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Digidesign's Digital Audio Engine; Inside Digidesign 882

Martin Russ brings you the latest news direct from an Apple R&D gathering, and takes a set of Allen keys to some expensive digital audio hardware...

On a hot and sticky evening earlier in the summer, Apple held the Broadcast Solutions Event at BAFTA in London. A team of evangelists from the Apple R&D laboratories were on hand to answer questions from an invited audience of TV, news, broadcast and media people — and me — and there was a demonstration of how to put a broadcast‑quality video together, from script to screen, in about 20 minutes.

I spoke to Jonathan Knowles, the Senior Product Manager for QuickTime, and he showed me QuickTime 2.5, which he claimed would be out by the time you read this. This is the version with the proper QuickTime Music Architecture built in, which means:

  • OMS support is now included;
  • You can now Drag & Drop AIFF soundfiles (and other formats) to provide sampled and synthesized musical instruments;
  • 44.1kHz/16‑bit sounds are now available (if your hardware can cope);
  • Yamaha, Korg, InVision and other sound sets will be available (these can contain synthesized and sampled instruments);
  • The QuickTime musical instrument editor has been greatly improved.

With this release of QuickTime, the MacOS (Macintosh Operating System) and Windows versions are finally synchronised, so developers can now provide moving pictures, audio and music across computer platforms.

I've been asked why I frequently mention QuickTime in this column. The answer would have been very apparent if you had been at the Broadcast Solutions gathering. Here was an event targeted at people who work in TV (not hi‑tech music) — and the major focus was to discuss the progress towards a universal digital media format — as well as try and push Apple‑based systems as a neat way to edit video. Acronyms and abbreviations were much in evidence: QT 2.5, QT3D, QTVR, QTTV, RAVE, 3DMF, AVI, OMF and more. With demonstrations of 'best of breed' ways of non‑linear editing audio and video from MediaSpec and the Tyrell Corporation, it was serious stuff.

This brings me to the answer. I mention QuickTime because it shows the way that audio, video and music are becoming ever more convergent. When I learn that the BBC have over 70 Digidesign Pro Tools systems, and the demonstator for the Media 100 video editor happily edited his video material and his soundtrack simultaneously using the same program, then anyone using a MIDI sequencer with a few audio tracks who is also sync'ing to video players should be aware of it. MacOS musicians need to keep aware of what is happening out there, because the future is wider than just CDs — the future is CDs, videos, on‑line magazines, TV programmes that look like magazines...

Having mentioned the BBC, their new multimedia site is worth a visit; it uses a host of Macs and QuickTime VR. Check out the web site given in this month's 'On The Net' box.

How It Works: TDM

Using a Digidesign Pro Tools system for a month or so (as I have done in order to write this month's Digital Performer review for SOS — see page 124), you come to appreciate how daunting Digidesign's products can appear from the outside. I've always aspired to buying one, but I've never quite got around to it, and so I had only a sketchy grasp of how it all fitted together. On the assumption that I'm not the only one, here's a brief guide to some of Digidesign's wonderful MacOS computer expansion goodies.

Digidesign's Audiomedia cards are straightforward in concept — they provide basic audio I/O capability with EQ as the only audio effect. But a Pro Tools system contains rather more. The underlying enabler is the Digidesign Audio Engine (DAE), which runs in the background — you can bring it to the front, but it has only a splash screen and a simple 'File' menu. This provides a standard interface between the Digidesign hardware, Audio I/O and DSP processing, and the software that runs on the MacOS computer. The DAE has the advantage that lots of third‑party software uses it, not just the stuff from Digidesign.

The other important piece of underlying technology is TDM (Time Division Multiplexing). This allows several different sets of audio information to be conveyed along a simple piece of ribbon cable by sending them at different times. Digidesign call this the Trans‑system Digital Matrix buss, or TDM buss for short. Physically, it looks like a short piece of blue ribbon cable with some IDC connectors pressed onto it, but in conjunction with the TDM software, it actually allows up to 256 channels of 24‑bit digital audio to be transferred between your computer and
plug‑in cards.

