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PCI Express: What Does It Mean For Mac Musicians?

Apple Notes By Mark Wherry
Published January 2006

With the new single-processor, dual-core Power Macs shipping, we continue to investigate the impact of PCI Express on the Mac audio and music world.

Forget about crocodile wrestling — writing about technology is perhaps one of the most hazardous tasks you can undertake. If being technically accurate isn't hard enough, the fact that technology changes constantly makes the job nigh-on impossible. The ink barely had time to dry on last month's Apple Notes (discussing the introduction of new Power Macs featuring PCI Express expansion slots that would make it impossible to run Pro Tools HD) when Digidesign announced PCI Express versions of their Core and Accel cards required to run the ubiquitous music production system.

PCI Express logo.

Digi Catch The Express

According to Digidesign, the company "is now concluding its qualification process of the PCI Express systems with the range of Apple Power Mac G5 computers." The new PCI Express Core and Accel cards are expected to ship before the end of the year (they may be available by the time you're reading this column) and will cost the same as the current PCI models, which will continue to be sold. Digidesign also confirmed that there will be "a crossgrade program for PCI users who wish to switch to a PCI Express solution." One point to bear in mind, though, is that 7.1 will be the first supported version of Pro Tools with the new PCI Express hardware, and while 7.x Sessions aren't compatible with 6.9 directly, it is possible to export them in a compatible format (see our Pro Tools 7 review, page 90, for more).

Since Apple's new Power Macs all have three PCI Express slots, those running an HD3 system will be fine. But what if you use an expansion chassis with a larger HD system? Hold on to your PCI cards, because Digi will also be introducing a new product, the Expansion HD six-slot PCI chassis, at the end of the year. That will be available with either a PCI Express or PCI card to attach to your host computer and can be effectively viewed as a PCI Express to PCI bridge. It will be interesting to see if an upgrade is offered for existing chassis users if the chassis itself isn't compatible with the new PCI Express bridge.

Digidesign will support Apple's move to PCI Express slots by offering PCI Express versions of their Core and Accel cards (the original PCI Accel card is pictured here), plus a new expansion chassis.Digidesign will support Apple's move to PCI Express slots by offering PCI Express versions of their Core and Accel cards (the original PCI Accel card is pictured here), plus a new expansion chassis.Whether this new Digidesign chassis will be a re-badged Magma ( device, as with previous Digidesign chassis products, is unclear, but Magma themselves also have a PCI Express to PCI six-slot chassis "coming soon." Interestingly, Magma are going to offer a 'conversion path' between the PCI-to-PCI chassis and the PCI Express model, so this might be of use to existing Pro Tools users who have a chassis already.

What About Everyone Else?

While the number of Mac owners using a Firewire or USB-based audio interface is probably quite large compared to those using PCI offerings, there are some products with certain specifications that are only available as PCI cards, RME's HDSP MADI card being one example. I know many Logic users who use this card with RME's ADI648, to integrate their sequencing and mixing environments, for example, and these are precisely the people who would benefit the most from the increased power of the Power Mac Quad.

I spoke with RME's Matthias Carstens [see also the Audio Interface Manufacturers' Round Table feature in our last issue), who confirmed that "Naturally we will add PCI Express versions of existing products to our line", and expected the first announcements to be made at Frankfurt Musikmesse. "Using the latest FPGAs [Field-Programmable Gate Arrays], we will be able to fully implement all currently known RME features. An example is the HDSP 9652, where the FPGA is completely filled in the current model. This card doesn't have Steady Clock, and also misses phase inversion and the optional +6dB gain in [the] Total Mix [mixer], but the PCI Express version would have these features. We will also make a PCI Express version of the current HDSP PCI card for Digiface and Multiface users, but this card will be function-identical to the existing PCI model, for compatibility."

There are no plans to offer an upgrade program at this time for those wishing to replace their PCI cards with the PCI Express alternative, and Matthias was keen to point out that Apple's announcement had no impact on the company's plans to bring PCI Express products to market. Although RME use FPGAs to implement their products, the reason why other manufacturers haven't specifically announced PCI Express cards could be the fact that there haven't been suitable off-the-shelf PCI Express solutions available, such as a PCI Express to PCI bridge chip, or more complete solutions like Via's Envy24 PCI audio controller chip, which M-Audio use in many of their products.

Apple News In Brief

  • Apple released Mac OS 10.4.3 at the end of October, offering numerous fixes for most areas of the system, including unspecified fixes for Core Audio. Quartz 2D Extreme, by the way (which will bring hardware acceleration to the 2D graphics used by applications such as Cubase SX), is still disabled and unsupported in Tiger. You can download the new version via Software Update or on the web at, where you'll also find more detailed information. Digidesign hadn't qualified 10.4.3 at the time of writing and still recommend 10.4.2, although I have used 10.4.3 with Pro Tools 7 and didn't experience any obvious problems.
  • RME have released an updated driver for users of the HDSP MADI and AES32 audio cards. The new release brings the Mac software into line with the Windows version and includes new Total Mix and Settings applications that enable Mac users to configure features such as the DDS (Direct Digital Synthesizer) for pull-up and pull-down options (related to film frame rates), with full varispeed support in 56-channel mode on the MADI card. The Total Mix mixer now supports a monitor panel, submix view, updated preferences and remote control via MIDI.

