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iZotope RX Noise Reduction Tips

Use these iZotope RX techniques to reduce or eliminate unwanted noises from your recordings By Jeffrey P. Fisher

As an audio-post-production professional, I'm often called upon to clean up the dialogue from the documentary, corporate, and narrative videos that come my way. The work requires a lot of patience and access to both basic and advanced audio tools. For me, the one must-have gizmo for audio cleanup is iZotope RX. This tutorial looks at ways this indispensable tool solves typical noisy problems that conspire to ruin your video soundtracks.

The iZotope RX program works stand-alone and as a plug-in for many audio software applications. I prefer to use it in stand-alone mode using copies of the files I need to address. The application is actually a suite of noise-reduction modules: Declipper, Declicker, Hum Removal, Denoiser, and Spectral Repair. The application also includes several extra processes including Gain, EQ, Resample, and Dither.

iZotope RX attacks a variety of noisy gremlins with its suite of must-have tools.

Clicks, pops, and other glitches are a common occurrence on many recordings. These tiny little transients are easy to eliminate in-between words and phrases, but when they, pardon the pun, pop up during dialogue, eliminating them is somewhat more difficult. Isolate the section where the pop occurs and launch the Declicker tool. You might want to start with one of the Presets and tweak for the best results. Click the Preview button to check your work and make adjustments.

For clicks and pops, use the Declicker tool.

Noise reduction processing is a trade-off between eliminating the noise and adversely affecting the quality of the remaining sound. While you can do some amazing things with these tools, they do leave artifacts in their wake. To help you manage this balancing act, RX includes an 'Output clicks only' checkbox. This monitors the effect in reverse so you can hear what's being cut out instead of what's left.

With this mode engaged, listen for any good signal getting through. You only want to hear the clicks and not the words. If you recognize speech, then you need to back off on the settings. If you don't, the speech you hear will be eliminated along with the clicks when you process the file. The resulting sound quality of the file may suffer undesirably.

Once you've found the right settings, click Apply to process the file. Be sure to uncheck the 'Output clicks only' box before you process the file, though.

This software works amazingly well on vinyl recordings by getting rid of all the clicks, crackles, pops, and other unwanted sounds and leaves a more acceptable recording.

Notice all the spiky glitches in this recording

A quick application of the Declicker restores the sound.

Spectral Repair
Pops and their ilk are higher frequency sounds, but what about lower frequency noises? Another common issue is thumps caused by talent accidently hitting the microphone during recording. The spectrogram view integrated with RX makes finding and eliminating these kinds of noises fast and easy. Note the bright orange-white color below the transient in the figure below; it's a low frequency thump.

iZotope Rx's spectrogram view quickly exposes problems such as this loud thump.

Switch the selection tool to Time-frequency by clicking its icon on the far right of the workspace. Move to the file and draw a box around the thump. Take care to get the bulk of the brightest part and avoid the surrounding area. Click the Spectral Repair tool to launch its dialog box and choose the 'Attenuate unwanted event' Preset. Because you are working in tiny increments, there is no Preview button here so click apply. You can always Undo your work, if needed. Note how the thump disappears in the figure below.

The Spectral repair can work like a surgical EQ helping to eliminate troublesome noises in tight frequency ranges.

Hum Removal
The problem with electrical hum is that it isn't just 60Hz but also harmonics of that frequency, too. That means the annoying hum is at 60, 120, 180, 240Hz, and so on. Employing a simple 60Hz notch EQ setting usually is not fully effective. RX includes a Hum Removal tool that uses a series of tight notches to reduce 60Hz and those pesky harmonics, too.

Combat irritating electrical hum with a series of tight notch filters.


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