Michael Barlowe, age 13, of Marion, North Carolina, for his question:
How can sound and pictures reach TV exactly together?
Today's question makes us think of the fabulous tale of the hare and tortoise. The fleet footed hare and the slowpoke tortoise agreed to a race. Everybody expected the hare to win but he did not try. The steadily trudging turtle came in first.
We live in a speedy age and the speeds of sound and light are fascinating topics. With a great deal of effort we have learned to make planes that can outrun the speed or sound, but we cannot equal the speed of light, and our brainiest experts suspect that we never will. The speed of sound varies, depending on the density and tempera¬ture of the material it travels through. For example, in ordinary air it travels at about 1,100 feet per second. The speed of light varies very little. It whips hither and yon through the cosmos at about 186,000 miles a second. If it could swoop around in rings, it could circle the earth's equator 7 1/2 times in about one second.
Sound, of course, carries noises to our ears and light carries visual images to our eyes. ATV program brings us both sounds and sights. The entire show reaches us from a broadcasting station, often many miles away. If the voices traveled at the normal speed of sound and the pictures at the normal speed of light, there would be a time lag. The sights would reach us long before the sounds. The dialog for the open¬ing scene might just arrive in time for the end of the program. If this were so, TV viewing would be an impossible jumble of nonsense.
The miraculous co ordination of sight and sound on our TV set is made possible by the use of carrier waves. These waves are electromagnetic energy beamed out from the broadcasting station. Before they leave they are modified to carry signals. These are miniature changes in the pulses of electromagnetic energy. They travel along with the carrier waves, silently and invisibly. The changes are made by microphones, cameras and other electronic equipment in the broadcasting studio. This equipment translates the sights and sounds in the studio into electronic signals.
The silent, invisible carrier waves, bearing their hidden signals, travel at the speed of light. They are captured by your antenna and sent down to a series of elec¬tronic gadgets in your TV set. This complicated process sorts the signals from the carrier waves and translates them back into the same sounds and sights that occurred in the studio. The sounds and sights are synchronized because the original signals from the studio were synchronized. The carrier waves act somewhat like a fast jet carrying two passengers, a here and a tortoise. The fleet footed here and the slowpoke turtle arrive at their destination at the same time.
Carrier waves, like all forms of electromagnetic energy, travel at about 186,000 miles per second. They fan out from the station antenna in straight lines, which means they cannot curve around the globes For this reason, we need a system of relays to angle them downward around the curving earth. Relay stations may use till antennas to capture and boost the signal bearing carrier waves and redirect them on their way. However, the relay system works fast and the synchronized sights and sounds appear on your TV screen in the same second they leave the studio.