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Digidesign Pro Tools

"It's Cruel To Make A Computer Work This Hard..."

Digidesign, pioneers of low-cost professional digital audio tools, have broken the multitrack barrier, pushing the Macintosh to its limits to offer four to 16 tracks of (relatively) affordable hard disk recording. Paul D. Lehrman can hardly believe his eyes...

Pro Tools is the latest step along Digidesign's ambitious journey to turn the Macintosh computer into a full-fledged, reasonably-priced audio production workstation. Following on the phenomenal success of Sound Tools, which the company claims has sold more units than every other hard-disk recording system combined, and its offspring Deck and Opcode's StudioVision, which combined hard disk recording with MIDI recording and playback as well as mix automation, Pro Tools turns the Mac into a true digital multitrack recorder and editor.

In its initial release, Pro Tools can handle four audio tracks, recording to and playing from a single hard disk, but the company will shortly be introducing hardware that will be able to handle eight, 12, or 16 tracks, on multiple hard disks. The system includes all of the audio editing, MIDI record and playback, real-time processing, and mix automation of its predecessors, and adds several layers of new features. It is far more than the sum of its precursors' parts: it's a highly integrated, comprehensive, genuinely professional system. It occupies a niche halfway between music composition and post-production, with enough features to attract both markets.


Pro Tools consists of four components: two hardware and two software. The hardware components are a NuBus card that fits into any Mac II (though the IIsi needs a NuBus adapter) and contains a pair of the ubiquitous Motorola DSP56001 chips; and an Audio Interface box containing four balanced (XLR) analogue inputs and outputs, plus one set each of AES/EBU (XLR) and S/PDIF (RCA) digital audio connectors. Although you can record and play back four tracks of analogue audio at a time, you can only work with two tracks of digital, and you select in software which digital input is active. There is an important reason for this, which I'll get into later. The interface box also contains indicator lights for incoming analogue signal levels and various statuses (stati?), as well as screwdriver trim pots for calibrating analogue levels.

The two software components are ProDeck and ProEdit. ProDeck is an evolutionary successor to Deck, with enhanced automation and realtime processing capabilities. ProEdit presents a graphic interface for placing and editing audio and MIDI tracks. ProDeck is where you would generally begin and end a project, because that's where the recording and mixing functions are. It also contains Playlist editing functions similar to Sound Designer II. ProEdit is most useful in the middle of a project, when the various elements are assembled.

The two programs are designed to work together under Multifinder (a Mac with at least 5MB of RAM is required, and at least 8MB is a good idea), and both manipulate the same files simultaneously. The files, collectively known as a 'session', consist of audio, MIDI, and automation data, and the software automatically arranges them for you neatly in folders when you start a new project.

Switching from one program to the other must be done from within the programs, using a menu item or the 'command-=' (command-equals) key combination, not by clicking on a window in the inactive program, or on Multifinder's mini-icon. If you do it wrong, you run a risk that recent edits made in one program will not transfer correctly to the other (Digidesign is considering changing this.)


You can work with up to 32 audio tracks, although only four of them can actually play simultaneously. You determine which tracks play back by assigning to each track one of four 'voices'. If a track has a unique voice assignment, it will play. If two tracks have the same voice assignment, then the lower-numbered of the two will take priority. Should that first track stop, the second track will immediately break in.

This 'patchwork' approach to audio assembly is conceptually not too different from many real-world multitrack sessions, in which individual tracks often only play during a small portion of a cue or song, and are silent the rest of the time. The analogy is strengthened when you realise that even though there are only four audio channels, each of the 32 tracks maintains its own identity and can have its own fader, processing, EQ, and automation.

If it turns out that two tracks assigned to the same voice need to play simultaneously, a portion of one of the tracks can be moved to a different track, or to a new track altogether, with a different voice assignment. If you need to play more than four tracks simultaneously, two or more can be bounced and mixed, entirely in the digital domain.

The four voices are not the same as the four physical audio outputs. Any track, regardless of its voice assignment, can be assigned to an output pair and a pan position within that pair, so there is no reason why at some point all four voices could not be routed through a single audio output.


