Acustica’s non-linear convolution technology is constantly evolving, and two new plug-in suites provide a dazzling showcase for their latest Core12 engine.
Acustica Audio have pursued their distinctive approach to replicating sought-after studio hardware for many years now, and the fruits of their labour are becoming increasingly hard to ignore. Both as individual plug-ins with custom user interfaces, and as libraries for their Nebula software, Acustica’s product range must be the largest collection of mouth-watering vintage and modern gear available for any software platform. And it’s crucial to note that these are not emulations or models, such as you’ll find in other manufacturers’ catalogues; Acustica products are lovingly and exactingly ‘sampled’ from original hardware using the company’s proprietary Volterra Series non-linear convolution technology. This is an advanced form of dynamic convolution which allows very accurate modelling of the time-dependent behaviour of non-linear analogue circuit components like inductors and capacitors.
What’s driving a rapid increase in the popular awareness and acceptance of Acustica’s plug-ins isn’t just the massive product range, or their sound quality. Acustica have also been working hard to overcome technical hurdles that have hindered the technology, most notably its reputation for high CPU load and sluggish or limited user control. The two products under review here represent the latest iteration in this technological conveyer belt, using a new processing engine that Acustica call Core12. Pink2 and Ruby are available for all major native plug-in formats on both Mac OS and Windows.
The original Pink plug-in appears to have been something of a milestone for Acustica, and with Pink2, they’ve really gone the extra mile to show what their technology is capable of. Pink2 is not just one plug-in but an entire suite, comprising preamp circuits, four-band semi-parametric equalisation, 10-band graphic EQ, and compression. All of these are included as separate plug-ins, and there’s also a channel strip plug-in that brings together most of these elements in a single insert slot. Thanks to the stylish and fairly faithful skeuomorphic graphics, you don’t need to be Hercule Poirot to work out that API hardware is the ultimate source of all of these processors. However, as well as including precise replications of well-known modules such as the 550 and 560 equalisers, Acustica have also combined and adapted aspects of the original gear to create plug-ins like Pink 7236, a multiband compressor that, to date, does not exist in hardware form.
Installation and authorisation of Acustica plug-ins has sometimes been a bumpy ride in the past, but the company’s new Aquarius download manager and licence centre worked painlessly for me. Another historical bugbear of Acustica plug-ins is the responsiveness of the user interface; there can be a perceptible delay between clicking on a button or turning a knob, and and visible or audible change taking place. This has been progressively reduced in more recent products, and I’m pleased to report that, for the most part, it isn’t a problem in the Pink2 plug-ins. Some of the buttons still have a delayed response, but they are mostly the ones that switch between different modes; the basic EQ and dynamics controls feel smooth and immediate.
A lot of work has gone into the graphic design of the Pink2 plug-ins, which look great. Although they’ve used convincingly API-styled knobs, Acustica have separated out any dual-concentric controls, which will come as a welcome relief to anyone who’s tried to use virtual dual-concentric knobs in other plug-ins. In general, the user interface is clear and easy to use, but Acustica have managed to throw in a couple of small curveballs. Each EQ band, and the compressor, features several different mode buttons and a power button. It takes a while to internalise the fact that when the power button is illuminated, this actually means the associated processor is in bypass mode; for it to do anything, you need to click one of the mode buttons, whereupon that lights up and the power button goes out. Some of the buttons governing the compressor functions are also unnecessarily cryptic, such as the use of the Venus symbol on the channel strip plug-in’s side-chain high-pass filter button.
The Venus theme, incidentally, continues in the PDF manual. This obviously started with thorough, clearly illustrated, well written text, which was then cut up, reassembled in a random order and interspersed with pages from an encyclopedia of the Solar System. Bonkers, but charming in its way.
As a plug-in suite, Pink2 is obviously designed to cater for every stage of conventional signal conditioning. In the hardware world, that would begin with preamp coloration, though naturally in DAW-land you are free to use Acustica’s Pink2Pre plug-in at any point in your signal chain. This is the simplest of the plug-ins, offering only a choice of eight preamp circuits and an Input Trim control. This last is automatically compensated for at the output, so doesn’t change the apparent loudness, but merely drives the chosen preamp circuit to a different extent. There is no metering, but it doesn’t really seem necessary since the effect is very subtle — even when I placed the plug-in on the master bus and cranked the Input Trim right up, I couldn’t get any obvious distortion out of it. Such effects as it has are mostly apparent as a tightening of the bass and a brightening or hardening-up of the mid-range. The differences between the preamps are most easily detected on electric guitars, but I liked some of them as master bus or drum bus processors also.
Acustica’s progress in making non-linear convolution CPU-efficient also means that you can use the Pink2Pre plug-in across multiple tracks in a mix, if you so wish. I tried this and liked the results, but found the effect very similar to that of using a single instance on the master bus. Given that there is no way of synchronising control changes across multiple instances of the plug-in, as you get in console emulations from the likes of Slate Digital, I’m not sure I would bother using it this way very often.
