native code for printing, redraws, and user-interface operations. The music-software companies will have to experiment with several approaches before deciding which solution works best.

The First Natives
Developers of business, graphics, and other general-interest programs are moving rapidly toward native-code versions. Apple recommends developers use a fat binary solution that provides both 680x0 and PowerPC code. A "smart" installer checks with the Mac CPU and installs native code for a Power Mac and 680x0 code for earlier Macs.

Software powerhouses such as Microsoft, Symantec, Claris, Adobe, Aldus, and Quark hope to offer native versions of some top programs either on, or within 90 days of, Apple's March 11 Power Macintosh ship date. However, many popular software applications won't go native until later this year.

Many of the larger music and multimedia software vendors hope to go native sometime this fall. Macromedia and Passport will port their multimedia authoring software later this year. Emagic has announced that they will port Logic Audio this fall, while Opcode and Mark of the Unicorn are testing the waters. However, many digital-audio sequencers rely on Digidesign Audio Engine (DAE) software to address Digidesign's audio DSP hardware. Digidesign is porting DAE to PowerPC before porting its other programs, while dependent software developers adjust their schedules.

Because PowerPC was derived from IBM's Performance Optimized with Enhanced RISC (POWER) architecture, used in the IBM RS/6000 workstations, software-development tools such as debuggers and compilers were supposed to already exist, though they needed to be optimized for the new chip. Theoretically, software developers should have a much easier tithe porting existing programs and writing new ones for the RISC machines thanks to these tools.

In fact, according to Passport Designs' Denis Labrecque, a lack of finished development tools is one of the main things slowing Passport's efforts to port its Producer Professional multimedia production software to native PowerPC code. Labrecque expressed sympathy for tool developers, noting that writing a development language is tough, and debugging a compiler can be torture. He sees this as a short-term problem. Once the development tools ate available, Labrecque expects things to move along quickly.

Power Audio
As mentioned earlier, the Power Mac is capable of recording and playing 16-bit digital audio without using a DSP coprocessor. How will porting digital-audio applications to native code affect existing Mac digital-audio hardware solutions?

Today, Digidesign's Motorola DSP56000-based NuBus cards (especially Audiomedia II, Sound Tools II, and Pro Tools) are unquestionably the top-of-the-line audio cards for the Mac. Their sound quality is superior to that of the AV Macs and will almost certainly exceed that of Power Macs. The Digidesign card is dedicated to processing digital audio; the PowerPC does that, plus many other functions.

In addition, Digidesign is developing a powerful audio-processing card, called a DSP Farm, that contains multiple DSP chips. The DSP Farms and compatible audio-processing cards communicate by way of Digidesign's special high-speed Time Domain Multiplexing (TDM) bus. (For more on TDM, see "Virtual Effects" in the March 1991 EM.) Some of this is relatively new technology, but clearly Digidesign audio cards will remain a standard among professionals.

Digidesign hardware is not the only digital-audio solution, of course. Media Vision offers an inexpensive card, the Pro Audio Spectrum 16 (reviewed in the April 1994 EM). But it lacks pro-quality software support, and its audio quality is not acceptable for serious recordists. It's okay for adding budget 16-bit sound to existing Macs, but unless Media Vision makes some major upgrades, the PAS 16 card will not tempt Power Mac users.

Several digital-audio programs support Apple Real-Time Architecture (ARTA) compatible DSP systems, such as the AT&T DSP3210 chip used in the Quadra AVs and in Spectral Innovations' NuMedia NuBus DSP card. Assuming comparable sound quality, if Power Macs are fast enough to perform audio DSP functions while maintaining the system and other applications, will the DSP3210-based cards die their infancy?

It's a fair question. Apparently, one problem with using the AT&T coprocessor is that the chip shares the main bus with the CPU, causing bottlenecks when the two vie for bus access. With the PowerPC chip handling both tasks, this isn't a problem. On the other side, the limits of the Power PC CPU's ability to simultaneously handle audio, other applications, and system software are untested. Apple representatives emphasize that the 601 is not intended to meet the heavy audio-processing needs of a serious studio. True, the AT&T DSP chip also is asked to carry out assorted coprocessor tasks, so it's not always completely available for audio. But overloading it shouldn't crash the system.

The Power Mac is new, and it will take time to properly test its digital-audio capabilities. If it really can handle everything asked of it, including audio, without slowing down or crashing, the AT&T solution probably is history. But that's a big "if." It seems more likely that a Power Mac with an ARTA-based card or Digidesign Audiomedia II card will prove a better solution for the serious hobbyist and semi-pro, while the higher-end Digidesign cards will serve the pros.

Power Mac and ARTA
At press time, newcomer Alaska Software was just beginning to ship its initial version of DigiTrax, a hard-disk recording program for the AV Macs and Macs with ARTA/AT&T cards. Alaska also is planning a native-code version of DigiTrax, which the company (perhaps optimistically) hopes in release in early fall. Alaska's projected approach to using ARTA cards on the PowerPC seems logical

and probably will be taken by other companies (including OSC when Deck II is ported to PowerPC later this year). Let's take a quick look at this plan.

