OTHER TECH

Hard-Disk Recorder Basics Let's begin with the most basic of digital basics: bits, as they say, is bits. A hard drive doesn't care if the digits it takes in, stores, and regurgitates represent video, text, graphics, or the latest Eminem opus. Any drive that can store enough bits, and stream them on and off disk fast enough, can do the job. But it takes a lot of bits streaming in and out at very high speed to create digitized video and audio. All digital video, be it from a satellite receiver, digital TV set-top box, digital cable box, or even a DVD, has to trade off image quality for bit rate. As the bit rate goes up, the quality increases and available storage time decreases. The average bit rate for a typical DVD is less than 1 MB per second, requiring around 2 GB to store one hour of a typical movie. High-definition TV takes much more, which is one reason we don't have high-def DVDs yet. If you're willing to accept lower-quality video, you can get by with much, much less storage space because the MPEG-2 encoding/ decoding system used in today's digital video recorders has an adjustable bit rate. This is how digital cable and satellite-TV providers manage to fit more and more channels into the same bandwidth. They lower the bit rate, and thus the video quality, of each channel just a little to fit 11 channels in the space that used to carry only 10. (Hey, the viewers will never notice!) Take a big, fast hard-disk drive, hook it up to an MPEG-2 encoder/decoder, drop in a TV tuner, and you've got yourself a video hard-disk recorder (HDR). And since you now understand its inner workings, you're able to see through the favorite parlor trick of every new HDR owner-pausing live TV. Of course, you can't really pause "live" TV any more than you can pause time itself. What you're really doing is pausing the playback of the video that was just recorded onto the hard-disk drive. (This is the same kind of buffering that keeps your portable CD player from skipping.) On an HDR, it lets you pause, stop, slo-mo, or catch up with a "live" TV program. Or if you program the HDR to keep a recording permanently, it can do everything a VCR can do (and much more). Plus you'll get better performance and greater flexibility, and it will be easier to use (no more blinking clock!). An HDR's capacity-how many episodes of The Osbournes you can store-depends on the size of the hard drive and the level of quality you choose for the recording. Most models let you select from several quality levels. The exception is satellite receiver/HDR combos, which record the bits directly as delivered from the satellite and thus don't need MPEG video encoders. While maximum quality is mainly a matter of bit rate, it can also depend on the performance, or "smarts," of the recorder's MPEG-2 encoder. -D.K.