Digidesign Pro Tools|HD

By now, you've probably heard of the new Pro Tools|HD system (the HD stands for High Definition) from Digidesign. There has certainly been enough talk 9/01/2002 8:00 AM Eastern

By now, you've probably heard of the new Pro Tools|HD system (the HD stands for High Definition) from Digidesign. There has certainly been enough talk about it, and its 24-bit/192kHz recording rate is raising plenty of eyebrows. The big questions on everyone's minds are, what does it sound like and is it time to update my system? In order to answer these questions, we installed a complete HD system (three cards and three interfaces for 32 channels of analog output, 16 channels of analog input and 32 channels of digital I/O) at the cozy and very reputable Infinite Studios in Alameda, Calif.

If you're familiar with the Pro Tools|24 MIX and MIXplus systems, then understanding the new HD system will be a walk in the park. There are three different setups to choose from: Pro Tools|HD 1, HD 2 or HD 3. (System prices are shown in the sidebar “Pro Tools|HD Prices.”) HD 1 includes a single “HD Core” card. Add one HD Process card (which is what the new DSP Farm cards are called), and you have the HD 2 system. Add two HD Process cards and, you guessed it, that's the HD 3. The cards are, as usual, PCI-based. Thirty-two channels of I/O are available per card, and each card packs nine Motorola 56k DSP chips, which are 25% more powerful than the MIX cards' chips; this translates to about twice the voice count and DSP power in a 44.1- or 48kHz session. Up to six HD Process cards can be used with a single HD Core card for a whole lotta dedicated processing power.

The maximum track count using the HD Core and at least one HD Process card, on a 48- or 44.1kHz session, is up from the previous 64 tracks to 128 tracks. Depending on a session's sampling rate, maximum track count will vary. For example, using the HD Core card alone at 88.2 or 96 kHz, you can have up to 48 tracks, while at 176.4 or 192 kHz, the maximum number of tracks is 12. Add an HD Process card, and the track count increases to 64 tracks at 88.2/96 kHz and 24 tracks at 176.4 or 192 kHz. (Adding a second HD Process card, like the HD 3 configuration, only increases DSP power and not track count.) Pull-up/pull-down sample rates are now available for every sample rate.

To run HD, you'll need a “Digidesign-qualified” Power Macintosh, which translates to a G4 (AGP-based) with as much system RAM as possible (crucial for high track counts). O.S. 9.1 through 9.2.2 are currently supported, and Digi is hard at work on OS X support. (No official release date announced yet.) Near the end of this field test, support for PC computers was announced with the release of Version 5.3.1 for Windows. The PC you'll need for Pro Tools|HD must have a P3 or P4 processor and must be using Windows XP, Professional or Home.


Digidesign's crowning new interface is the two-space 192 I/O. This is the box that allows 24-bit/192kHz recording and playback. It's designed with maximum flexibility in mind, having four I/O card bays, one of which can be loaded with your choice of analog or digital connections. For example, the stock configuration is eight analog ins on card bay 1, eight analog outs on card bay 2 and digital I/O in card bay 3. Card bay 4 is left open for you to add more I/O at your discretion. All of the analog connectors are of a DB-25 type and follow the same pin-out configuration as Tascam; Digidesign offers cables with a variety of breakout ends (if making cables isn't your cup of tea) called DigiSnakes. As usual, standard features include two channels of AES/EBU and S/PDIF, and Word Clock I/O is standard.

The analog inputs feature a Soft-Clip limiter that kicks in when a signal reaches -4 dBFS. The limiter can be turned on or off for each individual input channel (from the Hardware Setup window), giving you total control over which incoming signals receive the dynamics processing — very cool. The DB-25 can accommodate parallel +4dBu and -10dBV connections, allowing two input sectors per group of eight channels. With both sectors wired, you can use the Hardware Setup Input window to select which cable is feeding a channel. The 192 I/O's A/D card has a dynamic range rated at -120 dB (A-weighted).

The Digital I/O card (which is found in the 192 I/O and the 192 Digital I/O, a digital-only interface) can perform incoming real-time sample rate conversion. This is an especially nice feature, because you can fly in tracks recorded at different sample rates directly into the session's current sample without having to convert individual audio files offline — what a time-saver. Three types of digital formats are available on a single digital-expansion card: TDIF and AES/EBU have separate DB-25 connectors, and there are also ADAT Optical connectors.

