• Nick Rambo

Kicking the Door Down: An Interview with Neural DSP's Doug Castro

Doug Castro is a firm believer in splashy first impressions.


“When entering a new space that’s dominated by well-established and respectable players, you must make one hell of an entrance for people to notice and take you seriously,” he says. “Kicking the door down is more likely to work over quietly entering the room.”

Enter the Quad Cortex, the Neural DSP titan touted as the most powerful floor modeler on the planet.


“When we started conceptualizing Quad Cortex,” Castro continues, “there was a strange dichotomy regarding intuitiveness and power. The intuitive products were not all that great sounding and the better sounding units were incredibly convoluted. This made for an interesting scenario where people who wanted an uncompromising unit in terms of tone and configuration were willing to put up with a lot of pain in terms of ease-of-use.”


Castro and his team — now a 100-person syndicate that ranges from young-gun PhDs to aerospace engineers with decades of experience — considered this a false dichotomy and has set out to prove it.


“We thought that a device could be built that embodied everything that made all of the leading products great, but also have it be incredibly intuitive, and even fun, to use.”


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Castro thinks he should write a book — or commission a documentary, perhaps — about how the Quad Cortex came to be.


Of course, to tell the story accurately, you’d have to go back to where it all started — Darkglass Electronics.


“Darkglass was a company I founded and am still the owner and chairman of,” he explains. “Since I was a teenager, all I could think about was how to combine my passions for engineering and technology with music.”

Now 33, Castro moved to Finland 11 years ago to chase his dream — but it was a struggle.


“I suffered immensely to build Darkglass from the ground up. As an immigrant without two sticks to rub together, I ended up homeless a few times, having to borrow money for food or dumpster dive. I think of those times every single day.”


It was those experiences however — and the motivating reminder that everything he’s built could be taken away with a single mistake — that have been essential to his development as a business owner.


“I work tirelessly with the most talented and remarkable group of people I have ever met,” he says. “And out of everything I have built, there’s nothing I am more proud of than my team.”


One person on that team is Darkglass lead industrial designer Franco Azócar.


“One afternoon, I was having coffee with Franco and I asked ‘What types of devices do you think our users will expect 10-20 years from now?’”


Leaping from that initial quandary, Azócar and Castro began formulating specifications, interface designs and feature lists, and after a few more cups of coffee, had a working — albeit, rough — idea of what the future might look like.


Then came the second question: could their idea be fast-tracked and delivered years ahead of schedule.


The answer? Possibly.


But it was in that moment that the core of what Neural DSP would stand for came to be. And it’s the only thing Castro has been able to think about since.


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If you were aware of Neural DSP in the days before the Quad Cortex was unveiled, you undoubtedly knew the company as an emerging heavyweight in the audio plugins space.


In fact, notable players like Joe Duplantier of the French metal band Gojira and Animals as Leaders guitarist Tosin Abasi are featured as Neural Artists alongside Vulfpeck’s Cory Wong and solo artist Plini — and all have inspired Archetype plugins.


This, Castro says, is due to Neural DSP co-founder and CPO Francisco Cresp — a superbly talented producer and audio engineer with a distinct knack for distilling complex ideas and specifications into intuitive products.


“Francisco told me we should start by working on plugins and other audio processing software — something I found fascinating because until that point, my expertise as an engineer was in analog hardware. This vision of a company built fully around digital signal processing without any compromises became quite the obsession. In fact, we have made it our mission to accelerate the adoption of cutting edge technologies for music products.”


But where he believes Neural DSP has made its mark — and where it’s likely to find success in the monumental task of breaking away from the plugin marketing and moving into a hardware-based processor — is not in a particular product, but in the software that drives it.


“I firmly believe that what makes for a successful digital processor is actually the software; the hardware needs to get out of the way,” he says, adding that such a task is significantly more challenging than it sounds. “In that vein, a big part of what has made us successful in the plugin industry is the same thing that will help us succeed with hardware: extremely good sounding algorithms and a good understanding of what makes for an intuitive user experience.”


So for Castro and Neural DSP, the same passion and obsessive attention to detail that has made their software-based plugins successful, they hope, will drive lasting success on the hardware side — no matter how significant the leap from software to hardware-based designs.


Which brings us back to the Quad Cortex.


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According to Castro, there is currently no floor unit on the market that possesses anything close to the horsepower that the Quad Cortex has; it’s at least twice as powerful as the next-best-thing in terms of raw processing power.


That said — all the processing performance in the world is worthless without it sounding good, but this is where he feels Quad Cortex has the greatest opportunity for success.


“What our machine learning team achieved with Neural Capture is incredible,” Castro explains. “Being able to so accurately model an amplifier using deep-learning is a rare feat of engineering in itself, but when you make it a Quad Cortex feature, it’s borderline insane. To execute all the neural network training and real-time inference on processors — as far as we know — has never been done.”


And, obviously, it wasn’t easy.

“Development is still ongoing — and I don’t think it will ever end — but the moment we had it working perfectly on a very expensive GPU, we knew that none of it would matter if we couldn’t make it more efficient. Anyone who has worked in a complex engineering project knows that an order of magnitude improvement is extremely rare — two is just insanity — but that seems to be a standard MO for us at this stage,” he jokes, adding that Quad Cortex has been, by far, the most complex project for everyone at Neural.


