Spectral Repair Spectral Repair in iZotope RX 7 is the key to discovering what your waveform won't show you. Use familiar drawing tools to identify and select problem frequencies and unwanted sounds. Salvage unusable material by filling in audio gaps instantly. Apr 09, 2019 When ambient noise is more spread throughout the spectrum it is considered broadband noise. Tape hiss, white noise, and other non-harmonic sounds fall into this category, and they are easily removed with the Spectral De-noise module. Follow our step-by-step guide to removing ambient noise with RX.
As with medical diagnostics, the key to successful audio restoration lies in your ability to correctly analyze the subject’s condition. This can be a life-long, never-ending quest, constantly honing the ear to distinguish the noises and audio events that need to be corrected.
To get started, it’s important to identify the problems with your file and identify which tool(s) will give you the results you want. Let’s briefly look at how to examine your audio using the spectrogram and waveform display tools, then consider how to identify audio problems using these displays.
What’s the goal of using a Spectrogram?
The aim of any good visualization tool for audio repair and restoration is to provide you with more information about an audible problem. This not only helps inform your editing decisions, but, in the case of a spectrogram display, can provide new, exciting ways to edit audio, especially when used in tandem with a waveform display.
Hum
Hum is usually the result of electrical noise somewhere in the recorded signal chain. It’s normally heard as a low-frequency tone based at either 50 Hz or 60 Hz depending on where the recording was made If you zoom in to the low frequencies, you’ll be able to see hum as a series of horizontal lines, usually with a bright line at 50 Hz or 60 Hz and several less intense lines above it at harmonics. See the example below:
De-hum works best when frequencies of the hum do not overlap with any useful transient signals. You can learn more about the De-hum tool here.
Buzz
In some cases, electrical noise will extend up to higher frequencies and manifest itself as a background buzz. See the example below:
Hum-removal tools usually focus on low-frequency hum, so when the harmonics extend to frequencies above 400 Hz, the Spectral De-noise tool is often more effective at removing the problem.
Hiss and other Broadband Noise
Unlike hum and buzz, broadband noise is spread throughout the frequency spectrum and isn’t concentrated at specific frequencies. Tape hiss and noise from fans and air conditioners are good examples of broadband noise. In a spectrogram display, broadband noise usually appears as speckles that surround the program material. See the example below:
Clicks, Pops, & Short Impulse Noises
Clicks and pops are common on recordings made from vinyl, shellac and other grooved media, but can also be introduced by digital errors, including recording into a DAW with improper buffer settings, or making a bad audio edit that missed a zero crossing. Even mouth noises such as tongue clicks and lip smacks fall into the clicks category. These short impulse noises appear in a spectrogram as vertical lines. The louder the click or pop, the brighter the line will appear. The example below shows clicks and pops appearing in an audio recording transferred from vinyl:
The De-click tool can recognize, isolate, and then reduce and remove clicks like these.
Clipping
Clipping is an all-too-common problem. It can occur when a loud signal distorts the input to an audio interface, analog-to-digital converter, mixing console, field recorder, or other sound capture device. A spectrogram is not particularly useful for identifying clipped audio—for this you’ll want to work with a waveform display. As you’ll see in the image below, the clipping appears as “squared-off” sections of the waveform.
You can zoom in on a waveform and see in detail where the waveform has been truncated because of clipping.
The De-clip tool can intelligently redraw the waveform to where it might have naturally been if the signal hadn’t clipped. Sometimes, brickwall limited audio will also appear “squared off” when zoomed out, but this doesn’t necessarily mean it will sound as heavily distorted as clipped waveforms that have been truncated. You can zoom in to see if the tops of individual waveforms are clipped.
![]() Intermittent Noises
Intermittent noises are different than hiss and hum—they may appear infrequently and may not be consistent in pitch or duration. Common examples include coughs, sneezes, footsteps, car horns, ringing cell phones, etc. The images below represent two different examples of these noises:
The Spectral Repair tool can help isolate these intermittent sounds, analyze the audio around them and attenuate or replace them.
Broadband Noise Spectral Repair Izotope Rx 7Gaps and Drop Outs
Sometimes a recording may have short sections of missing or corrupted audio. These are usually very obvious to both the eye and the ear! See the example below:
Crack virtual dj 8. 2 mac torrent. Deleting the gap and then applying Spectral Repair to replace any missing audio can help fix these problems.
In its time, iZotope RX3 Advanced offered the most comprehensive suite of noise-reduction software—available as a stand-alone application and as bundled plug-ins—for post-production sound, along with extensive metering, time- and pitch-shifting processors, resampling facilities and other invaluable tools. RX 4 Advanced ($1,199) adds several workflow accelerators used to comply with various loudness standards and to quickly adjust level, timbre and ambience in tracks.
I reviewed Version 4.0.1 of RX 4 Advanced (its plug-ins in AU format) using Digital Performer V. 8.06 and an 8-core Mac Pro running OS X 10.9.5. For a refresher on RX 4 Advanced’s legacy features, check out my review of RX3 Advanced in the May 2014, issue of Mix.
Streamlined Interoperability
RX’s Spectral Repair plug-in—which was a bit of a kludge in previous releases—has been discontinued, made obsolete by the new RX Connect plug-in and alternative DAW interoperability. Roughly half of leading DAWs use RX Connect as a synchronized bridge to the stand-alone RX 4 Advanced application; you first select in your DAW the audio clip you wish to process, then launch RX Connect. Other DAWs (including DP) use RX 4 as an external editor: In DP, for example, you choose the RX application as DP’s external waveform editor and then open a region in RX via DP’s Audio menu.