ProDeck is usually where a session starts. In the Audio Mixer window, on each track you will find: a fader; Solo, Mute, and Record buttons; a pan control and output pair assignment; and a voice selector. In addition, there are two effects-send level knobs (you can use any two of the physical outputs as external sends during recording or mixing, and any of the inputs as returns), and a pop-up two-part processing module that acts on the signal in real time when you play it back. Each half of a processing module can be a single-band equaliser with selectable mode and frequency range; a digital delay with a maximum delay time of about 300ms; a chorus generator; or a delay-based stereo simulator.

When you are ready to record a track, you click Rec on one or two channels, make sure your levels are OK in the Input/Output window, and click on the Record and Play buttons in the Transport window. Click Stop when you're done, then Rewind or Return to Zero, and play it back. If you don't like the mouse, all of the Transport controls have user-programmable equivalents on the Macintosh numeric keypad.

The Transport window also lets you scrub recorded tracks, set up loops with programmable pre and post-roll, set punch-in and out points (punches are non-destructive, so the data underneath a punched section can be recovered at any time), and slow down the playback by up to 98%.

An individual audio track can consist of one continuous file, or it can be divided into an unlimited number of segments or regions, each one of which can be adjusted independently as to when it starts and how long it lasts. Once a region is recorded, it does not have to stay with its original track, but can move freely among any of them.

Region editing is handled in the Audio Playlist window of ProDeck, and all edits are non-destructive. In this program, regions are always butt-spliced to each other, so that one begins where the previous one ends. You can tell the system to create crossfades between adjacent regions up to several seconds in length. While Sound Tools kept its crossfades in RAM, thereby limiting significantly how many you could use and how long they could be, Pro Tools writes them to disk, giving you virtually unlimited space. You get to choose from seven different crossfade curves, and you can use dissimilar curves on the two sides of the fade, which can have some creative uses.

From this window you can also perform three destructive edits on one or more regions: hum removal, with selectable frequency; noise gating, with adjustable threshold; and normalizing.


Once you have all your audio recorded, it's time to move over to ProEdit. Here you have a highly intuitive graphic front-end for manipulating files, both audio and MIDI. As in ProDeck, nearly all of the editing functions are non-destructive, and merely move pointers around. (Destructive edits are the province of Digidesign's venerable — and optional — Sound Designer II, a new version of which has been released that recognises Pro Tools' audio card.)

Tracks are displayed as waveform drawings horizontally across the screen, either in full height for more detail, or half height so you can see more of them. (For a really fast display, the tracks can instead be shown as empty rectangles.) Across the top is a time scale, calibrated in film feet and frames, minutes/seconds/decimals, SMPTE frames, or bars and beats. At the left are buttons for adjusting each track's volume, pan position, voice assignment, and mute or solo status. When you go back and forth between ProEdit and ProDeck, these settings are carried across.

The ProTools Audio Card.

At the very top are icons for choosing the major operations: moving a region, either horizontally in time or vertically from track to track; scrubbing the audio, either one track at a time or all together; zooming in on the display; trimming a region or restoring it; and selecting a region for editing.

Regions can be isolated from within other regions, and moved around separately, so for example a drum fill can be extracted from a longer track and placed somewhere else, or duplicated and put several other places. Since all of the editing is non-destructive, these operations take up no additional memory and are quite fast.

Every time a new region is created it is given a name, which you can type in yourself, or the software will do it for you: each new region gets the original file's name, and an additional '+' sign. Alternate takes of a file get bullets after the initial name, so the fourth region of the third take of a file called "Wombat" would end up as "Wombat+++". A list of available regions appears at the right side of the screen, and to bring a region into a track, you simply click on its name and drag it to the track and insert point where you want it.

Besides ProDeck's way of dealing with regions in which they must always butt up against each other to form a continuous track, which is here called Shuffle mode, ProEdit offers a Slip mode, in which individual regions can be moved or trimmed freely, and space left between them if desired. If a region is moved so it overlaps another, the stationary one will be automatically trimmed to accommodate the one being moved.

