iZotope: Neutron Intelligent Mixing Plug-In

If I had to choose a single channel-insert plug-in for mixing, iZotope Neutron would be at the top of my list. Neutron, at its heart, is a multi-module channel strip. It includes four modules — Equalizer, Compressor, Transient Shaper, and Exciter — that can be enabled, disabled, and reordered in signal flow to your liking, with two Compressor instances available, for a total length of five modules in the signal chain. Moreover, every module has a wet/dry mix slider to implement parallel processing. In Neutron Advanced, the four module types can also be instantiated as separate plug-ins. In addition, there are two processing sections at the end of the plug-in’s signal chain — Neutrino and Limiter. On top of all this functionality, iZotope has baked in two standout intelligent features. Track Assistant analyzes the source audio and presents you with a recommended starting point. It’s almost like a virtual mentor that’s looking over your shoulder; when queried, it listens for a moment and then sets up your channel strip for you — “Hmmm, try this.” Masking Meter is a handy FFT-based tool that shows you how two tracks of your mix are “colliding” within the frequency spectrum, and it gives you immediate access to the EQs of both tracks so you can manage the collisions in the same window. Both of these features are very cool extensions to an already capable set of audio tools.

The Equalizer module offers twelve bands — eight parametric peaking bands, low/high shelves, and low/high–cut filters — whose EQ curves are superimposed on a real-time FFT spectral display. Conventional sliders and numeric input boxes can be used to change each band’s settings, or you can just click on the band’s graphical touchpoints and move them around. On my Windows 10 laptop, I had no problem using my fingers on the touchscreen to grab anchor points and pull splines to shape the EQ curves. A Learn button puts Neutron into a listen state, and after a few seconds, the plug-in centers all of the enabled EQ bands on fundamentals, resonances, buildups, and other “frequencies of interest” that have been identified. (None of the other band settings, like boost/cut or bandwidth, are adjusted by the Learn function.) I can imagine some engineers calling this a superfluous feature, since we should all be adept at identifying distributions of spectral energy by ear, but I found this function to be time-saving, especially when presented with highly distorted electric guitars or overly sibilant voices. In these instances, hitting Learn gave me a head-start in choosing which frequency regions to focus on.

Importantly, each of the EQ bands (except the two cut filters) can be individually configured for static or dynamic operation. In Dynamic Mode, the band works in a similar manner to a band-specific compressor or expander. A dynamic EQ can often sound more transparent than a static EQ, but you can also push a dynamic EQ to add “motion” to a sound by boosting or attenuating certain frequency regions to follow a beat, for example. For this kind of processing, Neutron’s Equalizer offers a powerful sidechaining function. You can use the full-bandwidth input to the plug-in as the key signal, or you can use any of the individual EQ bands; or the full-bandwidth or individual EQ bands from another Neutron instance.

Masking Meter allows you to associate one instance of Neutron Equalizer with another Equalizer instance, so that you can look at their two spectral displays together — one above the other — and operate their EQs from a single window. The premise is that spectral collisions between the two sources can result in masking of one source’s share of the spectral energy by the other’s. The collisions are highlighted in real-time as grey-to-white frequency bands (with the intensity of white matching the degree of masking) on the upper spectral display, while a histogram just above that estimates the amount of masking over a set hold period. Again, engineers with better ears than me might scoff at this functionality, but I found it to be quite useful and a real time-saver.

For example, on a recent mix with distorted bass and guitar, I was having difficulty choosing how the two instruments should sit together in the mix. Both needed to be prominent in the mix, but with both turned up, the mix was sounding hazy. After instantiating Neutron on each instrument and tying them together with Masking Meter, it was short work to set up dynamic EQs on both instruments to carve out space in the spectrum for each other. Granted, I had to dive briefly into the plug-in’s (mostly hidden) Options panel to adjust the Masking Meter’s Gain Offset for the instance of Neutron on the guitar track (because it had some post-Neutron level automation going on) so it wasn’t truly as easy as opening up the plug-in and jumping immediately into the EQ.

