iZotope RX6 Advanced: Versatile Audio Fixer

High-powered audio suite can “see” what is wrong with your audio … and fix it

Cambridge, Mass.-based iZotope produces software for mobile and club DJs, radio, sound for video, as well as measurement and metering. However, this review will focus on the company’s professional post-production tool, RX6 Advanced. Retailing at a hefty $799–$1,199 (an upgrade from a previous version is only $399), this package is for serious folks who earn their living from sound design, editing narration, and in particular, improving flawed audio from outside sources.

The spectrograph with the De-ess tool open.
The Voice De-noise tool provides numerous options for fine-tuning it operation.

I have used various noise-reduction and audio repair software over the last 25 years including DINR, now offered as a plug-in from Avid, and CEDAR, the U.K.-based noise reduction pioneer. I am pleasantly surprised at how differently RX6 Advanced operates. The user interface offers two ways to view audio: as the familiar waveform or as a spectrograph. You can also select any balance of the two, which are provided in contrasting colors for easy viewing: blue for waveforms along a timeline on the X-axis, and amber for frequency on the Y-axis. A slider allows you to select how much of each is seen.


I now find myself editing visually first and aurally second because one glance at the spectrograph shows me many common problems.

It is quite obvious when there is a nasty plosive, which shows up as a bright yellow blotch in the lowest frequency range. Similarly, I now can easily spot a sibilant “S” which appears as a vertical streak of bright yellow in the mid-range. General noise manifests as a hazy blue curtain, usually in the upper frequencies where hiss resides. Of course, before I make any changes to my audio I verify what I am seeing by listening, usually with earbuds or headphones to get the most detail.

Viewing this two-track editor in waveform mode provides the best way to work in a linear fashion, such as shortening a pause or removing a bad take. Usually the spectrum view is best for spotting potential problems in the audio itself. But RX6 Advanced has much more.

It would be impossible to detail all 40 of the production tools, but they are explained at the company’s website, www.izotope.com. While you will probably use a few modules repeatedly and some hardly ever, it’s worth checking them all out because you may discover a gem.

As an example, I had never investigated a repair tool called “interpolate.”

Much of what I use RX6 for is restoring ID jingle packages from the 1960s and 1970s, which were recorded analog on magnetic tape. One problem these relics often evidence is dropout, wherein the audio goes missing for a fraction of a second at points where the tape may have been creased or the oxide wore off. I zoom into the spectrograph view until I see a dark vertical line, which represents a disruption in the audio. I highlight just the dark line and hit “interpolate,” using the default setting. RX6 fills in that tiny fraction of a second using material from either side, all of which occurs in a flash. And then when I play that section back, the dropout has vanished.

Other useful tools in my workflow include “Spectral De-noise,” which takes a fingerprint of the background noise in a quiet part of the material, such as right after a song, or between paragraphs of a narration. Then I select the entire audio track and run this process. In a few seconds I have a cleaned up the offending noise. If necessary, I can make a second pass using a different section of noise as a sample.

With other software I have used there always seemed to be some unwanted resultant artifact such as a twisted reverb trail or a strange out-of-phase sound where noise reduction was used, but you can push RX6 Advanced hard and still not affect the underlying audio.

RX6 Advanced provides a “find similar” tool for locating and isolating for treatment repetitive annoyances such as chirps or squeaks.
RX6 Advanced can overlay spectrographs and waveforms.

For narration, I use several modules including “Breath Control” (which attenuates or removes breaths between phrases), “Mouth De-click” and “De-mouth Smack.” Then I run “De-plosive” to get rid of those overly aggressive Ps and Bs. The results sound quite natural. Again, each of these processing passes takes just a few seconds, and you can set-up an automated chain of your favorite features, in the order you choose, with the settings you want. This is a time-saver when multiple files require the same treatment.

I had often heard that one problem you could never fix was analog distortion. Once a microphone was over-driven it was all over. No more! Now you can highlight such an area and select “de-clip,” which rewrites those distorted peaks and makes the annoying break-up go away. There are YouTube videos that demonstrate this as well as all of the other audio restoration tools.

Besides running these processes across an entire audio file, you can also visually isolate an item you wish to remove, such as a truck horn beeping during an interview. You can see irritants like these as little yellow horizontal lines in the spectrograph. Select one of them using your choice of tools, then either greatly attenuate it or erase it entirely, filling in the space with surrounding material. If there are a number of such interruptions, use the “find similar” function and RX6 will identify everything that looks like your annoying beep and all can be treated at once. I was even able to remove some idiot’s shrill whistling amidst the applause during a recording of a concert. No one will know it but me.

But one feature still puzzled me, the “leveler.” It seemed to operate like a compressor, but not quite. I asked Mike Rozett, product manager for RX at iZotope, to explain.

“The ‘leveler’ automatically rides the gain in your file to even out the variations of the signal level,” he said. “The algorithm consists of a compressor with a makeup gain to achieve a smooth signal that’s aiming towards [though may not exactly hit] a desired target RMS level. The compressor has the ability to prevent pumping on speech pauses or breathing sounds, using the optimization mode, for either dialog or music. The level detector stage includes the K-weighting filter that helps equalize the audible loudness, not just RMS level. However, the ‘leveler’ module is designed for the smoothing of overall audio signals, rather than taking an entire signal and using a fixed gain to ensure it hits a loudness compliant LKFS level [Loudness, K-weighted, relative to Full Scale], which is the goal of the loudness module.”

Product Capsule

Audio Restoration Software

Thumbs Up

+ Innovative visual design offers the ability to view both waveforms and audio spectrum simultaneously or individually
+ 40 individual modules for repairing virtually any aspect of a narration track or musical recording
+ With practice and patience, the individual modules do an excellent job at their stated purposes
+ Good online support in the form of knowledge base and videos

Thumbs Down

– Lengthy wait time while repair modules work on longer audio segments
– Some modules have confusing or at least nonintuitive settings
– Price point makes this a tool that only professionals can afford
– Some overlap in module function is confusing

Price: $1,199 retail, starting at $399 to upgrade from earlier versions

For information, contact https://support.izotope.com

I have raved about many of the features of this versatile software, yet I could find very few negatives other than the wait time while a process runs on a long audio file. That is a first-world problem and far from a serious flaw. Thus I asked the RX product manager about common user complaints he has received.

“We hear two things pretty consistently,” Rozett told me. “The first is that most users would like to have more plug-in versions of our modules so that they don’t have to leave their DAW. Another aspect of RX that we are pretty aware of is the CPU cost. We always strive to optimize software but we would rather give the user more processing power.”

In summary, iZotope RX6 Advanced is a powerful and fairly intuitive product, once you understand the concept of viewing audio as both a waveform and spectrograph. While this took some getting used to, it was really worth it to enjoy such a diverse palette of audio repair and enhancement tools.

It should also be noted that iZotope offers cheaper noise reduction packages based on the same technology but lacking some of the fancier, higher-end tools.

Ken Deutsch is a recovering disc jockey and now works as a closed caption transcriber for the deaf. He has written two books about radio jingles, which are available on Amazon.

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