What is the difference between analog and digital?

Question

I assume there is no difference based on the context (analog vs. digital cable or analog vs. digital remotes or analog vs. digital radio).

Answer 1

Analog uses a signal that varies from one limit to another.  For instance an analog signal may vary from -5V to +5V.  The accuracy of the signal depends on the accuracy of the sending device, the receiving device, and any interference between the two.

A digital signal is a signal of bytes.  The signal is either on or off, there is no interference (unless it completely blocks the signal).  The accuracy of the signal depends entirely on the number of bytes.  Take an eight bit signal for example.  With eight bytes you can send 256 different signals.  Using the previous example (-5V to +5V) you would be sending the voltage in increments of 0.0390625V (10/256).  If you need more accuracy than that, then you would need to send more bits.

Generally digital is always better that analog.  Analog TV reception is almost always fuzzy, and hi-def is always crystal clear.  The only advantage of analog I know of is that if there is a lot of interference you will get no picture with digital and a fuzzy picture with analog (a fuzzy picture is better than no picture).  I remember as a kid trying to watch channels I wasn't supposed to have.  You could almost see a picture, and almost hear what's going on.  This won't be possible with digital.

Answer 2

Think of it this way.  Suppose you have no physical size.  At all.  You're traveling from Point A to Point B.  Now, go halfway there and stop.  Now, start up again, but go only halfway through the remaining distance, and stop.  Now go again only halfway through the new remaining distance, and stop.  Keep doing that, going only halfway and stopping.  Since you have no physical size to overlap and touch the end point, you'll never reach Point B.  That's digital.

In reality, you do have size, and you don't keep stopping repetitively.  Your speed may increase or decrease, but you'll still be moving.  Even if you do stop, eventually you'll be close enough that your physical size will determine when you've reached Point B.  That's analog.

Each has advantages and disadvantages.  Analog requires more power than digital.  Analog is subject to more interference than digital.  But digital requires a certain minimum to even be recognized or you get nothing at all, not even a weak transmission.  And the constant start/stop does lose some tiny infomration between steps.  And digital requires LOTS of circuitry to convert natural analog to binary digital, and then back again.  Pros and cons.  Digital does give choices that analog doesn't allow.

Answer 3

Analog refers a signal that is variable, in which small fluctuations are meaningful.  Digital refers to a signal that is not variable, and small fluctuations have no meaning.

In recording, an analog signal is recorded by converting sound pressure into mechanical force by a lever.  Typically this mechanical force is again converted to electrical force and stored on a magnetic medium.  Listening to an analog recording requires you reverse the process, turning magnetic recordings back to sound pressures.

Each step in this process introduces errors in the form of distortions and noise.

Digital recording instead samples the sound pressure at a certain rate for frequency and volume.  This sample is converted into an integer that represents that sound at a given time.  Digital samples are not continuous and represent a moment in time..  To make a recording that doesn't have gaps to our ears, they take very frequent samples so that we cannot perceive the missing information.

When we turn to digital transmission vs analog transmission the main discerning factor is interference.  Errors in an analog transmission sound and look like static.  Digital transmissions are much more resilient to errors because they only need to represent a binary state, 0 or 1.  Whereas analog transmissions must represent the actual signal and all its nuances.  The more interference the more the nuances are lost.

Answer 4

These are two ways of providing an intelligent signal.  In analog signals, a voltage goes smoothly up and down - there are an infinite number of states within the wave.  Picture a sine wave that moves from -5v to + 5v.  Measure it at an instant and it could be -3, +1, 0 - and anywhere in between.

Digital communication deals only with 1s and 0s so at the same instant where we measured the sine wave, the digital signal can be ONLY off or on, 1 or 0, up or down.

So, where the analog signal is telling the receiver to mimic the sine wave being received, and is subject to interference, weakness, and loss, the digital signal is telling the receiver to perform "Command number 14" or something.  It's not subject to interference and it's much more precise.

I hope that helps.