For a sound editor, this is probably the coolest feature in ProEdit. Moving files around to match a visual time scale or MIDI tempo map (we'll get to that in a minute), with as much precision as you want (just zoom in if you need more), is a very creative way of playing with audio, and should make the system very popular with broadcast and post-production people. You can also set up crossfades visually, merely by dragging the selection icon across the two regions you want to fade, for as long as you want the fade to last, and then selecting fade-out and in curves.

Another useful feature is Strip Silence which, as StudioVision fans know, lets you automatically chop up a long sound file into shorter ones, with breaks between them at pauses in the audio. You can specify how long a pause must be, in milliseconds, to qualify as a break point. You cannot, however, specify a minimum level, which seems to me an oversight.


Once you've assembled your audio where you want it, you will probably go back to ProDeck for automation and mixdown. Like its predecessor, ProDeck offers a combination of automation modes, which can be a bit bewildering at first. You can record up to eight real-time automation tracks, in which all fader movements are recorded just like events in a MIDI sequencer. You can play back any or all tracks simultaneously, and filter out data so that certain tracks only affect certain controls.

All of the program's controls can be accessed by the Macintosh mouse, which is okay when preparing tracks for recording or playback, but is pretty unwieldy when performing a live mix. Not only does the mouse limit you to moving one control at a time, but when audio is playing, screen updates are (quite rightly) given a very low priority by the computer, and trying to grab with the mouse a fader that is jumping around spasmodically is about as much fun as catching a live fish with your teeth [I wouldn't know — Ed].

The solution to this, as in the original Deck, is MIDI Mapping. To do this you open an Automation Sequence window, turn on the mapping function, click on any on-screen control, and then move a controller (mod wheel, foot pedal, etc.) on an external MIDI device. The control lights up in colour, and the MIDI controller will now operate it.

A single MIDI controller can be assigned to any number of on-screen controls, and you can store up to eight separate maps in one session. JL Cooper Electronics has produced an external control box, the CS-10, to exploit this feature fully. It has eight faders, several knobs and buttons, and a jog wheel. Although it is a generic MIDI (or serial) device, it automatically configures itself to work with Pro Tools when you hook it up and boot the software.

When you're recording an automation track, the program doesn't care whether the controls are being moved by the mouse or by an external device. Even better, it doesn't care whether a control is visible or not, so when you're done automating a channel, you can put its fader away and make room on the screen for other stuff.

You can take a 'snapshot' of all of the controls at any moment, load several of them into a list, and play them back as you record an automation track. For more precise control, you can record the current settings into one of 40 'mixer state' locations, which can then be recorded into an automation track, and moved around or duplicated in a Playlist editor similar to the one used for audio events. You can also instruct the program to move smoothly from one state to another. All automation moves are, of course, saved with the session files.

Prior to final mixing, tracks can be 'bounced', or more accurately, pre-mixed. One or more tracks or regions can be combined, in mono or stereo, complete with effects, EQ, and mix automation, into a new file and saved to disk. The pitch can even be dropped as part of the operation. Everything is done in the digital domain, of course, so no signal degradation occurs no matter how many times you bounce.

You can also mix directly to disk, creating a mono or stereo file. Once master files are on disk, you can use Digidesign's Master List software (provided with the system) to create a contents file for use by a CD mastering facility. You can also master to an external recorder using the digital or analogue outputs.

The front and rear panels of the ProTools audio interface.


Pro Tools rightly considers MIDI as an important tool for assembling audio tracks, and includes some useful features for recording, playing, and manipulating MIDI data. ProDeck includes a 'MIDI Sequencer' window, which lets you record and play back single or multi-channel MIDI tracks, with the same looping and punching facilities available as with audio. The current version allows access to two MIDI output ports — printer and modem — so you can address up to 32 channels. Future versions will support Mark of the Unicorn's MIDI Time Piece and Opcode's Studio 5 for many more channels.

You can also import Type 0 (single) or Type 1 (multi) standard MIDI files, and place them on a track. Once a MIDI track is in the sequencer, you can solo it, mute it, or overdub more data onto it.