On another mix, I was having some difficulty with a bright, percussive, acoustic guitar part conspiring with a ride cymbal in such a way that sharp, clicking-like sounds (akin to quick moments of digital overload) were produced whenever a guitar strum and a cymbal strike happened together. (Yeah, I know — very weird.) Once I discovered that the clicks could only be heard when the acoustic guitar and overhead tracks were both on, I gave Neutron’s Masking Meter a try. Sure enough, I could see the flashes of white in the spectral display corresponding to the clicks. I positioned a medium-bandwidth dynamic EQ band centered at 7 kHz on the acoustic guitar, sidechained to the overhead mic’s EQ band at the same frequency, to filter out just enough 5–10 kHz from the attacks of the acoustic guitar’s strums to dispose of the weird clicking. Why didn’t I just use a multiband compressor to do this? Because a dynamic EQ has target curves for frequency-response, unlike a multiband compressor’s flat bandpass lines. Plus, there’s less tweaking required, because there are no attack, hold, and release parameters to manage — as these are auto-set behind the scenes for the frequencies at play.

Masking Meter has an Inverse Link feature that, when enabled, automatically applies the reverse curve to the second instance of Neutron Equalizer, as you move and adjust the bands of the first instance. Its intended purpose is to facilitate “de-masking” of two sources, and again, it’s a great time-saver. But I also found this function to be quite fun and useful for “stereo-izing” a mono track. For example, I had a mono rhythm guitar track that sounded fine during the verses of a song, but it wasn’t really working when the energy of the vocals and other instruments picked up in the choruses. I decided that a stereo version of the guitar would be better, but I didn’t want to use the typical short-delay trick due to its tendency to sound “phasey.” I instead copied the guitar track and then placed an instance of Neutron Equalizer on each of the two tracks. Using Masking Meter with Inverse Link enabled, I drew out a sawtooth-shaped EQ curve on one track, from 1.2 kHz to 4.8 kHz, and the opposite EQ curve appeared automatically on the other track. With the two tracks panned full left and right, the guitar was no longer mono. It instead sounded wide, because its harmonics were pushed left and right. Problem solved.

The Compressor module in Neutron is straightforward in nature, and its controls will be immediately familiar to anyone who has used a multiband dynamics processor. Threshold, Ratio, Knee, Attack, Release, and Gain are all represented, as are controls to manage various compression characteristics as well as crossover frequencies. There are Modern and Vintage modes; RMS, Peak, and True detection schemes; and settings for Auto Gain and Auto Release. Similar to Equalizer, the Compressor module can be sidechained to the full signal or to specific bands of its own source or the source of another Neutron instance. Additionally, there are low and high–frequency resonant filters for the sidechain. A spectral display lets you visualize the adjustable crossover filters overlaying the output’s FFT, while a scrolling timeline above that shows the envelopes of output amplitude and gain reduction for the selected band. In Vintage Mode, the scrolling timeline is replaced by three VU meters showing gain reduction, one for each band. In this module, the Learn button sets the crossover frequencies based on spectral balance of the incoming signal. With so many modes and parameters to adjust, I found that Neutron Compressor can be carefully tweaked for transparent operation, or intentionally set for distortion — or anything in between. And because two Compressor modules can be enabled in a single Neutron instance, you can do serial and parallel compression. For example, on vocals, I like to use one Compressor in Modern Mode to really clamp down on the midrange “telephone” frequencies, adding in a parallel mix of the uncompressed signal, and then I follow that with a second Compressor set for lighter, broadband compression in Vintage Mode. This tactic can really tighten up a vocal performance and bring it out-front in the mix, while leaving enough of the emotive dynamics intact so that the voice retains intimacy. I also like to precede the Compressors with Equalizer configured for de-essing in Dynamic Mode.

