Edit Review: iZotope RX
Feb 1, 2008 12:00 PM, Reviewer: Gary Eskow
Audio editing application offers creative audio-restoration features.
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.
Denoiser
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.
