Guides

Analogue and Digital Video: What's the difference?

The ageing analogue process transmits video as complete frames, with the receiving device then interpreting and translating the signal into video and audio on a monitor. It is at this interpretation stage that a progressive loss of data, however small, leads to a loss in image quality.

Digital video, on the other hand, stays digital (such as '0's and '1's ) with the data constructed to describe the colours and brightness of a video frame. On the receiving end of this data transmission, there is no translation or interpretation, just the delivery of the data into another digital device. This consistency of delivery is the crucial advantage that digital video has over analogue video when it comes to working with video on the PC.

If you're still using an old 8mm or VHS handycam, now is the time to upgrade to digital.

FireWire (other terms include iLink, IEEE 1394 or 1394EEE) provided both the transfer speed, at 400Mpbs, and consistent rates to allow the average PC user to edit their video like a pro.

What About USB 2.0?

In the not too distant past, there was a clear distinction between USB and FireWire. USB 1.1 could not transfer high quality DV; loosely defined as 25 frames per second (fps) with each frame being 640x480 resolution, due to USB's transfer limit of around 11Mbps (or around 1.5MB per second). Transferring DV requires a transfer rate of at least 3.6MB per second, which left FireWire as the only option due to its ability to work at 400Mbps, or up to around 50MB per second. Then along came USB 2.0 with a transfer rate of 480Mbps or around 60MB per second.

At first glance it would appear that USB 2.0 is even faster than FireWire; however speed is not the only issue when it comes to DV. One serious issue with USB 2.0 is that it can not guarantee a specified data transfer rate. This is due to USB 2.0 being a master-slave technology, which means it needs a computer's CPU to coordinate the appropriate data transfers. While not a problem when dealing with low demand peripherals such as Web cams, scanners, printers etc, digital video requires dependable performance to avoid dropping video frames. (Incidentally, the currently-in-development USB 3.0 is targeted at 10 times the current bandwidth, roughly 4.8GBps, utilising a parallel optical cable.)

FireWire is a much more independent technology in that it works in a peer-to-peer relationship. More importantly, it delivers data consistently at a specific rate. If you want to work with video, even to edit the family movie, go with FireWire.