ProDeck also has a MIDI Playlist window where you can assemble MIDI tracks as if they were audio, while in ProEdit, MIDI tracks can be moved around in Shuffle or Slip mode, broken into regions, duplicated, channelised, have their overall volume adjusted, quantised, or transposed.

When combining audio with MIDI tracks, it's often good practice to record the MIDI first, and then use a click created from the MIDI sequence as a reference for laying down the live audio. ProDeck lets you generate a MIDI-note click, based either on tempo(s) that are imported with a MIDI file (if it has its own tempo map), or on a tempo and time signature that you specify. When you go over to ProEdit, the tempo map — imported or created — will show up in the time ruler at the top of the screen when you are in 'Bar/Beat' mode. If there are changes in the tempo, the distance between the beat markers will get shorter or longer. This makes it very easy to adjust audio events so that they fall on MIDI beats.

There's a Snap to Beat function, which is a clever way to help quantise the beginnings of audio or MIDI regions. When this is engaged, and you move a region, the cursor is restrained to move only within a specified rhythmic interval, which can range from quarter-note down to 64th note triplet.

You can also alter the tempo map itself by marking a beat where you want the tempo to change, and then literally moving that beat forwards or backwards with respect to the recorded track. Any beats that fall between two marked beats (or the beginning and the marked beat, if it is the first one) will shrink or stretch like a rubber band, and the click track will change accordingly. Unfortunately, the playback of the MIDI file itself remains unaltered. That would be a nice option, as would be the ability to view a timecode scale and the bar/beat scale at the same time. You could then move beats to specific frames, and stretch and shrink MIDI files to fit into designated time slots. Maybe we'll see this down the road.


Pro Tools can lock to MIDI Time Code, and both audio and MIDI can be synchronised and chased, so that starting playback in the middle of a file is no problem. The system offers two modes for syncing audio on playback: trigger and continuous resync. In trigger mode, the audio plays at its designated time, and then follows a clock generated by a crystal in the Audio Interface box. The playback will always be stable in terms of pitch, but should the timecode source (audio or videotape) be off-speed, the digital audio and the tape will drift apart. In continuous resync mode, tape and audio always stay locked together, but if there is a problem with the tape, the sample rate will speed up or slow down, and pitch changes may be audible. (Resync mode is not available when recording.)

Digidesign recommends trigger mode be used for short audio regions, and resync mode for longer ones, but this is not a hard and fast rule. In a professional environment with good time-code sources, the internal crystal is accurate enough that trigger mode should nearly always work perfectly well. In my own studio, working with two minutes of audio locked to a VHS tape, I heard no difference at all between the two modes.

ProDeck includes a nice 'spotting' feature that lets you capture a video frame number (it works best if you are using vertical timecode, or VITC) and assign it to the beginning of an audio or MIDI region in a playlist, or alternatively to any spot within a region for automatically backtiming a cue.

ProDeck's windows. Clockwise from top left: Audio Mixer; Automation Window; MIDI Sequencer; Transport Window; EQ and Effects.


No doubt about it, Pro Tools is an impressive system, and lets you do marvellously creative things with audio. There are many, many more clever and useful features that would require a review at least three times as long as this one (which is already too long) to describe. The three manuals that come with the system run to almost 800 pages, and there's not much in them that can be considered fat.

The two-pronged approach to software seems to have allowed Digidesign to cover a lot more territory than a single program would have. It's not necessarily the most intuitive way of doing things, and you sometimes find yourself confused over which application contains a particular feature, but you get used to it soon enough. Although they work well together, each application is not dependent on the other, and there will be situations in which using just one will be sufficient.

Visually, the software is very appealing. In grey-scale mode or on a colour monitor, it has a textured 'NeXT' feel, with buttons that light up or 'half-light', as on tracks that are muted while another track is soloed. When an operation is going to take a little while, the Mac's watch is replaced with an animated icon of a hand drumming its fingers on an invisible table top. If a file has clipped — that is, two or more consecutive samples are at maximum positive or negative level, those samples will show up on ProEdit's screen in red.

