# Signal to noise ratio

1. Feb 13, 2014

### cutesteph

What is signal to noise ratio ? And how do I calculate it with the wiener filter?

2. Feb 13, 2014

### maajdl

You need to know how the signal and the noise look like at the filter input and calculate what they will be at the output.
Usually a signal has a narrow spectrum, while the noise has a broad (almost flat) spectrum.
Apply a filter to that and see how much power is in signal and how much is in noise at the output of the filter.

3. Feb 13, 2014

### meBigGuy

What are you using the filter to do? Since a wiener filter can be used to improve signal to noise, are you actually trying to calculate the signal to noise ratio improvement by your filter?

Do you understand wiener design? Do you understand this? http://en.wikipedia.org/wiki/Wiener_filter

4. Feb 13, 2014

### cutesteph

I am using it to process a signal say x(n) = sin(nw+theta) +w(n) where w(n) is random noise and say I use a 2 and 3 tap and get wiener values …. [.5 ; -.4] and [-6 ; 15; -5] (note: these are not actual values). I want to calculate the SNR of the interference and SNR of the output. Is the SNR of the output just processing x(n) through each filter i.e. 1/(1-.5z^-1) and then 1/(z-.4z^-1)?

5. Feb 13, 2014

### maajdl

Yes, apply the filter on the signal (sin(...)) and the noise (w) and see what happens.