Although graphic equalisers are common in live sound and hi-fi, they are perhaps less often found in recording circles; but if you do see one in a studio, chances are it’ll be an API 560. This workhorse is faithfully recreated in Acustica’s Pink2 780 plug-in, complete with optional preamp circuitry. As with the hardware, the frequency of each band is well chosen, it sounds good, and what it lacks in flexibility it makes up for in immediacy.
Altogether more comprehensive, however, is the Pink2 1650 EQ plug-in, which collects together various other API and related designs under a single virtual roof. This too offers a switchable preamp stage, but also serves up fixed-frequency low- and high-pass filters as tasty hors d’oeuvres before a main course comprising four bands of semi-parametric equalisation. I’ve described these as semi-parametric because there is no bandwidth control, but each has a button that engages ‘proportional Q’ mode, whereby the bandwidth changes automatically as the gain is adjusted. The two outer bands also have buttons allowing them to be switched to a shelving response, while the two middle bands between them span the entire mid-range; the mysterious D equaliser, which is described as being “sampled from a very elaborate, ‘hot-rodded’ outboard processor”, was originally a three-band device, so its two middle bands are identical.
As described, the ‘power’ button for each band is actually the bypass mode, but there’s also another user interface quirk that is slightly annoying in extended use. Reflecting the original hardware, the various EQ modes have different sets of fixed frequency points, spaced differently around the range of the frequency knob. When you switch between two modes, the frequency knob snaps to whatever setting is graphically nearest, rather than to the closest frequency available in the new mode. So, for example, the upper mid band in both the A and B modes has a 3kHz setting, but if you choose 3kHz within the A mode, then switch to B, the pointer will appear at the 10kHz position. Reset it to 3kHz and switch back to A, and suddenly you’re boosting at 800Hz instead. It’s a minor point but one that I hope might be addressed in an update some day.
To my ears, it’s these equalisers that provide the strongest confirmation of the benefits of Acustica’s approach to recreating hardware, because not only do they sound a world apart from generic digital plug-ins, but there are also clear differences between the four EQ types. What they all have in common, though, is that their effect is immediately obvious as soon as you apply any boost or attenuation. Although the nominal gain range is ‘only’ ±12dB, I can’t imagine a situation where you’d ever want more, and during the entire review period I don’t think I ever found a need to go beyond 4dB of cut or boost. API gear has the reputation of sounding very ‘forward’ and aggressive, and that’s particularly true of the B and C equalisers. Still, none of them is exactly a shrinking violet of the audio world. I don’t think this equaliser will see much use on classical or soft jazz music, but for rock & roll, it is the proverbial canine’s frivolities.
And so to Acustica’s Pink 2412 compressor plug-in, which is not-so-loosely derived from the API 2500, I presume. It lacks that unit’s variable stereo linking control, but adds a wet/dry balance knob for parallel compression, and boasts an even more comprehensive range of side-chain filtering options, as well as the characteristic option to switch between feedback and feed-forward detection modes. There’s also the ‘shape modulation’ control found in other Acustica compressors such as their Sand SSL-a-like. This, in essence, controls the linearity of the onset of compression. At some point in the middle of its travel, the attack phase is broadly linear, so if you were achieving 10dB gain reduction at a 10ms attack time, 5dB of that would be reached 5ms after the triggering of compression. Lower values ‘front load’ this gain reduction so that more of it takes place earlier in the attack phase, whereas at higher values, most of the gain reduction occurs towards the end of the phase. This has a profound effect on the response of the compressor, especially in terms of its reaction to bass-heavy signals.
The 2500, or at any rate Acustica’s ‘sampled’ version of it, is actually a pretty versatile compressor. The original is, of course, one of the more celebrated master bus compressors around, especially for rock music, but it’s a lot more than that. At low ratios and with the knee set to its softest settings, it provides impressively gentle yet firm control over musical dynamics, and it’s also a very capable performer on individual sources such as drums, vocals and bass guitar.
Of all the Pink2 plug-ins, however, the one that saw the most use in my own mixes was the Pink 2715 channel strip. This surprised me, because I don’t usually like channel strips. In general, I’d rather add EQ and dynamics separately as and when I decide that something needs them, but in this case, Acustica have cherry-picked features from the other plug-ins in exactly the right way, creating a channel processor that is versatile and powerful, yet lean and focussed.
In essence, this plug-in combines a single preamp circuit with most of the core features of the 1650 equaliser and 2412 compressor, but it leaves out a few specialist options in each case. So, for instance, the D equaliser type is missing from the EQ section, while the compressor has a single high-pass filter button in place of the 2412’s comprehensive selection of filter shapes and frequencies. It also lacks the latter’s shape modulation and programme-dependent release time settings, and whereas the 2412 operates permanently in the CPU-intensive ‘insane’ mode, this is a switched option here. Collectively, these omissions contribute to making Pink 2715 light enough on system resources to be usable across individual channels within a mix, without seriously impairing its flexibility. The only feature that I imagine some people will miss is the option to switch the compressor before the EQ in the signal path.