Although it's complex, few of Pro Tools' features seem to have been added gratuitously, or just to show off. In fact, one of its design goals seems to be to let the user get as much as possible out of it without needing to know everything about it, and for the most part this works. If you want to do list editing, you don't have to know all there is about manipulating graphics, and vice versa. Some post-production engineers I spoke to almost never use ProDeck, but do all their assembly in ProEdit, and mix down through an external board or dump to multitrack without ever leaving the program.

The system is not without its growing pains. I remember some years ago a reviewer wrote about an early Mac sequencer that I helped develop, "It's cruel to make a little computer work this hard". The computer has gotten a lot bigger, but this puppy really makes it work hard, and when you're at the cutting edge of performance like this, things can get squirrely.

Hard disks are just one issue. A 300MB drive would seem to be essential for any serious work — remember, you're using 20MB a minute, and that's without any alternate takes. Those megabytes have to be fast — my trusty SyQuest removable, which works fine with Deck, is not up to the task, and many other drives that may have been fine for earlier tasks will be too slow for Pro Tools. (When you're shopping for a drive, the access time is not the only specification to look for — you must also check continuous throughput speed).

Digidesign has introduced its own line of hard and magneto-optical drives which it guarantees to work, but they are bulky (mostly because they're rack mountable) and far more expensive than the drives of the same size and from the same original manufacturer (there are really only a handful of disk drive makers, like VCRs) that you can find in any computer magazine.

Another issue is computer speed, at least until the System Accelerator (see box on p22) is available. I had no trouble using the system on a IIex, but had I wanted to use MIDI Manager, I would have been up the proverbial creek. Fortunately, Digidesign have included their own SampleCell driver in the software, so that users of slower machines who have that sampling card are not forced to use MIDI Manager to access it, but MacProteus users, or folks who want to run multiple MIDI applications along with Pro Tools, are not so lucky.


As with any new and potentially revolutionary software, there are bound to be bugs, and I found a few, plus I experienced a number of crashes. I also found a few features that could be implemented better. For example, handling of Type 0 MIDI files is good, but importing Type 1 MIDI files will use up all your available tracks in a hurry, and they also don't play back correctly. There is no program change or controller chasing in the MIDI playback, so if you start playing a MIDI file in the middle, you may hear the wrong patch or incorrect volume settings.

Post-production professionals will miss the lack of any way to directly import an Edit Decision List (EDL) from a video-editing system, the way that Digidesign's earlier Q-Sheet software can. There is also no 'fade to silence' command, which is certainly one of the most commonly used edit operations, although Digidesign assures me it's coming. Also useful to post-production people (especially those who work primarily with ProEdit) would be a way to change the volume of individual regions within a track, without bothering to automate the session through ProDeck.

Another missing feature is time compression, either, as discussed earlier, for MIDI or for audio. You can export an audio file into Sound Designer II, and use that program's facilities, but it has never worked all that well (though Digidesign says they're about to release an algorithm that sounds much better), and it's a clunky and time-consuming procedure. Same thing with MIDI files: you have to export to a sequencer, edit, and import again.

On the up side, Digidesign are eagerly taking suggestions from all segments of the industry, and working hard to incorporate them into future versions. They have told me that the current design team is committed to staying on the project for at least the next year, so the prognosis is excellent that most of these problems will be licked and the necessary features included before long.


Pro Tools is letting Digidesign expand into a new market position. More than just a 'digital Portastudio' (Deck with an Audiomedia card fills that role at one-quarter the price), this is a serious multitrack recording and post production system, with high-end features, and a price that for the first time begins to approach that of the 'big boys'. While they are certainly not abandoning their lower-end customer base, Pro Tools makes it just a little harder harder to continue to think of Digidesign as the low-priced Mac-based David up against the dedicated-hardware Goliaths of SSL, NED, AMS, etc. Sonic Solutions, for example, has an 'entry-level' Mac-based system that compares in price with Pro Tools, and although it doesn't have nearly as wide a range of features, its user interface is more squarely aimed at post-production professionals.

