Sound Radix Auto-Align 2

Auto‑Align 2 automatically groups related tracks on which an instance of the plug‑in has been inserted, and aligns the time and phase of all tracks internally within the group.

This powerful alignment tool is now easier to use and boasts new functions — along with impressive results.

Sound Radix tend to create original and innovative plug‑ins that address common problems in audio production. I’ve reviewed some of their software in SOS, and often use their excellent Surfer EQ and Drum Leveler plug‑ins in my mixes. Under review here is an updated version of probably their best‑known, most widely used plug‑in: Auto‑Align. A time‑alignment tool, it’s intended to help engineers optimise the phase relationship between multiple mics/DIs used to capture the same source. Auto‑Align 2 runs on Intel/Silicon Macs (macOS 10.9 and up) and Windows (10 and up), and supports the usual plug‑in formats as well as ARA2. For this new version, Sound Radix have rewritten their algorithms, added important new features, and made it far quicker and easier to use.

Mic Interactions

Before I assess Auto‑Align 2 itself, it’s worth spelling out the issues it aims to address. When we record anything with multiple mics, each one will pick up the same sound (broadly speaking) at slightly different times, due to the different distances at which they’re placed relative to the source. When the mics’ signals are mixed together, these timing differences mean that the similar signals aren’t fully in phase: there will be some degree of comb filtering, often perceived as a ‘hollowing out’ of a sound or a lack of ‘fullness’, and transients can sound a bit soft or smeared.

This can apply to anything where you use more than one mic simultaneously, even if using separate mics on different instruments in close proximity. For example, with a singing guitarist you might have one mic on the guitar and another on the vocal; each mic will pick up some of both sounds. But the classic example is a multi‑miked drums: a kit will typically be captured with a selection of close, overhead and room mics, and there will be timing differences between the various mics, with the close mics picking up spill from the other kit elements and each hit inherently being earlier in time than in the main overhead/room mics. The more mics you use, the more complex the time and phase relationships become.

As you gain experience as a recording engineer, especially if you have the luxury of a settled studio setup and good monitoring, you’ll develop an ear for how the mic signals interact, and learn to adjust mic placement accordingly, carefully moving them around and listening for changes. You’ll also learn to check the effect of inverting the signal polarity, and you might even start measuring the distance between the key mics and kit pieces (particularly the snare and overheads) to minimise problems between them. But, eventually, you’ll reach the point of diminishing returns (and impatient artists!) and must hit the Record button. And, of course, we’re not always at the recording session; increasingly, I’m asked to work with recordings made in a home studio, where the limitations of the space, monitoring and perhaps gear usually mean there’s limited scope to fine‑tune the mic placement.

Either way, once the signals have been committed to ones and zeroes in our computers, we might still hear problems and feel the need to refine the relationship between the tracks by nudging the audio for different mics forward or back, and experimenting with polarity inversion. This can sometimes deliver improvements but it can be very time‑consuming and often unsatisfying: given the number of individual mic‑to‑mic relationships, an improvement in the sound of one kit piece can easily have unintended consequences for another.

Instant Fix?

Wouldn’t it be great if there were a quicker, easier and more effective way for people to make all these tracks work together better? Auto‑Align aims to be just that. The original version was a real‑time plug‑in (AAX, VST, AU) that required you to place a separate instance on every track you sought to align. You specified which instances were references, and which were to bring the audio into alignment with those references, choosing to align in terms of time and/or signal polarity. The timing was sample accurate, and while the routing and detection was only possible in the real‑time version, Pro Tools users could also copy the results to an offline AAX AudioSuite plug‑in for processing. That it quickly became popular is not a surprise — it was a much more efficient way of performing a task that had hitherto been a painstaking manual one — but there were some mental gymnastics involved in organising the multiple instances to secure the very best results and, as with manual nudges and polarity inversions, there were still some issues that it struggled to address.

In Auto‑Align 2, Sound Radix have simplified the user experience considerably, as well as providing greater functionality and helpful visual feedback. Notably, they’ve added ARA2 to the list of plug‑in formats, which is welcome news, since Auto‑Align 2 is intended for use at the beginning of the signal chain. The ‘listening’ process is now only required when using the non‑ARA version of the plug‑in — the real‑time version of the plug‑ins must be allowed to ‘listen’ to at least 30 seconds of audio. But capturing can also be done faster than real time by simply bouncing the project’s range: when playback is stopped, either by the user or when the bounce is complete, Auto‑Align 2 will automatically analyse the audio and apply its processing.

Another key new feature is the inclusion of all‑pass filtering, or ‘phase rotation’ as it’s sometimes known. This allows the algorithms to optimise the phase relationship between tracks with far greater precision than can be achieved with a combination of nudging and polarity inversion alone. There’s also revamped visual feedback, with options to display what AA2 is doing as waveforms or a correlation meter.

The correlation meter view, which takes the place of the waveform view in the main picture.

In their promotional material for the release of AA2, Sound Radix recommend putting an instance of Auto‑Align 2 as the first plug‑in on every track in your session. There’s nothing really to be gained from putting it on any tracks that have no time or phase relationships with others, but neither will it do any harm to tracks it doesn’t need to process, and putting it on every track would avoid you having to think about which tracks may benefit and which won’t.

With your multiple instances in place, there’s none of the faffing around the original version required. You don’t need to decide and specify which tracks need to reference which others: you simply hit the Align button in any one instance. Auto‑Align then sorts the various instances into ‘correlation groups’ based on what its analysis suggests they have in common, and attempts to correlate all the signals in the group with each other, aligning everything to the earliest signal in that group, and then applying polarity inversion/phase shift as required.

