iir: Separate out filter design from benchmark

Author: jonnor

benchmarks/iir/iir_benchmark.py

@@ -21,22 +21,6 @@
     print(e)
     pass
 
-# https://stackoverflow.com/a/20932062
-def butter2_lowpass(f, sr):
-    ff = f / sr
-    ita = 1.0/ math.tan(math.pi*ff)
-    q = math.sqrt(2.0)
-    b0 = 1.0 / (1.0 + q*ita + ita*ita)
-    b1 = 2 * b0
-    b2 = b0
-    a1 = 2.0 * (ita*ita - 1.0) * b0
-    a2 = -(1.0 - q*ita + ita*ita) * b0
-
-    # Return in biquad / Second Order Stage format
-    # to be compatible with scipy, a1 and a2 needed to be flipped??
-    sos = [ b0, b1, b2, 1.0, -a1, -a2 ]
-
-    return sos
 
 def make_two_sines(f1 = 2.0, f2 = 20.0, sr = 100, dur = 1.0):
     n = int(dur * sr)

benchmarks/iir/simplefilters.py

@@ -0,0 +1,59 @@
+
+"""
+Filter design for simple low/high/band-pass filters
+"""
+
+import math
+
+# https://stackoverflow.com/a/20932062
+def butter2_lowpass(f, sr):
+    ff = f / sr
+    ita = 1.0/ math.tan(math.pi*ff)
+    q = math.sqrt(2.0)
+    b0 = 1.0 / (1.0 + q*ita + ita*ita)
+    b1 = 2 * b0
+    b2 = b0
+    a1 = 2.0 * (ita*ita - 1.0) * b0
+    a2 = -(1.0 - q*ita + ita*ita) * b0
+
+    # Return in biquad / Second Order Stage format
+    # to be compatible with scipy, a1 and a2 needed to be flipped??
+    sos = [ b0, b1, b2, 1.0, -a1, -a2 ]
+
+    return sos
+
+# https://stackoverflow.com/a/39240059
+def butter2_highpass(f, sr):
+
+    # low-pass filter prototype
+    ff = f / sr
+    ita = 1.0/ math.tan(math.pi*ff)
+    q = math.sqrt(2.0)
+    b0 = 1.0 / (1.0 + q*ita + ita*ita)
+    b1 = 2 * b0
+    b2 = b0
+    a1 = 2.0 * (ita*ita - 1.0) * b0
+    a2 = -(1.0 - q*ita + ita*ita) * b0
+
+    # convert to high-pass
+    b0 = b0*ita*ita;
+    b1 = -b1*ita*ita;
+    b2 = b2*ita*ita;
+
+    # Return in biquad / Second Order Stage format
+    # to be compatible with scipy, a1 and a2 needed to be flipped??
+    sos = [ b0, b1, b2, 1.0, -a1, -a2 ]
+
+    return sos
+
+def butter2_bandpass(low, high, fs):
+
+    hp = butter2_highpass(low, fs)
+    lp = butter2_lowpass(high, fs)
+    bp = hp + lp
+
+    return bp
+
+
+
+