Behind The Numbers
Some readers shy away from the "in the lab" boxes in our test reports, probably because it's hard to judge what represents desirable performance if you don't have a lot of experience with the kinds of figures we publish. To help you interpret how our numbers relate to what you see and hear, we're going to lead you through the data in a series of articles discussing each of the major equipment categories, starting with DVD players.
For simplicity, assume that we've tested a DVD player equipped to play the new multichannel DVD-Audio music discs. Instead of actual test results, the "in the lab" box printed on the facing page shows the ideal result for each parameter. How to evaluate a real player's measured deviations from theoretical perfection, or zero error, makes up the rest of the story. First, though, let's take a look at how our test-data boxes are organized in general.
The Layout Each "in the lab" box is separated into sections covering the tested component's performance in its major operating modes. Here it is a player's video performance with DVD-Video discs and its audio performance with DVD-Audio discs and CDs. We'll discuss Dolby Digital performance, which can make up a large part of some players' test data, later in this series when we cover lab data for A/V receivers and amplifiers, where it's more relevant to a purchase decision. (It's better to have Dolby Digital decoding done at the end of the signal chain, where it can serve other source components, such as a satellite receiver or a high-definition TV tuner, in addition to the DVD player, and where the bass-management facilities may be better.)
Each section starts with a list of significant test conditions, which are chosen to represent typical equipment settings and typical input signals. We list these because they sometimes differ from "standard" industry practice, especially with receivers and amplifiers. Fortunately, few user settings on a typical DVD player affect measured performance, and we normally test a player with its default, straight-out-of-the-box settings. At the end of each lab box we print comments by the tester, who will usually discuss any particularly surprising or unusual results or put the findings of key tests in perspective.
DVD-Video Performance Unlike the multiple audio measurements that appear in a player test, the video results are straightforward. The reason we use a composite-video connection for most of these measurements, by the way, is that it typically represents the worst-case output. S-video measurements, when applicable, will almost always be equal or better, so if the player performs well with composite connections, you can assume it will perform well with S-video, too.
Maximum white-level error indicates any errors in overall picture brightness that might need correction using your TV's brightness controls. Many players come out of the box with a video output voltage that is too "hot" (high), and they can look slightly brighter than players with no maximum white-level error, measured in IRE (1 IRE is 1/100 of the ideal dynamic range of the luminance, or brightness, portion of a video signal). If you compare two DVD players that have significantly different maximum white levels (a disparity of 3 or 4 IRE) without compensating for the difference, you'll probably prefer the one that produces a brighter picture, all else being equal, even though it may be a less accurate image.