The three-band Transient Shaper module offers band-specific envelope and global algorithm presets for reshaping the attack and sustain of the signal. Its two display panes work like the Compressor’s, showing its frequency and timeline curves overlaid onto the post-process spectrum and amplitude envelope displays. I’ll admit that my favorite envelope shaping plug-in is Sonnox Oxford Envolution [Tape Op #113] because of its powerful parametric spectral controls and its difference (effect-only) function, but in many ways, Neutron Transient Shaper is easier to use. Plus, when combined with the Exciter module, Transient Shaper really shines.

When I’ve got a track that I want to be liven up (or damp down) in Neutron, I usually begin by hitting Transient Shaper’s Learn button to start with the recommended crossover points. Depending on my vision for the track, I’ll choose either the Precise or Balanced global recovery algorithms (while rarely choosing Loose, which is designed for long sustains). From there, I’ll adjust the Attack and Release gain sliders while switching between the per-band Contour selections. In this way, drums can be made to really pop — or sound totally dead. Acoustic guitars can be turned into percussive elements — or softened into near-ambience. And so on. I then like to follow the reshaped sound with Exciter.

Like Compressor and Transient Shaper, the Exciter module is also a three-band processor with a Learn button for auto-setting the crossover points. Each band in Exciter has a two-dimensional “pad” with four quadrants that represent the saturation and distortion personalities of Tube gear, Tape machines, Retro transistor circuits, and Warm analog equipment. Choose the mix of these personalities by moving the selection point within the X/Y pad. Drive and Blend sliders adjust the effect amount and wet/dry mix for each band. The controls provide enough range and flexibility to really overdrive a sound, but when Exciter is used subtly, especially in conjunction with Transient Shaper, it can add flavor to a sound in a delicious but not overly spiced way. With that said, it’s way too easy to go overboard here, so what I tend to do is tweak settings with the module’s overall Mix control at 100% wet, and then I turn down the mix to something closer to 50%.

Following the five-module signal chain explained above is the Neutrino Spectral Shaping section. This process deserves its own chapter-length description of what it does and how it operates, but iZotope’s one-liner is that Neutrino can be thought of as “a 32-band dynamic equalizer, with individual band filters for every band, each automatically setting thresholds, time constants, and reduction amounts based on tuned models for each sound source.” The spacing of the bands is based on the mel scale, which follows the findings of perception studies rather than mathematical intervals. Four Neutrino modes are available — Vocals/Dialogue, Guitar/Instrument, Bass, Drums/Percussive — and a Clean mode bypasses the process. Detail and Amount sliders adjust the granularity and amount of effect. Even with both sliders at 100%, Neutrino is quite subtle, and it isn’t until you enable Neutrino across most or all of the individual tracks in a mix that you can appreciate how Neutrino is able to reduce mud and add clarity and focus to a whole mix. In that regard, I pretty much leave Neutrino untouched within Neutron. Instead, I prefer to use the free-to-download dedicated Neutrino plug-in because I can quickly instantiate it across all of my tracks — and easily enable/disable them at once using modifier keys in Cubase or Pro Tools.

The Limiter section is at the very end of Neutron’s long signal chain. Limiter is dead simple to operate but wonderfully effective. The master output fader of Neutron sets the input level of Limiter. You can choose from three algorithms — IRC II, IRC Low-Latency, and Hard. And there are three modes — Clear, Smooth, and Thick — that change the chosen algorithm’s adaptive responsiveness. A slider that’s overlaid onto the plug-in’s output meter sets Limiter’s output Ceiling. The two IRC algorithms offer BS.1770-2/3-compliant True Peak limiting — at the expense of latency. The zero-latency Hard algorithm is a brickwall limiter that is the least CPU-intensive. I’m not a mastering engineer, so I’m not going to judge Neutron Limiter in that context, but I will say that I’ve applied IRC II Limiter to rough and audition mixes that I’ve given to artists, and not a single person has complained — not even the mastering engineers.

