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Opcode Digitrax, OSC Deck II & Digidesign Session

Apple Mac Software Roundup By Paul D. Lehrman
Published March 1996

Several software houses are producing modestly priced programs which take advantage of the audio capabilities of the Apple Power Macs. The result can be high‑quality multitrack digital audio at a suprisingly low cost. Paul D. Lehrman finds he's got the Power...

It's amazing how much the 'entry fee' for high‑quality digital recording has come down. Around 10 years ago, the cheapest multitrack digital system cost tens of thousands of pounds — and that was just for a single tape machine, with no editing or mixing capabilities. Digidesign's launch of Sound Tools in 1987 abruptly changed the world of two‑track digital editing, for the first time bringing it within reach of a project studio budget. It also represented a sea‑change in audio editing user interfaces, and a few years later, Pro Tools did the same thing for multitrack recording, mixing, and editing.

Now the RISC‑based Power Macintosh computers from Apple have arrived, and the field has changed again. Apple's design includes data and disk I/O paths that can support multiple streams of digital audio inside the computer's central processor, and 16‑bit, 44.1kHz A/D and D/A convertors, so that no additional hardware is required for work with high‑end audio. For the first time, multitrack digital production is almost entirely a software issue. With the hardware already provided, the only decisions to be made are what features the software should have, and how the user interface will look and behave. With Power Macs now available for under £1000, and the necessary software costing no more than a good MIDI sequencer, musicians and engineers can now own a system for what, only a few years ago, it would have cost to rent one for a day.

For the first time, multitrack digital production is almost entirely a software issue.

To be fair, maybe we shouldn't go quite that far — the audio capabilities of the Power Macs don't really equal those of a dedicated digital recording system. For instance, you can only record two tracks at a time, and you only have two output channels. In addition, you're unlikely to want to master CDs from a Power Mac's audio outputs. Owing to considerations of cost and the exigencies of computer design, the A/D and D/A circuitry in the Power Macs is pretty low‑rent: inputs and outputs are via mini‑jacks, and the convertors are capable of a dynamic range of about 76dB — not exactly Super bit‑mapped CD quality.

Still, it's a lot better than any computer has provided before, and entirely adequate for multimedia applications. If you need higher quality, bringing the Power Mac up to hi‑fi standards is not at all difficult: buy (or borrow) a Digidesign Audiomedia II card (£1056.33 from Digidesign UK) and use it at the recording and final output stages. It will increase the dynamic range to about 86dB, and also provide S/PDIF inputs and outputs, so that you can import files from digital sources without compromise, and send your final stereo mix directly to DAT. You can still use the computer's convertors to hear what you're doing during editing and mixing, and the process won't affect the fidelity of the data itself.

The Three Contenders

There are currently three programs designed to take advantage of the Power Macs' audio facilities. OSC's Deck II (£399) is the senior member of the club. Originally, Deck was marketed by Digidesign as a way to bring multitrack audio to its lower‑end customers (ie. Audiomedia card owners), but Digidesign gave it back to OSC a couple of years ago. Deck runs native on the Power Mac, as well as on the short‑lived Quadra AV series of computers, which used the AT&T DSP 3210 chip for high‑quality audio, as opposed to the more common Motorola 56001 chip. It will also run on any NuBus Mac equipped with RasterOps' MediaTime or Spectral Innovations' NuMedia cards, both of which use the AT&T chip, or with any Digidesign (Motorola‑based) hardware, except Pro Tools III. Got all that? The version in general use as I write is 2.2, though 2.5 is shipping, and may be generally available by the time you read this.

Next up is Digitrax (£189), which was recently obtained by Opcode Systems from a company called Alaska Software. Digitrax was originally designed for use with the old AV computers, and the AT&T‑chip NuBus cards. The new version (which is still being shipped with Alaska's manual) has been optimised for Power Macs. It still does not, however, support any Digidesign hardware. The current version is 1.2.

The newest contestant is Digidesign's Session (£175). Like the original Deck, Session is a low‑cost alternative to Pro Tools or the company's mid‑range Session 8. Besides being Power Mac‑native, it supports Audiomedia II, and in pre‑Quadra computers it may run (although the company doesn't guarantee it) with the original Audiomedia or Audiomedia LC cards. For more on Session, check out David Mellor's full review in SOS December '95.

Recording And Editing

The overall operation of the three programs is similar. Audio is recorded through the Mac's input jack, or imported from a QuickTime movie, an audio CD, or other source. One or two tracks can be recorded at a time, and tracks are displayed on the screen in dedicated 'timeline' or 'tracks' windows as waveforms; you can zoom in and out to see either greater detail or more of the file. Additional tracks can be added while you listen to the original tracks. Automated non‑destructive punch‑in and punch‑out are provided, and Digitrax also supports punching on the fly.

