Review: iZotope's RX 4 Advanced
Erik Vlietinck
Issue: November 1, 2014

Review: iZotope's RX 4 Advanced


PRODUCT: RX4 Advanced

PRICE: Advanced: $1,199; RX 4: $349


iZotope’s RX 4 Advanced sound repair kit is the most advanced audio repair software available. The latest version contains several new modules, including Clip Gain, Leveler, EQ Match/Ambient Match, Dialogue Denoiser (RX 4) and RX Connect.

The RX Connect plug-in that comes with both the RX 4 and RX 4 Advanced is a DAW plug-in to either analyze an audio clip or repair it. There’s one plug-in with two different ways of working. With ProTools, you can select multiple clips and the plug-in itself is selected from the Noise Reduction category in the AudioSuite menu. In other DAWs on the Mac, the plug-in must be loaded as an AU or VST effect. I tested the plug-in with Logic Pro X and found I didn’t need RX Connect to roundtrip with RX 4. The integration with Logic Pro goes deeper, as Logic Pro X supports External Sample Editors.

I could test RX Connect with Sony Sound Forge Pro, though, and in repair mode I could roundtrip between the two apps. iZotope also found a way to circumvent the monopolization of the system’s audio drivers by some DAWs. This monopolization prevents RX 4 from playing audio through the same audio device, but the RX 4 Monitor plug-in solves that problem. 

One of the most important new features of RX 4 Advanced is Clip Gain. A Clip Gain envelope allows you to adjust the gain of an audio clip over time and consists of nodes on a curve. The curve or envelope initially is a straight line, representing no change in gain. By clicking the curve, you add nodes at your preferred time intervals, e.g. where you want to increase or decrease the gain. Clip Gain envelopes allow you to fade in/fade out parts of your audio, adjust the gain of individual nodes and adjust the gain of an entire envelope selection.

The concept of an “empty” envelope, which allows you to drag gain nodes as you go — visually correcting gain — is incredibly intuitive, but it can take much time on a file with many gain problems. However, iZotope has made it so that the envelope appears populated with as many nodes as necessary when you first use the Leveler module (RX 4 Advanced only) and then select the Clip Gain option from the View menu. 

Your workflow will obviously dictate what you prefer, but the envelope itself, being fully controllable by dragging control points, really gives you an edge when quickly adjusting clipped sound or boosting parts that were recorded with gain settings that were too low. 

Clip Gain is going to be a real boon for the video post production crowd, especially when correcting recordings of interviews or other sounds by amateurs. “Quick-and-dirty” video journalists are becoming more important in today’s online publishing environment and they don’t hire professional and dedicated sound engineers who continuously adjust recording levels. Instead, many times they set their audio level at some default value when they start recording and leave the value at this setting throughout the recording — audio really isn’t their “core business.” But the value may become too low or too high over the course of the entire recording time. The Clip Gain envelope then gives a very easy, very visually-rich way to quickly correct for such under/over “exposures.”

In RX 4 Advanced, the Leveler module will automatically ride the gain to even out the variations of the signal level. The algorithm consists of a compressor with a makeup gain to achieve the desired Target RMS level. The compressor has the ability to prevent pumping on speech pauses or breathing sounds. The level detector stage includes a K-weighing filter that helps equalize the audible loudness, not just RMS level. The result is much the same as when you would be adjusting the Clip Gain envelope yourself, only much faster and in some circumstances better and more accurate and tight.

Unlike the Loudness module, which applies a constant gain to the whole file, Leveler applies a time-variable gain. The Loudness module is great when you need your audio file to comply with one of the current broadcasting loudness rules, such as EBU R128.

Of course, the modules that were already time-savers in RX 3 are still there. Dialogue Denoiser, for example, is now available in both RX 4 and RX 4 Ad-vanced. I’m still amazed by how accurate the automatic Dialogue Denoiser is. You can fine-tune by having the Dialogue Denoiser learn and then adjust the levels yourself, but it’s rarely ever needed.

That, by the way, is the reason why iZotope RX 3 and now RX 4 have such an appeal to professional sound engineers as well as semi-pros — the ability to automate pretty much every aspect of correcting audio and still return home with a good result.