The ATSC (Advanced Television Systems Committee) is a group of people who moderate the standards for digital TV transmission, which has replaced the analog NTSC system entirely in the US. In Canada, they will all be replaced by August 31st, 2011and in Mexico by December 31st, 2021. As of now, the U.S., Canada, and Mexico are the only users of the ATSC standard. Other standards include DVB-T and ISDB-T.

The ATSC supports various aspect ratios, forms of scanning, framerates, pixel aspect ratios, and resolutions. Here is a listed example of different options:

• Aspect ratio: 4:3 or 16:9
• Forms of scanning: progressive or interlaced
• Framerate (Hz): 23 - 90
• Pixel aspect ratio: square or non-square
• Resolution: 352 x 288 - 1920 x 1080

The higher resolutions tend to share the same square pixel aspect ratio, and most of the lower resolutions share the non-square pixel resolution. The framerates vary quite a bit.

What codec is used?

In transporting the data, the MPEG-2 codec is used in the transport stream and from there is received by the ATSC receivers built into TVs, DVRs, VCRs, and other TV top appliances. The ATSC receivers then decode the stream into the video and audio you see and hear on your TV set. While MPEG-2 is used for video encoding, AC3 is used for the audio codec. The AC3 codec can produce theater quality sound, because it can support 5.1- channel surround sound. ATSC also uses 8VSB (8-level Vestigial Side-Band) modulation.

How does a ATSC receiver work?

Simply put, an ATSC receiver performs about 8 different methods in converting the transport stream to what you see and hear on your TV. These methods include AV synchronization, decompression, demodulation, error correction, image reformatting, trans-port stream demultiplexing, and finally selective tuning. Not all receivers include of of these functions (as error correction isn’t mandatory to be built-in to receivers), but most do. AV synchronization does things such as making sure that the video and audio are in sync, where decompression performs the task of unpacking the stream it receives, as the stream is compressed before it’s sent. However, when the signal is received, the unpacking process causes some quality to be lost. The difference between the original video and the new video and audio isn’t too drastic, so it’s not considered to be any real loss.

For more information on ATSC receivers, see this article. It goes more in-depth with how each function works in the process of making sure the video and audio are perfect for your TV.

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