RX by iZotope has long been a top application for audio restoration and noise reduction. In addition to being a staple in post-production houses, RX’s feature set is also quite useful for music production. In this article, I’ll look at ways in which you can use it to help eliminate sonic issues on your recordings. RX is a deep program with a huge number of features — too many to completely cover here. Instead, I’ll focus on the ones I’ve found most helpful when producing music.
RX is offered in three versions. RX Advanced ($1,199) contains the complete feature set. RX Standard ($399) has fewer features, but still has most of the ones I’ll be discussing in this story. The least expensive version, RX Elements ($129) has only a few features and is missing most of the tools covered here, so it won’t be in this discussion.
RX is an audio editor with a modular set of tools that can be opened individually and applied to entire files, sections of files, or even, multiple files together.
The application interacts with various DAWs differently. In many, you can designate it as an external audio editor and open up files in it from within your DAW. Pro Tools has the most extensive file-exchange integration with it, via the RX Connect plug-in. Any region you select in a Pro Tools track can be sent to RX for editing using RX Connect as an Audiosuite plugin, and then brought back into Pro Tools and rendered over the original file.
In addition to running as a standalone editor, many of RX's tools also come as individual plugins that you can open right in your DAW. Whether you use the standalone or the plugin depends not only on which modules are available as plugins, but how you want to apply the processing. The plugins mainly apply their correction non-destructively, which gives you options for changing settings as you get deeper into the mix process.
SPECTRAL VS. WAVES
One of the unique parts of the standalone version of RX is its display, which gives you a standard waveform display overlaid on a spectrogram (see Fig. 1). A slider lets you change the ratio between the two display types. The default is a 50:50 ratio, but you’ll find yourself adjusting the position of the slider depending on what you’re doing. Once you get used to editing in RX, you’ll see how powerful the spectrogram is for spotting glitches and other characteristics of the audio.
Let’s look at some of the key ways you can use RX in your music production workflow. Space doesn’t allow covering every aspect, but here are the most significant ones.
DON’T FREAK OVER A SQUEAK
One of RX’s most potent modules is Spectral Repair, which can be used to get rid of glitches in your audio without damaging it. One of the most common applications for it is to remove finger squeaks from recordings of guitars, basses and other stringed instruments.
You start by selecting the squeak or glitch in the display. Spectral Repair looks at the audio before and after the glitch (or above and below it, if you choose the Vertical option), and using interpolation, creates a replacement for the selection that represents what the audio would have been had the glitch not been there.
Like most of the processes in RX (or any audio restoration software), the trick is to apply it as subtly as possible. The Spectrogram display is particularly helpful when using Spectral Repair. Loop the area right around the squeak and play it back while looking at the display. You’ll quickly learn how to visually identify squeaks and other glitches, which appear irregular compared to notes from an instrument or voice (see Fig. 2).
Once you’ve figured out where the squeak is, you can use one of RX’s selection tools to select it, and then apply a repair algorithm. For most squeak situations, you’ll use the Replace option. However, there will be times when you may want to go with the Attenuate algorithm instead. Rather than replacing the squeak completely, it reduces the level of the glitch in a natural-sounding way.
After processing, if you hear any degradation of the instrument sound where the squeak was removed, undo it and try making the selection a little smaller, or adjust one of the parameters. These include Surrounding Region Length, which shortens or lengthens the area around the selection that RX makes its calculations from. Also, Before/After Weighting, which lets you skew the results towards before or after the selection.
Spectral Repair is not just for squeaks. You can use it for getting rid of many types of glitches including one that plagues many recordings, a random noise such as a chair squeak, accidentally recorded at the end of a track when the last note is ringing out.
WEED OUT THE BLEED
The De-Bleed module is a powerful tool for reducing or removing leakage, such as the click track bleeding onto an instrument or vocal track. In order to work, De-Bleed requires two different files that are time-aligned: the track with the bleed on it (called the Active Track), and the track that caused the bleed (the Bleed Source Track). Sometimes, duplicating each track and using the new copies as Sources only can generate better results on both the original tracks.
De-Bleed also works amazingly well with drum leakage. For example, I was mixing a song where the snare and kick tracks leaked significantly into each other. De-Bleed allowed me to remove most of the kick from the snare track, and virtually all the snare from the kick track. It sounded more natural than using a gate and made it easier to get a good drum mix.
Another useful way to utilize De-Bleed is for getting rid of click-track bleed that leaked into a mic from an instrumentalist’s headphones during tracking. You’ll have to print the click to a separate track so that you can designate it as the Bleed Source Track to make that work.
High-gain guitar amps and distortion effects — or amp modelers emulating them — can cause a lot of buzzing that invariably gets onto the track. RX’s Spectral De-Noise module, which also comes in plug-in form (see Fig. 3), is excellent at reducing buzz and other broadband (steady) noises such as air conditioners or fans. It’s quite powerful, but you do have to be careful to use only as much of the process as you need, because if you apply it too heavily, it can create artifacts.
The key to getting the best results is to find a spot in the source track where the noise is in the clear. According to iZotope, about half a second is optimal. Select that section and press the Learn button, which teaches Spectral De-Noise the noise profile. It automatically calculates what the best possible settings are and sets the module to them. If you can’t find a noise-only spot for RX to learn from, use Adaptive Mode, which automatically sets the profile based on the incoming audio.
You can adjust the Reduction and Threshold sliders yourself if you’re not happy with the results or the processing is creating artifacts. In some ways, I like the plugin workflow for Spectral De-Noise, because of its non-destructive nature. However, if you’re working destructively in the application, you have the advantage of being able to do a second pass with the reduction. Sometimes it works better to use lower reduction settings and process more than once.