If the 192 I/O is too much for your needs, a 96kHz interface is offered. The two-space 96 I/O allows 16 simultaneous channels of I/O; there are 20 I/Os total, including eight analog channels on ¼-inch TRS, ADAT optical, and 2-channel AES/EBU and S/PDIF connections. There are no I/O card expansion bays, and the Soft-Clip feature is missing, but at half the price of the 192 I/O, the 96 I/O is still a good deal. All of the new I/O boxes feature a Legacy Port for daisy-chaining your old Digidesign I/O boxes with the HD system (up to 16 channels per HD interface). To access the 96 I/O's other eight inputs (or outputs), you can use its Legacy Port with an older-model Digidesign interface, or feed its ADAT optical ports with one of the many compatible Lightpipe interfaces on the market.

In addition to the I/O boxes, Digidesign has announced three other companion interfaces to create a fully self-contained HD system. The SYNC I/O is a single-rackspace synchronization device that reads and writes time code in all of the standard frame rates and features a large, 7-segment time code display that's easy to read from a distance. Though SuperClock is still supported (for example, SYNC I/O can receive a 1x wordclock and will output a 1x-based SuperClock), Digidesign decided to focus on wordclock as the primary clock source. The single-space MIDI I/O has 10 ports and is USB-powered; the two-space PRE is an 8-channel mic preamp that can be remote-controlled from Pro Tools. (We didn't actually get to try these units because they weren't available yet, but should be by the time you read this.)

All of the units have an identical look, sporting silver-aluminum face plates and blue plastic trim. When they are rackmounted together, they're impressive, even if they do appear a little glitzy. The 192 I/O has two rows of eight 4-segment LED meters that show input and output signals. These meters have less resolution compared to the meters of the 888 interfaces, but then the 888 interfaces can't display inputs and outputs simultaneously because they only have eight meters (albeit bigger meters). We much prefer to see all of the inputs and outputs at the same time, even if the meters are limited by their LED segments. Most users will simply use the high-resolution onscreen meters.


We were determined to give Digidesign's new flagship system a serious workout. No matter how you go about upgrading, it's a challenge that's not for the faint of heart. Moving up to an HD system from an earlier Pro Tools rig does require purchasing at least one new I/O peripheral, and to soften the economic bite, Digidesign offers a variety of hardware-exchange upgrade plans, as well as financing through Avid Financial Services. Details on both programs can be found on Digidesign's Website.

To keep our businesses running smoothly, we depend on our recording studios, so installing an entirely new multitrack recording/editing system for this testing is a major operation. We decided we could either close up shop while we installed the new system or set up Pro Tools|HD on a second computer, totally separate from our main working Pro Tools|24 MIX3 system. With the help of the people from Apple, who were gracious enough to loan us a computer, we were able to set up a second system to test that didn't interfere too badly with our daily routines.

Pro Tools | HD 1 $7,995
Pro Tools | HD 2 $10,495
Pro Tools | HD 3 $12,995
Process card $3,995
192 I/O $3,995
192 A/D expansion card $1,295
192 D/A expansion card $1,195
192 Digital I/O expansion card $995
96 I/O $1,995
SYNC I/O $2,095
MIDI I/O $595
PRE $2,495

Rather than go with the ultimate CPU for our testing, we opted for a mid-line, single-processor, G4 867MHz machine with 1.12 GB of system RAM and a dual-SCSI ATTO card, and we did not have any problems. The computer was running O.S. Version 9.2.2, and we used external, 15,000 rpm Seagate Cheetah drives for audio storage and playback. After the cards were installed, we ran the DigiTest application, as directed, to check if they were operating properly. The HD Core and both HD Process cards passed with flying colors.

The Pro Tools software that controls the new cards is Version 5.3.1. It looks and feels the same as previous versions, but it supports the new interfaces and sample rates, so the Hardware Setup and Setup I/O windows appear quite a bit different. The software now automatically recognizes all of your Digidesign HD interfaces, which means that you don't need to spend time manually entering your interfaces in an initial Hardware Setup window anymore. The 5.3.1 release also features DigiTranslator and Unity, and pull-up/pull-down sample rates are now available for every sample rate. Currently, only Mac versions of the software support AVOption, AVOption|XL, Unity, Post Conform, PRE and DigiStudio.

The computer and interfaces were installed in the studio's machine room to ensure a dead-quiet control room where we could scrutinize our 192kHz recordings. The 192 I/O interfaces were connected to an Otari Concept Elite console. Several inputs on the first 192 I/O were also left open to record direct into Pro Tools using Infinite Studio's collection of vintage mic pre's and microphones. The 192 Digital I/O interface was connected to an Otari FS96 to transfer outside sessions into Pro Tools. And the SYNC I/O was connected, as directed, in a closed-loop circuit with the interfaces.

