Digidesign is one of the pioneers in digital hard disk recording. As its products have increased in sophistication, it has gone from merely replacing

Digidesign is one of the pioneers in digital hard disk recording. As its products have increased in sophistication, it has gone from merely replacing the multitrack tape deck to offering the promise of a complete computer-based recording studio.

Does the hardware/software package of Pro Tools/24 Mix and Pro Tools 5.0 fulfill that promise? Before I answer that question, allow me to set the stage for a moment with an overview of Pro Tools and the 24 Mix system.

WHY PRO TOOLS?More companies than ever are making digital audio workstations that promise to transform your computer into a desktop studio. Most of these products are host based, which means your CPU does most or all of the processing and disk I/O. While a host-based system lets you handle sessions that incorporate lots of tracks and effects, you will have less flexibility when it comes to real-time processing on larger projects. To get around this, you will need to perform file-based processing.

Several other factors become important in host-based environments, including Digidesign's own Digi 001. First, getting signals in and out of a computer involves an inherent latency (the delay that occurs when you're recording or playing through the system). Under ideal circumstances, you can get the latency down to approximately 11 milliseconds, which sounds like phasing or flanging. In the majority of host-based systems, though, timing is typically in the realm of a slapback echo. Delays of this nature can be problematic when it comes to multitrack overdubs.

Second, even a fast CPU has a limit to the number of tracks and effects it can handle simultaneously. For example, time-based effects (such as delay and reverb) require tremendous processing power compared with EQ and compression. With host-based processing, you might squeak out 24 tracks with EQ and compression on all the tracks plus one or two time-based effects-assuming that your CPU is fast enough.

Finally, with your processor scrambling to keep up with tracks and effects, few clock cycles are left over for software synthesizers and samplers. Enter the dedicated hardware processing of the Pro Tools system.

CHIPS TO THE RESCUEThe Pro Tools system offloads all the processing for track count, mixing, and effects onto a bank of Motorola DSP chips that are optimized for such tasks. This relieves the CPU of the majority of the work and leaves you plenty of clock cycles for software synths and other applications. There is still a degree of latency in the system-1.5 ms at both the input and output for a total of 3 ms, according to Digidesign-but the delay is acceptable in most situations.

Digidesign further exploits the power of the DSP chips with its proprietary TDM architecture for routing and mixing. TDM (short for time-division multiplexing) provides 256 channels of 24-bit data paths, including 64 simultaneous audio tracks and 32 buses. This provides the core technology for digital signal processing, multitrack recording, and the routing power required for sophisticated mixing.

While TDM is the enabling architecture, the Digidesign Audio Engine (DAE) is the engine. DAE runs concurrently with Pro Tools. This independence allows third-party developers to tap the power of TDM hardware for their own digital audio sequencers and editors.

MEET THE FAMILYThe Pro Tools/24 Mix and Mixplus systems consist of hardware and software components. I will examine the hardware first.

In regard to performance, the Mix systems go well beyond their predecessor, the Pro Tools/24 system ($5,995 without audio interfaces). As the names imply, all three systems offer 24-bit internal processing. However, a closer look at Pro Tools/24 will illuminate the benefits of the Mix system.

A Pro Tools/24 system requires a minimum of two PCI cards: the d24 card for 16 channels of I/O and 32- track playback, and the DSP Farm card for additional I/O, mixing, and effects processing. The latest generation of Macs have only three card slots; consequently, the two-card requirement of Pro Tools/24 leaves only one open slot. This may not be enough room if you want to increase your track count and DSP capabilities with additional cards.

Pro Tools/24 Mix, on the other hand, puts the power of the two Pro Tools/24 boards into a single PCI Core card. Moreover, the DSP chips in the new system are Motorola's 80 MHz 56301 Onyx chips, which are much more powerful than the 56002 chips in the previous system. As a result, a single Mix Core card doubles the track count-for a total of 64-and more than triples the DSP power of the Pro Tools/24 system, for only $2,000 more.

A Pro Tools/24 Mixplus system is a 24 Mix system with the addition of a Mix Farm card that sports another six Onyx chips. This essentially doubles the processing power of the Pro Tools/24 Mix system and surpasses the power of the non-Mix system by a factor of seven.

