What is ATSC?

Lonnie C. Best

The Advanced Television Systems Committee (ATSC) is the developer of a set of digital television standards. Under the ATSC's high definition standards, digital television signals are broadcast in resolutions up to 1920x1080 pixels with a wide-screen aspect ratio of 16:9, though standard definition images may also be broadcast. The standard can also transmit audio signals in Dolby Digitalâ„¢ 5.1 surround sound.

The ATSC develops digital television standards.
The ATSC develops digital television standards.

In the United States (US), the Federal Communications Commission (FCC) adopted the ATSC standards in 1996. The new standard replaced the older National Television Standard Committee (NTSC) analog signal standard on June 12, 2009, and other governments have adopted the standard as well – including Mexico, Honduras, Canada, South Korea, and El Salvador. Transmission of the new digital signals means that older television sets without an ATSC tuner capable of decoding the signals require an external tuner.

A digital TV antenna can be hooked to a television and used to pick up over-the-air broadcasts.
A digital TV antenna can be hooked to a television and used to pick up over-the-air broadcasts.

In the US, the change launched criticism from many consumers who were forced to purchase a tuner if they did not already have compatible equipment. This prompted the issuance of coupons which saved the consumer most of the cost of the purchase of a tuner box. The majority of high definition television sets are already equipped with both tuners, and set-top boxes provided by cable companies are also equipped to decode the signals; therefore, consumers owning either of these at the time of implementation of the new standard were already prepared for the change.

Like NTSC, ATSC broadcasts using a 6 megahertz (MHz) bandwidth, and utilizes the MPEG-2 codec for video transmission. The new specification allows for several different resolutions to be broadcast within a single channel, allowing stations the ability to broadcast in various standard definition resolutions to fit different television screens. Stations may also still broadcast analog signals, though the new standard requires an entire channel for broadcasting; stations that choose to broadcast in both digital and analog must broadcast on two separate channels.

Local broadcasting stations, called terrestrial stations, broadcast using a different method of frequency modulation than cable broadcasters. The ATSC specifies several different methods of modulation. Terrestrial broadcasters operate using the 8VSB specification, which allows for a maximum transfer rate of 19.39 megabits per second (Mbs), while cable broadcasters can transmit at 38.78 Mbs by making use of the 16VSB or 256-QAM standards, the latter of which is not defined by the ATSC but rather by the Society of Cable Telecommunications Engineers (SCTE).

Though ATSC provides a generally strong signal service, one of the negative aspects of its transmission lies in the fact that signal interruption or poor signal strength results not in poor-but-accessible audio or video for the viewer, but rather a complete freezing or disappearance of audio and video. For the end-user, this can create a broken and interrupted viewing experience. As the standard continues to gain acceptance, better performance of the standard likely can be expected.

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