Making the cables and connecting all of the hardware to the console took some time, but installing the HD Core and Process cards, connecting them to the interfaces and updating the Pro Tools software was quick and painless. Unfortunately, making sure that all of our plug-ins were HD-compatible was not so simple. Because Infinite Studio is a busy mixing facility, there are a lot of plug-ins constantly in use, and the sheer logistics of upgrading such a slew of plug-ins was clearly daunting and potentially expensive. If your setup is simple — a couple of interfaces, a console for monitoring Pro Tools stereo bus outs and not too many plug-ins — you can get an HD system installed and running inside of a day. By its very nature, a complex setup such as ours required more time.


Digidesign and its third-party plug-in developers are fed up with cracked plug-ins cutting into their livelihoods. We don't blame them. To counter this ongoing problem, an iLok USB Smart Key copy-protection dongle is now being employed. This is a small plastic USB dongle that utilizes an electronic copy-protection “License card” to install the authorizations (about the size of a thumbnail). The card is inserted into the end of the dongle, and you publish your authorizations on it (up to 99). When you buy an HD system, an iLok Smart Key comes standard. It's an annoying system because the dongle is easily misplaced and simultaneously gets in the way, but until a more convenient protection system is invented (there's an oxymoron) or hackers stop cracking protection protocols (we won't hold our breath), we're just going to have to deal with it. On the plus side, the license card approach allows portability: You can use your own authorized plug-ins wherever they're installed.

Currently, all of Digidesign's HD-compatible plug-ins are protected using the iLok; your existing plug-ins require a Smartdisk VST Floppy Drive (the only drive that supposedly works) for old-fashioned floppy authorization. Digidesign provides floppy-based authorization versions for the convenience of users who are upgrading to an HD system. Most third-party developers are reportedly implementing the iLok protection scheme, as well. Again, most don't have it in place yet.

Every HD system comes with the standard set of Digidesign DigiRack plug-ins (EQ, Compressor, Delay, D-Verb, etc.). The HD 2 and HD 3 systems come with additional plug-ins that vary, according to whatever promotional bundle is being offered at the time of your purchase. Our HD 3 system's bonus plug-ins were Focusrite d2, Bruno/Reso, Reverb 1, Maxim, D-fi, DPP-1, Wave Mechanics' Pitch Doctor, the Bomb Factory's LA-2A and 1176 classic compressor plugs, and the Access Virus. Not every plug-in we needed was HD-compatible at the time of this field test. Of those plug-ins that weren't yet compatible, most were promised in the next few months.

The third-party plug-ins that we were able to give a thorough workout included the Waves Platinum bundle (with Waveshell Version 3.5), Metric Halo's Channel Strip and SpectraFoo, Antares' Auto-Tune, McDSP's Filter Bank and Compressor Bank, and DUY's DSpider Global Bundle — they all passed with flying colors. And, when opening up older Pro Tools sessions in Version 5.3, we did not encounter any plug-in instantiation problems; all of the new HD plug-ins replaced previous instances of themselves and operated as expected.

When upgrading your plug-ins, be aware that some third-party HD plug-ins are not 192kHz-capable, and a few aren't even 96kHz-capable yet. A Plug-In Finder on Digidesign's Website shows HD compatibility and supported sample rates for all plug-ins. If you plan on running a majority of your sessions at 192 kHz, you may find your plug-in choices limited. Digidesign reports that, given time, most plug-ins should be able to make the switch to 192 kHz; time will tell.

RTAS is still alive and well and working in Version 5.3.1. But keep in mind that an RTAS plug-in, though it may work in an HD session, isn't an HD-compatible TDM plug-in. Some third-party developers run rather misleading ads that simply say that their plug-ins work with Pro|Tools HD. But with the advent of RTAS, you can't assume that just because a plug-in works in Pro|Tools HD that it's a TDM plug-in. RTAS is a wonderful feature, but if you own HD DSP cards, you'll want to use the TDM plug-ins whenever possible, and also take full advantage of the system's “power-on-demand” DSP functionality — a significant improvement over tapping into CPU power to run plug-ins. Keep in mind that an RTAS plug-in passing a 192kHz signal requires a lot more native processing power than the same plug-in passing a 48kHz signal. If you plan on performing this maneuver regularly, make sure your computer's CPU is up to snuff.