In addition to the Mix Core card, you can have up to nine Mix Farm cards in a system-enough processing power for the most ambitious projects. Mix Farm cards themselves list for $3,995 each. With that in mind, the cost of a Mixplus system ($9,995) is a relative bargain.

The Mix and Mixplus systems each allow you to use up to 72 channels of I/O. Keep in mind, however, that the audio interfaces are not included in the prices stated here and must be purchased separately.

I had no problem with the installation and setup of my Pro Tools/24 Mix Core card or the subsequent addition of a Mix Farm card. The long heritage of this product showed itself in sound quality, ease of use, and stability.

SYSTEM REQUIREMENTSBoth Pro Tools 5.0 and DAE each need about 30 MB of RAM. Pro Tools also uses another 40 MB of memory for hard drive buffering. With an operating system that requires 20 MB (Pro Tools/24 Mix requires Mac OS 8.6 or greater), your minimum system requirement is 128 MB of RAM. You'll need to allocate another 20 MB to DAE if you plan to run a lot of plug-ins or use other applications simultaneously.

Because a Pro Tools/24 Mix system doesn't rely much on the CPU, you can get away with running it on older computers, such as a Mac 9500/150 MHz. (As a matter of fact, 9500s and 9600s have maintained their market value because they are the last Macs to have six PCI card slots.) I currently run a Pro Tools/24 Mixplus system on a beige G3/300 MHz, with two of the three slots filled with Digidesign cards. Since my machine has video and SCSI support on the motherboard, I still have a slot free for a SCSI accelerator if necessary.

The Mac G4 is another story. Because it doesn't have a built-in SCSI port, you'll be forced to devote a slot to a SCSI card. (Digidesign says that you can run small sessions using an internal IDE drive, but the company doesn't recommend it.) If you need additional card slots, expansion chassis are available from third parties (see the sidebar "Accessorizing Pro Tools").

Your choices are more limited on the PC side of things. The bittersweet news is that TDM-based Pro Tools runs only under Windows NT (specifically Workstation 4, Service Pack 5). The NT version requires 192 MB of RAM to record 32 tracks, and 256 MB of RAM for 64 tracks.

However, due to the complexities of the PC world, Digidesign has certified only a single non-Mac machine for use with Pro Tools-the IBM IntelliStation M Pro. That's not to say that it won't run on other CPUs, but you're basically on your own-especially when it comes to SCSI implementation. The IBM IntelliStation M Pro gives you five free PCI slots for Digidesign hardware.

Although the IntelliStation M Pro has more slots and potentially more power than a Mac, it costs around $4,000. By comparison, you can get a decent Mac for about $1,600. The Pro Tools hardware itself is identical for Macs and PCs, so you can migrate your investment if you need to.

It's interesting to note that much of the music and post-production world is Mac-based while the corporate and broadcast crowd gravitate toward NT. And, there are more add-ons, such as third-party software, available for the Mac platform.

DRIVES AND SCSIRegardless of platform, the days of connecting dedicated audio drives directly to Digidesign PCI cards are long gone. The ability to use standard SCSI ports (internal or external) makes drive management easier and more flexible than with older Pro Tools systems. In theory, you can even record to the drive where your system software resides. However, this is not recommended, in part because audio drives should be defragmented regularly: the hidden authorizations of music applications and plug-ins on the system drive make that a nightmare.

Similarly, the speed of today's hard disks means that there's no longer a need to adhere strictly to Digidesign-certified drives-although by doing so, you can be confident that the drive you purchase will perform up to Digidesign's standards. The company tests drives using a 32-track session with three edits per second and plenty of crossfades. Theoretically, if a drive can keep up with that unlikely scenario, it should be able to handle most anything.

The point at which your system needs a SCSI accelerator card varies because SCSI performance is influenced by session bit depth, edit density, and track count. As a rule of thumb, you can run 16 to 24 tracks with a low edit density before you'll need an accelerator. If you spring for an Ultra-Wide accelerator, it's almost guaranteed that it will keep up with any drive you purchase in the near future.

