Later this month, Avid will be releasing a new version of Pro Tools that unlocks their HDX cards so that they can be used in full conjunction with the host computer’s CPUs. In this article post-production and Dolby Atmos specialist Jamey Scott explains how the upcoming new HDX Hybrid engine will revolutionise his workflow.

The History Of DSP Accelerated Pro Tools Systems

For many Pro Tools users, DSP-accelerated HDX cards are largely a solution that we needed when computer processors were nowhere near as powerful as they are now unless you need zero-latency recording and monitoring. As James Richmond wrote in his article Avid Pro Tools Hybrid Engine - Massive 2048 Voice Counts Are Coming…

"In the early days of Pro Tools, DSP acceleration was essential in computer audio systems. For example, Mike Thornton reminded me that his first Pro Tools HD system was using Nubus cards running on a PowerPC 7100 Mac computer with a 66MHz clock. That computer could run 16 tracks of audio with DSP powered plugins. You can learn more in our History of Pro Tools - 1994 to 2000 article.

Compare that now to my 16-core Mac Pro with processors running at 3.2GHz, the difference is huge. However as we have all found, as CPUs have become faster and more powerful and the amount of RAM available has increased, more and more of the audio processing can be handled on the computer’s own processors, rather than shipping it off to dedicated processors."

The latest iteration from Avid - Pro Tools HDX was released in October of 2011, the HDX PCIe cards empowered Pro Tools users to run loads of DSP powered plugins, up to 192 IO channels, and up to 768 voices, which enabled professional audio users the ability to do pretty much anything they could imagine in pro audio.

But a decade is a long time in modern technology and what people can imagine doing has evolved significantly since 2011. Modern native CPUs now run circles around the DSP capacity of even a 3-card array of HDX cards and in most cases, for everyday playback and production, HDX cards offer very little advantage over a purely native solution and in many cases are a hindrance, except when you need zero-latency recording and monitoring.

However, from my perspective, this latest opening up of the HDX cards, with the new HDX Hybrid Engine is nothing short of a giant gift from Avid for post-production power users like me who benefit from the advantages of the hardware but also want to take advantage of the native CPU power of modern computers. It is truly a best-of-all-worlds scenario.

Who Still Needs Low Latency HDX Systems?

I know that a lot of music professionals still use HDX to track instrumentalists with zero latency, but I cannot speak to the experiences of that crowd as that is not a general part of my work world. My world is Hollywood audio post-production and for me and most of my pals who hang around LA dubbing stages, and zero-latency is still a very big part of our rigs.

I am a professional freelance film sound editor, re-recording mixer, and Pro Tools user for the past 28 years and a Pro Tools beta tester for the past 8 years. I’ve used most of their hardware, starting with a Session8 back in 1994, and then moving on to TDM and then HD systems. I’ve been using an HDX system since they were released and have slowly but surely expanded and exhausted its capabilities, particularly over the last few years while transitioning to mixing films in object-based multichannel Dolby Atmos.

500 Track Dolby Atmos Template Stretching HDX3 System To The Limit

Mixing a large-scale action film in Atmos with the Dolby Atmos Mastering Suite (DAMS) with my stems and recorder tracks in the same session brings my Pro Tools HDX3 system to a pretty hefty huff ’n puff. My mixing template starts at 500 tracks and then gets bigger as the mixes evolve. With these kinds of mixes, the DSP slots on the HDX cards fill up with mixers quickly and leave very little room for DSP-powered plugins as you can see from the image above. You can click on it to see a larger version.

Once I start to stack up plugins on my native CPU under the HDX Engine, my 2019 Mac Pro Rack starts to sweat a little bit, with my 12-core CPU hovering between 30-50%. The fans are running, but it’s all very doable and I’ve been turning over massive mixes during what I consider Pro Tools’ greatest era.

HDX Hybrid Engine Is A Game Changer

I’m really loving Pro Tools these days; I rarely have problems and my day to day is normally just a sit-down-and-get-to-work scenario. My days under the desk seem like a thing of the past these days. But now… in walks the new Hybrid Engine functionality for my HDX cards and let me tell you, it is nothing short of a game-changing transition for me.

After switching over to the new HDX Hybrid Engine, my system is running smoother than ever, my capabilities significantly expanded, and my native CPU, which last month hovered between 30-60% on my big mixes, now hovers between 5-10%. Yes, you read that correctly. My 12-core Mac Pro CPU rarely raises above 10%. 

What Does This New Native Functionality Do?

I was not involved in the alpha stage of this HDX evolution but in talking to my fellow testers I heard about what was happening and I was excited for it to move into the beta stage where I could get my hands on it.

I’ve been testing the beta for about 5 weeks now and when I first switched my Playback Engine to the HDX Hybrid Engine, I watched my HDX usage disappear to completely blank slots like it looks when I don’t have a session open. I pressed play and without a hitch, the session played perfectly. All of my routing switched over to Native and all of my plugins worked in Native Mode as they did in AAX DSP Mode. My IO stayed the same and all of my connections to the DAMS stayed in effect and played strong without any troubleshooting at all.

As the beta rolled on, bugs were squashed and stability became even more impressive. Preferences were added to the Playback Engine window, which improved things incrementally, such as an Intel Turbo Boost activation switch, a low-buffer optimizer, and the ability to limit the number of real-time threads, which reduces contention with non Pro Tools processes, perfect for running the DAMS in the background).

