Digidesign Pro Tools HD

Change is guaranteed in all things. But when it comes to digital hardware, change comes quickly, and it always means more, faster, and better. Digidesign,
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Change is guaranteed in all things. But when it comes to digital hardware, change comes quickly, and it always means more, faster, and better. Digidesign, the 100-ton gorilla of the digital-audio-workstation (DAW) industry, has changed most of its Pro Tools product line with the introduction of the HD system (HD stands for high definition — in this case, 24 bits at 192 kHz). Its new TDM-based system boasts more digital-signal-processing (DSP) power, better I/O, and higher sampling rates at roughly the same price as its previous TDM systems.


At the heart of the Pro Tools|HD are two 64-bit PCI cards: HD Core and HD Process. As in previous Pro Tools systems, one master card (in this case, HD Core) provides basic system processing as well as some plug-in processing power. Additional DSP cards (called HD Process) provide more processing juice. The HD 1 system consists of an HD Core card and no HD Process cards. The HD 2 and HD 3 consist of an HD Core card and one or two HD Process cards, respectively. Additional HD Process cards are available at $3,995 each. Not one of these bundles comes with an audio I/O device: the I/O devices are sold separately.

The HD Core card supports as many as 96 tracks simultaneously (provided, of course, that you have enough SCSI throughput to shovel that much data through the system), can connect to two I/O units with as many as 32 channels, and provides a serial port for direct connection to the Sync I/O. The HD Process card is physically identical to the HD Core card but is used only for plug-in processing. Each HD Process card can connect to two additional I/O units.

The HD Process card is an improvement over the Pro Tools|24 Mix Farm cards of the previous generation. They use the same family of Motorola DSP chips but with a couple of important differences. First, there are nine chips on each HD Process card, compared with six on the Mix Farm card. Each of the newer chips is about 25 percent faster than those on the Mix Farm card, which means an HD Process card has roughly twice as much processing capacity. In addition, RAM is available on all chips (which was not the case in the Pro Tools|24 Mixplus system), which means that there is less internal shuffling of RAM-intensive plug-ins such as delays and reverbs.

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In addition, the new TDM II architecture promises more efficient DSP management, all of which points to about 2.5 times more power in an HD Process card over a Mix Farm card. I tested this by seeing how many instances of the Focusrite D2 six-channel EQ I could get on each card, running at 24 bits, 48 kHz. I got 36 instances on the Mix Farm card and 63 instances on the HD Process card. Thus, in my real-world test, the HD Process card had 1.75 times the processing capacity of a Mix Farm card.

This extra power does come at a price. The TDM II system requires upgrades to all your existing plug-ins. As of this writing, major TDM plug-in manufacturers — such as Waves, McDSP, and, of course, Digidesign — have ported their families of plug-ins to the new platform. According to Digidesign, it and a few of its partners (Focusrite, McDSP, and Aphex) offer free plug-in upgrades to registered owners, whereas IK Multimedia, Waves, and Wave Mechanics, among others, require upgrade fees.

Moreover, higher sampling rates require proportionally more DSP time for plug-ins. A compressor running at 192 kHz requires four times as much DSP as the same plug-in running at 48 kHz. That leads to a limitation in high-resolution sessions: a single instance of a plug-in must fit within one DSP chip. If a particular plug-in requires enough DSP horsepower to take up more than 25 percent of a single chip at 48 kHz, it will not run at all at 192 kHz. That means that manufacturers need to optimize their processor-intensive plug-ins in order to run at 192 kHz.

Digidesign adds that plug-ins used in a 192 kHz session will require four times the RAM as that same plug-in in a 48 kHz session. That means, for example, that there may be enough MIPS available on a DSP chip to run a particular plug-in at 192 kHz, but there might not be enough RAM. To solve this problem, Digidesign introduced a new plug-in category called HTDM plug-ins. Like RTAS plug-ins, HTDM plug-ins run on the host CPU and use host RAM.


The 192 I/O ($3,995) is Digidesign's new flagship audio interface (see Fig. 1). Boasting 16 simultaneous channels, sampling rates as high as 192 kHz, superb audio quality, and a wide range of format connectivity, it is a big step forward.

The only control on the front panel is a power button. Six LEDs indicate the sampling rate, and four others show the clock source for the 192 I/O. The Loop Master light shows whether the unit is acting as master clock for the whole system. The 192 I/O has four-segment LED meters for each of the 16 input and output channels. However, high-resolution systems demand high-resolution metering: I wish that these were 16- or 20-segment meters instead.

