpful when editing two hours of field recordings, stacked one after another.
RX Monitor. Insert the RX Monitor plug-in into a track in your favourite editing app. This allows you to work in RX and hear audio playback via your editing app’s monitoring set-up.
Clip Gain. This is a viewing mode that provides point-and-click gain modification on the sample level. This is RX’s version of Pro Tool’s pencil tool, but is much better. It’s easier to use. It changes waveforms on the fly. It’s also non-destructive.
Reverse selection. This tool is similar to other reverse plug-ins. One cool difference for sound designers: it can take advantage of RX’s frequency-selection tool to reverse only certain frequencies instead of the entire timeline.

Minor Feature Changes

Design. The interface has been updated. It’s cleaner and sharper.

RX3 Edit Window

RX4 Edit Window
Timecode support. Right-click the timeline to select timecode options.

RX4 Timecode Option
New codecs. RX4 can export in FLAC and Ogg Vorbis formats.

RX 4 New Codec: FLAC

RX 4 New Codec: Ogg Vorbis
Export marker regions as files. This option has been added to the “Markers and Regions” window.

RX4 Export marker regions
Metadata display. See ID3 tags and broadcast WAV metadata, such as source timecode, and so on.
Documentation. RX is a complicated app. The manual, while lacking in previous versions, continues to improve.

RX4 Documentation
Saving options. Saving methodolgy has altered. The default CMD-S keystroke now saves changes as an “.rxdoc” RX document. That preserves your work in the RX format. Want to save overtop of your existing WAV file as you did in previous versions? That’s now CMD-OPT-S.

New RX4 Repair Modules

RX’s “repair modules” include:

Declip.
Declick & Decrackle.
Remove Hum.
Denoise.
Spectral Repair.
Deconstruct. (Advanced only.)
Dereverb. (Advanced only.)

So, RX4 doesn’t add any new repair modules. It does tweak a few existing modules, though:

Remove Hum. This adds two new options: manual and adaptive.

RX4 New Hum Removal Options
Denoise. Repair time seems to have improved slightly. Here are benchmarks for repairing a 12-second 192 kHz/24-bit file using Denoise’s “D” profile on a quad-core 2.8 gHz i7 machine:

RX Denoise Repair Time Comparison

New RX4 Production Modules

RX4 introduces five new “production modules”:

Leveler. Set a desired RMS level, click the button, and the Leveler dynamically adjusts the clip selection to even out levels automatically. Did your finger slip on the gain knob while recording and created a sudden spike? Is the dog you’re recording wandering up to and away from the microphone? The leveler will even out these levels.

RX4 Leveler

The “speed” setting alternates between precision and subtly. The “amount” setting compensates for the amount of dynamic range. “Noise” is a threshold setting that rejects lower-level audio.
EQ Match. This module grabs a tonal template from one clip, then applys it to another. This can be used to match the tone of music recordings or vocals. Of course, EQ matching will only be as good as the source EQ curve. Could it help sound fx pros? Possibly. It could be handy for matching the tone between multi-microphone field recording arrangements with varied microphones, for example. EQ Match was perviously available in iZotope Ozone.
Ambience Match. This module copies tone from one selection and merges and tucks it behind other audio. It was designed to help dialogue editors apply elusive room tone.

RX4 Ambience Match, tone extracted from selection

To use it, select a clip and click “Learn.” RX4 will intelligently pluck low-level tone from amongst the other audio in your clip. Then, select the new area where you’d like the tone to appear. Click “Process.” RX4 will tuck your newly-generated tone underneath the audio.

It’s important to note that Ambience Match ignores principle audio. So, when learning tone, you can safely select a span of audio with both tone and dialogue. RX4 will ignore the dialogue and grab just the tone. It works similarly when adding tone to new clips, too. It will apply the new tone “behind” any existing dialogue. Simply select an entire conversation and click “Process.” RX4 will slide the tone seamlessly behind the dialogue without damaging the principle conversation at all.

It’s impressive. The tone loops are pretty good. The loop point can be audible at times, but it’s minor.

Can this be used in sound effects mastering? Sure. Click the “Output ambience only” option, choose a long selection, and apply. You’ve created a room tone track ambience. This could have cool applications with sound design drones, too. Confession time: I’ve also used the Ambience Match to smooth out jagged edits beneath atmosphere recordings.
Time & Pitch. Time stretch and pitch shift options. Includes settings for solo (working with a single subject) and mixed (many sounds or subjects together).

RX4 Time and Pitch settings
Loudness. This module alters audio to meet a one of seven loudness standards.

Changes Between RX3 and RX4

RX4 clearly offers many new features. But what’s changed between RX3 and RX4?

