diff --git a/fakebox/dsp.py b/fakebox/dsp.py
index 7de6117..7c6ea64 100644
--- a/fakebox/dsp.py
+++ b/fakebox/dsp.py
@@ -5,9 +5,10 @@
 from fakebox.conf import DEFAULT_SAMPLE_RATE, DEFAULT_BIT_N
 
 DSPFloat = np.float64
+DSPEpislon = DSPFloat(1e-8)
 DSPZero = DSPFloat(0.0)
 DSPOne = DSPFloat(1.0)
-DSPOne_L = DSPFloat(1.0 - 1e-8)
+DSPOne_L = DSPFloat(1.0) - DSPEpislon
 
 class DSPContext(object):
 
diff --git a/fakebox/stdlib/env.py b/fakebox/stdlib/env.py
index c8d1272..876abe6 100644
--- a/fakebox/stdlib/env.py
+++ b/fakebox/stdlib/env.py
@@ -1,4 +1,4 @@
-from fakebox.dsp import DSPObj, DSPZero
+from fakebox.dsp import DSPObj, DSPZero, DSPEpislon
 
 class LineSegs(DSPObj):
 
@@ -34,7 +34,7 @@ def _tick(self, ins):
             time_points.append(time_points[-1] + dur)
 
 
-        if running_time > time_points[-1]:
+        if running_time > time_points[-1] - DSPEpislon:
             self.running = False
             return DSPZero
 
diff --git a/fakebox/stdlib/math.py b/fakebox/stdlib/math.py
index 6c4d386..1aae860 100644
--- a/fakebox/stdlib/math.py
+++ b/fakebox/stdlib/math.py
@@ -1,7 +1,7 @@
 import numpy as np
 from fakebox.dsp import DSPObj, DSPZero, DSPOne
 
-def Sum(DSPObj):
+class Sum(DSPObj):
 
     def __init__(self, c=None, in_n=None):
 
@@ -22,7 +22,7 @@ def _tick(self, ins):
         return res
 
 
-def Mul(DSPObj):
+class Mul(DSPObj):
 
     def __init__(self, c=None, in_n=None):
 
@@ -43,7 +43,7 @@ def _tick(self, ins):
         return res
 
 
-def Neg(DSPObj):
+class Neg(DSPObj):
 
     def __init__(self):