# Electronic – Are the noise floor and signal to noise ratio same things

noise

I have a problem in understanding clearly what noise floor is. The term SNR is more clear which is the ratio of the signal to the noise in dB.

In wiki the term noise floor is explained as:

In signal theory, the noise floor is the measure of the signal created
from the sum of all the noise sources and unwanted signals within a
measurement system, where noise is defined as any signal other than
the one being monitored.

I still don't understand what it means mathematically or graphically. It says " measure of the signal created from the sum of all the noise sources and unwanted signals within a measurement system,.." I don't get what "measure of" means in this context.

How can noise floor be explained in a more clear way?

A helpful way to think of the two concepts is suppose your final measured signal is a superposition of two functions:

$$f = f_s + f_n$$ where \$f_s\$ is your signal, and \$f_n\$ is the noise.

The signal to noise ratio would be a measure the relative power of these two signals:

$$SNR = \frac{P(f_s)}{P(f_n)}$$

Note that the SNR doesn't tell you anything about the "absolute" power of the noise; it is only a relative measure of how much stronger your desired signal is vs. the noise. You can have a lot of noise, but as long as your desired signal is much stronger you can still have a good SNR (think of someone using a megaphone in a really large crowd).

The noise floor is just a measure of the noise itself; that is, you can think of it as \$P(f_n)\$; how much noise do you have, regardless of whatever signal there is. This is like asking the question "how loud is the crowd I'm in?", and doesn't depend on any signal at all.