Earlier quoted context omitted.
In a math sense, the signal to noise ratio on FB became much higher over the last decade. At inception, it was a focused way to directly communicate with a close college circle. Now its effectively as open as Myspace, bombards you with ads, and as with all wide networks, the discourse has dropped to meme / quiz bot level I think you mean "much lower" signal to noise ratio.
I'm a non native English speaker. Which one is more suitable for "less quality"?
High SNR = Much signal, little noise
Low SNR = Much signal, much noise