Review: iZotope Neutron

A powerful processing plug-in that features artificial intelligence
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Artificial intelligence is being put into all sorts of products these days, so it’s not surprising that it’s made its way into music software. Neutron, for example, is a multi-processor mixing plug-in that uses AI to analyze the audio on your tracks, and then makes suggestions for initial settings on the various modules (see Figure 1). It includes a groundbreaking feature called the Masking Meter, which helps you see areas in which tracks are competing with each other frequency-wise. Neutron also incorporates the Spectral Shaping technology that was introduced in iZotope’s free Neutrino plug-in.

Fig. 1. The Neutron GUI lets you choose and re-order processors. Here the compressor is set to Vintage mode with RMS metering selected.

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Neutron is available in standard ($249) and Advanced ($349) versions. In addition to surround-sound support (up to 7.1), the Advanced version lets you open the various components in Neutron as separate plug-ins. Other than that, both versions have the same components. Installation is easy, and the authorization process is quick and painless.


Neutron’s modular structure is similar to iZotope’s Ozone mastering suite. The five main processing components, shown near the top of the GUI, are feature-laden and powerful. They include an equalizer, two compressors, an exciter, and a transient shaper. You can turn each one on or off, and slide them around to change the signal order. Each processor has a mix slider that lets you dial in as little or as much of it as you want. In other words, you get individual parallel processing for each component.

The Equalizer can have up to eight bands, plus two filters on each end of the spectrum. You can make any of the bands dynamic. That means that the equalization only kicks in when the signal exceeds a user-adjustable threshold. The sidechain implementation on the Equalizer is impressive, allowing you to use not only external signals for the sidechain, but the signals from other bands in the EQ.

The compressor modules have identical features, but so much variety is built in that you can set them to sound and react quite differently. In Digital mode, they offer transparent compression, whereas Vintage mode adds coloration to the sound. Neutron is the first iZotope product to have this particular Vintage compressor algorithm.

The compressors have three adjustable bands, and offer plenty of other useful features such as sidechaining for each band; RMS, Peak, and True detection (the last is similar to RMS but with fewer artifacts); Auto Gain; Auto Release; and much more.


The three-band Exciter can be used to add presence to a specific frequency range as well as utilize one or more of its four modeled distortion types—Tube, Tape, Retro, and Warm.

The Transient Shaper is also a multiband processor. It allows you to change the attack and sustain characteristics of an instrument. For example, you can use it to make a snare drum sound more ringy or tight.

The metering for each of these processors is excellent, and they include real-time analyzers. As a nice touch, the sliders return to their default positions when you option/alt-click them.


Each instance of Neutron has a button on it called Track Assistant, which analyzes your audio and suggests settings for it. The folks at iZotope stress that these are only starting points: Essentially, the Track Assistant creates customized presets based on your program material.

Using Track Assistant is a breeze. Hit Play on your DAW, press the Track Assistant button, and a screen will appear telling you that the software is working on your audio. In 10 seconds or less, you’ll have a comprehensive setting for your track, featuring as many active processors as the system deems necessary. It seems always to include an EQ and at least one compressor. The second compressor and the Exciter and Transient Shaper are activated less frequently.

The algorithm is smart enough to detect whether it’s hearing an instrument, drum, or voice, and then assign it to one of the four Neutrino modes (Vocals/Dialogue, Guitar/Instrument, Bass, and Drums/Percussive) in the Spectral Shaper at the output. It uses the same algorithms that are in the free Neutrino plug-in. (More on the Spectral Shaper shortly.) Where it cannot characterize the audio, it assigns it to a category called Clean.

In my testing, the settings the Track Assistant comes up with were usually solid starting points, but I almost always wanted to do some tweaking. One of the best aspects of Track Assistant is that it comes up with useful settings for the multiband processors, which are more tricky and time consuming to set.


There are preferences for the Track Assistant that allow you to choose whether it should aim for “Broad Band Clarity,” “Warm and Open,” or “Upfront Midrange.” You can also choose among three modes—Subtle, Medium, and Aggressive—that control how light or heavy a touch it has.

Even if you don’t want to go the full Track Assistant route, each processor has a Learn button, which in the case of the Equalizer will assign EQ nodes at relevant frequencies (no boosts or cuts, though) and set the frequency boundaries for the multiband processors.

Fig. 2. The Masking Meter in action. The top EQ is the initial track and the one below it is linked.TAKING OFF THE MASK

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Neutron’s unique Masking Meter is designed to help you carve out space for a track when its being masked by another track in the same frequency range and isn’t cutting through the mix enough (see Figure 2). To use it, open Neutron on at least two tracks, then open the plugin window for one of the tracks and press the Masking button in the Equalizer. Then, select another track to link with from the drop down menu. An EQ display for the linked track appears underneath.

Next, hit Play and Neutron will indicate—via flashing white lines on the EQ’s frequency display and a real-time bar graph above it—the frequency ranges where the two tracks are masking each other. This provides you with a good idea of where to add cuts or boosts to create more space for the track. As far as I know, no other equalizer does this. One very cool option is called Inverse Link. When activated, boosting on one of the linked tracks causes an equal cut at the same frequency in the linked track and vice versa.

The Masking Meter and its related features give you a perspective on your mix you wouldn’t get otherwise. It’s not a panacea, however: You still need to use your ears to find what works.


The four different Neutrino modes in the Spectral Shaper module have what the manual describes as “dozens of psychoacoustically spaced frequency bands, each with an adaptive threshold based on the audio signal’s RMS.” When the signal of the track goes above the threshold, it gets attenuated in that range. It behaves partly like a multiband compressor and partly like a dynamic EQ; control it with the Detail and Amount sliders.

However, the Spectral Shaper’s impact on your audio is often quite subtle. On some tracks, I cranked the controls and didn’t hear much of a change, but on others, it added a pleasing smoothness.

Neutron also includes master input and output sliders. You can switch in a limiter on the output, using one of three limiter algorithms—IRC LL, IRC 2, and Hard. The latter is a brickwall limiter that I found useful for keeping tracks from going over 0 dBFS. The other two modes can cause latency: Hit the Zero Latency button to return to the latency-free Hard mode.


Because you get the best results using Neutron on multiple tracks, CPU efficiency is an important aspect. I tested Neutron on a 2.6 GHz MacBook Pro with 16 GB of RAM. Running in MOTU Digital Performer with 10 instances of Neutron open and a buffer setting of 2,048, my CPU load was below 30%.


Although it is powerful and sounds excellent, it’s not the processors in Neutron that make it unique. It’s the inclusion of the Masking Meter and, especially, the Track Assistant. The latter has engendered a bit of controversy, as some people feel it lets the computer make processing decisions best left to the engineer. I, too, felt a little trepidation at first, but after using Neutron for a while I came to realize that its features are only intended to give you a customized starting point for processing a track. In that sense, I could really see the value of what Neutron can do, especially when you compare it to a conventional plug-in that offers only generic presets.

It’s probably not a good tool if you’re just learning to mix, but if you already know the basics, Neutron gets you where you want to go a lot faster.

Powerful suite of processors. Track Assistant. Masking features let you see where tracks are competing sonically. Powerful EQ. Multiband compressors. Exciter offers multiple distortion types. Transient shaper. Parallel processing for each processor. Flexible sidechain.

Limiter can cause latency. Spectral Shaping can be extremely subtle.


Mike Levine is composer, producer, and multi-instrumentalist in the New York area.