Dropped Frames with Daisy-Chained FireWire Drives

Symptom #1: Dropped Frames During Playback and Recording to Daisy-chained FireWire Drives

"I'm getting dropped-frames alerts while using my FireWire drive and a FireWire deck. I've used both on other systems that worked fine. I have the FireWire deck connected to the FireWire drive, which is connected to the Macintosh."


A FireWire chain consists of multiple FireWire devices strung together in a straight cable path directly to the computer. Thus, the Macintosh FireWire port is plugged into a FireWire device, which is connected to another FireWire device, which is connected to another FireWire device, and so on until you reach the last device. In general, FireWire DV cameras and decks always occupy the end of a FireWire chain, because they don't have a second port to loop through to another device.

The difference between a FireWire port and a FireWire bus is an important distinction. A bus is a primary interface with the motherboard of the computer. We say that your Macintosh has an ATA bus and a FireWire bus because these buses are direct interfaces with the motherboard. A port, on the other hand, is a connector that allows you to interface with a bus. A motherboard has a bus (typically, one FireWire bus per Macintosh), and a bus can have one, two, or even three ports. Thus, your Macintosh might have two ports on the single FireWire bus, whereas your PowerBook might have only one port on the one FireWire bus.

When two devices are connected to a single bus, they can interfere with each other's data interchange with the motherboard, slowing all operations.


For extremely high-demand uses, such as high-data-rate uncompressed and HD video, make sure that you don't share a FireWire bus between both a deck and a drive. Doing so is almost guaranteed to cause bottlenecks and dropped frames. When using the AJA I/O Standard Definition Uncompressed capture device, for example, you absolutely must add a second FireWire bus to your Macintosh, typically by adding an inexpensive PCI FireWire expansion card.

If you're not running uncompressed or HD video, you might expect to be able to get away with sharing a single FireWire bus between a DV deck or camera and a FireWire drive. But this is still far from optimal since even the most advanced FireWire deck interfaces are built to deliver data at a dramatically slower speed than hard-drive bridges and generally provide only about one-quarter of the top possible FireWire 400 throughput (about 12.5 MB per second, as opposed to a potential 50 MB per second).

The only way to guarantee that bottlenecks and data collisions in the FireWire bus won't cause dropped frames and other issues is to move either the FireWire drive or DV deck or camera to another FireWire bus. This is easier and cheaper than you would imagine. A PCI FireWire 400 or 800 expansion card can be found for around $30 and will solve the question completely. For PowerBook users, a similar solution can be found with PC Card or Cardbus FireWire adapters. Alas, iBooks have no such Cardbus slot and will be more limited in this regard.

Apple Pro Training Series. Optimizing Your Final Cut Pro System. A Technical Guide to Real-World Post-Production
Apple Pro Training Series. Optimizing Your Final Cut Pro System. A Technical Guide to Real-World Post-Production
Year: 2004
Pages: 205

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