On the screen, audio can be moved around in time, and referenced to a ruler showing seconds and SMPTE frames or other scales. The audio sections can be trimmed from the beginning or the end, or chopped up into pieces which can then be moved around — all non‑destructive procedures. Besides letting you create complex layerings and montages of sounds, this also makes it easy to assemble pieces of different takes of a track, to make a perfect one — and it's very fast.

Non‑destructive editing... makes it easy to assemble pieces of different takes of a track, to make a perfect one — and it's very fast

To help you find your edit points, there are markers, sync points, and/or auto‑locate registers, and in Deck and Digitrax, audio can be scrubbed. Digitrax's scrubbing, however, only works in a forward direction, and is always exactly half the normal speed of the audio, while Deck's goes in both directions over a wide range of speeds. Deck and Session provide four memories for location and zoom settings, so that you can recall a screen setup instantly — very useful when you're lost in a long file.


The number of tracks which can be displayed and played varies between the three programs (see box 'How Many Tracks?' for full details). However, in all of the programs, the volume levels of the various tracks are controlled in real time from mixer windows, all of which use a mixing console presentation, with faders, mute and solo buttons, pan sliders, and other familiar controls. Fader movements and pan position can be recorded. In Digitrax, adjacent fader pairs can be linked, following each other directly. In Session, up to four different fader groups can be created, and the faders within a group maintain their relative position to each other when one is moved. In Deck and Session, you can use an external MIDI controller, such as a JL Cooper MixMate, to move the faders, and these can be recorded with the session, just like on‑screen moves. Deck also includes 'state' automation, in which all of the current control settings are memorised and stored. Any state can be recalled at any time, and the transition time between states is adjustable. All three programs include visual editing of automation moves in the timeline window, so you can see the moves overlaid on the visual waveforms, using rubber band‑like 'breakpoints'. Session includes a feature called 'Smart Breakpoints': this means that if you're editing automation within a selected region, the levels at the very beginning and very end of the region are automatically preserved, regardless of how you change levels within the region.

A crossfading function is available in Deck and Session, which automatically overlaps two pieces of audio on the same track — up to several seconds' worth. You can specify the curves of the fade‑out and fade‑in with great precision. Crossfading is non‑destructive: the fades themselves are stored as separate audio files on disk. To accomplish the same thing with Digitrax, you have to use up two tracks, overlap them, and create manual fades on each.


Effects are an important part of any multitrack studio, but they are not easy to implement in a computer‑based digital system: even Pro Tools, for which a huge variety of real‑time effects is available, needs expensive extra hardware (DSP farms) to use more than a handful of them at a time (for more on using Pro Tools with effects, see Mike Collins' two‑part feature on TDM plug‑ins, which started in last month's SOS, and continues this month). The three programs under examination here, because of their non‑destructive orientation, lag behind even such comparatively primitive programs as Macromedia's SoundEdit 16 in the types of effects they can impose on the audio. Deck and Digitrax provide a short list of destructive functions, including normalising, reverse, and invert (flipping the phase). Deck lets you normalise a group of files in one operation, looking for the single maximum level and adjusting all the files accordingly.

Digitrax also includes a 2‑band parametric EQ for each track, which can be applied non‑destructively (as the session plays) or destructively. Unfortunately, the EQ clips badly if you apply any boost at all to the signal, and there's no way to pad down the input to keep this from happening. Also, the real‑time EQ is disabled when you're doing a mix to disk (as opposed to simply recording the Mac outputs). The program has flanging and chorusing effects, but they only work on AT&T‑chip systems, not yet on Power Macs.

Session includes two single‑band non‑destructive EQs on each track, which work well. They seem to be post‑fader, so there's no problem with clipping. For other effects, we'll have to wait until later this year, when Digidesign release the Audio Suite set of plug‑in processors. Likewise, Deck owners have to wait for fancy effects, but they should arrive soon: the forthcoming revision 2.5 of the program (possibly out by the time you read this) will be compatible with audio plug‑ins created for use with Adobe Premiere, and these include an impressive palette of time‑ and frequency‑based processing algorithms from Invision Interactive, known as Cybersound FX (and for more on this, see my article on software synthesis in last October's SOS). The Cybersound processing, unlike Pro Tools' TDM plug‑ins, is non‑real‑time and alters the actual audio files.

Exporting And Mastering

Besides saving a session as a QuickTime movie (see box 'QuickTime & CDs'), all three programs give you a number of options for a finished project. You can simply play it through, recording to another medium like DAT or videotape, or you can 'mix to disk', creating a new hard disk file containing the finished stereo mix, in AIFF (the Apple audio standard) format. Session and Deck can also save files as Apple SND resources, or in the DOS world's ubiquitous WAV format. (They can import those file formats too.)