One seemingly minor feature that’s worth mentioning is True Bypass, which shows up as a toggle within Neutron’s Options pane. When enabled, hitting the master Bypass button above the Limiter section completely bypasses the plug-in, so that it contributes zero gain and latency to the track. But this means that you’ll hear a click — and in some DAWs like Cubase, a pause in playback — whenever you hit this switch. On the other hand, if you disable True Bypass and concurrently enable Auto Gain for the bypass function, hitting the master Bypass button immediately switches — without clicks or pauses — to a pseudo-bypassed state with the dry signal volume-matched (to the best extent possible) to the wet signal (and keeping the same latency too). This is how I prefer to use Bypass. With so many modules and sections in the signal chain of the plug-in making it impossible to maintain a target volume throughout the plug-in, having this Auto Gain for the bypassed dry signal greatly facilitates A/B comparisons between wet and dry. (I can always use the disable button that Cubase binds to the plug-in to truly bypass the plug-in anyway.) Unfortunately, loading any of the global presets inconveniently re-enables True Bypass.

And finally, let’s talk about Track Assistant. When you trigger this feature, it analyzes the incoming audio for 4–10 seconds and then generates a recommendation that amounts to a unique preset with settings that span the whole plug-in. Track Assistant has three modes (Subtle, Medium, Aggressive) and three preset “directions” (Broadband Clarity; Warm and Open; Upfront Midrange) from which you can choose — a total of nine combinations — that affect how the recommendation is generated. Under the hood, it’s Neutrino’s analysis engine that identifies which of the four instrument categories the incoming audio falls into — Vocals/Dialogue, Guitar/Instrument, Bass, Drums/Percussive — or the “none of the above” category of Clean. Each category has five “smart templates” associated with it, and each template has its overall signal flow, number of bands, and some EQ shapes, as well as a few other parameters, preprogrammed. The nine mode/direction combinations influence which of the templates is chosen from the identified category; and deeper analysis sets EQ points, crossover frequencies, compressor thresholds, and so on. As I described this feature earlier, it’s more like a mentor, or perhaps even a co-producer, than it is an assistant. The recommendations it generates are often educational in the sense that you get to see and hear the effect of settings that you might not have discovered on your own without a lot of tweaking. Or another way to look at it — it’s an effortless way to arrive at a starting point. On the other hand, I can quickly audition three or more traditional presets from Neutron’s Global Presets library in the same amount of time that it takes me to generate and then listen to a single recommendation from Track Assistant. So, in that regard, the regular preset library is a faster way to audition and learn from settings that aren’t your own. Also, each module type has its own preset library to choose from. With all that said, the biggest pitfall of relying too much on the preset library or Track Assistant is that neither of them knows what’s going on with any of the other tracks in your mix — or what you’re striving to achieve with the mix, for that matter. So keep that caveat in context, as you adjust your Neutron channel settings within the context of the whole mix.

All in all, I’m very impressed with iZotope Neutron. It’s an incredibly powerful channel-strip plug-in that also happens to be an educational tool in its ability to make recommendations and highlight potential masking problems. Its interface looks gorgeous, with informative meters and displays that are all implemented well. Thankfully, there’s no skeuomorphism to detract from actual usability. (There isn’t even a single virtual knob to “turn.”) Importantly, Neutron is capable of a wide range of sonic manipulation, and it sounds great.

Three versions of Neutron are available for purchase. Compared to standard Neutron, Neutron Elements comes with fewer presets, and it doesn’t include Masking Meter, Dynamic EQ Mode, Limiter, serial compression, and sidechaining functionality. Neutron Advanced adds individual plug-ins of the four module types, as well as 7.1 support. Visit the iZotope website to download a full-featured 10-day trial of Neutron. While you’re there, grab the free Neutrino plug-in.