With digital TV, WBAY can transmit higher-quality TV programs and sound, and yet we're sending less information through the airwaves to your DTV set. That's because a digital TV signal can be compressed.
If you've downloaded software for your computer, you know about compression. It's why you can fit all the music from a CD into a memory card for an MP3 player. It's why that one-megabyte program you downloaded swallowed up more than five megabytes of your hard drive after you installed it-- after you "decompressed" it.
Before the DTV signal leaves the transmitter, the digital information is run through a compression algorithm. This does some complicated mathematical stuff (this is why you're supposed to pay attention during math class).
For one thing, it gets rid of extraneous information, like sound at levels beyond human hearing. Zap, it's outta there. Already that's less data to send. It also gets rid of subtle differences in color you wouldn't notice anyway. Why color a sky with 1,000 shades of blue when 800 will do?
The algorithm also looks for redundant elements in the video and sound-- several lines with the same color of blue, the red and white stripes in a U.S. flag. It also looks for elements that don't change from frame to frame-- the wallpaper in the background of a scene, Al Gore standing at a podium. Remember, in digital TV all these images are a flow of ones and zeroes. To the compression algorithm, the redundant information looks like a repeating pattern in the numbers.
When these repeating patterns are found, they're removed and a special code representing each pattern is inserted into the data. Your DTV receiver receives the special code, which tells the TV how and when to decompress the patterns. Less information needs to be sent.
In our grossly oversimplified illustration above, we've highlighted different patterns with different colors, and as the patterns are compressed you see there's less information being sent.
Using compression, the digital TV signal squeezes a lot more information into the same 6 megahertz of bandwidth as a conventional signal. This is what makes all the extra features of DTV possible.
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