Bard plays the same song twice: once from his grandfather's vinyl record, once from the music file on his phone.
The record stores the song as a groove whose wiggle the needle rides. The phone stores the same song as a long string of 1s and 0s. Two completely different ways to carry one piece of information, and the difference has a name on each side.
Both the groove and the file are signals: each carries information in a physical form.
Look at the groove's wiggle traced over time. It glides smoothly through every in-between height. At any moment it can sit at any value in its range: a little higher, a tiny bit lower, anything.
A signal that varies continuously like this is called an analog signal.
Now look at the file's values traced over time. Every value is a 0 or a 1. Nothing sits in between: the signal holds one value from a set list, then jumps to another.
Separate allowed values from a set list, with nothing in between, are called discrete values.
A signal that carries information as a sequence of discrete values is called a digital signal.
One read decides every case. Ask: can this signal sit at any value in its range, or only at values from a set list?
On an old cassette tape, the magnetization along the tape rises and falls smoothly with the recorded sound. Is the tape's signal analog or digital?
The one read: can the signal sit at any value in its range?
The magnetization glides through every in-between strength: it varies continuously.
Analog. The tape's signal varies continuously.
A text message crosses the network as a stream of 1s and 0s. Is that signal analog or digital?
The one read: only values from a set list?
Every value is a 0 or a 1, with nothing in between: discrete values.
Digital. The message is a sequence of discrete values.
In a microphone's cable, the electrical signal rises and falls smoothly, following every detail of the singer's voice. Is that signal analog or digital?
Ysolde signals her campsite with a flashlight: on for a long flash, off, on for a short flash, using only on and off. Is her signal analog or digital?
Amity says: 'A signal that can sit at any value in its range, not just at values from a set list, is an analog signal.' Is Amity correct?
Which statement tells an analog signal from a digital signal?
Four signals are described below. Which one is digital?
A weather station reports temperature two ways: over one wire, a voltage that rises smoothly as the temperature climbs; over the other, a stream of 1s and 0s. Which line names the two signals correctly?