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Understanding Digital and HDTV Broadcast Standards

Television broadcast standards are government-issued guidelines that dictate how TV signals are broadcast, transmitted, and received. In the 1940s, the National Television Systems Committee (NTSC) created a set of standards for analog TV—the signals that are broadcast to and received by conventional (non–high-definition) TVs.

In 1996, the Advanced Television Systems Committee (ATSC) set forth new standards for digital TV (DTV), or signals that are transmitted digitally in high definition. Digital TV standards offer highly detailed images, movielike “widescreen” formats, and crisp sound.

Broadcasting Basics

The images you see onscreen consist of still images that are shown so quickly that they seem to move in sequence, like a cartoon. Each frame of video appears on the screen in horizontal lines. Lines can be scanned, or displayed, across the screen in one of two ways: interlaced or progressive.

Interlaced scan: Lines are displayed in two repeating passes down the screen. The first pass displays all the odd-numbered lines from top to bottom; the second displays the even-numbered lines. Interlaced scan is represented by a lowercase i next to the TV’s resolution measurement (see “DTV (Digital TV) Standards” later in this section).
Progressive scan: All the lines of visual information on the screen are read in one pass, resulting in better image quality than in interlaced scan. Progressive scan is represented as a lowercase p next to the TV’s resolution measurement.

DTV (Digital TV) Standards

There are three digital TV standards offering varying levels of picture quality: SDTV (standard-definition TV), EDTV (enhanced-definition TV), and HDTV (high-definition TV).

EDTV and SDTV have a higher resolution than analog TV, meaning that they display more lines of pixels on the screen—which results in better picture quality. HDTV has an even higher resolution than EDTV or SDTV.

SDTV: SDTV sets are listed as 480i, meaning 480 lines on the screen. The “i” refers to interlaced scan—480 lines of resolution are read in an alternating sequence (odd-numbered lines first, even-numbered second).
EDTV: EDTV sets are listed as 480p or 525p. The “p” refers to progressive scan—the 480 or 525 lines of resolution are read in one pass. EDTV sets can deliver HDTV broadcasting, whereas SDTVs cannot.
HDTV: HDTV offers the highest resolution of the three digital TV options. There are three HDTV standards:
- 720p: 720 lines are read progressively. 720p was the old standard for high definition.
- 1080i: 1080 lines are read interlaced. 1080i, is the newest standard for high definition.
- 1080p: 1080 lines are read progressively. 1080p is the most detailed resolution currently available.

HDTV vs. HDTV-Ready

When shopping around, you’ll encounter both HDTV sets and HDTV-ready sets.

HDTV sets: These TVs have built-in HDTV tuners (also called digital tuners or ATSC tuners) in addition to standard analog (NTSC) tuners. They can receive HDTV signals on their own—no extra equipment is necessary.
HDTV-ready sets: Typically less expensive, these TVs must be connected to a separate, external HDTV tuner (you can buy one at an electronics store for about $100–200) in order to receive HDTV broadcasts.

EDTV or HDTV Monitors

An EDTV or HDTV set that’s described as a monitor doesn’t have a built-in tuner at all—not even an analog one. Monitors can work with external tuners, though.

Transition to All-Digital Television

Starting on February 17, 2009, analog signals will no longer be broadcast—all broadcasts will be digital. As a result, the Federal Communications Commission (FCC) has mandated that all TVs made as of March 1, 2007, must have built-in HDTV tuners (unless they’re monitors, in which case they can still be manufactured without any tuner at all). This doesn’t mean that analog-only TVs will become obsolete, though. You’ll just need to receive digital signals through a digital cable box or satellite box or buy a set-top digital-to-analog converter.

Coupons for Digital-to-Analog Converters

From January 1, 2008, through March 31, 2009, the U.S. government’s National Telecommunications and Information Administration (NTIA) will offer a subsidy program through which $40 coupons (limit two per household) will be offered to consumers who still have analog TVs. Each coupon can be used to buy one digital-to-analog converter, which will provide standard-definition programming to any TV that has an analog-only tuner. The coupons must be used within 90 days of the date of issue. For more information, see www.dtvtransition.org.

Acknowledgments & Disclaimer