And that’s just one example, he says.


“I could write pages and pages with similar stories on industrial design, UI/UX design, hardware, embedded software development, cloud infrastructure, etc. Everything about this project has pushed us beyond our limits — but we live for that challenge.”


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When the Quad Cortex made its debut at Winter NAMM 2020, intrigue was feverish, to put it mildly, but some post-event reviews were mixed. Many saw possibility in what the unit could be, but there was a heavy amount of skepticism in what was on display — even if it was just an early prototype.


However, many things about the Quad Cortex changed after NAMM and in the days leading up to the initial Tier 1 pre-order units being shipped in March 2021.


“Hardware-wise, the production model is very different from what we had at NAMM,” Castro says. “We replaced the slave SoC as the original chip we had in the NAMM version because it became extremely hard to source once COVID-related supply chain disruptions began. Such a major change late in the project is always super stressful, but in the end the extra internal memory yielded a more power device — so we were glad things played out the way they did.”


The team also discovered an anomaly in the touchscreen on the prototype units and upgraded the screens, as well as several parts that created issues in beta testing — but that’s a normal aspect of designing and mass-manufacturing complex systems like the Quad Cortex, Castro says.


The core vision, concept and design, however, have remained remarkably unchanged since the product was first envisioned in late 2017, something Castro reveals has been the hardest part — sticking to the original vision and refusing to compromise, even when the likelihood of success seemed extremely low.

And his tireless approach has paid off in a unit that’s still generating an unprecedented amount of buzz, in large part to a forward-thinking feature set that includes a drag-and-drop touchscreen, rotary actuators, WiFi capability with cloud integration and, of course, Neural’s proprietary capture technology.


“Nothing helps make a statement more than having a few superlatives in areas users care deeply about,” Castro says. “In our case we wanted to make a statement on our ability to execute and outperform anything currently in production in four aspects: processing power, flexibility, intuitiveness and portability. With the latter, a lot of mechanical engineering and industrial design was necessary to build something compact and light, yet durable.”


To achieve all their goals — even with a flashy 7” touchscreen onboard — Castro and the Neural DSP team believed the Quad Cortex’s haptic experience should be driven by necessity.


“Everything is right at your fingertips — it’s really quite something," he says. "But people love turning physical knobs. One of our sound designers suggested that using the footswitches as knobs could help us save significant real estate, as well as avoid the most common cause for gear failure, which is usually mechanical, not electronic. You can press and turn our footswitches hundreds of thousands of times — or punish them with over 500 pounds of pressure — and they’ll be just fine, which is simply impossible with a regular knob.”


Similarly, the design choice to exclude a fixed expression pedal should benefit users who have their own preferred expression pedal, while also eliminating the likelihood of a mechanical failure.


And the WiFi integration with cloud sharing means that Neural can easily build a community around the product — something only a select few manufacturers have done particularly well.


“We love to share and learn from each other, so adding these features to Quad Cortex will make it easier for users to connect and discover new sounds,” Castro says. “Cortex is a very deep device with almost endless choices, and having a rich community with tons of user-driven content will help users explore in an enjoyable and effortless way.”


Regarding the durability challenge, Castro cites his background in building hardware as testament to the Quad Cortex's potential staying power.


"It has to be durable. Fortunately, I've spent the last decade building some of the industry's most reliable hardware at Darkglass Electronics — so a lot of that know-how and experience has been key for Quad Cortex."


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As of this writing, more than 5,000 Quad Cortex units have been shipped worldwide and in their wake, a flurry of updates.


In April, several Quad Cortex bugs were fixed. In May, several more were resolved, along with a few cabinet models and a flanger being added to a library that already features 50+ amps and 70+ effects. Also in May, Neural announced that two new reverb algorithms, several amp models and an intelligent pitch shifter/harmonizer were all in the works. Finally, in June, an update for the Cortex Mobile app was offered featuring a variety of tweaks and bug fixes.


Solid progress and strong signal of Neural’s commitment to its user base for regular updates.


“Neural DSP exists to reinvent the standards of what people should expect from their music tools,” Castro says. “Better engineering cannot accomplish this alone. Everything else must be executed just as deliberately and with just as much passion and strive for excellence. Supporting the product and the community is just as important. The best product in the world is doomed without equivalent support. Regarding the update cadence, it will depend on several factors, but we would like to update and add new features as quickly as possible.”


As far as what kinds of new features to expect — that’s as secret a sauce as exactly how Neural’s capture technology works, but suffice to say: there’s plenty of potential.


“We want to make a product that is future-proof and can be expanded and taken into directions we could not possibly foresee. Quad Cortex shipped with about 5% of what it will eventually be — but if you consider that two years ago we pretty much had nothing other than an idea, imagine what we’ll be able to add to it in the next year or two.”


Possibilities aside, Castro is grateful.


“Since that first conversation many years ago, Quad Cortex has been the only thing on my mind and every waking second of my life has been dedicated to it. Every book I read, every email, every call. To give your entire life in the attempt of making something so difficult and audacious is very intense and the worst fear you can have is that when you’re ready to tell the world about it — nobody cares. I did agonize over that prospect a great deal and it’s amazing to see that those fears could not have been more unfounded. We had very, very high expectations for Quad Cortex, but what it has become is completely beyond our expectations. I feel like the luckiest man alive.”


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