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Field Test: Digidesign Accel PCI DSP Card

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.

Digidesign’s new Accel PCI DSP cards deliver nearly double the DSPpower of the original Pro Tools|HD DSP cards, resulting in almost a50-percent increase in the number of available voices across all samplerates, from 44.1 kHz to 192 kHz, as well as support for DSP-intensiveplug-ins that will work only on an Accel-enhanced system. For those ofus who jumped directly from Pro Tools|24 Mix systems to Accel, that’squadruple the power of the old Mix DSP cards and triple the voicecounts at 44.1 kHz/48 kHz. Accel cards retain two of the HD ProcessCard “Presto” chips, but add new 321 chips for DSPprocessing.

Configurations include HD 2 (an original Pro Tools|HD Core Card andone Accel card) and HD 3 (HD 2 and another Accel card). HD 2 supports64 channels of I/O with Pro Tools audio interfaces, while HD 3 supports96 channels. With either HD 2 or HD 3, you can have up to 192simultaneous 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 36audio tracks.

If you already have a Pro Tools|HD system, then you can add Accelcards to your system — they’ll co-exist peacefully. The onlycaveat is that systems using an expansion chassis must use a certaincard order: core card first, then Accel cards and then HD Processcards. All plug-ins that work with Pro Tools|HD first-generationsystems, including TDM, HTDM, RTAS and AudioSuite formats, should workwith Accel-enhanced systems, because the new systems include the olderCore card.

To run an Accel-enhanced Pro Tools|HD system, you’ll need asupported PC running Windows XP Professional or Home with Service Pack1 or a Macintosh G4 or G5. G4s require Mac OS 10.2.6, 10.2.8 or Pantherwith Pro Tools 6.2. G5s need OS 10.2.7, 10.2.8 or Panther with ProTools 6.2r2. Users should check for updatedrequirements and new revisions.


I chose to order an HD 3 system and two extra Accel cards. Thisarrived with the current HD pack of bonus plug-ins that includedImpact, an “Accel-only” compressor, and Pro Tools Version6.2, which is required to support Accel configurations.

My Pro Tools|HD 3 Accel “plus two” arrived with ProTools|HD Pack V. 5.0, a collection that varies in number depending onthe size of the purchased system. For HD 3 Accel, it included theDigirack plug-ins, as well as d2 and d3 by Focusrite, Virus Indigo byAccess Music, Amp Farm by Line 6, Speed by Wave Mechanics, Oxford EQ bySony 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 Worksprovide Accel-ready updates for their plug-ins. To check on currentcompatibility, visit

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

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


Pro Tools 6.2 includes a few new features in addition to Accelsupport. It is the first release to support the new 96i I/O audiointerface, a 96kHz-capable audio interface for HD only with 16 inputsand two outputs. It also adds support for Windows Media Audio 9 formaton the Windows platform, with import and export. Version 6.2 offerscross-platform compatibility with systems running Pro Tools TDM/LE 5.1,as well as import for older Pro Tools sessions. Additional featuresinclude Tempo Query and Custom Shuttle Lock Speed. Tempo Query issupported by some delay plug-ins such as Mod (or Medium) Delay II. Thisallows the plug-in to check the session tempo and align delay timesaccordingly. Custom Shuttle Lock Speed is used for transcribing. Youcan custom set the speed of (keypad)9 inPreferences/Operation.


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

Was it worth it to upgrade? Definitely. We have a few other ProTools 24|Mix systems at JamSync and though I still use them, they’refirst 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 ofJamSync, a surround production/mixing facility on Nashville’s famedMusic Row.