DSP Hardware-Based Plug-Ins

The biggest distinction among various plug-in formats is whether the software algorithms that do the processing are designed to run on dedicated DSP chips (DSP "hardware") or to run "native," using the host computer's CPU. The original SD II plug-ins ran on the Motorola DSP chip on Digidesign's Audiomedia II and earlier versions of Pro Tools cards. In 1994, Digidesign carried the idea further with TDM (Time Division Multiplexing), creating a processing buss analogous to the effects send and receive busses used in consoles.

TDM gave users a "virtual" alternative to racks of signal processing gear. Running on Digidesign's higher-end versions of Pro Tools hardware, TDM was the first workstation-based technology to offer:

• access to a complete suite of processors across multiple channels
• non-destructive, realtime effects, available during recording or playback
• automation of plug-in parameters

Digidesign's top-of-the-line TDM platform, Mix 24 Plus -- available for both Mac and Windows NT operating systems -- now ships with a total of 12 DSP chips; users may add more DSP power with optional DSP Farm (as in "grow your own effects") cards. In addition to Pro Tools software, TDM plug-ins can also be used with Digital Performer, Logic Audio, and other TDM-capable host applications. (Regardless of which host app you use, you'll also need a relatively expensive TDM-equipped version of Pro Tools hardware.)

Digidesign makes a few plug-ins of its own, but the bulk of TDM plug-ins come from third-party developers, many of whom -- attracted by Digidesign's huge market share -- got in the game years ago. Digidesign's stable of TDM developers now includes high-profile companies that made their names building rack gear, including Aphex, Dolby, Focusrite, Lexicon, and TC Electronics (now marketing plug-ins as TC Works).

Soundscape Digital Technology's Mixtreme platform (Windows) also uses onboard DSP to interact with third-party plug-ins. The growing list of companies supporting the Soundscape format includes TC|Works, Wave Mechanics, Arboretum, Aphex, Apogee, Dolby, Sonic Time Works, Cedar, and more.

Compared to native processing, DSP hardware-based systems are generally more costly. A maxed-out Pro Tools system can also eat up all of your computer's PCI expansion slots, leaving little or no room for other slot-inhabiting hardware like video cards and SCSI accelerators (unless you want to spring for a costly PCI expander). Nonetheless, they've found favor at the mid-to-high end of the workstation markets in applications such as multitrack music production and sound-for-picture. With processing activity kept entirely on dedicated DSP chips, DSP-based plug-ins are isolated from the multitude of competing demands that can take your CPU's attention away from your audio: Thus the total DSP power is always available. According to Digidesign's Sean Carson, the freed up CPU resources can be put to musical use. "Putting the plug-in load on a DSP system makes it that much easier for your CPU to handle additional tasks -- such as software synthesis -- at the same time."

Yamaha's popular DSP Factory mixing card offers software control of a hardware mixer, and the mixer can be accessed from within programs such as Logic, Cubase, MixTest, and others. But the effects offered by the mixer are not technically plug-ins: They're fixed algorithms that are part of the mixer's hardware. Third party developers cannot write software that directly alters the functionality of the DSP Factory's effects.

Waves' UltraPitch plug-in (included with the Waves Pro-FX TDM Bundle; also available for other formats) was used on this bluesy vocal riff to create a rich major triad. The original vocal provides the root note. [sample MP3 (152 kb)]

Native Processing-Based Plug-Ins

In contrast to DSP-based formats such as TDM and the Mixtreme format, native plug-ins piggyback on the existing processing power of the CPU -- saving you the expense of dedicated DSP chips. Though dedicated DSP retains its hold at the higher end, native processing has grown more popular as CPUs have grown more powerful.

The Adobe Premiere format has long been popular for native processing on MacOS machines, and is supported in programs such as BIAS Peak, Emagic Logic Audio, Opcode's late and lamented Studio Vision Pro, and Deck. But today the most widely used native format is Steinberg's VST (Virtual Studio Technology), which is supported not only by Cubase but also Emagic's Logic Audio, Vision DSP and Studio Vision Pro, TC|Works Spark, and the current version of Peak.

According to Steinberg's Rodney Orpheus, more than 300 VST plug-ins are now available, something he attributes to the company's relaxed attitude toward third-party developers. "The VST development system is open to everyone," he says. "Anyone who wants to make a VST plug-in can just go to our Web site and download the development kit." (In contrast, anyone wanting to develop plug-ins for one of Digidesign's formats will need to run that company's fairly rigorous licensing gantlet.)

Though Steinberg has historically been active in the world of TDM, the company recently announced a decision to concentrate entirely on native plug-ins. "The future of computer-based audio is in the computer processor itself," Orpheus says. "Buying external DSP is never going to be a good investment in the future, because computer technology is moving very, very fast, and computer processors are getting faster all the time."

As for proprietary formats on the Mac, Mark of the Unicorn's MAS (MOTU Audio System) format is alive and well, but currently supported mainly by MOTU's own Digital Performer. Digidesign, meanwhile, has two proprietary native formats: AudioSuite (for off-line processing of files) and the new RTAS (Real Time Audio Suite). RTAS gives users of Pro Tools 5 LE (the non-TDM version of Pro Tools) a host-based solution that boasts some of the same real-time functionality and automation found on TDM systems at a fraction of the cost. Emagic's Logic Audio series comes with an arsenal of proprietary plug-ins that can be used alongside VST effects within Logic. Unfortunately, the Logic plug-ins cannot be ported over to other VST compatible software.

The Windows situation is somewhat less complicated, with both VST and DirectX being popular alternatives. DirectX enjoys the backing of its omnipotent creator, Microsoft, and is supported by a wide variety of host software, including the popular Sonic Foundry products such as Sound Forge and Acid, Cakewalk, and Syntrillium's Cool Edit Pro. But Orpheus is quick to claim "big advantages" that VST on Windows has over DirectX. "VST plug-ins are fully automatable," he says, "while there is no automation with DirectX. And VST is also a lot more efficient in the way it uses processing power. In Cubase, we allow you to use VST plug-ins or DirectX, but most people will run VST once they've compared the two."

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