diff --git a/lib/svf.py b/lib/svf.py
index df047db..74762e1 100644
--- a/lib/svf.py
+++ b/lib/svf.py
@@ -17,6 +17,13 @@ def svf_core(w0, Q, m, shelfA=1, gain=1):
     v1 = np.array([a2, a1, -a2])
     v2 = np.array([a3, a2, 1 - a3])
     C = v0*m[0] + v1*m[1] + v2*m[2]
+    #   result.append(np.dot(C, np.concatenate([[x], y])))
+    #   y = B*x + np.dot(A, y)
+    # so a FIR would be
+    # C = [fir coefficients go here]
+    # B = [1, 0]
+    # A = [[0, 0]
+    #      [1, 0]]
     return A, B, C