Storage requirements depend a great deal on the bit rate: 24-bit sessions require more storage space, obviously, than 16-bit sessions. In a 24-bit session, you get about 130 minutes of track time for each gigabyte of storage, while a 16-bit session yields about 200 track minutes for each gigabyte. A 9 GB drive holds about 1,100 track minutes of 24-bit audio, or about 45 minutes of a 24-track session. And the arithmetic scales linearly: an 18 GB drives yields 2,200 track minutes of 24-bit audio, or 90 minutes of a 24-track session.

MIX IT UPPro Tools' Mix Farm cards are identical to Mix Core cards, with one exception: core cards have a special ID chip that Pro Tools needs to see in order to run. This means you can't short-cut the system price by purchasing just a Farm card.

Both Mix PCI cards attach to the hardware interface with a 50-pin connector via a 12-foot cable. Each card can handle 16 audio inputs and outputs using either a single 16-channel interface or two 8-channel interfaces connected with a Y-cable. You can mix and match interfaces in a system, up to a maximum of 72 hardware inputs and outputs. You can also use inputs to bring line-level instruments (such as synthesizers, samplers, and other gear) into a mix. The limit for real-time mixing is 64 simultaneous digital audio tracks and 64 live inputs, for a total of 128 channel strips.

The Mix cards also include a 9-pin serial-port connector, which you can use to connect Digidesign's Universal Slave Driver or an external controller. Because older Pro Tools systems usurped modem or printer ports for this purpose, the 9-pin connector is a welcome addition.

GOOD HOUSEKEEPINGWhen calculating DSP power, what is commonly overlooked is that mixing requires DSP as well. Specifically, you can run up to 26 channel strips from one chip.

As mentioned earlier, Mix Core and Mix Farm cards each have six Onyx chips. Three types of Onyx chip RAM configurations are on each card, and the way the system uses a chip depends on the presence and type of RAM on the chip. For example, each card has one chip without RAM that is used for mixing, EQ, compression, and other non-time-based processes. The two DRAM chips on the card are typically used for time-based effects, such as delays. Also on the card are three SRAM chips, which are optimal for RAM- intensive time-based effects like reverbs.

Pro Tools sessions larger than 32 tracks on a single PCI-card Mix system use two chips for mixing-a non- RAM chip and an SRAM chip. In a Mixplus system, the non-RAM chip on each card is assigned to mixing tasks, leaving all the DRAM and SRAM chips in the system free for effects processing.

In addition to the upgraded DSP complement, Pro Tools/24 Mix systems provide for DSP sharing by way of Digidesign's MultiShell technology. In previous versions of Pro Tools, the first instance of a given TDM plug-in-say, a compressor-took over a DSP chip. You might be able to get a number of instances of the compressor from the same chip, but the chip was otherwise unavailable to additional plug-ins, even if it had unused processing power in reserve.

Digidesign's new DSP Manager dynamically allocates the processing power of the Onyx chips as MultiShell plug-ins are added to a session. If several instances of a MultiShell plug-in use only part of a chip, the remainder of the chip's processing power is available to other MultiShell plug-ins when a new TDM plug-in is invoked. Together with DSP Manager, a maximum of five MultiShell TDM plug-ins can share the same DSP chip at once. Developers can require that their plug-ins be loaded on a specific type of chip or merely given a preference for a certain chip type.

For example, consider a session in which a reverb plug-in that prefers (but does not require) an SRAM chip is allocated to one. If you add another reverb plug-in that explicitly requires SRAM, the DSP Manager shuffles the original reverb to a DRAM chip to make way for the higher-priority reverb plug-in.

Pro Tools 5.0 allows you to monitor DSP usage and other system resources in real time. If you find yourself regularly hitting the DSP ceiling in 24-bit sessions, running a 16-bit session will, in most cases, allow you to run more plug-ins. The sound quality of the 16-bit session won't be as high as that of 24 bits, but it will be far from shabby.

INTERFACES PRIMERAs I mentioned earlier, the prices of these Mix systems do not include the hardware audio interface. Although an interface adds to the cost of a system, the number of I/O options available gives you a large degree of flexibility in customizing your setup.

The Pro Tools/24 Mix system is also backward compatible. For example, I was able to use the 882 I/O from an old Digidesign Session 8 system as the interface for the Pro Tools/24 Mix system.