Acustica Audio’s products have long had a devoted cult following of engineers who are convinced that nothing else quite captures the sound of analogue in the way that non-linear convolution can. For purists, the sheer quality of the sound has always outweighed the negatives that have accompanied the technology, such as heavy CPU load. Over the last few years, Acustica have put an enormous amount of work into overcoming these negatives and, to my mind, they’ve reached the point where there really isn’t much difference from a usability point of view between these Core12 plug-ins and high-quality modelling processors from other manufacturers.
At the same time, they’ve not only maintained but actually improved the quality of their ‘sampling’, thanks to the use of a new and advanced noise-reduction process that is said to preserve transients more faithfully. And, with plug-ins like the 7236 multiband compressor, they’re actually starting to go beyond the capabilities of the original hardware that’s being sampled. I don’t think the day is quite here yet when you can run a busy mix on a single computer using only Acustica plug-ins, but the need to ration their usage is declining, while the sonic benefits continue to pile up. If you’ve not yet dipped a toe into the non-linear convolution waters, I urge you to try out one of the new Core12 suites.
There are numerous emulations of API gear that use modelling rather than non-linear convolution technology, including officially licensed plug-ins by Waves and Universal Audio. I don’t know of any other plug-in that recreates the DW Fearn VT‑5, though.
If I had to mix using Acustica’s Pink 2412 and no other compressor, I can’t imagine there’d be many situations where I felt restricted; but were I to find myself in a hole, it’s quite possible that their Pink 7236 plug-in would help out. This employs elements from the Pink2 plug-ins and other Acustica products as building blocks to create a three-band compressor that is both authentically API and unique to Acustica.
The control set begins with another preamp emulation, before the signal encounters a crossover. This provides what looks like two of the EQ bands from the 1650 plug-in, with a selection of stepped frequency points; to form a crossover, though, they need to behave as high- and low-pass filters, and since there’s no suitable API original from which to ‘sample’ these curves, they are taken respectively from Acustica’s Titanium, Ivory and Emerald plug-ins. Each of the three filtered frequency bands then passes through what is, in effect, a full-blown version of the 2412 compressor with its own control set. The only compression parameter that is common to all three is the feedback/feed-forward setting, though there is the option to link controls so that you don’t have to do too much clicking and dragging.
It is, I think, fair to say that Pink 7236 is likely to get more use in mastering contexts than in mixes, if only for purely practical reasons. Although Acustica have generally done an impressive job of getting the CPU load down in the Pink2 plug-ins, a single plug-in that combines three exhaustively sampled compressors, a preamp and two EQ bands inevitably eats CPU cycles like they were going out of fashion. Introducing it onto the master bus in a mix usually caused my Mac to cough apologetically and give up. I also thought it a shame that there are no presets supplied; as this is a complex plug-in with no real-world counterpart, it would be nice to have a few typical setups available at the click of a mouse to help the user explore what it can do. However, this is not a major obstacle as long as you’re familiar with the basic operation of a multiband compressor.
In use, it quickly becomes apparent that this is not only a very versatile processor, but one that sounds great almost regardless of how it’s set up. Starting with the most vanilla settings I could think of, I loaded it up on an indie-rock mix I was working on, and the effect was impressive: although the gain-reduction meters were clocking scary amounts of compression, the music still felt full of life and energy, and by adjusting each band’s threshold and make-up gain controls, it’s possible to make fairly radical alterations to the tonality of a track without giving the impression that it ever sounded any other way. Parameters such as the shape modulation and the feedback/feed-forward toggle make substantial changes to the effect, but although the alternatives can sound very different from one another, they often sound equally good. I found Pink 7236 particularly valuable for its ability to make almost any mix sound bright and vibrant without ever getting harsh or spitty.
At the time of writing, one other plug-in besides the Pink2 suite is available using Acustica’s Core12 technology: Ruby, an officially authorised recreation of the DW Fearn VT-5 stereo valve equaliser. This is a unit that retails somewhere around the £8000 mark, so the benefits of having an affordable software recreation are obvious!
The VT-5 is one of many ‘Pultec-inspired’ designs that use a passive inductor-capacitor circuit to perform tonal changes, with a valve gain stage making up the resulting loss of level. As such, it was interesting to compare the Ruby plug-in with Acustica’s White, which ‘samples’ another Pultec-based mastering equaliser, because the two sound surprisingly different.
In both cases, it’s possible to switch the valve gain stage on and off, but whereas the White amplifier is quite warm-sounding and a bit hairy if pushed hard, the valve circuitry sampled here tends to add sparkle at the high end, and perhaps to tuck the mid-range in somewhat. The equaliser itself is also noticeably different from the White equivalent, and not only because of the slightly different selection of switched frequency points. The White sound tends towards the soft and forgiving end of the spectrum, and in comparison, Ruby is more authoritative: never harsh, but focused and clear, and invariably requiring less dramatic cut or boost settings on the same material.