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Breaking Down iZotope’s RX 4


A while back we reviewed iZotope’s RX 3 Audio Repair program, and with their RX4 version now on the market, we’re offering this update to cover some of the new features added to the program.

Many of the modules are pretty much the same, though the user interface has been updated. We didn’t find much difference between the RX 3 and RX 4 in the Dialogue Denoiser, Declick, Denoiser, and Dereverb modules, though Dialogue Denoiser is now available in both Advanced and regular versions of the program. They all worked just as well in RX 4 as they did in RX 3, with no drop-off or noticeable improvement.

There was a slight change to the Hum Removal module. In RX 3 you chose the fundamental frequency, like 50Hz, for the hum in your clip, and that was that. If the hum shifted at all, you had to manually adjust the notches yourself. But in RX 4, you can set the Hum Removal module to Adaptive mode and let the module track the hum for you. For instance, if you have an analog recording where the hum moves frequencies slightly, maybe dipping down to 49Hz or up to 52Hz as the clip goes on, the ‘adapt’ feature in Hum Removal can follow the fundamental frequency of that hum as it shifts and adjust the other notches accordingly, ensuring a much more complete removal of the hum from the clip.

The biggest change between RX 3 and RX 4 is the addition of RX Connect as an AudioSuite plugin. Basically all this plugin does is act as a bridge between your DAW and the stand-alone RX 4 program. You select a clip you want to process, click “send,” and the RX 4 stand-alone program opens up and you can repair the audio. Once you’ve finished, you need to send it back to your DAW, then render it out. IZotope says this is so you can repair a clip without slowing down productivity, while taking full advantage of all the tools RX 4 has to offer within the stand-alone program. However, we found it frustrating to use, mainly in regards to Spectral Repair. In RX 3, Spectral Repair was its own plugin in our DAW. But to now use Spectral Repair, you must first go through RX Connect, send the clip to the RX 4 stand-alone program, repair the audio, send it back, then render it, adding more steps to the process. Is this the end of the world? Of course not, and after time, we’re sure it would become second nature to use RX Connect to send clips to the stand-alone program. But we felt it was a hindrance in our workflow, at least during the time we were using the tools.

However, once you’ve made your peace with the fact that you need to send your clips out of your DAW to use the RX 4 modules, you’ll find there are a lot of useful tools to utilize. In addition to the Spectral Repair tool, the new features in RX 4 include Leveler, EQ Match, Ambience Match, and Loudness.

Leveler is essentially a normalizer, but it’s much smoother than any normalizing tool we’ve ever seen. That’s because instead of applying clip gain over the whole clip, then compressing it to prevent clipping, the Leveler actually mixes the clip – it uses nodes and dips down for loud sections and ramps up for softer sections. Really, instead of Leveler, it should be called Mixer, because that’s essentially what it does. It works well with documentary-style interviews and was also impressive with recordings from the field. It’s still faster for a rerecording mixer to use his own nodes in the DAW or ride the faders rather than process every single clip, but if someone had hours of raw recorded material, this could be a useful tool to balance the audio before editing a piece together.

And if you don’t like having the program do your mixing for you, RX 4 has a non-destructive clip gain feature that allows you to create your own nodes and raise or lower the gain throughout the clip manually.

EQ Match allows the user to read the EQ curve from one clip and apply it to a second clip. This is useful for matching ADR or any instance where production has given you audio from two different types of microphones. It works best when the two clips are recorded in a quiet setting with similar room tone. We tried using the EQ match on a clip recorded in-studio as ADR to audio recorded in the field, and while it helped some, we still needed to go through additional EQ processing from another plugin to match the clips. One welcome feature on this module is the ability to adjust the smoothness of the EQ curve, giving you the ability to soften the EQ processing if the mics are similar and just need a little touch of EQ matching.

Anyone who has received a timeline from a video editor knows the pain of finding a dialogue clip cut up with obvious gaps in ambience, and having to go through and try to pull out the heads and tails of each clip to find some ambience that’s a) clean, and b) actually matches the rest of the background noise in the dialogue clip. Too often you find just a small section of ambience that kind of works, then you have to loop it and edit it to make it sound natural, then boost the music bed to hide what you’ve done, and then maybe you’ve solved the problem. All that work is a thing of the past with Ambience Match. Ambience Match allows the user to analyze the background ambience in a dialogue clip and create a new clip of only the ambience, to fill those gaps. And the best part is, it sounds pretty good. We tried it on a noisy dialogue section at night with wind and crickets, and the Ambience Match module created ambience beds for the gaps that were nearly seamless. Huge props to iZotope for adding this time- (and headache-) saving module in RX 4.

The Loudness module is a loudness compliance tool. It allows users to process a clip to ensure it meets any loudness standards required in their specs, such as BS.1770-3. Since the CALM Act was introduced here in the United States, we’ve had to find a way to preserve the integrity of our mix, the “life” of the mix so to speak, while remaining compliant with the required levels set forth by our network clients. Templates were created, and extra paths for signal flow were necessary, but this module eliminates all those extra hoops. Now, we can finish off an entire mix, create the audio stems necessary for delivery, and before sending them off, use the Loudness module to analyze our finished product and process it to ensure we are compliant with the required levels set forth in our specs.

Overall we found the new modules to be welcome additions to the program that are both useful and easy to use. iZotope’s RX Audio Repair program may be the best overall audio repair tool on the market and these additions only serve to bolster that claim.


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