From f382efe609f049c7e78171a76e9d0c550521958b Mon Sep 17 00:00:00 2001
From: Roman Zeyde <roman.zeyde@gmail.com>
Date: Tue, 26 Aug 2014 17:24:55 +0300
Subject: [PATCH] dsp: Filter should hold processing state

---
 amodem/dsp.py | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/amodem/dsp.py b/amodem/dsp.py
index 8037f12..45e1f91 100644
--- a/amodem/dsp.py
+++ b/amodem/dsp.py
@@ -13,10 +13,12 @@ class Filter(object):
     def __init__(self, b, a):
         self.b = np.array(b) / a[0]
         self.a = np.array(a[1:]) / a[0]
+        self.x_state = [0] * len(self.b)
+        self.y_state = [0] * (len(self.a) + 1)
+
 
     def __call__(self, x):
-        x_ = [0] * len(self.b)
-        y_ = [0] * (len(self.a) + 1)
+        x_, y_ = self.x_state, self.y_state
         for v in x:
             x_ = [v] + x_[:-1]
             y_ = y_[:-1]
@@ -25,6 +27,7 @@ class Filter(object):
             y = num - den
             y_ = [y] + y_
             yield y
+        self.x_state, self.y_state = x_, y_
 
 
 def lfilter(b, a, x):