add makenotch script

git-svn-id: https://bucket.mit.edu/svn/nilm/zoom@7711 ddd99763-3ecb-0310-9145-efcb8ce7c51f

pc/data/20090722/makenotch.m

@@ -0,0 +1,14 @@
+function [b,a] = makenotch(Fs, W0, BandWidth)
+
+Fn = Fs/2; % Nyquist freq [Hz]
+w0 = W0*pi/Fn; % notch frequency normalized
+B = BandWidth*pi/Fn; % normalized bandwidth
+k1 = -cos(w0); k2 = (1 - tan(B/2))/(1 + tan(B/2));
+b = [1+k2 2*k1*(1+k2) 1+k2];
+a = [2 2*k1*(1+k2) 2*k2];
+
+#figure(1); % look at the frequency response of your filter
+#freqz(b,a);
+
+
+# now filter(b,a,input)