TDM is also the key to providing software plug‑ins that work like outboard effects units, but which use the hardware DSP chips inside the computer. There are a huge and expanding range of plug‑ins, from the dynamics, delays and EQ that you might expect, through to some very complex and sophisticated specialist tools (for an overview of some of these, see Mike Collins' article 'Plugging Into Pro Tools', which ran in the February and March issues of SOS this year). Non‑TDM hardware, like the Audiomedia cards, or the basic Pro Tools, still provide EQ.

TDM‑based systems come with some useful software accessories. I used the DigiTest application to check the exact hardware lurking in the Power Mac 7100/80AV that I used for my Digital Performer review. The screen shot shown is a composite, because you actually need to click on each of the card slots to get the text report shown at the top of the screen — but DigiTest still detects the model of MacOS computer, the number of slots, and the cards in the slots. In this case, there were two cards: the Disk I/O card provides a specially dedicated SCSI2 interface, which is for the hard disk that will be used for the audio files. Having a separate SCSI buss keeps the audio data separate from the computer's own SCSI buss. The Disk I/O card also has the socket for the 882 or 888 Audio I/O boxes. The DSP Farm is just a card full of Digital Signal Processing hardware — and is used to provide the effects processing for TDM plug‑ins.

Apple News In Brief

    Don't bother looking up Apple's share price. At the time of writing, the price was the lowest for many years, and this year's ongoing descent shows no sign of slowing. Repeated warnings that the recovery was going to be tough and would not happen immediately appear to have been correct. But don't write off this column just yet!
    Roland's PMA5 music pad is yet another MIDI device with a serial interface, so it can be connected directly to the two major brands of personal computer. But the combination of a touchscreen user interface, an 8‑track sequencer and a MIDI interface is something more unusual — and might indicate the future direction of hi‑tech electronics: purpose‑designed gadgets for specific market sectors. When the next version has 32 tracks, audio tracks and waveform editing, your Mac can start worrying!
    Apple and BMW may not seem the likeliest of partners, but check out this web site:

It shows how the two companies have joined forces to reinforce the links between two high‑quality, well‑engineered products by utilising the Internet.

On The Net The Beeb Digidesign Tom Cruise & the IMF! BMW via Apple MediaSpec UK Wallace & Gromit!

Mission: Impossible

Also heavily featured by Apple at the Broadcast Solutions event was the TV advert for the Power Book — even though the Impossible film itself has a Mac with the least Mac‑like user interface I've ever seen! But to immerse yourself in even more Impossible material, you could try the web address shown in this month's 'On The Net' box.

Inside The Digidesign 882

Since I had a captive Digidesign system for the purposes of writing this month's Digital Performer review, I took the opportunity to have a closer look at it. I always open up hardware boxes, and the Digidesign's 882 Audio I/O box was no exception, even though I needed to find some Imperial Allen Keys to get inside!

The inside of an 882 is more or less filled with a large double‑sided PCB. The design and construction is of a very high quality — there were no visible corrections or modifications, and the audio/digital areas were clearly defined by the ground planes used for the audio sections. The majority of the board components were surface‑mounted, with just a few through‑hole components. The BNCs for the clock I/O were hand‑soldered.

The main Analogue‑to‑Digital Converters (ADCs) were eight Philips SAA7360Ps, with PMI Op‑amps buffering and filtering the audio inputs. On the output side, eight AK4318 Asahi Kasei Digital‑to‑Analogue Converters (DACs) were used, with PMI SSM2142 VCA, and an Analogue Devices ADG412BR DAC was used to control output level. An Actel gate array forms the bulk of the control logic; the remainder was made up of small gate‑count DIL packages.

The umbilical cable that connects the 882 to the host computer is buffered using standard 26LS31 and 26LS32 line drivers, whilst the power cable to the external power supply unit has RF filters plus 2 large chokes and several 220µF electrolytic capacitors around the 5V regulator.

Overall, this is a very nicely constructed and designed unit. Having the audio inputs and outputs remote from the computer enables a much more flexible placement of the computer, and provides high‑quality audio conversion.