The four are: De-click, De-hum, De-clip, and Dialogue De-noise all ported from iZotope's RX 5 Audio Editor. The plug-ins can be used to remove clicks, crackles, hum, fix distortion caused by over loading (clipping) and remove unwanted wideband noise from audio.

I tested all four of these audio repair plug-ins as AAX processors in Pro Tools 12 HDX and found many uses in my music mixes. While experimenting, I discovered some happy accidents that changed the sound in a good way useful for my mix beyond noise reduction.

I found using them as AudioSuite processors an excellent way to handle each file with just the right amount of cleanup per instance. Sometimes more than a single pass was require--for example an audio track that has clip distortion and also a loud, 60 Hz hum. You would De-clip first and then use the De-hum plug-in.

There is the RX Audio Cookbook available for free at: rxcookbook.izotope.com that will have many suggestions and tips to get the most out all four of these plugs. This Web site walks you through the operation and how they each work plus has an excellent tutorial explaining each parameter and each control's functionality.

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Dialogue De-noise

Dialogue De-noise has 64 "psycho-acoustically spaced band pass filters" with user defined thresholds for each filter. Although all four of these plug-ins work as AudioSuite processors in Pro Tools, Dialogue De-noise is designed to also run real-time and on multiple tracks with minimal CPU and delay compensation required.

The Auto mode works well analyzing the incoming dialog audio and automatically adjusting for changes in the noise floor. Manual mode is better for de-noising music recordings and allows for creative special effects and gave me ideas for certain lo-fi treatments when I set it to extreme reduction amounts. I liked the Preset collection and the ability to reset it to default.

De-clip

De-clip repairs "overs" that can happen in live recordings or in the studio with unexpected level jumps while recording. De-clip will fix clipping whether it came from analog tape or an overloaded A/D converter. Many times they are unavoidable such as during interview recordings where the level jumps radically. I like that you can zoom into the waveform in the GUI for setting the threshold accurately and the built in Post-limiter to control the final output level. In affect, De-clip automatically redraws the tops of the waveforms to what they would have been had not the (recording) system overloaded. It works and sounds great!

De-click

I found De-click to work transparently on short pops and ticks that seem to come up here and there in digital recordings. Static discharges, vocalists lip smacks and mouth noises, drummer stick clicks, digital clocking/error issues are all easily removed with De-click. When mixing I would select one of three algorithm, click type and set the Sensitivity fader to selectively remove just about any tick or pop. I remixed an already mixed stereo percussion track by removing stick hits and using the "Output clicks only" mode to put them on their own track. Awesome!

De-hum

De-hum will remove low frequency hum (usually 50 or 60 Hz) and up to seven harmonics of related energy above it. There are two modes: Manual for fixed hum frequency such as 60 Hz AC line and Adaptive where De-hum looks at a changing hum frequency and constantly follows and eliminates its. Adaptive is useful for suppressing the whine and hum related to varying machinery noise that changes over time. De-hum will clean up any noisy guitar amp recording--guaranteed. Just chopping out the space between guitar entrances gets rid of noise between them but the hum is still there when the guitar part plays. De-hum it without affecting the guitar tone significantly.

An awesome collection to have at the ready when mixing, the RX Plug-in Pack is available at www.izotope.com/rxpluginpack at: $129 MSRP. Check: www.izotope.com/rxpluginpack.