Field Test: Digidesign Accel PCI DSP Card

Feb 1, 2004 12:00 PM, By K. K. Proffitt


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Digidesign's new Accel PCI DSP cards deliver nearly double the DSP power of the original Pro Tools|HD DSP cards, resulting in almost a 50-percent increase in the number of available voices across all sample rates, from 44.1 kHz to 192 kHz, as well as support for DSP-intensive plug-ins that will work only on an Accel-enhanced system. For those of us who jumped directly from Pro Tools|24 Mix systems to Accel, that's quadruple the power of the old Mix DSP cards and triple the voice counts at 44.1 kHz/48 kHz. Accel cards retain two of the HD Process Card “Presto” chips, but add new 321 chips for DSP processing.

Configurations include HD 2 (an original Pro Tools|HD Core Card and one Accel card) and HD 3 (HD 2 and another Accel card). HD 2 supports 64 channels of I/O with Pro Tools audio interfaces, while HD 3 supports 96 channels. With either HD 2 or HD 3, you can have up to 192 simultaneous audio tracks at 44.1 kHz or 48 kHz. At 88.2 kHz or 96 kHz, the number drops to 96 tracks, and at 176.4 kHz or 192 kHz, you get 36 audio tracks.

If you already have a Pro Tools|HD system, then you can add Accel cards to your system — they'll co-exist peacefully. The only caveat is that systems using an expansion chassis must use a certain card order: core card first, then Accel cards and then HD Process cards. All plug-ins that work with Pro Tools|HD first-generation systems, including TDM, HTDM, RTAS and AudioSuite formats, should work with Accel-enhanced systems, because the new systems include the older Core card.

To run an Accel-enhanced Pro Tools|HD system, you'll need a supported PC running Windows XP Professional or Home with Service Pack 1 or a Macintosh G4 or G5. G4s require Mac OS 10.2.6, 10.2.8 or Panther with Pro Tools 6.2. G5s need OS 10.2.7, 10.2.8 or Panther with Pro Tools 6.2r2. Users should check for updated requirements and new revisions.


I chose to order an HD 3 system and two extra Accel cards. This arrived with the current HD pack of bonus plug-ins that included Impact, an “Accel-only” compressor, and Pro Tools Version 6.2, which is required to support Accel configurations.

My Pro Tools|HD 3 Accel “plus two” arrived with Pro Tools|HD Pack V. 5.0, a collection that varies in number depending on the size of the purchased system. For HD 3 Accel, it included the Digirack plug-ins, as well as d2 and d3 by Focusrite, Virus Indigo by Access Music, Amp Farm by Line 6, Speed by Wave Mechanics, Oxford EQ by Sony and five other plugs by Digidesign: Maxim, D-Fi, Reverb One, Bruno/Reso and SoundReplacer.

Fortunately, third-party developers like Waves, Wave Mechanics, Sony, Access Music, Eventide, Aphex, Crane Song, Focusrite, Line 6, Emagic, INA-GRM, DUY, Massenburg Design Works, McDSP and TC Works provide Accel-ready updates for their plug-ins. To check on current compatibility, visit

Also in the pack was Impact, a mix bus plug-in designed to emulate console-style compressors. It supports up to 7.1 channels and up to 192 kHz, but not both at the same time. (7.1 is not supported at 192 kHz.)

Controls for Impact include four selectable compression ratios and variable controls for attack, release, threshold and makeup gain. Sidechain accepts a Pro Tools audio track for external keying, and you can listen to the key audio program. There's also an analog-style gain reduction meter. While novices may be perplexed by Impact at first, those who have used the SSL Quad Compressor “make it bigger” button know exactly this plug-in's purpose: monster drums that punch and pump. You can make subtle changes with Impact, too, but to hear it at its best, run a slammin' rock mix through it and squash to taste.


Pro Tools 6.2 includes a few new features in addition to Accel support. It is the first release to support the new 96i I/O audio interface, a 96kHz-capable audio interface for HD only with 16 inputs and two outputs. It also adds support for Windows Media Audio 9 format on the Windows platform, with import and export. Version 6.2 offers cross-platform compatibility with systems running Pro Tools TDM/LE 5.1, as well as import for older Pro Tools sessions. Additional features include Tempo Query and Custom Shuttle Lock Speed. Tempo Query is supported by some delay plug-ins such as Mod (or Medium) Delay II. This allows the plug-in to check the session tempo and align delay times accordingly. Custom Shuttle Lock Speed is used for transcribing. You can custom set the speed of (keypad)9 in Preferences/Operation.


I ran the HD 3 Accel system on a dual-Gig G4 with OS 10.2.6 with very few snafus. Armed with plenty of FireWire drives, I often gobble up lots of hard drive space recording at 192 kHz. There's something about recording guitars with, say, an AKG C426B with figure-8 capsules in X/Y configuration at 90∞ that is difficult to put into words, but rich detail, clarity of perceived depth of field and palpable room ambience are certainly some of the phrases that come to mind.

Was it worth it to upgrade? Definitely. We have a few other Pro Tools 24|Mix systems at JamSync and though I still use them, they're first on my list to replace when we write the new acquisition budget. Once you've driven the Accel system, it's hard to go back.

Digidesign, 650/731-6300,

Composer/engineer/producer K. K. Proffitt is the co-owner of JamSync, a surround production/mixing facility on Nashville's famed Music Row.

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