No matter which protocol your DAW uses, after the RX application opens you can edit the selected clip using any processing (not just Spectral Repair) it provides. Different (fast and simple) methods are used, depending on your workstation, to return the processed clip back to your DAW in perfect sync with the original clip. Because some DAWs (including Pro Tools) monopolize the system’s audio drivers, an additional plug-in dubbed RX Monitor is included to enable hearing the RX application’s output; RX Monitor interacts with your DAW like an instrument to play the RX application’s audio through the DAW’s driver.
The updated Remove Hum plug-in and module—all modules belong to the standalone application—include an Adaptive mode that analyzes your audio and automatically notches out fundamental hum-related frequencies that change over time (such as in audio for a scene that was shot in multiple locations).
The updated Time & Pitch module provides an option to run Radius processing in real time, for those tasks in which you need fast processing. The tradeoff is lower quality than with offline processing (which is still available).
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New Modules
The new Leveler module uses a compressor with automatic makeup gain to curb fluctuations in signal level. Use its Target RMS slider to adjust the K-weighted RMS level of your clip. The Speed slider alters how quickly gain is adjusted. Drag the Amount slider to limit the maximum amount of gain (boost or cut) that can be applied, and raise the Noise slider to reduce potential pumping when breathing or other broadband noise occurs during gaps in dialog. You can view the gain changes that Leveler applies and edit them by dragging up and down one or more nodes at once on a graphical curve (dubbed the Clip Gain envelope; see Figure 1).
The new Loudness module automatically applies a fixed amount of gain to your entire clip (or a selected region) to instantly make it comply with a specific standard, such as BS.1770, selected from a drop-down menu. Alternatively, you can use two sliders to manually set the desired loudness (in LKFS units) and maximum true peak level of the clip. A post-limiter is automatically applied as needed to meet the selected true-peak spec.
The new EQ Match module applies static equalization to purportedly make one region’s spectral balance conform to that of another. Simply select a region (such as a phrase in a VO track) that sounds great, click Learn, select another region that sounds bad, and click Process. EQ Match lets you save spectral profiles as presets, speeding your workflow.
The Ambience Match module does for noise what EQ Match does for timbre, with one caveat: It can’t decrease the amount of ambience that already exists in a selection; it can only increase it. This is an invaluable tool for matching an ADR track’s ambience to that of the recording being replaced. You simply make a selection of the noise in the live recording, click the module’s Learn button, make a selection in your ADR track where you want the same-quality noise added, drag the Trim control to adjust the level of the ambience to be added, and click Process. Noise snapshots can be saved as custom presets.
In Post-Production Sessions
I used RX 4 Advanced extensively while working on five video projects containing many dialog tracks, music and B roll. The new Leveler module gave me excellent results easily and exceedingly fast, smoothing levels no matter the track’s spectral balance. It controlled boomy-sounding peaks beautifully, often precluding the need to de-boom using multiband compression. With moderate settings—the Amount control set no higher than 4 dB—I got more natural-sounding results than when using my go-to compressors and limiters. After rendering the processing, I could mouse-drag one or more nodes at once in the automatically generated clip-gain envelope to alter Leveler’s gain changes in select spots (see Fig. 1).
The Loudness module conformed my mix to any of seven different loudness standards with just a couple of mouse clicks—a real timesaver. Using the Ambience Match module, I could capture the room tone on a dialog track and add it to another track that sounded too dead; a trim control let me adjust the level of the ambience ±6 dB without affecting the level of the dialog. Listening to the generated ambience in isolation, it was apparent it was synthesized. But in the mix, it worked inconspicuously if applied sparingly to tracks in select, short gaps.
I tried a couple dozen times to use EQ Match to smooth spectral balances on dialog tracks, but I always found I got better (and more predictable) results using a combination of static and dynamic equalization plug-ins.
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Any editing performed on tracks in the RX application is destructive once sent back to DP (overwriting the original file everywhere it occurs in DP), a disadvantage compared to working with RX 4 Advanced’s nondestructive plug-ins. Overwritten files initially played back as—and looked like, in DP’s Sequence Editor—full-scale, broadband noise in DP; rebooting DP would always permanently restore pristine playback, but I’d sometimes also need to bounce the file to a new track to restore proper waveform display. This appears to be a bug in DP, not in the RX application.
On startup, the RX application would often arbitrarily reroute consistent output assignments to different MOTU I/O boxes or banks—sometimes to those disabled in the MOTU PCI Audio Setup utility. And I often heard distracting crackling noises and clicks while working with the application, especially while previewing a module’s processing. (An associate of mine confirmed hearing the same artifacts using RX 4 with a different system.) Thankfully, the artifacts did not print when files were overwritten back to DP; nor did they ever occur when using the RX plug-ins.
Purchase in Advance?
iZotope also offers a less-expensive “standard” version, which doesn’t include the Dereverb, Deconstruct, Leveler, Loudness, EQ Match, Ambience Match, Radius RT (Time & Pitch) and Insight (metering suite) modules and plug-ins. It also lacks the center-channel extraction and azimuth alignment features for the Channel Operations module and some extra controls for Denoiser, Spectral Repair and Declick. Many of these additional features included with the Advanced version have proven to be indispensible in my work; they are well worth the extra cost.
If you work in post-production sound, restoration or audio forensics and don’t already own RX3 Advanced, buying RX 4 Advanced is an absolute must—if only for its incredible legacy plug-ins. If you can tolerate the RX application’s intermittent routing and monitoring problems, the Leveler and Loudness modules make an upgrade from RX3 Advanced worthwhile.
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Mix contributing editor Michael Cooper is a recording, mix, mastering and post-production engineer.
Broadband Noise Spectral Repair Izotope Rx Reviews
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DP can send only one region at a time to an external editor such as RX 4 Advanced. If you want to send an entire track containing non-contiguous soundbites, first make a time-range selection in DP for the entire track and select Merge Soundbites (option-shift-M).
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