All of Digidesign's interfaces include a pair of BNC connectors that provide Superclock word-clock I/O for synchronization with other interfaces or digital devices. Superclock runs at 256 times the sample rate, which accommodates TDM's 256 pathways.

Digidesign's hardware interfaces will automatically slave to a valid clock when in internal sync mode. The interfaces can also sync to an external clock when a signal is present at the first two channels of digital audio inputs. While all Digidesign inputs have status lights for sync mode, sample rate, and input mode, the switching of settings is done from the software.

The interfaces handle both 44.1 and 48 kHz sampling rates. Digidesign has no immediate plans to implement 88.2 and 96 kHz sampling capabilities.

THIS YEAR'S MODELThe interface you choose will depend on both your studio setup and the way you like to work. If you prefer working on a traditional mixing console, you may want an interface with a large number of outputs. If you enjoy tackling complex mixes on the computer, and you have the RAM and cards to do it, a pair of outputs for making 2-track masters may be all you need. However, the more inputs and outputs you have, the more connectivity you have with the outside world.

888/24 I/O. The flagship of Digidesign's interface line is the 888/24 I/O ($3,695). On the front panel of the 888/24 I/O (see Fig. 1) are 15-segment LED ladders, which display the output level for each channel. (The input levels are displayed onscreen.) However, the main action is inside the interface and on the rear panel.

The 888/24 I/O offers eight analog inputs and outputs on XLR connectors and 24-bit converters. While the unit is factory set to +4 dBV, you can switch each port individually to -10 dBu by removing the cover and changing the internal jumpers. It also ships from the factory with the analog ins and outs calibrated at a nominal level of -18 dB, thus providing 18 dB of headroom. A front-panel trim pot for each input and output allows you to calibrate the levels.

The 2U device also offers eight channels of AES/EBU I/O on XLR jacks and two channels of S/PDIF I/O on RCA jacks. The active inputs are selected in pairs via software. All three output formats (one analog and two digital) are always live, allowing you to monitor the analog outputs while sending digital signals to digital devices. The unit also acts as an 8-channel A/D/A converter when your computer is off or disconnected.

As you might expect at this price, the sound of the 888/24 I/O is excellent. Discussions of whether the unit's converters sound better than high-end third-party converters boil down to a matter of taste. There's a small amount of fan noise in the Digidesign unit, but it will be masked in many rack situations.

882/20 I/O. The 1U 882/20 I/O ($1,245) is a 20-bit device with 8 inputs and 8 outputs on balanced TRS jacks (see Fig. 2). The input levels are switchable between +4 dBV and -10 dBu as a bank rather than individually. The same applies to output levels. Factory calibration is at -14 dB, for 14 dB of headroom.

The 882/20 I/O can function as a stand-alone 2-channel A/D/A converter, but it sends and accepts only S/PDIF digital signals. LEDs for each channel indicate the presence of signal above -30 dB. Like the 888/24 I/O, inputs are monitored via software. This interface has 20-bit converters and pads the LSB to fill a 24-bit file. Conversely, the output of 24-bit sessions is truncated to 20 bits: the Dither plug-in allows you to convert a 24-bit signal to 20 bits more elegantly.

1622 I/O. Once you get used to the power of TDM mixing, it's natural to want to insert the audio from your MIDI gear and outboard effects into your Pro Tools system. The 1622 I/O ($1,595) is designed specifically to accommodate this.

The 1622 I/O offers 16 inputs and 2 outputs, all on balanced 1/4-inch TRS jacks. Two of the inputs are on the front panel for easy access. The 1622 I/O has the same 20-bit converters as the 882/20 I/O does. It is calibrated for 14 dB of headroom and includes S/PDIF and Superclock I/O.

However, the 1622 I/O has several features not found on its siblings. In addition to a 3-LED meter on the two outputs, each input channel has a 3-LED input meter. (You get software input metering, as well.) Each input has gain-staging accessible via software, not only -10 dBu and +4 dBV, but also higher, in increments of 2 dB. This allows the inputs to accommodate synths, samplers, and effects without patching through a mixer to get more gain. The unit also remembers all gain settings, allowing it to function as a stand-alone 16-by-2 mixer when your computer is off.

