iZotope RX 2 Advanced review: pt.3/3

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The other rather exiting tool which is included is the ‘Spectral Repair’. It’s designed for Intermittent Noises allowing you to select and remove intermittent noises and replace them with re‐synthesized content based on the surrounding audio. It also claims to resynthesize gaps in audio, sometimes of up to a half second long or more, by using information around the gap to fill in the missing information using patterns and advanced re‐synthesis. I was instantly drawn to this as I couldn’t quite believe what they were saying! So I had to put this to the test!
The first thing you’ll need to do is choose from one of Spectral Repair’s four processing modes. Each of these modes uses a different technique for making a repair. You may want to try each of these in turn on the same noise to see which works the best. Here are some general guidelines on how to use each:

This mode is great for blending noises into the background of a recording and making them inaudible.
Unlike Attenuate mode which gently blends the selection into the background, Replace mode completely resynthesizes the selected area. Replace mode works very well when there is a sustained musical part or other tone that is interrupted by an unwanted sound, and can also be useful when removing noises from dialog. This mode can also be used to close up gaps, dropouts and corrupted sections of audio.
This mode searches for a pattern in the surrounding material and uses it to replace the selection. Pattern mode is particularly useful for gaps and badly damaged or corrupted sections of audio. Try using Pattern mode on drop outs in rhythmic parts like drum tracks—it can work wonders.
This mode can be thought of as an advanced version of Replace mode. It is also a good choice for sustained musical material and tones. When used carefully it restores harmonics of the audio more accurately. It can even track changes in pitch between the beginning and end of a gap. Partials+Noise mode links detected harmonics by synthesizing them through the selection, and interpolates the rest of the signal using the Replace method.

I thought I would try out a few different types of audio, a sustained orchestral sound, an evolving pad sound and a drum beat to see how this worked out.

First of all have a listen to this drum beat

Now hear it with slices cut out of the file.

And its Spectrograph.

Using the Replace algorithm have a listen to the results

And its Spectrograph.

The results are not as I expected. There are some obvious problems here and despite taking a lot of time to correct this I couldn’t get anywhere near how I wanted it. But to be honest I did like the new artifacts that have been produced and I could see how this could be useful for creating new sounds altogether.

Now with the Orchestra I decided to use the Partial+Noise algorithm as this is meant to do more complex sums.

First of all have a listen to this Orchestral sustained note.

Now hear it with slices cut out of the file.

And its Spectrograph

Using the Partial+Noise algorithm have a listen to the results

And its Spectrograph

I was particularly happy with the results of this. There are no obvious deviations unless you really listen hard and to be honest I dont think you would notice this when used in the context of a mix. I must also applaude how well it performed on the decay of the note too.

Now with the evolving pad sound which I again decided to use the Partial+Noise algorithm.

First of all have a listen to this Pad sound.

Splice Sounds

Now hear it with slices cut out of the file.

And its Spectrograph.

Using the Partial+Noise algorithm have a listen to the results

And its Spectrograph

Again I feel this worked really well and even the chorusing effect on the sound is maintained to a degree. I noticed that the Partial+Noise algorithm took much longer to process than any of the others and with any of these algorithms. I found the more audio you gave either side of the ‘gap’ for it to analyse produced better results. Please note though that the Spectral Repair does not work in Logic as Logic does not support offline processing.

On top of all of these audio repairing tools there are some other more general tools which can be applied to specific sections or the whole file such as EQ, Gain, Resampling, Dithering, Pitch and Phase adjust. I was particularly impressed with the flexibility and overall quality that these plugins provided and also the ability to focus on specific parts of the sound by using a kind of ‘magic wand’ toll which you would find in Photoshop. By simply highlighting areas which it can do for you or by manually drawing around areas you are then able to apply these effects to those parts alone. So for example, using the spectrograph you can easily highlight all the upper harmonics or even the fundamental frequencies and pitch them, phase them, EQ, and Gain them as you wish turning this whole program into a sound design program. Additionally you can load your installed AudioUnits and VST plugins right inside the standalone program and edit the sound in the same way using them. Again this really turns the program into a sound design tool in some respects.

iZotope RX 2 is the most complete and expansive audio repair toolkit on the market, enabling you to remove noise, hiss, buzz and hum, eliminate clicks and crackle, restore clipped audio, visually select and suppress unwanted sounds, resynthesise missing audio and much more. There is no doubt in my mind that with some time and patience you can manipulate audio to such an extent that you wouldn’t know it has been. Perhaps some of the processes do take a long time to do, but ultimately quality comes at a price and if it means I can drink more tea while I am at my desk then thats not a bad thing. You could always leave the program to do its job utilising the batch processing while you get on with your other mixes. Perhaps it would be great to use all of the plugins in series and hear multiple effects being applied at once without committing to a particular process before moving on, but I have a feeling that even the most advanced computer would have troubles computing these tasks. As I have also mentioned the sound quality is fantastic and the whole Spectral Repair tool blows my mind, opening up the possibilities for sound design.

iZotope RX 2 $349
iZotope RX 2 Advanced $1,199
(check the features comparison on the first page of the article)
A demo version is available, saving is disabled.

…RX 2 is the most complete and expansive audio repair toolkit on the market…

Product page


  • Precise restoration functionality
  • Spectrogram make editing a whole new experience
  • Spectral Repair blows my mind


  • Perhaps too much to handle for the average user


  • The Advanced version is not cheap
  • Some tasks are hard on the CPU

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