Audio Units Meet VST Instruments

In October 2005's Apple Notes we looked at the free AU Lab Audio Units host application that Apple include as part of the company's developer tools package, supplied free of charge with every copy of OS X. After reading the article, someone at the studio where I work asked if AU Lab could be used with Cubase, to run Audio Units alongside VST Instruments, and the answer is yes.

One nice thing about AU Lab is that for every Audio Unit Instrument you add, the application will put a virtual MIDI port on your system (for as long as AU Lab is running) that lets you trigger each Instrument from another application. So, for example:

  • Open AU Lab and create a new Project with the default options.
  • Select Edit / Add Audio Unit Instrument.
  • Choose a plug-in and make sure the MIDI Input Source is set to 'None', because we want to trigger the Audio Unit via another application, not directly from a hardware MIDI input.
  • Load Cubase and create a new MIDI track. You should be able to set the MIDI output of that track to the AU Instrument in AU Lab (a port will be available with the same name as the plug-in you added).
  • Play some MIDI data to this virtual port and you should hear the AU Instrument being triggered. I've noticed on occasion that if there's no sound at first, you need to double-click in an empty area of the Instrument Channel in AU Lab, set MIDI Source to a physical port, trigger some data from that port, then set it back to None. After this, you should be able to trigger the AU Instrument from Cubase.

Jack Plugs In

Here you can see an AU Instrument plug-in, running in AU Lab, being triggered from a MIDI track in Cubase. Its audio output is being routed into a Cubase audio track, via Jack and a clever VST plug-in included with the Jack OS X distribution.Here you can see an AU Instrument plug-in, running in AU Lab, being triggered from a MIDI track in Cubase. Its audio output is being routed into a Cubase audio track, via Jack and a clever VST plug-in included with the Jack OS X distribution.

So now you can trigger an Audio Unit plug-in from Cubase via MIDI. But wouldn't it be great if there was some way of routing the audio output of the AU Instrument back into the Cubase Mixer instead of going directly to a hardware audio output? You might remember a utility called Jack, which I've written about in previous columns, that can do just what we need. Jack is similar to Rewire in that it's basically a virtual cable for routing audio between applications, but it also supports physical audio hardware and is compatible with any application that makes use of Core Audio.

  • To start with, download and install Jack (, run the included Jack Pilot application, then click Start in the Jack Pilot window.
  • Next, run AU Lab, start a new Project, choosing Jack Router as the Audio Device, and add an Audio Instrument as before.
  • In Cubase, set up a MIDI track, route its output to the port labelled with the name of the AU Instrument you added in AU Lab, and create an audio track.

One really nice thing about the Jack OS X installation is that it installs a special plug-in (in VST and AU formats) that allows you to route the audio output of an application into a plug-in (or the audio output of the plug-in to another application). So by adding Jack-insert as an insert plug-in on our newly created audio track in Cubase, we'll be able to stream AU Lab's output into that track.

  • In Jack Pilot, click the Routing button on the main window and you should see the Connections Manager window, which consists of three columns: Send Ports, Receive Ports and Connections. Send Ports shows all audio ports (whether applications or physical hardware) that can send audio to a Receive port, and Connections shows whether there is a connection between the currently selected Send Port and a Receive Port. Jack uses your Mac's built-in audio hardware by default, but if you want to use additional audio hardware you can set this via Jack Pilot 's Preferences window. If you click on AU Lab in the Send Ports column, you'll see that its output has automatically been routed to the physical audio hardware output. To remove this assignment, double-click each entry in the Connections column
  • To route the output of AU Lab into Cubase, expand the Send and Receive Port entries to show all available audio streams, by clicking on the little triangle next to a Port's name.
  • Next, select AU Lab 'out1' and double-click Cubase 'VSTreturn1' to make the assignment for one stream in AU Lab to the Jack-insert plug-in within Cubase. Repeat the process for AU Lab 'out2' and 'VSTreturn2'. Cubase itself talks to Core Audio directly, so Jack is only needed to route the output of AU Lab into the Jack-insert plug-in.

That's it — and it should be less complicated to do than to explain. Play the AU Instrument from your MIDI track in Cubase and you should notice hear the audio come back in via the Jack-insert plug-in to the audio track. Pretty neat. And while this example is for AU Lab and Cubase, the technique will work with any application that supports Core Audio in OS X, so there's plenty of room for experimentation.