Ysolde texts a photo to a friend, who forwards it on, and on again. The tenth copy looks exactly like the original.
Her grandfather's cassette copies never did that: each copy of a copy hissed a little worse. The difference is not better wires. It is a power only digital signals have.
Every signal picks up noise on its way: small unwanted changes added by the cable, the air, the equipment.
Watch noise hit a digital signal. The sender transmits values from a set list, say 0 and 1. The cable adds small changes, and a sent 1 arrives as 0.9.
The receiver knows the list. It asks one question: which valid value is this closest to? 0.9 sits closest to 1, so the receiver records exactly 1.
The small noise is gone. Not covered up: gone, because the recorded value is exactly a value from the list again.
An analog signal has no list. Every value in its range is a legal value, so a slightly changed value looks exactly as legal as the original. The receiver has no way to know what was sent, and the added noise stays in the signal permanently.
Copying tells the same story. Each digital copy is restored on arrival, so the tenth copy matches the first exactly. Each analog copy keeps its new noise and adds more, so copies of copies drift worse and worse.
A receiver using the valid values 0 and 1 receives the values 0.08 and 0.94. What does it record?
One question per value: which valid value is this closest to?
0.08 sits closest to 0.
0.94 sits closest to 1.
It records exactly 0, then exactly 1. The added noise is removed.
Zeno copies an old cassette tape, then copies the copy. Why does the second copy sound worse than the first?
The tape's signal is analog: every value in its range is legal.
Each copying pass adds its own small noise, and nothing can restore the values, so each copy keeps all the noise so far.
The noise builds from copy to copy, and the distortion is permanent.
A receiver using the valid values 0 and 1 receives the value 0.12. What does it record?
An analog voice signal picks up small random changes while crossing a long cable. What happens to those changes at the receiving end?
Zeno says: 'A music file can be copied many times and still match the original exactly, because each copy's values are restored to the nearest valid value.' Is Zeno correct?
Why is sending a recording as a digital signal more reliable than sending it as an analog signal over the same noisy cable?
A receiver using the valid values 0 and 1 receives the value 1.1. What does it record?
Amity records her band two ways and sends both recordings down the same long, slightly noisy cable: one as an analog signal, one as a digital signal. Which statement describes what arrives?