Digital TV provides a better viewing experience compared to analog. There’s no signal loss the further you are from the transmitter, and both audio and video are sent through the same signal. Although some people still use analog, it’s considered an outdated technology. The U.S. government mandated that all analog low-power TV stations and transmitters must convert to digital by July 13, 2021.
Analog TV Basics
Before the digital transition, analog TV signals were transmitted similarly to radio signals. Video signals were transmitted in AM, while audio was transmitted in FM. The transmission was subject to interference, such as ghosting and snow, depending on the distance and geographical location of the TV receiving the signal. In addition, the amount of bandwidth assigned to an analog TV channel restricted the resolution and overall quality of the image. The U.S. analog TV transmission standard is called NTSC. It was adopted in 1941 and became popular after World War II. It’s based on a 525-line, 60 field/30 frames-per-second at 60 Hz system for the transmission and display of video images. This is an interlaced system where each frame is scanned in two fields of 262 lines, then combined to display a frame of video with 525 scan lines. One drawback is that color wasn’t included when the system was initially approved and implemented. It wasn’t added until 1953, a weakness of the system.
Digital TV Basics
Digital TV, or DTV, is transmitted as data bits of information, just as computer data is written or the way music or video is written on a CD, DVD, or Blu-ray Disc. A digital signal is composed of 1s and 0s. This means it’s either on or off. Unlike analog TV transmission, there’s no gradual signal loss as the distance from the transmitter increases. If the viewer is too far from the transmitter or is in an undesirable location, the station is not accessible. Also, unlike analog TV, digital TV transmission is designed from the ground up to take all the main factors of the signal into consideration: black and white, color, audio (including surround sound), and text. Video can be transmitted as an interlaced (lines scanned in alternate fields) or progressive (lines scanned in sequence) signal.
Analog and Digital TV Differences
Since the DTV signal is made up of bits, the same bandwidth size that takes up a current analog TV signal, it can accommodate high definition (HDTV) images in digital form, and the extra space can be used to transmit:
One or more digital secondary (aka sub) channels in addition to the main channel. Surround sound. Multiple language audio. Text services.
Another difference is DTV transmission supports the widescreen (16:9) aspect ratio format. This matches the aspect ratio of most digital and HDTVs, which more closely resembles the shape of a movie screen. This enables you to watch a movie as the filmmaker intended. You see more of the action in one camera shot during a sporting event, such as viewing the entire length of a football field without it looking like it’s far from the camera. A 16:9 aspect ratio television set can display widescreen images without a large amount of picture space taken up by black bars on the top and bottom of a widescreen image, which is what you see if such images are shown on a standard TV. Even non-HDTV sources like DVDs can take advantage of a 16:9 aspect ratio.
Beyond DTV
The transition from analog to digital and HDTV was only one step. Many televisions now come in 4K resolution (referred to as ATSC 3.0 or NextGen TV Broadcasting), bringing enhanced picture and sound quality, over-the-air broadband, and other capabilities. As with the transition from analog to digital TV, ATSC 3.0 requires new tuners (as add-ons or built-in to TVs) to receive the signals, but support for the current DTV and HDTV system will remain in place for some time. Beyond 4K, there’s 8K resolution. However, it’s beyond most consumers’ reach, and few cameras can shoot in the format. Because of this, 8K likely won’t become mainstream for a couple of years.