CLEANING UP AFTER SINGERS
RX features a number of modules that are specifically designed for dealing with problems that occur when you record the human voice, whether for dialog or vocals (see Fig. 4).
The De-Plosive module (RX Advanced) is absolutely brilliant at removing popped P, B and other consonant sounds from vocal tracks. Although you can also remove these manually in your DAW using volume automation, RX does it much faster, and it’s impressively accurate.
You can go about the removal in a couple of different ways. I prefer to open the vocal track in RX, find the plosives and process them one at a time. The presets are helpful starting points for settings. Preview the removal and then hit Process.
You can do something similar without leaving your DAW if it has a destructive processing feature such as Pro Tools’ AudioSuite or Logic Pro’s Selection Based Processing. In the app and the plugin, you also have the option to apply the process to the whole track, with the algorithm automatically detecting the plosives. You can do this from the module in the application or from the plugin right in your DAW. I don’t recommend this for music tracks, however, because it can affect the overall sound quality.
Breath Control, which is available only in the standalone app, is a module that’s extremely easy to use and allows you to remove breaths entirely or just reduce their level. It makes the process very fast and saves all the manual editing that would otherwise be involved. Use Preview to get the settings to where you like them, and then you can apply it to the whole vocal track.
Of the two main modes available, you’ll probably use Target Mode the most. It allows you to set the level of reduction when RX detects a breath, which lets you control the amount of attenuation. Gain, the other operating mode, lets you set an absolute reduction level.
RX’s De-Esser is offered both as a module in the standalone or as a plugin. It’s a powerful de-esser that you can apply across an entire track, or use for individual sections of a vocal, depending on the severity and consistency of the “ess” sounds in the audio. Two modes are available: Classic and Spectral. The former is a broadband de-esser, and the latter lets you target specific frequency areas for reduction. The Output Ess Only button lets you hear just the esses that are being detected. It’s beneficial for fine-tuning the parameter settings, and if you hear the vocals coming through in that mode, you know you’ve set the detection too high.
Singers can sometimes make random clicking and smacking sounds during a take. RX’s Mouth De-Click tool lets you remove such sounds either individually or across a full track. Available both in the standalone app and as a plugin, Mouth De- Click is simple to use and effective.
EQ Match is an easy-to-use matching equalizer that you may not use that often, but when you do it will be incredibly helpful. It looks at the frequency content of a source track of your choosing and creates an EQ curve that can be applied to another piece of audio to make it sound similar. It can be convenient in situations where you had to say, go back and revise a portion of an instrument or vocal part but couldn’t use the same gear or record it in the same location and the sounds don’t quite match. EQ Match can make your overdub sound a lot closer to the original. It won’t be exactly the same, but often you can get it close enough that the difference won’t be noticeable in the context of the full mix.
The Time and Pitch module offers high-quality time-stretch and pitch-change algorithms that can be used for seamless edits. For example, I was working on a project with a multitrack drum recording that was tracked too fast. I opened the tracks in RX, put it in composite mode — which allows you to edit multiple files simultaneously — and was able to easily apply the tempo change (-3 BPM) to all the tracks at once. There was no audible degradation from the processing.
CLICKING AND CLIPPING
There may be times when you end up with random clicks on your tracks, and the RX’s De-Click tool, whether used in the application or as a plugin, can be quite helpful. You can process an entire track with it and get rid of multiple clicks simultaneously. There are several different algorithms offered, giving you a lot of options, depending on the source of the clicks. One of the choices, Multi- Band, features a “protection algorithm” that avoids removing characteristic audio elements in vocals and brass instruments, that might otherwise be detected and removed as clicks.
The De-Clip tool, which comes in the app and as a plugin, can be helpful if you have occasional minor clipping on a file. It analyzes the waveform and calculates what it would look like if it hadn’t clipped. De-Clip is not going to clean up the sound of a file with significant digital distortion, but it can alleviate minor clipping issues.
AUDIO EDITOR FUNCTIONS
The hybrid display in the RX application is useful for spotting and editing problems in your tracks that you can then go in and fix. For example, it allows you to select specific time and frequency areas within a waveform, even if they’re non-contiguous, and then apply processes to them. It also lets you play back only what’s in your selection, which is extremely useful.
The RX application includes many tools for adjusting levels and dynamics. It features excellent Gain and Normalize modules. The Leveler module, although mainly designed for dialog, can be used to smooth out dynamics on music tracks. The Loudness module is excellent for conforming a mix to a particular loudness standard. It includes presets for seven different ones. The EQ module is quite powerful.
RX also lets you host external VST2, VST3, or AU plugins, which you can open (one at a time) from inside the RX interface and render to the audio. Also included are useful tools for adding dither and adjusting phase. RX features an easyto- use undo list, which lets you backtrack, even after applying destructive processing.
RX 7 IMPROVEMENTS
At the time of this writing, RX 7 is still in beta, and its full lineup of new features isn’t yet available. The new version should be released by the time you read this.
Among its new features will be a module called Music Rebalance, which will let you to take a mix and raise or lower the vocals, bass, percussion and the rest of the instruments (see Fig. 5). The Repair Assistant feature will analyze an audio file for problems and offer suggestions for which modules to use to repair it.
As detailed in this story iZotope RX is incredibly useful for ameliorating a host of sonic issues. As a long-time user, I can’t imagine doing music production work without it. You can get 10-day demo version of RX from iZotope, so I recommend giving it a try. You’ll be amazed at its power.
Mike Levine is a composer, producer, and multi-instrumentalist from the New York area, and is the Technical Editor — Studio for Mix. Check out his website at www.michaelwilliamlevine.com.