Not only did my DSP Usage Meters disappear, but my overall native CPU overhead dropped dramatically as well, to the point where my sessions idle at around 2% total and expand up to around 10% during playback, which frankly is something I simply cannot believe. How I’m able to run this many tracks, with this much routing, and this many plugins and still only use up 10% of my system during heavy loads is just shocking to me, and it shows how optimized and lean Pro Tools is becoming.

I’ve always felt that with the power of multi-core modern CPUs this kind of performance was possible but now we’re truly seeing it happen in full glory.

How is it doing this?

Beyond the obvious optimizations of running the mixers on the Native CPU, where it does so far more efficiently and streamlining host processes to ease resources when not being actively used, I honestly don’t know… I’m sure engaging the Turbo Boost on my CPUs is contributing, but from what I’ve been reading on the beta forums, one thing that we all seem to agree on is that having at least one HDX card in the system dramatically optimizes the Native load, more-so than without one and I can fully testify to that experience on my end.

Hybrid Engine, Full HDX, And DSP Safe Mode

So what about if you want to use the DSP on the HDX cards for low latency AAX DSP Plugins? Well… you can.

What’s more, you can do it in a multitude of flexible ways. You can assign specific tracks to run on the DSP and you can also assign entire bus lines with sends and receives to the DSP card. It’ll move the bus mixers onto the card and start filling up those usage lanes for as much or as little as you like.

Also, there is a DSP Safe mode, which allows you to mix both native and AAX DSP plugins in whatever order you like, just like how it used to behave in full HDX mode. Keep in mind that when using this mode, you’re building up latency by making trips back and forth from the computer’s CPU to the HDX cards, so you’ll want to keep your ordering tight so as to not build up too much latency and throw things out of whack. If you want to know more about the importance of the order of Native and DSP plugins then check out our article Avid Pro Tools Hybrid Engine - Massive 2048 Voice Counts Are Coming.

I’ve found that it’s just easier to run it all in Native Mode and stop sweating the DSP stuff. Yeah, the AAX DSP plugins cost twice as much, but it’s time to come to grips with the sunken cost factor and just move on; for me, and what I do, there’s really no advantage to AAX DSP plugins anymore, but the good news with the new HDX Hybrid Engine, is that if you want to use AAX DSP Plugins, you can.

If running in Native is so much better than HDX, then why am I keeping my cards at all?

Well, this is a real point that needs to be considered individually but there are things that still cannot be done without an HDX system, even with the Hybrid Engine. For me, I’ve trimmed down my system from an HDX3 to an HDX2 and it’s the perfect sweet spot for my current and future system. I’ll be keeping my 3rd card around in case I need more outputs to send to a stage or a remote recorder. If you’re considering dumping your HDX cards entirely, consider these remaining advantages:

1. Being able to assign tracks to record with zero latency. This is really big for me because of ADR. Talent hearing their latent echo in their headphones is just unacceptable so being able to put some tracks into zero-latency solves that. Sure, you can keep your microphone and headphone chain analogue but for me, it’s easier just to route and monitor through Pro Tools. It’s one less thing for me to think about in high-dollar sessions with impatient actors and directors and producers breathing down my back. 

2. IO options beyond 64 channels. For daily Atmos work, I send 128 channels to the Dolby renderer out of Pro Tools via 2 HDX cards (4x32 channels for each DigiLink port) into the MTRX, which is then converted to Dante and sent back into my Mac Pro over a RedNet 128ch PCIe card. You can’t do this with a Native card or Thunderbolt box which is limited to 64 channels. If you’re planning on doing work in Atmos, you’ll need a lot of IO.

3. The mysterious optimized CPU usage factor. As explained above, I’m not sure why, but having an HDX card in the system dramatically improves performance and keeps my CPU running at a cool, low hum with so much headroom I doubt I could ever actually max it out without trying to intentionally break it.

4. Syncing to multiple systems. In my own mix room, I mix by myself so I can do it all on a single system, but when I take my system to a stage to mix with another mixer and record to an external recorder, I need a way to sync to their systems. Connecting with a Sync I/O or Sync X is a critical way to do that and the cards are needed for that serial port connection.

What Does It Cost?

And here’s the real sticker shock…

It’s free with the regular updated perpetual license or subscription to Pro Tools Ultimate! This is the kind of stuff that I believe will earn customer appreciation.

Is this a strategic move or is it just kicking a dead horse?

This is adding significantly increased value to an existing product, which is hugely beneficial to current high-end users and sets us up for many more years of use from our hardware investments.

As computer processing power has increased, more and more Pro Tools users have decided that they can no longer justify the additional cost of a DSP Accelerated system. However, I believe that my use case proves the modern viability of Pro Tools HDX in critical-use professional scenarios… and there are a LOT of users like me.

I for one am hugely grateful for Avid for this move and praise their bold choice to move forward with it. 

In Conclusion

Since I started working with digital audio in the early ’90s, my work has always pushed Pro Tools to the highest limits of my systems. Because my productions have always been closely tied to the reliability of Pro Tools hardware, newer and faster computers didn’t really have a tremendous effect on my capacity, and I would have to wait for new Pro Tools hardware to see any real gains.

When HDX was released, it was powerful enough to last for a good long time, and it absolutely did, almost a full decade of daily use!

With this new era of my HDX cards being able to work cooperatively with the power of the host computer’s CPU, my capabilities are massively expanded to the point where I’m having a hard time imagining how I could ever need anything more. But then, I’ve thought that before and my learned perspective assures me that time and water always fills the empty river bed. That said, I’ll be good to go with my current system for a long time and I’m super pleased to be spending more time focused on creative ideas instead of watching my usage meters.