In the late 20th century, many countries began converting audio and video broadcasts, or sound and pictures, from analog to digital signal technology. Traditional analog broadcasts, used for radio and TV broadcasts since the early 20th century, used a continuous signal resembling waves passing over water. Analog to digital signal processing became possible with a technology called sampling, which converted the signal waves into a series of numbers.
Sampling an analog signal can be described as taking many repeated snapshots of the wave, and converting each snapshot to a digital signal using a series of zeros and ones, called binary numbers. The resulting numbers were transmitted as a broadcast, and converted back to analog signals by the TV or radio. Digital programming could be sent over an analog signal, and some countries were doing this in the late 20th century. Using a fully compressed signal of binary numbers was an advantage due to the amount of information that could be sent over a much smaller frequency range, or bandwidth.
Digital compression used a number of different technologies, but a typical compression system took each frame, or a single snapshot of a broadcast, and converted it from an analog to digital signal. The system looked at the next frame, and compared it to the previous one. Only the parts of the image that changed, such as a moving object or a changing color, were transmitted. This process repeated itself continuously; since only the changes in a picture were transmitted, a great deal less data was required.
Adequate sampling and error correction, a technique used to eliminate digital values that did not fit the signal, were both needed to successfully an analog to digital signal. Errors could occur from random signal noise that occurred during the transmission, and software was developed to check the signal, a technique also used in compact disc (CD) devices to remove signal errors that occurred from scratches or age. Digital broadcast signals were an advantage to the companies creating programming, for a number of reasons. In many countries radio and TV signal bandwidths, or frequencies available for broadcasting, were limited; broadcasts had to compete with frequencies used for emergency services, wireless telephone and radio signals, and many other uses. Converting from analog to digital signal broadcasts, combined with data compression, allowed broadcasters to send more information and better video over the same frequencies.
The late 20th century brought an interest in high-definition (HD) television, to provide improved broadcast picture quality. Broadcasters could send more data by a digital signal than with analog, which caused HD improvements at the same time as digital. Adding signal compression, which permitted a higher-density signal to be sent, further improved signal quality with existing bandwidths.
The growth of Internet-based communications became a growth market for digital broadcasting, because the signals were easily sent to viewers through existing high-speed connections. On-demand movies, Internet radio and other markets expanded in the early 21st century, all taking advantage of digital signals, benefiting broadcasters and providing many more choices to consumers. Customers in remote areas gained an advantage from digital programming; analog TV signals became weaker as the receiving antenna moved further from the transmission tower. A digital TV will convert the values back to a high-quality picture as long as the signal can be received. Remote customers can see the same picture on a TV that a local customer will receive, because distance does not degrade the picture.