"Deck and Session are running neck and neck, piling features on with each new revision."

When you mix to disk, you have the option to trim down the audio to 8‑bit, and/or lower the sample rate. Digitrax can handle all common sample rates, and simply truncates the samples. Deck lets you resample only at half or a quarter of the original rate, but it does provide four different bit‑conversion options, including fairly decent‑sounding dithering, which reduces quantisation noise at low levels. Session can save at any sample rate, and five levels of quality are available for the rate conversion — the best one can take literally hours to work, but for critical applications the results might be worth it. When it deals with word length, the program will round off the samples, or 'squeeze' them, using a fairly aggressive form of audio compression that keeps the level consistently high. It's nowhere near as sophisticated as Waves' L1 Ultramaximizer for Pro Tools, but it does the job.

Sync And MIDI

The programs are all designed to synchronise to SMPTE timecode, via MIDI Time Code. The timecode is handled either with Apple's MIDI Manager (in Digitrax — surprising, for an Opcode product) or Opcode's OMS (in the others). Audio is usually played from timecode in 'trigger' mode: once the code is read and the audio starts, it chugs along, following the Mac's internal clock. In long files, or when locked to an unsteady source of sync, such as a consumer VCR, this can lead to drift between the digital audio and the master tape, so Deck offers the option of 'continuous resync' mode (as featured in Pro Tools), where the audio's clock constantly monitors the SMPTE frame numbers and makes periodic adjustments in the playback rate. This mode places a heavy load on the CPU, however, and in some cases the program will simply refuse to use it (and will tell you so).

Deck also has a SMPTE capture function, which grabs frame numbers on the fly, so you can easily spot sound effects or automation moves — particularly useful if you're using vertical timecode (VITC), which can be read while a video deck is paused. In Digitrax, sad to report, SMPTE sync doesn't work: hopefully, Opcode will fix that before too long. Similarly, all three programs are designed to sync to MIDI sequencers, using internally‑routed MIDI Time Code. This feature, however, is not working in the current version of Digitrax.

For serious MIDI users, Deck gives three additional options for linking with a sequencer: first, you can import a Standard MIDI File right into the session, and play it back along with the audio. The time ruler can be set to display the tempo of the imported file, and you can tell the program to 'snap' audio events to MIDI beats or bars, which can be a great help when you're aligning audio tracks or sound effects to sequenced music. But there are two major problems with this feature. One is a limitation of MIDI Files themselves: a MIDI File cannot (although this may change before long) address multiple MIDI ports. So, if you've created the sequence in a multi‑port MIDI studio using an interface such as Mark of the Unicorn's MIDI Time Piece or Opcode's Studio 5, you won't be able to play it correctly from Deck. The other problem is that if there are any tempo changes in the MIDI File, they won't show up on Deck's ruler — so unless you're doing tracks that never change tempo, the MIDI‑based ruler is actually pretty useless.

The second option for working with a sequencer is using OSC's Metro, a full‑featured sequencer designed to work symbiotically with Deck — it syncs automatically, and even uses a common transport window. The third option is setting Deck to generate MIDI Time Code, so that a sequencer can sync to it.

Which One Is For Me?

Unless you're a complete beginner at digital audio, my recommendation would be to stay away from Digitrax, at least for now. It's not that I don't like it — it's simple and sleek, its limited talents are actually very well suited to the majority of conventional audio needs, and a couple of its functions (such as auto‑starting CD audio and on‑the‑fly punching) are very cool. But when Opcode purchased it from Alaska Software, I feel they got (to coin a phrase) a half‑baked product. The EQ is not much good, and there's a serious problem with tracking when two faders are linked as a stereo pair: at the bottom of their range, the difference between them is 6dB, with the result that as you fade a signal out, it skews over to one side. The screen doesn't scroll automatically as the audio plays, so after a few seconds you can't see what you're hearing. The lack of a crossfade function is annoying, and basic editing operations, like butting sections up against one another, are clumsy. The sync'ing problems are inexcusable, but hopefully they will go away when Opcode makes the program OMS‑compatible. Digitrax is worth watching — despite its problems, it could grow up to be a good program.

Deck and Session, however, are running neck and neck, piling features on with each new revision — and both are already excellent tools. If you're into MIDI (and what reader of this magazine isn't?), you may feel that Deck's superior handling of MIDI files and integration with Metro give it the edge. But the lack of support for MIDI tempo changes in files created with other programs is unfortunate.

