diff --git a/codec2_model.py b/codec2_model.py
index 51b5448..2687629 100755
--- a/codec2_model.py
+++ b/codec2_model.py
@@ -26,7 +26,7 @@ def read(filename):
     # Determine number of records in file, not very Pythonic I know :-)
 
     nb_samples = 0
-    with open('/home/david/codec2/build_linux/hts1a.model', 'rb') as f:
+    with open(filename, 'rb') as f:
         while True:
             try:
                 model = codec2_model.parse_stream(f)
@@ -43,7 +43,7 @@ def read(filename):
 
     # Read Codec 2 model records into numpy arrays for further work
     
-    with open('/home/david/codec2/build_linux/hts1a.model', 'rb') as f:
+    with open(filename, 'rb') as f:
         for i in range(nb_samples):
             model = codec2_model.parse_stream(f)
             Wo[i] = model.Wo
diff --git a/plot_n0.py b/plot_n0.py
index a527f40..deb5f7e 100755
--- a/plot_n0.py
+++ b/plot_n0.py
@@ -6,6 +6,18 @@
 # Plot n0 estimates on top of speech waveforms for a few test frames
 # to see if n0 estimation is working.
 
+'''
+Usage:
+~codec/build_linux$ ./misc/timpulse 1 | ./src/c2sim - --modelout imp.model
+~codec/build_linux$ ./misc/timpulse 1 | ./src/c2sim - --modelout - | ./misc/est_n0 > imp_n0.txt
+~phasenn$ ./plot_n0.py ~/codec2/build_linux/imp.model ~/codec2/build_linux/imp_n0.txt
+
+Green line (phase_n0_removed) should be flat, as the phase of an
+impluse train is comprised of just a linear time shift component, and 0
+dispersive component.
+
+'''
+
 import numpy as np
 import sys
 import matplotlib.pyplot as plt
@@ -29,8 +41,14 @@ print("removing linear phase component....")
 phase_n0_removed = np.zeros((nb_samples, width))
 for i in range(nb_samples):
     for m in range(1,L[i]+1):
-        a = n0_est[i]*Wo[i]*m
-        phase_n0_removed[i,m] = np.angle(np.exp(1j*a))
+        phase_n0_removed[i,m] = phase[i,m] - n0_est[i]*Wo[i]*m
+        phase_n0_removed[i,m] = np.angle(np.exp(1j*phase_n0_removed[i,m]))
+
+f=10
+print("frame: %d Fo: %f L: %d" % (f,Fs*Wo[f]/(2*np.pi),L[f]))
+print(A[f,1:L[f]])
+print(phase[f,1:L[f]])
+print(phase_n0_removed[f,1:L[f]])
 
 # TODO: some how choose random set up vectors to plot.  Want them above a certain level, and mix of V and UV
 frame = range(20,32)
@@ -59,10 +77,11 @@ if plot_en:
     for r in range(12):
         plt.subplot(3,4,r+1)
         f = frame[r];
-        plt.plot(phase_n0_removed[f,1:L[f]]*180/np.pi,'r')
         plt.plot(phase[f,1:L[f]]*180/np.pi,'g')
+        plt.plot(phase_n0_removed[f,1:L[f]]*180/np.pi,'r')
         plt.ylim(-180,180)
     plt.show(block=False)
+    print("Green: input phase Red: phase with n0 removed (should be zero)")
     
     plt.figure(3)
     plt.title('Time Domain')
@@ -71,7 +90,7 @@ if plot_en:
         f = frame[r];
         s = sample_time(f)
         plt.plot(s,'g')
-        mx = np.max(s)
+        mx = np.max(np.abs(s))
         plt.plot([n0_est[f],n0_est[f]], [-mx/2,mx/2],'b')
     plt.show(block=False)