You are getting confused by the variable names that you have used inside the function. These are irrelevant. It does not matter at all what names variables have inside the function, because inside the function is a different workspace to where you are calling it. You specify the name of the output variable when the function is called. For example:
function ns = add_white_noise(t_spalte, recSignal)
ns = recSignal + 1/64*randn(size(t_spalte));
end
can be called like this:
>> noiseSignal = add_white_noise(4,[1,2,3,4])
noiseSignal =
0.98118 1.98118 2.98118 3.98118
You might like to read this:
And note that how to call functions is also covered in the introductory tutorials, which are highly recommended for all beginners:
