Sharing the Load

When you see an audio plug-in running on a computer, it's natural to assume that the processing is being handled by the computer. The digital signal processing
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When you see an audio plug-in running on a computer, it's natural to assume that the processing is being handled by the computer. The digital signal processing (DSP) software, however, may actually be running on a PCI card inside the computer or on an external hardware device connected to the computer by USB or FireWire. When DSP is carried out inside the computer, the processing is called native; software that uses additional hardware connected to your computer for its DSP is called hardware accelerated, and the additional hardware is called DSP-accelerator hardware. Traditionally, hardware-accelerated systems have been the realm of the high-end production studio, but today some DSP-accelerator cards are even less expensive than native plug-in bundles. In this article, I'll discuss various DSP-accelerator-hardware options and how they compare with native solutions.

Hardware-accelerated DSP offers some significant advantages, the most obvious being that it adds processing power to your computer. Arguments about whether native or hardware-based systems are more powerful miss the point; DSP hardware supplements, rather than supplants, native processing. With a Pro Tools Time Dimension Multiplexing (TDM) system, for example, you can use the DSP power of your hardware to run TDM plug-ins, and the native power of your computer to run RTAS and HTDM plug-ins. When using Universal Audio UAD-1 Powered Plug-in or TC Electronic PowerCore, you can run DSP-based and native plug-ins on your host application. You'll always get more processing power when you use a combination of hardware-accelerated and native processing.

DSP Flavors

DSP-accelerator hardware comes in a variety of flavors. PCI cards that fit inside your computer, such as the UAD-1 PCI card (see Fig. 1), the PowerCore PCI card, the Digidesign Pro Tools HD|Accel system, and the CreamWare Pulsar/Scope system are the most common. External rackmounted DSP-based hardware devices that connect to your computer via USB 2.0 or FireWire have also begun to appear. TC Electronics' PowerCore FireWire is one example.

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FIG. 1: Universal Audio''s UAD-1 Powered Plug-in PCI card runs software models of classic analog hardware compressors and EQs, such as this emulation of the Fairchild 670.

There are two types of hardware-based DSP systems: self-contained systems and systems that work with a variety of native software hosts. With a self-contained system, everything related to audio processing is handled by the DSP hardware, including audio input, all signal processing and mixing, and audio output. Only the proprietary editor software runs native on the computer. The best known proprietary system is Pro Tools TDM. With a Pro Tools TDM system (there are Mix, HD, and HD|Accel versions available, each with different track counts and DSP power), the TDM hardware handles audio I/O using special TDM-only audio interfaces, mixes audio together with its 48-bit hardware mixer, and provides for effects processing using hardware-based TDM effects. The Pro Tools software serves as a native front end for the TDM hardware. Merging Technologies' Pyramix system is another self-contained audio production solution.

Nonproprietary hardware accelerators are not limited to working with a specific native-audio engine and allow you to integrate their DSP with plug-ins running natively in your chosen host software. Examples include the UAD-1 and PowerCore PCI cards. Those run proprietary plug-ins on their DSP hardware that integrate with plug-ins in formats such as VST, AU, and DirectX that are running native in your host software.

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FIG. 2: The PSP Audioware ProZilla series of plug-ins allows you to use a VST host application to configure the plug-in before transferring the effect to the Manifold Labs Plugzilla.

Some hardware DSP devices offer several options. CreamWare's Pulsar/SCOPE is a PCI-card system that can be used as a self-contained system or as a DSP accelerator, allowing its proprietary plug-ins to be used alongside native VST plug-ins. Manifold Labs' Plugzilla and Muse Research's Receptor offer hardware-based VST plug-in hosting as well as standalone use when disconnected from the computer (see Fig. 2). That is especially useful for performing musicians who want to take their VST plug-ins on the road.

Extra Power

Another advantage of hardware-based DSP systems, which applies only to self-contained hardware systems such as Pro Tools TDM and Pyramix, is that they don't have the recording latency inherent in native audio systems. For those not familiar with this phenomenon, let me explain.

When you record audio on your computer, your audio interface converts the incoming analog signal to digital form, and then your computer stores chunks of the digital data in a temporary memory buffer before passing it on to your audio software for processing and writing to disk. The size of the temporary buffer determines the lag time between when the data enters the computer and when it reaches your audio software. Smaller buffers offer lower latency, but they increase the demands on the CPU because the data in the buffer has to be shuttled to the software more often. As a real-world example, recording at a sampling rate of 44.1 Hz with a 512 byte buffer calculates to a latency of 11.6 ms, a noticeable lag. DSP-based systems, on the other hand, devote their DSP hardware solely to processing the incoming audio and do not experience any buffering at all. That is why a Pro Tools TDM system can record an entire symphony orchestra with virtually no latency.

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FIG. 3: The Sony Inflator plug-in runs on the TC Electronic PowerCore series of DSP accelerators and can be accessed in any VST- or AU-compatible native audio software.

DSP hardware-based systems offer higher quality processing than native systems. Native software can, in theory, do everything DSP-accelerated software can; however, native systems have to do a lot more than process audio. DSP-accelerator hardware is completely dedicated to audio processing, and developers do not need to compromise performance to leave time to run the computer's operating system and other software applications. Developers can therefore design complex, DSP-intensive applications that would bring a native system to its knees. Some of the most sought-after plug-ins are available only for hardware-accelerated systems because they are too processor intensive to run native (see Fig. 3).

For a Price

Using DSP hardware accelerators is not always a bed of roses. For starters, there is the price. Self-contained DSP systems tend to be very expensive — even the least expensive Pyramix or Pulsar/SCOPE system with enough DSP to record and mix a complete song will cost you more than a couple of PCs. The least expensive Pro Tools Mix system and interface retails for around $6,000. A cutting-edge Pro Tools HD|Accel rig with a high-end Digidesign 192HD interface will set you back three times that amount. Increased DSP power and I/O costs even more. Recently, DSP-accelerator hardware that's more affordable (under $500), such as the UAD-1 Project Pack or the PowerCore Element, have begun to appear, but adding more DSP or additional proprietary plug-ins can still boost the price to above that of the computer itself.

If you opt for one of the nonproprietary DSP accelerators to integrate with your native software, plug-in latency will be the bane of your existence. When you mix hardware DSP with native software, you are routing the audio from your native software to your accelerator hardware and back again, which takes time. Using DSP hardware plug-ins in native software will roughly double your latency, and unless you use delay-compensating plug-ins or manually shift your audio tracks, tracks that use DSP hardware plug-ins will not be in sync with tracks that don't. Thankfully, most audio applications are now able to compensate for this delay automatically when playing back audio. Unfortunately, it is not possible to compensate for this latency on live inputs, so it is generally not feasible to use hardware based DSP plug-ins during recording, at least if you want to monitor the results.

Perhaps the most significant price for integrating DSP hardware with native software is that there are more — and potentially more serious — compatibility issues to deal with (see the sidebar “DSP Hardware Hell”). Sometimes there are basic platform compatibility issues: for example, CreamWare is still working on OS X compatibility for the company's Pulsar/SCOPE system, the Pyramix system is PC only, and many Pro Tools TDM plug-ins are Mac only. Other times there are more subtle and insidious problems such as your PC's video card causing problems with your DSP card, your Mac's PCI cards not being arranged properly to get the best performance out of your DSP hardware, or too many FireWire devices adversely affecting the throughput of your FireWire DSP hardware.

Although some people never experience any hardware issues, others are unable to ever get their hardware DSP devices to work together properly. Generally, the fewer unknowns in your system, the less likely you are to have problems. For example, Pro Tools users can rely on the Digidesign compatibility charts to determine if a particular computer model is approved for a given setup. On the other hand, users trying to integrate DSP hardware into an already extensive native setup encounter many more variables, and manufacturers' guidelines are far less specific.

DSP in the Balance

The ultimate questions are does DSP-accelerator hardware live up to its hype, and how do the negatives play out in the real world? Quality DSP-accelerator hardware really does make the grade. The UAD-1's simulations of analog compressors and EQs are spectacular. PowerCore has world-class proprietary effects and excellent third-party plug-ins. CreamWare offers some of the most well-regarded synthesizers available. The sound of the Pro Tools HD and HD|Accel mixer is practically unmatched, and many TDM plug-ins surpass anything available for native systems.

For those on a limited budget, however, self-contained hardware systems are most likely out of reach. Although a project-studio owner may be able to stretch for a Pulsar/SCOPE system or mortgage the house for a Pro Tools HD rig, that money might be better used buying a collection of high-quality microphones or other essentials. On the other hand, DSP-accelerator cards do offer a fantastic value for both project studios and home users. If you are considering spending $400 to $500 on a plug-in bundle for your desktop computer, it's definitely worth considering buying a DSP-accelerator card.

Orren Merton is the author of Logic 6 Power! (Muska & Lipman, 2003) and GarageBand Ignite! (Muska & Lipman, 2004). He can be reached

I recently assembled what I considered to be a dream system: a dual-G5 2 GHz PowerMac, a TC Electronic PowerCore PCI card, a Universal Audio UAD-1 Powered Plug-in PCI card, and a Metric Halo ULN2 FireWire audio interface. I combined the most powerful Mac ever built with two spectacular DSP-accelerator PCI cards that have excellent plug-ins and arguably the most professional-sounding FireWire audio interface on the market. I chose a FireWire interface on the assumption that keeping audio I/O on the FireWire bus instead of running everything on the PCI bus would result in better performance. So much for assumptions.

I immediately encountered an apparently intractable problem with the combination of PCI and FireWire — FireWire audio intermittently sputtered and dropped out. At times, switching applications appeared to be the culprit, but other times the audio would die without any discernable cause, and the only way to recover it was to reboot. It was clearly a G5 FireWire-compatibility problem, because it didn't happen with built-in audio or USB audio or on a PowerMac G4. My ideal system was seeming less ideal by the minute!

At first I suspected the FireWire interface, but it turned out that the problem was always immediately preceded by a specific FireWire-driver failure that was not generated by the interface. Next, I turned my attention to the DSP cards and the various native plug-ins I had installed in my system. I consulted with the various manufacturers, who were all very helpful but were completely stumped.

After months of troubleshooting, a definitive solution has still not been found, but the problem has been identified as a low-level FireWire driver-controller issue with the G5 motherboard. That manifests itself only when the G5's PCI-X slots are filled with high-bandwidth PCI cards and audio is being streamed to a FireWire audio interface. Due to some bus arbitration issue, FireWire audio is being cut off. Until Apple delivers a system or firmware update, or developers figure out a way around this issue, I'm out of luck.

So did I give up on hardware DSP accelerators? No. I knew I was on the cutting edge and, unfortunately, got sliced. I switched to an RME Hammerfall DSP 9632 PCI card for my audio interface and can now use my G5 with both DSP cards for audio processing, the ULN2 converters for their sound quality, and the RME card for audio I/O. Having the quality of the DSP cards was well worth the hassle and expense.