For a traditional rock band mix, for example, Auto‑Align 2 would typically place all the drums into one group, and align the other tracks to the timing of the kick or snare close mic. It would create another group for the mic and DI of a bass, and align to the DI. It would make another for any guitar part recorded with multiple mics... and so on. There are no interactions between the different groups, but the timings we’re dealing with here aren’t going to interfere on a musical/rhythmic level, and it’s also possible to go in and reassign tracks to different groups manually should you feel the need.

With a bare minimum of user input, then, AA2 can automatically optimise the time differences between your mics in a way that ensures maximum reinforcement and minimum cancellation. It saves a lot of time compared with manually nudging tracks into place, and if that’s all you need to do it could quickly earn its keep. But the real impact of this tool lies in its ability to manage the complex phase relationships between different mics. Described by Sound Radix as a “spectral phase optimisation” stage, all‑pass filters are used to shift problematic frequencies on one track to bring them into alignment with corresponding frequencies on another. This is static filtering, similar to that used in Auto‑Align Post 2 to compensate for the use of a fixed high‑pass filter being used on one mic but not others. We don’t have the ability of that plug‑in or Sound Radix’s Pi (both of which are worth checking out!) to dynamically manage the phase rotation, but a benefit is that after the initial alignment the plug‑in has done all its work, so your CPU is freed up for other things.

In Practice

That’s the theory, but how good have I found this plug‑in in practice? As soon as I got my licence, I downloaded and installed AA2 (a painless process) and put it straight to work on a mix I was doing for a rock/emo band I’d recorded in my studio. I was especially keen to hear what it would do to my drum recordings. I take great care when recording drums at my studio, and wasn’t looking for AA2 to ‘repair’ anything, but I had to admit that it made the close and outside kick drum mics sound fuller and more punchy — definitely a worthwhile improvement. The toms also seemed to benefit a lot from the processing, and I was struck by how much more pronounced the stereo imaging was when the drummer moved from the rack to the floor tom during fills. Overall, there was a clearly audible positive effect on the drum sound as a whole, and the thing I was most pleased about was that it seemed to sound natural, artefact‑free and generally not ‘mucked around with’. Not bad for the push of a button!

The other source in the same mix that had the potential to benefit from AA2’s processing was the bass guitar, for which there were separate tracks for the close‑miked amp, a clean DI, and a stereo room mic that I’d left up from the drum tracking. I felt that this was a good test for AA2, because before any processing I could hear some interesting ‘phase issues’ when bringing up the room mics that resulted in a pleasing, full‑bodied bass sound. After AA2’s processing, the combined bass channels seemed to have less of the ‘subby’ low‑end, but the bass did feel more solid around 75‑150 Hz — subjectively, I’d say there wasn’t really a clear ‘winner’, as there had been with the drums, but AA2 did present me with a different and still appealing option which I could decide upon in relation to the rest of the mix.

I also tried AA2 on a few other projects, in which the recordings were a bit more delicate and less drum‑heavy. On an acoustic guitar recording, I liked how it naturally seemed to pull together different microphone options from the same take and make it more viable to use a combination of channels and adjust their balance without unexpected changes in tonality. Again, the differences were most audible towards the lower end of the frequency spectrum, which is where phase problems often tend to present themselves. Getting into even more delicate territory, I used AA2 on a harpsichord recording session. I was experimenting with finding the best way of capturing the sound of an instrument that I wasn’t very familiar with, and found that AA2 worked superbly for combining two mics that were focused on different aspects of the instrument.

The results were much more dramatic and impressive than I’d expected...

I also made a point of seeing what AA2 could offer me on some material that someone else had recorded in a home studio, and which I’d been tasked with mixing. The results were much more dramatic and impressive than I’d expected, and with a drum recording on which, frankly, everything was out of phase, it made a huge difference to every aspect of the drum sound. The snare sounded much fuller, the low end of the kick drum became powerful, transients generally were much more pronounced, and the sense of stereo placement was dramatically improved. Very impressive! AA2 is not a reason to throw good engineering (or studios) out of the window, but it is a great tool for bringing a sub‑par recording up to a workable quality level.

Stars Align?

While I’d been impressed with the original version of Auto‑Align, it could sometimes be a faff to set up and I was sometimes left with the sense that I could hear subtle artefacts, where the processing struggled to make the most of the recordings. I had no such sense with AA2, which seems better in every way.

The automatic grouping saves so much time, and the results have so far always been good. For those working with material that hasn’t been professionally recorded, this plug‑in could have a hugely significant impact, since its ability to improve recordings laid down in less than optimum settings is very impressive indeed. But what most impressed me was the subtle improvements it can make to already good recordings. Without wishing to blow my own trumpet, I’m a drummer as well as an engineer and have learned over many years to hear how phase problems affect mic setups and recordings. For a user like myself, AA2 is a simple, reliable option for subtle but worthwhile ‘enhancement’ — I’ve used it on every project since downloading it! It also has plenty of potential as a tool that allows you to get more creative at the recording stage, for example trying mic options you previously couldn’t get to work phase‑wise, or experimenting with more assertive EQ.

Drums may be the most obvious candidate for AA2 treatment but it works great for guitars, acoustic instruments and, in fact, any source recorded with multiple mics or channels. It’s a plug‑in that is very easy to use and well worth demo’ing on your next project. Just promise me you won’t let it lead you to make lazy recording decisions!