Tuning (or how to avoid problems)

A number of people encounter problems when capturing and editing video. Some folk argue that the only way to avoid these problems is to install a second hard drive, which in my opinion is a fallacy. Its better (and considerably less expensive) to remove the underlying causes rather than rush out and spend needless money on another hard drive.

This page explains how to:

Though readers can simply follow the directions given here, its better to have a little understanding of the reasons why problems do occur - which in turn requires a little knowledge about the way that Windows works in three areas: in talking to your camcorder via firewire, in power supply issues on your computer's PCI bus, and in the way Windows uses memory and the hard disk. If the tekkie stuff goes over your head, don't worry - just carry out the procedure to correct matters.

Windows & Firewire Communication

All communicatiions (e.g. reading and writing via your firewire card) and handled using interrupts. These are numbered from 1 to 15. Each device (e.g. firewire card, printer etc) which uses an interrupt has a priority - and the impoortant thing to grasp is that this priority is not related to the interrupt number but in the order in which the associated device drivers are installed.

Things get even worse if we examine how Windows services the interrupts using polling. What this means is that when an interrupt is serviced the computer (instead of carrying down the priority list) goes back to the top of the priority list to ensure that another card/service with a higher priority than your firewire card needs attention. If your firewire card was installed late it has a low priority, and as a result gets little attention. Unfortunately, your firewire card is usually one of the last to be installed, so its priority is way down the list - and doesn't get sufficient attention to properly handle the transfer of video, thus you start getting problems.

The priority of devices are set in stone (actually they are buried in your registry) - the next time you switch on your computer your firewire card is still at the bottom of the priority list. Unless of course you change the priorities, giving your firewire card first bite of the cherry.

The procedure to do this will take a little while, but its well worth doing. Also, once done you won't have to do it again. Here's what to do:

1. Get all your device drivers together. Its a good idea at this time to check the
manufacturer's web sites to ensure that you have the latest version of the
drivers, and update if necessary.

2. Uninstall all your computer's drivers.

3. Close down Windows and switch off your computer, and remove all the cards from the PCI bus.

4. Install the firewire card in the slot nearest to the CPU (that's under the fan you can see).

5. Switch on your PC, and when asked, install the firewire card device driver.

6. Close down Windows and switch off your PC.

7. Repeat 4 through 6 for each of the remaining cards.

Because the firewire card was the first to be installed, its interrupt will have the highest priority and can operate at optimum efficiency.

PCI Bus Power Feed

Firewire cards are sensitive to the voltage level provided to the card. A lot of PCs (even those with a high spec) tend to cut corners on their power supply. In the normal course of events this wouldn't be an issue, but the extensive use USB devices can affect the power available to the firewire card via the PCI bus (which uses an RC filter to protect against noise - and the R (resistance) drops voltage when the supply is heavily loaded by the USB card). Result - the firewire card may find itself working without sufficient voltage supply. Fortunately, many USB cards make provision for this, but for some reason PC manufacturers cut corners and don't use the special provision of a direct voltage feed from the power supply to the USB card. Have a look and if your USB card has an unoccupied 4-pin socket, connect a spare connector from the hard disk to this board. If there's no spare connector a splitter/extender cable is inexpensive. If a connector is already available on your PC but won't reach, try moving the USB card.

Memory & Hard Disk Interaction

Those who forceably recommend the provision of a second hard disk (using one disk for the programs and one for the video) don't seem to understand how Windows (or any operating system) use memory and the hard disk.

Firstly, when you run a program, it isn't run from the hard disk but is first copied to the memory and then run. While you're loading your program into memory you aren't actually doing any capture or editing - so in spite of what some misinformed folk might argue - a second hard disk has no advantage (providing you take the precautions outlined later).

Windows (like most operating systems) has a mechanism to stop your computer crashing if you run out of memory - its called "virtual memory". When memory gets short your computer will begin to work more slowly because the virtual-memory mechanism automatically kicks in and adversly affects the performance of programs like video that require a lot of memory and good disk-access facilities.

The virtual-memory mechanism, when memory gets short, pages (swaps in and out) parts of the memory to the hard-drive. Every time your computer need a bit of video or a program fragment that has been paged onto hard-disk, it has to write out some data/program to hard-disk to make room for the data/program that it needs, then read in the required data/program from hard-disk into memory. Additionally, yur CPU has to do a lot of processing in managing (keeping track of what's where) the virtual-memory mechanism. So it makes sense to make sure that your computer has all possible memory for your video editing. The means to do this is simple. Before you start video editing:

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