The rear panel (see Fig. 2) is divided into five regions: four I/O bays with removable cards and a permanent I/O section. Three of the removable bays come with cards installed, and the fourth bay is empty but ready for expansion. The first bay, for analog input, has two DB25 connectors for eight +4 dBu balanced and -10 dBV unbalanced ¼-inch inputs. The analog output bay has a single 8-channel, +4 dBu DB25 balanced output connector, but a special cable can be purchased to pad the levels to -10 dBV.

Soft-clip limiting is now available on all analog inputs, which is great for eliminating digital overs while maintaining a healthy gain structure. Another cool touch is that the analog I/O bays each have two sets of trim screws. With these trims, you can store two sets of calibration settings for the system, such as differing headroom amounts for film and music applications.

The third bay holds a digital I/O card, which supports eight channels of AES/EBU, TDIF, and ADAT Lightpipe. The AES/EBU and TDIF ports use DB25 connectors, whereas the ADAT ports use standard Lightpipe connectors. You can send signals to multiple ports and then switch between them in software. This is terrific for, say, recording in through a digital mixer and then laying back your mix to a Tascam DA-88 or an Alesis ADAT. Note that the AES/EBU port can handle eight channels at 96 kHz but only four channels at 192 kHz in Dual-Wire mode. Real-time sampling-rate conversion allows you to stream 48 kHz input over a Lightpipe or TDIF connection directly into a 96 or 192 kHz session as well as 96 and 192 kHz data into a 44.1 or 48 kHz session over AES/EBU.

The fourth bay can be loaded with an additional analog input, analog output, or digital I/O card. Installation is easy and can be done by the user.

In addition to the I/O bays, there is a permanent set of connections. These include additional pairs of AES/EBU, S/PDIF, and Lightpipe that can each support two channels at 24-bit, 96 kHz audio. Word clock comes in and out on four BNC connectors: one pair in the high-resolution Loop Sync format and a pair in the older 1× or 256× word-clock standards.

The new DigiLink port is for connecting I/O units to each other and to the Pro Tools cards. The 192 I/O has a primary DigiLink port to connect to the cards and an expansion port to connect to another new I/O unit. DigiLink cables can run as long as 100 feet for sessions at 96 kHz (50 feet at 192 kHz), making the connection between computers in a machine room and the I/O units much easier than before.


In an effort to allow you to retain some of your older Pro Tools gear, Digidesign has included a legacy peripheral port. This port lets you connect 16 channels of older I/Os (888/24, 882/20, 1622, or an ADAT Bridge, but not a 16-bit 888) to your Pro Tools|HD system. On first glance, that seems like a great idea. However, the legacy peripherals cannot be used on sessions running at sampling rates higher than 48 kHz.

One of the main reasons for using the HD system is to take advantage of high-resolution recording. If you are upgrading and need a large simultaneous channel count, you might want to consider selling all your old units and buying a 96 I/O as a second unit instead of using legacy I/O.

My biggest gripe about the 192 I/O is that most of the multichannel connections come in through DB25 ports. This means that special snakes will need to be made or purchased, requiring significant revision (and expense) in order to integrate it into an existing studio. Digidesign offers DigiSnakes for use with the 192 I/O.

Digidesign's previous generations of I/O had separate XLR connections for each analog channel and each pair of AES/EBU channels. However, the vast number of ins and outs on the 192 I/O would have required three or four rackspaces to accommodate all the individual jacks. Nonetheless, I would have preferred 56-pin Elco connectors as a standard instead of the DB25s, because they are sturdier and can stand up to more abuse.

Gripe No. 2 is the inclusion of a fan to disperse heat. I record a lot of Foley and quiet acoustic music in my studio. The fan on the 192 I/O is quiet, but not quiet enough for my critical recording tasks (pro studios will want to stash it away in the machine room). I wish the company had used a passive heat-dispersal system instead. But Digidesign maintains the fans are necessary to combat the heat generated by 192 kHz A/D converters: the fans turn on only when needed, and the fan speed varies with the internal temperature of the device.


The Sync I/O ($2,095) is a high-resolution replacement for Digidesign's Universal Slave Driver (USD; see Fig. 3). Invaluable in film work, the Sync I/O acts as a master clock for a post-production studio, slaving to and generating various types of time code and word clock. It can handle pull-ups and pull-downs and can even overlay a SMPTE window burn over a video signal.