The first thing we did after Pro Tools|HD was up and running was to open a previously recorded Pro Tools|24 MIX3 session. There was a definite improvement in sound quality listening back through the 192 I/O interfaces when compared to our usual 888|24 interfaces and the RADAR's 24-bit converters. The clarity and imagery of the stereo field and the definition at the bottom end was noticeably better. Even an 888|24, which we had plugged into the first 192 I/O's Legacy Port, sounded a little sweeter. The mixes we did through the new 192 I/Os, despite the fact that the recordings were only 48 kHz, rocked the house. (I'm sure this had something to do with the fact that we were working with higher-performance AD/DA converters, tight low-jitter clocking and a greatly improved mixer with 48 dB of headroom!) And, even after instantiating a ton of plug-ins, we didn't come close to running out of DSP power on the HD cards.

To try out the 192kHz recording rate, we recorded a session with African drums and flamenco guitar. Everything was recorded straight into Pro Tools through Vintech Audio X73 mic pre's (duplicates of the Neve 1073), which were plugged directly into the 192 I/O. A djembe drum was miked using a Sony C800G tube and a Shure FM7; a talking drum had a C800G at its head and a Nuvistor tube AKG C61 miking its bottom. For the nylon guitar, we employed a Tracy Korby-modified Neumann U67 and a KM254c. All of the tracks were recorded at 24 bits, but we recorded different sampling rates for comparison purposes. We also recorded with the Soft-Clip Limiter on and off and hit the inputs really hard.

There was a significant difference in sound quality between 48 and 96 kHz, and a smaller difference between 96 and 192 kHz. Either way, this added up to a very large difference between 48 and 192 kHz. Recordings made at the new rate had a wonderful depth of field, and the details in the instruments' tones seemed to stay cohesive longer as they decayed. The talking drum sounded amazing, and you could hear every nuance, from the sidestick to the dynamics of the skin; the recording breathed. The Flamenco guitar sounded clear and natural, pulling you inside the guitar with every finger strike. Interestingly, the clarity of the 192kHz rate was just too much for the djembe. Recording this drum at 48 kHz produced a more contained-sounding track, which just goes to prove that even sample rates are sound-sculpting tools; as with any good EQ, you need to know when to use it. We can't wait until multi-bit and -sample rate sessions are supported.

Having the Soft-Clip Limiter active when recording hot signals, like the percussive transients of the drums, was, in some cases, preferable to having it off. When hitting it hard, it sounded smooth and natural, imparting what might be described as a very subtle analog-tape saturation effect. The 192 I/O input circuitry is actually pretty forgiving and can even handle occasional peaks without perceivable digital distortion, but having the Soft-Clip Limiter on comfortably protected the circuit from ever reaching its maximum headroom.

Though we didn't have time to do a side-by-side comparison in sound quality with different master clock sources, we can safely say that the system's ultra-low-jitter clocking affects the “Pro Tools sound” in a positive way. In a typical high-end system, a master clock's signal goes to a distribution amplifier and is then split off to each interface. The SYNC I/O works a little differently and may throw some people for a loop (pardon the pun) because it uses a closed-looped protocol. There are concerns about a looped circuit corrupting the loop sync clock, but Digidesign states that it has taken into account all possible jitter sources in order to generate an extremely stable clock, which is especially crucial with the new higher-sampling rates. Digidesign explains that the process is as follows: Every input clock is automatically divided to reach a base rate of 44.1/48 kHz; each interface taps off the loop sync and then re-creates an ultra-low-jitter local clock, which is then scaled internally according to the session's sample rate. This methodology also allows any interface to be declared the sync master, not just the top I/O.

With Pro Tools|HD, Digidesign has addressed the two main concerns people have had with its product: coloration and clocking, both of which impact sound quality. The 192 I/O and 192kHz sampling rate change the whole coloration picture for the better, and the ultra-low-jitter circuits certainly cleans up previous clocking issues. If these are concerns that you had with Pro Tools|24 MIX, then Pro Tools|HD may be the system you've been waiting for.

The Pro Tools|HD system is a fabulous tool that sounds terrific. But the industry is so saturated with 24-bit/48kHz PT systems that setting a new 192kHz standard, no matter how great it sounds, will be an uphill battle. Pro Tools|HD won't be the right move for everybody because of costs and plug-in development schedules; however, for those who are ready to trailblaze and make the kind of recordings that sets standards, it's the only way to go right now.

Digidesign Inc., 2001 Junipero Serra Blvd., Daly City, CA 94014; 650/731-6300;

Visit Erik Hawkins' record label at and check out his new virtual studio recording book, Studio-in-a-Box (Artist Pro/Hal Leonard). Michael Denten is an independent engineer/producer and owner of Infinite Studios in Alameda, Calif. Special thanks to Randy Squires, Infinite Studios' second engineer, and all of Digidesign's third-party developers who authorized their HD TDM plug-ins for our tests.