Analog and digital

[sram]

How would you explain the difference between analog and digital and what they realy are to

1- Somebody whose field of study has nothing to do with engineering OR an illiterate

2- Somebody who just finished high school and is about to study electronic engineering

 

[dknguyen]

There are four definitions to consider if you want the full answer. Consider a X-Y graph where X=time and Y=signal value

analog/Digital refers characteristics of the Y-axis
Continuous/Discrete-Time refers to characteristics of to the X-Axis

Analog/Continuous-Time means that the function (on the respective axis that the word describes) can take on any value...
1,2,3,4, 1/4, 2/3, 3.1415, a million and ten billionths. It doesnt matter.

Digital/Discrete-Time means just the opposite. The numbers on the respective axis cannot be any and every number. It can only be certain values like
{1,2,3} OR
{0,1} OR
{0, 1/4, 1/2, 3/4, 1}
For each set of numbers, the axis can only take on those values and ONLY those values. No numbers in between. For {1,2,3} its either 1 or 2 or 3. Not 0. Not 1/2. Just 1,2, or 3.

You can pair ip Digital/Analog with Discrete/Continous-Time any way you want to get four types of signals.

I will make some graphs. BRB. Very easy to see. The definitions come very easily.

 

[dknguyen]

However in normal language, when people say:

Analog- they usually mean analog-continuous time
Digital- they usually mean digital discrete-time

These terms just refer to the "type" of signal. Examples are a cassette recorder which is analog because it records sound at every instance in time at the sound's exact "loudness". An MP3 player is digital because it only records the sound every (let's just say) 1ms. And each time it records the sound, it does not record it as its exact "loudness", instead it rounds off the "loudness" to a number that is closest to the "set" of predetermined values stored internally and instead stores that number. If the "loudness" was actually 49.8 but the set of numbers that the MP3 player could store was {1,2...49, 50...} it would round the 49.8 to 50 and store that instead.

Here is the image.

Note that:

for discrete time signals, there is a Y-value only at certain points in time
for continuous time signals, there is a Y-value only at ALL points in time
for digital signals- Y values can only take on certain numbers
for analog signals- Y values can only take on ANY number

CORRECTION FOR IMAGES: the bottom left graph should have Y values 1,2,3,4 because it is digital (not analog).

 

[RadioRon]

Here's my attempt

Analog is like a violin. The player can choose to make any pitch of sound he wants by choosing to put his finger anywhere along the string. His selection of where he puts his finger is "analog" or anywhere. Digital is like a piano. The range of tones is broken up into "notes" represented by keys and the player has only the choice of which key he may play. Each key is a "digit" that plays one tone and he cannot play a note that does not have a key to play it with.

They are both able to make beautiful music.