For post‑production work, Deck's ability to continuously sync to SMPTE, and its frame‑capture feature, are very useful. Other advantages are the advanced scrubbing, flexible automation, normalising, and off‑line no track‑limit mixing, as well as a feature that automatically removes silences from a track, and some very clever key‑cursor combinations that make many editing operations a cinch. Deck is also the only one of the three programs considered here to support Pro Tools (although not Pro Tools III). Using the optional 16‑Track Tool program, it can squeeze 16 tracks out of a single Pro Tools interface (when it's hooked up to a Power Mac), which is more than Digidesign can! The program has been around for several years — always a nice thing to know — and it works perfectly happily with only 8Mb of RAM, although you'll want more if you're sync'ing up to Metro.

Session's built‑in CD‑audio importing (which OSC says will be in Deck's next revision) and multiple sample‑rate algorithms are a big plus for multimedia work. The 'squeezing' 8‑bit export algorithm, while it may not please everybody, will help a lot of multimedia soundtracks, and the non‑destructive EQ is likewise genuinely useful. The program has a brilliant, continuous zoom function, that should (and no doubt will) be emulated by every other audio program, and the interface in general is quite stunning. The lack of scrubbing, however, is a drawback.

Session uses Digidesign's DAE audio engine software, which makes it a glutton for memory: you shouldn't consider running it unless you have at least 16Mb of RAM. But it seems very stable, especially for a new program, and it's cheaper than Deck. It should be interesting to see what happens to the program, as Digidesign's recently‑announced software‑only version of Pro Tools (which will run native on Power Macs) becomes available. Will Session continue to get better and more feature‑laden, to keep up with Deck, or will the company allow it to drop back, to differentiate it from Pro Tools?

Regardless of what the future holds, Session and Deck are good products today. Both companies are well‑established, and know their fields thoroughly. If their record so far is any indication, the best is yet to come. But right now, if you want to mix audio on your Mac, I doubt you can go wrong with either of these programs.

Sound And Vision: Quicktime And CDS

For multimedia types, all three programs can import QuickTime movies directly. If the movie already has a soundtrack, it can be discarded, or incorporated as a session track (or tracks, if it's stereo), and in Session you can bring in audio from other movies as well. When you play, locate, or scrub around the audio, the movie's video will follow. In Deck it also works the other way: when you scrub the movie, the audio scrubs with it. This is particularly useful when you need to drop a piece of audio into a particular video frame.

When you finish a session, you can save it all — sound and video — as a QuickTime movie. In Session, you can offset the video start time, which is a useful feature if you want to add opening or title music to a movie, but unfortunately, you can't save the result as a movie: instead you have to save the soundtrack as an audio file, go into your QuickTime application and insert time at the beginning of the movie to accommodate the music, then import the soundtrack.

Another feature of interest to multimedia producers and sound editors is the ability to control audio CDs, and to import tracks, or sections of tracks, directly from them into the program. Session and Digitrax both include control panels for selecting and auditioning tracks from a CD that's in an internal CD‑ROM drive. In Digitrax, the CD and main transports are integrated: you can cue up the CD player to a certain point, then put the program into record, and it will automatically start recording from the cue point on the CD — a big time saver. On the downside, the program uses an analogue signal path from the CD to the Mac, and relies on the CD player's and the Mac's conversion circuitry, which some people will not be happy with.

Session offers either an analogue path or a SCSI path, which keeps the data in the digital domain. The analogue path uses the AppleCD Audio Player desk accessory. The SCSI method (in which the audio track is treated like a movie) can also access an external CD‑ROM drive.

Deck can import CD audio over SCSI, using Apple's MoviePlayer, but it's a two‑step process, because the file that MoviePlayer produces is interleaved stereo, and it must be broken down into two mono tracks before Deck can deal with it.

How Many Tracks?

Digitrax displays and plays six tracks, regardless of hardware configuration. With the others, the situation is a bit more complex, and the number of tracks that can sound simultaneously is determined by the hardware used.

Deck will play:

  • Eight to 16 tracks on a Power Mac, depending on CPU speed.
  • Four tracks with an Audiomedia card or Sound Tools.
  • Six tracks on a Quadra 660 AV or AT&T NuBus card.
  • Eight tracks on a Quadra 840 AV.
  • Either eight or 16 tracks with a Pro Tools system, using optional software. (If you have Sound Tools II or Pro Tools hardware, you also get four discrete output channels.)

The program can show up to 999 tracks on the screen: when the hardware limit is exceeded, the excess tracks are simply muted. However, a 'virtual' off‑line mix‑to‑disk function is available, which can handle as many tracks as you want — you just can't hear the mix until it's done.

Session plays:

  • Four tracks with an Audiomedia II card.
  • Eight to 16 tracks on a Power Mac, depending on speed.

It will display up to 16 tracks, but once you have created and edited a track, you can store it off‑line as a 'Playlist in a bin', from which it can be dragged onto the screen any time. The number of Playlists in a session is unlimited.