As DTV sales stagnate, specs proliferate
-- EDN, January 4, 2001
Digital-TV sales remain in neutral or-if you believe recent return-rate rumors-in reverse. In an attempt to simplify the public's purchasing decisions, the CEA (Consumer Electronics Association) has issued a series of acronym-heavy terms and definitions that its members, the equipment manufacturers, swear they'll follow from here on out. Ignore the proliferation of "DTV-capable," "digital-ready," and similar television-advertising messages you've been bombarded with this holiday season; those terms are headed for the scrap heap. And it remains to be seen whether the new guidelines will enlighten or just further confuse even technologically savvy customers.
An HDTV (high-definition-television) monitor can display at least 720 image-carrying horizontal-scan lines in progressive (p) mode, and at least 1080 lines in interlaced (i) mode. Of those lines, at least 540 must be active when displaying a 16x9, wide-screen, 720p incoming signal and at least 810 lines should be viewable for a 16x9, 1080i signal. An HDTV tuner can tune in over-the-air DTV broadcasts, whose modulation scheme is still under debate; hence, the interest in decoupling tuner and monitor. Such a tuner can also decode all ATSC video formats and can either play back Dolby Digital audio signals through its own speakers or pass them on to an external amplifier. Conversion between 720p and 1080i before passing the analog-video-output signal to a HDTV monitor is acceptable, as are digital, full-resolution handoffs. Also, HDTV tuners need not scale up lower resolution input signals, such as 480p. Full-blown HDTVs combine monitor and tuner functions into one unit.
A new product category, EDTV (enhanced-definition digital television) covers EDTV monitors, which can display at least 480 progressive scan lines with no specified aspect-ratio requirements. EDTV tuners have identical audio- and video-decoding requirements to those of HDTV tuners, but they can downscale high-resolution input signals to a 480p analog or digital output. As before, EDTVs combine the tuner and monitor functions and specifications.
A third category, the now significantly neutered SDTV (standard-definition digital television) covers SDTV monitors, which is a fancy way of describing NTSC TVs with video inputs. SDTV tuners have identical receiver specifications to those of their HDTV and EDTV counterparts but have to output only good old NTSC; that is, 480i, analog-only resolutions. And SDTVs need only to receive and output "usable"-read low-fidelity, mono-audio. So, what's the only practical difference between today's NTSC TVs and tomorrow's SDTVs? Manufacturers can attach the all-important "digital" advertising label-sarcasm intended-to SDTVs.
CEA, 1-703-907-7675, www.ce.org.
-by Brian Dipert