Alaska will use a fat binary installer. When the installed application boots, it will look for an ARTA-compatible DSP chip. If the software finds the ARTA DSP chip, it will run the audio on it, using native Power Mac code for the rest of the application (mainly the user interface). If no ARTA chip is present, the applications uses the PowerPC chip to do everything, including audio.

What about running audio on both ARTA and PowerPC for multiple tracks? Synchronization is the big problem here. To understand why, let's take a brief look at how the AT&T DSP chip and PowerPC chip get their audio timing. The DSP chip processes audio in frames of 240 samples each. As the audio streams in, the DSP's Direct Memory Access (DMA) section writes the 240-sample frame into a buffer, where the signal is preprocessed and held until the DSP is ready to process it. While the DSP is processing one frame, the DMA is working on the next frame. When the DMA is finished, it sends an interrupt message to the DSP saying that the half it is working on is ready to go. The DSP takes over the prepared frame, while the DMA works on the next 240 samples.

One problem with ARTA's time-slicing approach is that if you try to overdub on existing audio, monitoring the old and new tracks together, the DSP has to line up the two separate data streams. Inevitably, there's at least a 5 to 10 ms processing delay, so overdubs aren't quite in real time. But that's just for starters.

ARTA includes built-in sync between DSPs, but at an unacceptable price for audio applications. TO sync two DSPs, the slave DSP has to ignore its own DMA interrupts and strictly follow the master DPS chip's timing. But because the slave is ignoring its DMA, it doesn't know when the next frame is ready for processing and therefore cannot run smoothly in time with its own incoming audio data stream. Thus, the slave could look for incoming audio at the wrong time, stumble, and miss a frame. A 240-sample frame takes about 5 ms to sample, so if the timing of the interaction between DMA and DSP drifts by one frame, it's unacceptably noticeable.

Apparently, PowerPC chips sync in roughly the same way and pose similar sync problems. Until a way can be found to have a common clock for both processors, it probably won't be practical to use the two chips simultaneously for multitrack audio.

These issues might not be resolved soon and may prove moot. Apple's decision not to include a DSP chip on the Power Macs may foreshadow ARTA's early demise. So far, Apple has not indicated whether it will revive ARTA, replace it with something new, or put the whole issue on the back burner indefinitely.

The Power To Succeed
Assuming you have decided you need some sort of upgrade, the biggest questions pit cost and compatibility against investment in a coming technology. Skepticism is usually justified regarding claims of compatibility with upgraded hardware and operating systems. But because of Power Mac's hardware-level 68LC040 instruction set, there's good reason to believe you'll have few compatibility problems with software that runs cleanly on a Quadra. (That's not a promise.)

Power Mac will provide an immediate speed boost for some users, and there will be much better performance when native-code programs arrive. Eventually, we'll see real-time capabilities not possible on a 68040. In addition, if you want to experiment with hard-disk recording but don't need (or can't afford) the quality of a Digidesign card, Power Mac gives you an as-yet-undetermined degree of 16-bit audio recording.

Still, I don't think all Macintosh users should go to Power Mac immediately. (You will eventually.) Most Quadra owners won't see much improvement with their present software, and the 840AV might even run some programs faster than the Power Mac. If you have a 68040-based machine, or can make do for awhile with your IIci, wait to move to a Power PC until your critical programs go native (which night take as long as a year in some cases). When the time comes, you can decide whether to buy an accelerator (see sidebar 'Power Upgrades"), a logic-board upgrade, or a new computer.

In addition, the prices on 68040 machines are dropping and will undoubtedly drop some more. If you have anything slower than a IIci, especially a compact Mac (Classic, SE/30, etc.), and are looking for a short-term, low-cost solution, a Quadra or 68040-based LC or Performa should satisfy you for the next year or two, and perhaps longer. (A fast 680x0 accelerator card might even do the trick.) You can always add a PowerPC accelerator later. However, keep in mind that accelerators don't speed up I/O operations, including accessing SCSI and NuBus, which digital-audio programs use a lot. Thus, for digital-audio applications, you're better off with a new computer built around a faster CPU.

Given that, if your machine is slower than a Ilci and you can budget $2,000 to $3,000, consider going straight to Power Mac. You won't get as much speed in the short run as you would with, say, a Quadra 650. But next year, when most major applications are native, you'll get a big boost for the price of a few software upgrades. If you have a PC-compatible and are considering switching to Mac, you absolutely should go Power Mac, as you call still run DOS and Windows business programs at acceptable speed under Soft Windows.

Maybe I'm past the point of being old and jaded and have reached the senile innocence of second childhood, but I am extremely optimistic and enthusiastic about Power Macintosh. Sure, native applications will take awhile, and 680x0 emulation isn't as fast as I'd like. And as always, something better will come along later, such as the PowerPC 604 chip. But the 601 offers enough power that the "rest of us" working stiffs on a budget can confidently upgrade to the new generation of desktop computing.

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