# What exactly happens in correlation?

I have understood convolution and it seems almost same as correlation mathematical expression wise. But in terms of signal processing,both are different operations.

The difference between convolution and cross-correlation from a signal-analysis point of view

I have read above answer and i some how understood through it that correlation is a technique used to detect presennce of a signal in a noisy background

But how correlation works? Can it only detects presence of original signal or can it also reconstruct and recover original signal?

Especially i am unable to understand the following sentence in MBaz answer

"If the correlation is large for a given time delay τ, then we may be confident in saying that the answer is yes"

Can someone please elaborate this sentence?

• This question may help as an answer. Aug 9, 2022 at 17:18
• My recommendation to you is to experiment with simulation using Matlab or Python to get a better intuitive understanding. If you plot the output of cross correlation when a signal is present and when it is not present you will very quickly see what is going on. In the simplest terms, correlation tells you how much of one signal is in another signal, so that when they overlap, you get a big strong spike. That is the exact sample (or time) the signal starts. Aug 9, 2022 at 19:27