Analog signals are continuous and usually have a wide range. Analog signals can be difficult
to process and quality is lost as copies are made. Analog signals are usually converted into
digital signals for processing on modern computers. Digital signals are just a set of numbers
used to describe the analog signal. The more numbers we use to represent the analog signal,
the better the representation gets, but using more numbers uses more digital memory and
processing power - so tradeoffs are made. Beyond a certain point, more precise representations
of an analog signal consume considerably more memory and processing power without much (if any)
discernible difference in the result.
The numbers that digital systems use end up being just a stream of 0s and 1s. Digital devices
can represent those 0s and 1s with almost anything that can be recognized as two different states.
Inside the computer, it could be a high voltage and a low voltage. On a hard drive, it could be
a magnetized or a non-magnetized area. Optical disks use a highly reflective spot (called a "land")
for one value and a less reflective spot (called a "pit") for the other value. In the old days,
paper tape and cards had a hole for
one value and no hole for the other value. In any case, they all represent a stream of 0s and 1s,
and that in turn represents everything the computer can process - sound, text, graphics,
programs, etc. One really useful quality of digital signals is that you can quickly make as many
perfect copies of that signal as you want.
Listening to a concert and old vinyl LPs are examples of analog signals. CD and MP3 recordings
of that same music are examples of digital signals. Keep in mind that information is usually
lost when converting an analog signal into a digital signal - sometime a great deal of
information. Once a signal is in digital form, it becomes
easy to make copies of it, process it with digital computers, and transfer it quickly over
great distances without any loss of quality. Analog signals may start off with better quality,
but they suffer quality loss when making copies and are harder to store, process, and
transfer.