The Sync I/O behaves almost identically to the USD, except in two ways. First, it handles every sampling rate up to 192 kHz (although the film world has certainly not made the switch to these higher sampling rates yet). Second, the separate 1× and 256× word-clock inputs and outputs (necessary on a Mixplus system to accommodate 1× digital mixers and recorders in conjunction with 256× Digidesign I/O units) have been combined into a single pair of BNC jacks. The 256× clock has been superseded by Digidesign's new Loop Sync standard.


In addition to its flagship 192 I/O, Digidesign is offering a series of other I/O units for different needs. These include the 96 I/O ($1,995), a less expensive, less flexible 16-channel unit that is limited to 96 kHz. The Pre ($2,495) has eight mic preamps that connect directly to Pro Tools I/O and can be controlled from within the Pro Tools application.

The MIDI I/O ($595) is a ten-input, ten-output USB MIDI interface that supports Digidesign's MIDI time-stamping feature for accurate recording and playback. Unfortunately, not one of those devices was ready as I prepared this review, but they will be shipping by the time you read this.


Are the benefits of 24-bit, 192 kHz audio perceptible? Can the difference between 192 and 96 kHz even be perceived?

I must confess that I was skeptical about the sound quality promised by the higher sampling rates (see the sidebar “A Solution in Search of a Problem?”). The move from 16- to 24-bit recording certainly makes sense to me: the greater dynamic range, for example, seems to be a quantifiable improvement. But humans can't hear frequencies above 20 kHz, so is it really worth the large amount of additional data to create a high-sampling-rate recording?

I decided to answer the question with a sampling-rate shoot-out at Spark Recorders in Emeryville, California. Spark boasts a pristine recording environment and a terrific-sounding Yamaha Disklavier grand piano. Engineer Mike Bemesderfer miked the piano with a pair of Neumann KM 184s running into Millennia Media Origin STT-1 channel processors and then straight into both Pro Tools|HD and 24 Mixplus systems. We played the same quiet, subtle classical piano piece on the Disklavier into both systems at 24 bits, 48 kHz and then into Pro Tools|HD at 24 bits, 96 kHz and 24 bits, 192 kHz. We also recorded acoustic guitar, rain stick, and jingle bells the same way. Monitoring took place directly out of both systems through a Digidesign Control|24 control surface into Meyer HD-1 monitors.

The results made our jaws drop. There was a startling difference between the Mixplus system's 888/24 and the HD system's 192 I/O running at the same sampling rate and bit depth. The Mixplus system's recording was an accurate rendering of the piano, with a decent amount of detail and the full frequency response of the instrument. But the 192 I/O brought a musicality to the sound that was not present in the 888/24. The 192 I/O created a fully fused, integrated stereo experience, whereas the 888/24 sounded like dual mono. The 888/24 sounded flat and lifeless in comparison with the 192 I/O.

We then listened to the Pro Tools|HD at various sampling rates. We found virtually no difference between the 48 and 96 kHz sampling rates. But 192 kHz was another ball game entirely. All of a sudden, each piano note took on a separate, distinctive life of its own. The cohesive, integrated stereo performance had a three-dimensional depth that seemed to extend far behind the speakers. The frequency response had not changed, but the instrument had a gorgeous, musical sheen. It was simply the best digital piano recording that I have ever heard.

Recordings of the steel-string guitar, rain stick, and jingle bells reinforced our impressions. In each case, the depth and musicality of the instrument was greatly enhanced at 192 kHz. Each pebble in the rain stick became an individual, discernable element. The jingle bells, our acid test of high-frequency material, maintained coherency and sounded smooth and beautiful, without a trace of the brittle harshness I have grown used to in recording metallic sounds digitally. The guitar took on a larger-than-life character that sounded (dare I say it?) decidedly analog.


Despite the sound quality, the question remains: is such high-resolution audio worth the investment? If you don't already have a Pro Tools system and you think the increased power and resolution will be good for your business, then I recommend investing in an HD system.

If you are already a Pro Tools user, the learning curve is nonexistent but the upgrade is costly, and rethinking your existing digital-hardware layout can be a real headache. For example, the price of an upgrade from a Pro Tools|24 Mixplus system to an HD 2 system is $4,995, and you will still need to purchase at least one of the new I/Os. If you have any 16-bit 888 I/Os, you won't be able to use them because the Pro Tools|HD supports only 20- and 24-bit legacy I/Os. Of course, if you are planning on using any legacy I/O devices, you will not be able to run the Pro Tools|HD at sampling rates above 48 kHz.

