Edit Review: iZotope RX

iZotope RX audio-restoration software comes in basic and advanced versions. The functions in RX Advanced give you deeper editing control, but at a steeper price point.

During the post process, how often do you find problems with audio captured in the field? Frequently — particularly if you're using the microphone that comes with your video camera rather than one that's synced to it. Even if you have an excellent audio-capture plan in place, there are certain problems that can't be avoided in real-world situations, including clipping, dropouts, and the presence of AC hum. You just have to contend with these issues in post.

Fortunately, over the last several years, software companies have introduced a number of restoration packages that help clean up poorly recorded audio material and tracks that suffer from these problems. Some of these products are components of larger applications. Last December, for example, I reviewed the spectral tool that ships with Adobe Audition 3. (See digitalcontentproducer.com/soundforpic/
revfeat/adobe_audition_2) This time, I'll take a look at iZotope RX, a nifty application that offers several functions that similar products don't.

RX is available as a download that can be purchased directly from the company's website, www.izotope.com. It's available as a standalone application, and just this month, it was also released as a plug-in that will work in your favorite digital audio workstation. RX can run on either a Windows or Mac computer, and all iZotope products, including RX, are compatible with Mac OS X 10.5 (Leopard). RX can be purchased in one of two flavors: basic and advanced. We'll discuss the differences during the course of this review. If you choose to purchase the basic version, you can upgrade to RX Advanced later.

The main screen of this application is uncluttered and pleasing to look at. An overview of the entire waveform appears as a narrow image at the top of the screen, and a larger, zoomable view sits directly below it. Using these two views in conjunction with each other is critical because the application doesn't have a scrub tool, which I would like to see. Fortunately, it's easy to set markers around a section of your waveform if, for example, you're trying to isolate a single offensive pop or digital clip: Zoom all the way in on the bottom screen, and then slide the view backward and forward using the upper view.

Removing offensive broadband noise is perhaps the most essential task that any audio-restoration product needs to be able to handle, so I started my review by throwing an extremely difficult problem at RX. I have a recording of a concert featuring a soprano and classical guitarist that was recorded directly to cassette tape in the late 1970s. This recording was handled well, but cassette recordings have an inherent hiss, which the ensuing years have exacerbated. Additionally, on quiet material such as this, the presence of transport noise is almost impossible to avoid.

At just less than an hour, this file was too large to be imported directly into RX, so I opened it up in Steinberg WaveLab 6, set CD markers around the individual numbers, and exported several of them as separate .wav files, which RX was able to open. (Note: iZotope claims that RX is able to open files even longer than this complete one.) Using the tools available in the basic package, I isolated a noisy portion of the file and hit the Train tab, which tells RX to take a profile of this section. I then applied this profile to the entire song.

How well did RX perform? Better than any other application I have put to this particular test. The noise reduction was almost complete, and the application detracted nothing from the audio that remained that I could detect. However, the second test of a section of the guitarist on the same tape was even more difficult because it was recorded much too softly. Under the same settings, RX introduced a flanging effect that I hadn't noticed in the first track. It sounded to me as if by removing the noise, it amplified and distorted the sound of the cassette motor. After several passes, I ended up with a compromise file that kept some of the noise and avoided most of the distortion. I then opened up the doctored file in WaveLab 6 and raised the level by 4dB.

RX has a nice way of handling the all-important preview procedure. You can get your settings in place and tell it to preview in realtime. Alternatively, order RX to compare these settings with the original audio, and a screen pops up that lets you toggle between the two. When you're satisfied with the results, hit the Apply button and save your work. RX also has a strong Undo component that lets you restore your file to its original state — even if you have closed the application and had a few beers in the meantime.

The Denoiser also has an Auto-train function, which works very well on audio that has no passages of noise that are in the clear. Both versions of the application divide the audio spectrum into tonal and broadband segments and give you independent control over each — but the control options are deeper in RX Advanced. I used these controls on several selections, but at this time, I'm unable to say with certainty how valuable they will turn out to be in the long run.