ADAT Bridge I/O. The ADAT Bridge I/O ($1,245) provides 16 channels of Lightpipe I/O for devices bearing the ADAT Optical logo. This interface (see Fig. 3) eliminates the need for an ADAT card in digital mixers such as the Yamaha 02R and 03D.

Two channels each of S/PDIF and AES/EBU I/O are provided, and the unit can also perform format conversion from Lightpipe to AES/EBU or S/PDIF, and from AES/EBU to Lightpipe. A stereo pair of analog outputs are included for monitoring.

FLEXIBILITY IS KINGI successfully ran an 888/24 I/O and an old 882 I/O together from the same Mix Core card via an optional Y-cable, and a 1622 I/O from the Mix Farm card. Basically, I used the 888/24 I/O for tracking, stereo out, and effects sends and returns, and the other two interfaces for synth inputs. The connectivity of these interfaces with TDM essentially turns the array into an analog and digital audio patch bay.

Pro Tools includes software that helps you correctly set your interface's levels for your system. Be forewarned that the interfaces are extremely hot to the touch while running.

NEW SOFTWARE TOOLSPro Tools 5.0 is a major update to the Pro Tools system and includes a host of new features. One of the most important additions is the integrated MIDI sequencer. Prior to version 5.0, your options for using MIDI with Pro Tools were either importing MIDI files or synchronizing with a third-party sequencer application.

The basic, no-frills sequencer in Pro Tools 5.0 lacks many of the refinements found in other digital audio sequencers. Common features missing from Pro Tools 5.0 include an event list, song mode, the ability to record multiple channels of MIDI simultaneously, step recording, and notation. If you are into loop-based music, note that Pro Tools doesn't offer a convenient looping tool or have groove quantization, which you'll find in programs like Sonic Foundry's Acid. Digidesign plans to add features to the sequencer in future revisions.

The Mac version of Pro Tools requires the beleaguered OMS but does not allow you to create multidevice instrument definitions. Unlike some third-party sequencers, however, the preset selection window remains open so you can audition a series of patches before you exit the dialog box. Digidesign created its own MIDI management system on the PC side.

Digidesign's late entry into the sequencer game has an advantage. While digital audio sequencers tend to clock audio to MIDI, Pro Tools clocks MIDI to audio at an unprecedented resolution of 960,000 ticks per quarter note. In practice you're recording and doing basic editing at 960 ppqn. However, you can simultaneously display and edit MIDI and audio data with sample accuracy at any visual resolution in the same window.

Although the high clock rate of Pro Tools requires it to be the master, you can slave it to a third-party sequencer via MIDI Machine Control.

The feature set in the TDM version of Pro Tools 5.0 and the host-based version of Pro Tools LE are very similar. Both have several nice enhancements designed to reduce the amount of clicking you have to do. The Smart Tool intelligently combines the Selector, Grabber, and Trimmer tools depending upon where you put the cursor in the waveform or MIDI block. Also, memory locations can now include zoom settings and other preferences.

The playback view can remain stationary while the tracks scroll, minimizing that pesky page jump found in so many timeline-based programs. However, scrolling on my machine was a bit jerky, even when I set the display to 256 colors.

Because the recent Digi 001 review covered Pro Tools LE (see the April 2000 issue of EM), from here onward I'll focus on the features that are specific to the TDM version of the program.

POSTMODERNThe most obvious advantages of Pro Tools 5.0 for TDM are card-based DSP, a simultaneous track count of 64 (rather than 24 in LE), and 32 buses (instead of 16). Other TDM-only features optimize the system for post-production work. For example, the SMPTE timeline allows you to spot and place events at specific time-code locations. There's also a provision for displaying multiple time rulers and counters, and you can now use the numeric keypad for advanced edit and transport functions.

The Replace Region command lets you replace all instances of one region in the playlist with another region. This particular command is handy for replacing music loops or post-production sound effects.

You can set the Trimmer to automatically invoke the Time Compression/Expansion AudioSuite plug-in to scale the length of one region to another region or a video clip. Similarly, you can drag a region from the playlist into an edit selection and force it to scale automatically to the selection. (These time-scaling features will also let you match audio segments exhibiting different tempos.) The TDM version outputs MTC and supports MMC.

