Recording - November 2010 - 6

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FireWire Hubs and audio: Just say no
Dear experts: I own a Mac mini (late 2009) that only came with a FireWire 800 port. My soundcard, an MAudio ProFire2626, has a FireWire 400 port, so I have to plug in a FW800 to FW400 wire to make it work. I also have an external drive that supports FW800. In an ideal world, I would like to use the external drive with the FW800 hookup, because of the increase in speed. When I plug my external drive into my Mac mini with the FW800 cable, and then my ProFire to the FW400 port on the external drive with a FW400 cable, it does not work. On the external drive, there are two FW800, one FW400 and one USB 2.0. I thought that I could have hooked up the drive on the FW800 port of the Mac and the ProFire to the FW400 of the drive, but someone told me that it would not work because of the FW400 vs. 800 protocol. I’ve heard about FW800 hubs. I had originally wondered if there was a way to connect both the external drive and the ProFire in the FW800 mode using a FireWire hub. Does anybody know if it would help, or am I only going to buy something that won’t resolve my problem? Thanks in advance,
Pascal Des Marais Les Productions MusiMarais Canada

First, I suggest you try using the devices alone, one at a time. Make sure the drive works alone, and the ProFire works alone, without the other on the bus. If they do, then you could have a bad cable, but the other thing to try would be to move the drive to a USB port since it has that capability and leave the ProFire alone on the FireWire port. You’ll be moving disk data at 480 Mbps rather than 800, but it should be more reliable (and can easily coexist with your mouse and keyboard). If the ProFire works alone, see how many channels of audio it can move before it begins to choke; the new minis are pretty fast, but you’re asking a lot of one if you are trying to move 16 channels of 24/96 audio at a time. You might also consult M-Audio and see if you have the latest drivers and if they’ve heard of this problem before and have solutions I haven’t yet suggested. Good luck and tell me how your tests come out! Best—MM Pascal replied: Thanks a lot for this fast answer. The two units are working fine by themselves, my current hook-up is, the Profire on the FireWire bus and the external drive on the USB bus and this setup is working okay. Thanks again and by the way, I’m a reader of your magazine since the last 5 years. Keep up the good work!—PDM I am very glad I was able to help, Pascal. As I predicted, the problem was your FireWire bus; there was a conflict between isochronous data from the audio interface (meaning data that must arrive at a particular time rather than being sent in bursts — audio can’t be buffered to allow for traffic, or it will stutter or hiccup or just plain stop!) and the non-isochronous data bursts from your drive. What you’ve done is to move the non-isochronous data to the USB data bus inside the Mac mini, where it only has to fight with your mouse and keyboard, and can send data in bursts without any trouble; the FireWire bus now belongs to your audio interface, which can use it efficiently since there is no conflict with anything else. The only downside to this is that your drive is now running at USB 2.0 speed, which is a hair better than FW400 but nowhere near as fast as FW800 (or eSATA, an option that doesn’t yet exist for Apple computers out of the box). But for most multitrack applications, I think you’ll find USB 2.0 will be plenty fast enough to store the data you’re creating. There’s enough confusion in this one issue to warrant an entire article, and your letter’s inspired me to write one! Look for it in an upcoming DAW Details column. And thanks for the kind words!—MM

Pascal, thanks for your question and thanks for reading. When you say “It doesn’t work”, do you mean that there is no communication at all with the ProFire, or that there is spotty communication, buffer underruns, etc.? My guess is that the conversion from FW800 to FW400 is not the problem; what is far more likely is that you’re saturating the FireWire bus. One of the most common problems that FireWire users run into is that daisychaining FireWire devices can create severe bandwidth problems; just because the protocol says you can connect up to 64 devices doesn’t mean they’ll work properly, and devices like the ProFire which need precise timing on all data can fail spectacularly if they have to share the data bus with an external drive that is trying to move large chunks of data at high speed. Don’t blame this on having only one FireWire port on your Mac mini, either; even Macs with multiple FireWire ports have only one internal bus and multiple ports, i.e. the ports are like a “hub” built right onto the computer. The only way to truly have multiple FireWire busses is to put a separate PCI card into a tower computer. A FireWire hub is mainly useful for boosting the power on long cable runs; it can make matters worse by convincing users that they can get away with plugging in more devices than will actually work. It certainly won’t fix this problem!

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RECORDING NOVEMBER 2010

Recording - November 2010

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