If you have a digital mixer that runs at less than 192 kHz, you will have to replace it or else you will not be able to hear the increased sampling rate (analog mixers still work just fine). If your Mac is older than an AGP graphics-based G4, you will need a new computer.

Additionally, all of your existing plug-ins will need to be upgraded. If you have a USD, it will need to be sold or traded in, and a Sync I/O will need to be put in its place.


Digidesign completely revamped its Pro Tools TDM product line to allow increased audio quality, I/O flexibility, and DSP power at the same price point as its previous generation of hardware. The Pro Tools|HD system is a powerful and stable DAW that sounds excellent and should last for a long time.

Whether you already have a TDM-based Pro Tools system or are starting from scratch, be prepared to make a serious financial investment. With the Pro Tools|HD system, you definitely get what you pay for.

Nick Peckcreates sound for film and games (www.perceptivesound.com) and will have just gotten hitched by the time you read this article. You can reach him by e-mail atnick@tyedye.com.


Pro Tools|HD
digital audio workstation
HD 1: $7,995
HD 2: $10,495
HD 3: $12,995


PROS: Spectacular sound quality. More DSP power than previous systems. Flexible I/O units. Connections for all popular formats.

CONS: Very expensive. Fan noise on the 192 I/O. Most multitrack connections are DB25. Not all plug-ins have been ported. Not all plug-ins will work at 192 kHz. Easier to start from scratch than to upgrade an existing system.


tel. (800) 333-2137 or (650) 731-6300
e-mail prodinfo@digidesign.com
Web www.digidesign.com

PRO TOOLS|HD Specifications

Sampling Rates 44.1, 48, 88.2, 96, 176.4, and 192 kHz Bit Depths 16, 24 Simultaneous Audio Tracks 128 Simultaneous MIDI Tracks 128 Simultaneous I/O Channels 96 Plug-In Architectures TDM II, HTDM, RTAS, AudioSuite Interface Connection DigiLink (cable runs up to 100 feet) Card Type 64-bit PCI II
192 I/O

Analog Inputs 8 channels +4 dBu; 8 channels -10 dBV (all on DB25 connectors) Analog Outputs 8 channels +4 dBu (all on DB25 connectors) Digital I/O 10 channels AES/EBU; 16 channels Lightpipe; 8 channels TDIF; 2 channels S/PDIF Simultaneous Audio Channels 16 I/O Card Bays 4 Sampling Rate 44.1, 48, 88.2, 96, 176.4, 192 kHz ±10% Dynamic Range A/D 120 dBA, 118 dB (unweighted) Dynamic Range D/A 118 dBA, 115 dB (unweighted) Total Harmonic Distortion + Noise A/D 0.00035% (-109 dB); +21 dBu, 20 Hz-20 kHz Total Harmonic Distortion + Noise D/A 0.00056% (-105 dB); -1 dBFS @ 997 Hz Frequency Response A/D ±0.05 dB @ +2 dBu, 20 Hz-20 kHz Frequency Response D/A ±0.05 dB, -20 dBFS, 20 Hz-20 kHz Digital Sync Loop Sync I/O; 1×/256× word-sync I/O Additional ports Main DigiLink; Expansion DigiLink; Legacy I/O; Accessory Dimensions 2U × 15" (D) Weight 19.65 lb.

Frame Rates 30 drop/nondrop, 29.97 drop/nondrop, 25, and 24 fps Clock Sources video ref, video signal, LTC, AES, word sync, biphase, internal Time-Code Formats LTC, VITC, biphase, MTC out Digital Sync Loop Sync I/O; 1×/256× word-sync I/O; AES null clock out Additional Ports (2) 9-pin machine control ports; host serial port Video Window Burn SMPTE (hours:minutes:seconds:frames) Dimensions 1U × 10.5" (D) Weight 5 lb.


Although there is no doubt that audio recorded at high sampling rates sounds great, the question remains: who will actually hear it at that quality level? Consumers have yet to embrace a standard for delivering 192 kHz audio, though the industry has been pushing for quite some time to make it so. The average consumer still listens to compact discs at 16 bits, 44.1 kHz, as well as the convenient but decidedly low-fi standard MP3. Theatrical releases continue to use the Dolby Digital standard (a compressed format) for which 16-bit, 44.1 or 48 kHz audio is perfectly adequate.

There is a high-resolution turf war between DVD-Audio and Sony's SACD format, but consumers have not flocked to either camp yet. However, if you are authoring for standard DVD-Video, you can take advantage of its 96 kHz sampling rate and 24-bit word depth. High-resolution audio is in the future, but its development is still in the early stages.