While Pro Tools hardware and session files are compatible between the Mac and PC, and the software is 99 percent identical between platforms, a few operational differences are worth noting. There is currently no integrated video support on the PC side, whereas Mac users can view QuickTime movies within Pro Tools or Avid-compatible video using AVoption hardware (Mac; $7,995).

In Pro Tools 5.0.1, the ability to export MP3 files under the Windows NT version has been added (after a 30-day demo period expires, a licensing fee of $19.95 is required for the download). In addition, the NT version has the ability to tag a sound file so that it remains associated with a session, even if you move the files between directories or drives.

Pro Tools/24 Mix interfaces reasonably well with the rest of the world. Third-party products, such as BIAS's Peak, TC Works' Spark, Mark of the Unicorn's Digital Performer, Emagic's Logic Audio, and Opcode's Studio Vision, support TDM hardware. Compatibility with Standard MIDI Files, Sound Designer II files, and OMF (Open Media Framework) give you quite a bit of connectivity. Furthermore, edits in Pro Tools sessions translate directly to track IDs in Digidesign's MasterList CD.

PLUG-IN POWERPro Tools ships with DigiRack, a suite of factory TDM and AudioSuite plug-ins offering a number of processing staples. Many include presets to get you started. The EQ II 1-band and 4-band equalizers provide highpass, low-shelf, peak, high-shelf, and lowpass equalization. The Dynamics II plug-ins include a compressor, a limiter, a gate, and an expander/gate, all of which can accept external side- chain sources. The Mod Delay effects provide delays ranging from 23 ms to 3.68 seconds and allows for LFO modulation. The Dither plug-in optimizes the reduction of 24-bit tracks to lower bit depths for mastering or output on lower-resolution interfaces.

Additional AudioSuite plug-ins provide phase inversion, normalization, file reversal, DC offset removal, signal generation, and pitch-shifting. The Time Compression/Expansion plug-in also allows you to adjust the duration of a region without altering its pitch.

Digidesign's in-house reverb, D-Verb, is also included. The latest version can handle twice as many simultaneous instances as the original version.

All in all, the factory plug-ins sound great, use DSP efficiently, and can be automated. Purists will cite that they don't sound as warm as outboard analog processors do-and they would be right. On the other hand, the convenience of onscreen controls, automation of all parameters, and a lack of inherent noise is easy to get used to. If you're still looking for a warmer sound, many third-party plug-ins use modeling technology for tube-warmth emulation.

Digidesign has also just released the DirectConnect plug-in for TDM, and has made it available for free from its Web site. DirectConnect allows you to feed the signal of a DirectConnect-compatible software synth or sampler into an aux input of the Pro Tools mixer. I found it both useful and fun to work with the DirectConnect versions of Koblo's Studio9000 and BitHeadz's Retro AS-1 and Unity DS-1.

OPTIONS FOR SUPPORTGiven the price, features, and myriad options of the Pro Tools system, I expected a video tutorial that I could watch either on tape or within Pro Tools. However, there's no tutorial whatsoever, even in print. The documentation is serviceable, but doesn't go very far in providing examples. Likewise, within the application there is no help system or provision for pop-up hints. The Quick Reference card and key cap labels come in handy.

Digidesign's support policy covers you for one year from the date of purchase. After that, you'll have to choose from the various cost-based support plans. That strikes me as slim, considering the price of the system. The quality of responses to my anonymous tech support calls ranged from testy to excellent. To Digidesign's credit, you can purchase additional support right away, including 24-hour pager response. Digidesign's Web site also offers good support resources. And to its credit, Digidesign has a trade-up policy, so you can upgrade your system to the latest version.

FINAL MIXPro Tools/24 Mix and Mixplus systems with Pro Tools 5.0 indeed fulfill the promise of a complete computer-based recording studio-if you have the wallet for it. If you're comparing Pro Tools/24 Mix and Mixplus with a host-based system (including Digidesign's own Digi 001), you're likely to get sticker shock.

However, if you were to assemble a package that included a digital multitrack recorder, a digital mixer, a sequencer, and high-quality effects, consider the functionality the Pro Tools/24 Mix system offers for similar money. The sound quality, flexibility, expansion capabilities, TDM architecture, and minimal latency you get with the Pro Tools system is well worth the outlay.

Jeff Burger is a multimedia producer, author, and songwriter based in Sedona, Arizona.