The Dialogue Denoiser was previously only available in the RX3 Advanced software. It’s been demoted. It’s now available in all versions of RX4.
The Spectral Repair plugin has been removed from RX4. It’s only available in the standalone app (or via RX Connect).
RX4’s menus are more streamlined and understandable.
The standalone app’s Spectrum Analyzer module has been removed. It is now found in the Window menu item as a floating, windowed display instead.
For some reason, saving files in RX3 didn’t affect pre-existing Soundminer metadata. Changes could be saved repeatedly and your metadata would remain intact. There was no need to re-embed metadata on top of new saves. Now, saving edits in RX4 wipes pre-existing Soundminer metadata. I discovered this one the hard way.
RX4 Advanced adds these new modules:
- Leveler.
- EQ Match.
- Ambience Match
- Time and Pitch
- Loudness.

Differences Between RX4 Vanilla and RX4 Advanced

RX4 is offered in two versions: Standard or “vanilla” ($349) and Advanced ($1,199). How do they differ?

These are the most significant differences:

RX4 Advanced adds new modules: Leveler, EQ Matching, Ambience Match, Time and Pitch, Loudness, Dereverb, and Deconstruct.
RX4 Advanced improves upon existing modules:
- Spectral Repair adds multi-resolution features.
- Denoise includes additional fine-tuning settings.
- There are a few minor features added to Channel Ops, Declip, and others.
RX4 Advanced bundles iZotope’s Insight software.

Should You Buy RX?

So, is it worth upgrading to RX4 from RX3? Should you choose RX4 vanilla or RX4 Advanced?

Overall, RX4’s quality remains high. The software is responsive, and looks great. But you don’t buy RX for its good looks. The core of RX is its audio repair modules. As with earlier versions, each module works well. Of course, successful restoration relies on how much time one has spent with the app. Even so, beginners will be able to get good results from the Declipping and Decrackling modules without too much effort. Denoising and Spectral Repair will benefit from more time spent inside the modules. So, the modules work as intended. Performance and speed changes don’t seem dramatically different than RX3. Just the same, RX’s modules are powerful and indispensable. Many of them aren’t offered anywhere else for the same price. RX is quality software.

But is it worth upgrading from RX3? That answer isn’t as clear. After all, an upgrade is only worthwhile if the new features offer value to you as a sound effects editor.

Part of this is determined by how often you’ll use a feature. Is it worth buying a car if you drive only once a year? I looked at the RX4 improvements the same way. How much would sound effects professionals benefit from RX4’s new features? How often would they use them?

As with RX3, choosing the Advanced version of RX4 unlocks key features sound effects pros will need. In particular, the additional Denoise options add more flexibility and power to sucking out excessive noise floor.

In addition, RX4 offers RX Connect. That’s a significant improvement. Since RX4 removed the Spectral Repair plug-in, RX Connect is the only way to access that module from Pro Tools. (You may also use the RX3 plug-in in parallel.) RX Connect also streamlines a sound pro’s editing workflow considerably.

What else? Hum Removal’s adaptive mode may help editors deal with cycling HVAC and flourescent hum.

Of course, RX4 Advanced adds five new modules: Leveler, EQ Matching, Ambience Match, Time and Pitch, and Loudness. These are excellent modules that work perfectly. Will a mixer use them often? Yes. Dialogue editors? Absolutely. However, the new modules don’t compliment a sound fx mastering tech as neatly as other audio pros.

The Loudness module isn’t relevant to sound fx library mastering. Other features are duplicated by existing editing software. For example, some may claim that skillful mixing sidesteps the need for the Leveler tool. Additionally, mismatched audio levels are rare in field recording. Clip Gain is a handy tool while repairing audio, yet overlaps Pro Tool’s pen tool.

Similarly, EQ Matching also has limited use for FX crew. Competitive EQ-matching products Elevayta’s FreEq Boy ($29.95) and Voxengo’s CurveEQ ($89.95) may be more economical options.

Sound fx editors will continue to get a lot of use from RX4’s Denoise and Spectral Repair modules, which are both excellent. Mastering techs will commonly turn to the Clipping and Declicking modules. All of the repair modules are reliable and exceptional. But those are included in RX3 already. The RX4 counterparts offer minimal changes.

And the other modules? While impressive, the new modules aren’t really designed for sound fx pros, and will find limited use. There is one exception, however: RX Connect is a powerful workflow tool that may be worth the price of admission alone. So, upgrading sound pros will need to ensure they will get enough use of the improvments to justify the cost.

And those of you new to RX?

RX is exceptional audio repair software. The tools are sensible and easy to use (yet difficult to master). It’s capable of repairing even serverely damaged audio and recovering mistakes made in the field. You won’t be disappointed by having it in your editing arsenal.

Download a 10-day demo of RX4.