The manual that comes with the application is skimpy, and the terminology iZotope uses, such as “residual whitening” and “musical noise suppression,” is not standard. To be fair, iZotope is constantly updating the manual based on user feedback, and tutorials that cover the application's feature set can be found online. Nonetheless, I would have to spend a lot more time working on multiple files in both versions before determining whether the substantial price of the advanced version is vital for getting excellent results from RX.

No matter how careful you try to be, the time will come when your signal has been recorded too hot. Clipping — particularly the digital variety — is obnoxious. Fortunately, the Declipper in RX is quite good. Reversing the effect is a fairly simple procedure, and this function is the same whether you're using the advanced or the basic version of RX. You can choose a multiband processor, but most of the time, single-band mode will work fine. You'll be able to scale back the offending portions of your audio with just a little experimentation with setting the threshold level.

Although they can be used to fix a myriad of problems, Declickers are most often the go-to tool when vinyl recordings are transferred to digital media and the operator wants to remove the damage that phonograph needles introduced to the original. The RX Declicker will eventually get the job done, but it cannot process — or even preview — more than 4 seconds at a time in either the basic or advanced Manual mode. If you need to preview your work in even a slightly longer context, you must use the Automatic mode, which offers you control over the sensitivity of the operation and the width of the audio that you're attempting to declick. For detailed work, you need to zoom in to a particular click, zap it, and then listen to it in context. If you're unsatisfied with the results, you can undo your operation. I did not find the Declicker to be the most intuitive or effective component in RX.

Air conditioners — can't live without ‘em, but they can wreak havoc on your audio tracks. In order to get the most out of the Hum Removal tool in RX, you need to be comfortable working with filters. Hum Removal is essentially a powerful multiband equalizer that lets you isolate the frequencies where line noise is most often a problem (50Hz and 60Hz), or operate in Free mode. In Free mode, you can roam freely across the audio spectrum searching for the exact spot where a problem occurs and attenuate it appropriately. If you're timid about working with filters, don't worry — the presets in Hum Removal should solve most of your problems.

As I mentioned in my Audition review, spectral analysis is one of the hottest areas in audio-restoration work, and the hype is justified. There's something magical about visually identifying an unwanted sound — a car horn blasting away during an interview, for example — and zapping it instantly without compromising any of the material that surrounds it.

RX's Spectral Repair has something special going for it. If your audio includes a temporary dropout — lasting less than a second or two, ideally — Spectral Repair can help enormously. Instead of simply borrowing material from either side of the gap and smudging it into the empty space, Spectral Repair analyzes the data on both sides and does its best to create audio as it would have appeared had there been no disruption of signal.

For example, iZotope sent me a sine wave that sweeps from low to high. This file has a gap of approximately 1.5 seconds in it. By creating a region around the gap, zooming in all the way in order to butt the edges of the region right up to both ends of the remaining sweep, and instructing Spectral Repair to do its thing, I was able to fill in the sweep perfectly. Impressive.

On the other hand, no application I've seen so far, including RX, beats the Pan View feature that Audition 3's Spectral Frequency display offers — particularly when cost is factored in.

Is RX the right tool for your studio? A better question might be, does RX — or any other piece of software — have anything going for it that other applications don't? In my opinion, the Denoiser alone makes RX (the basic version, at least) a worthy contender for almost any audio studio that does repair work. Even if you're looking for a Swiss Army knife and can only afford to purchase one application of this kind, the RX demo is worth downloading and checking out.

Company: iZotope www.izotope.com

Product: RX

Assets: Outstanding Denoiser and spectral synthesis function, basic version provides high performance value.

Caveats: Advanced version expensive, confusing nomenclature, Declicker requires finesse.

Demographic: Audio post professionals looking for an effective noise-reduction tool and videographers who work on their own audio tracks and need an all-in-one toolset.

PRICE: $349 (BASIC); $1,199 (ADVANCED)

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