This is mainly to have a way to transmit multiple baseband information
through the same medium(air, a cable, optic fiber)
Imagine you have two audios (e.g rock, jazz) as there is people who
like rock, there is whose who like jazz, nevertheless they share the
same medium(air), so in order to no have a wire running to anyone of them
what you do is use these audios to modify a well known reference signal
(one for rock, one for jazz), then add together the modified signals
and throw them into the air JAYYY!
How do rock people distinguish their music from others?!!
everything is weirly blended together!!
well not quite...
Make your job easy, made the reference signals
When you get the all blended signal, you know the reference used
for rock so you just have to check the difference between what you got
and your own reference and that difference is the audio signal.
jazz is there too .... mmm somewhere(?) in the all blended signal
doesn't it interfere?
well... yes but no, it's complex,
just limit the amount of difference you will accept, Ok?
Easy, isn't it?
well now the real Sh t,
Ok no, first the ideal Sh t,
taking a reference signal , sine/cosine
it does't mater, you have to change it acording of the input audio (e.g ) one way is by changing the reference's amplitude (AM: amplitude modulation) other is by slightly changing the frecuency
now let's give things a name:
Your reference signal is called "carrier" because it is a mean of info transportation
your audio signal is called "modulation" signal
Here is a form of AM: double side band AM
this means 1 by your carrier equals your carrier, so you will be sending a carrier only signal, then your audio by the carrier,
using this identity:
so your output is:
this means that you multiply your carrier by your modulating amplitude
with the side efect of generating two signals at your carrier frequency plus/minus your modulating frequencies, whatever! you only care about
the amplitude change!
the other way: FM
yeah, I know it doesn't seem friendly but it is even easier than AM
look!, forget about the integral (the funny s-like symbol)
It's easy just change your carrier frecueny by the scaled amplitude of
your modulating signal,
The integral? mmmm math suff he he
Maybe tomorrow I will update with a practical example
I'm a DSP engineer working for a radio company