However, for the general-purpose, high-quality, full-featured digital recording and editing system that it is, Pro Tools is remarkably inexpensive, and very much in the Digidesign tradition of making professional tools available at significantly lower price points. The company is also offering trade-in deals to Sound Tools owners upgrading to Pro Tools, worth £300 for each piece of hardware (Sound Accelerator card, AD-In etc.), which makes it even more of a bargain. I foresee Pro Tools becoming an extremely popular system, and I look forward to working more with it and watching it evolve.

Further information

Pro Tools £6,122 inc VAT.
System Accelerator £3,356 Inc VAT.
4-track Expansion Kit £5,106 inc VAT.

Sound Technology plc, (Contact Details).

The Future

Early in 1992 Digidesign will be releasing larger versions of Pro Tools: up to 16 tracks, in increments of four tracks, using multiple hard disks.

Trying to get a lowly Mac to play 16 tracks of audio through its own SCSI bus is like stuffing two dozen clowns into a Volkswagen: it might be fun to watch, but you wouldn't want to try it yourself. The secret is to use a separate processor, almost a 'computer within a computer', to handle the hard disk input and output. Digidesign's processor will be a NuBus card called the 'System Accelerator', with a 25MHz 68030 CPU (the same as a Mac IIci), and a highspeed SCSI2 bus for the drives. It will allow the Mac to concentrate on things like MIDI and screen redraws.

Unfortunately, it's not cheap, and the card is the reason why, as you may have noticed from the advance publicity. Pro Tools is one of the few audio products whose 8-track version is more than twice as expensive as its 4-track version. On the other hand, you only need one System Accelerator card to run 16 tracks, so things eventually do get cheaper as you expand.

There's another issue to deal with when working with multiple channels of digital audio, which has sort of been under wraps until recently, but is slowly being forced into the industry's consciousness. It has to do with the fact that the AES/EBU digital audio specification does not have a separate clock signal. (S/PDIF can, for all practical purposes, be considered part of AES/EBU.)

For ordinary stereo applications, such as transferring data from a CD to DAT over an AES/EBU cable, a dedicated clock is not needed, because the two channels are part of the same signal and therefore are always in sync. However, when you are mixing more than two channels, and those channels are coming from different sources, as for example they might be in a studio that is using voices from a D2 video deck (which has AES/EBU audio), music from DAT, and sound effects from a sampler, there is no way to ensure that the signals will be in sync with each other, or even have the exact same sample rate. Trying to mix these signals can result in clicks, dropouts, and other types of distortion.

The process of reconciling two or more different incoming AES/EBU signals is fiendishly difficult, and Digidesign have wisely chosen not to attempt it in the four-channel version of Pro Tools — that's why there is only a single (stereo) digital input on the Audio Interface. (It's also a major reason why Yamaha use their own proprietary digital format on their DMP7D and DMR8 mixers.)

One solution, however, is to make sure that all of the sources coming into a digital system are locked to a common clock with the receiver. Often that clock can be based on a stable video signal — what is usually called 'house sync'. While getting all of the possible sources to lock to house sync is beyond the resources of any company, Digidesign have figured out at least how to get Pro Tools to do so, and two devices will do the job: the company's new Video Slave Driver, and the upcoming Micro Lynx from TimeLine.

Even without the Slave Driver, multiple Audio Interfaces can have their inputs and outputs locked together by daisy-chaining the 'Slave Clock' connectors on the rear panel. The crystal of the first box in the chain will serve as the master for all of the others, ensuring perfect sync. This way, at least, all of the outputs will be in sync, and an external mixer will have a relatively easy time dealing with them.

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Six Of The Best

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Making Your Own Video

Sound On Sound - Copyright: SOS Publications Ltd.
The contents of this magazine are re-published here with the kind permission of SOS Publications Ltd.


Sound On Sound - Jan 1992

Donated & scanned by: Mike Gorman

Gear in this article:

Software: Sequencer/DAW > Digidesign > Pro Tools

Gear Tags:

Mac Platform

Feature by Paul D. Lehrman

Previous article in this issue:

> Six Of The Best

Next article in this issue:

> Making Your Own Video

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