diff --git a/scripts/selcald/analyze.py b/scripts/selcald/analyze.py
index 82cc839..fabe65e 100644
--- a/scripts/selcald/analyze.py
+++ b/scripts/selcald/analyze.py
@@ -51,8 +51,8 @@ def butter_bandpass_filter(data, lowcut, highcut, fs, order=5):
 # tone synthesis
 def note(freq, cycles, amp=32767.0, rate=44100):
     len = cycles * (1.0/rate)
-    t = np.linspace(0, len, len * rate)
-    if freq is 0:
+    t = np.linspace(0, len, int(len * rate))
+    if freq == 0:
         data = np.zeros(int(len * rate))
     else:
         data = np.sin(2 * np.pi * freq * t) * amp
@@ -244,7 +244,7 @@ def analyze(file_name):
     ax_S.axis('off')
 
     fig.set_tight_layout(True)
-    fig.show()
+    plt.show()
 
 
 if __name__ == "__main__":
diff --git a/scripts/selcald/correlate.py b/scripts/selcald/correlate.py
index 5b587c0..b43292b 100644
--- a/scripts/selcald/correlate.py
+++ b/scripts/selcald/correlate.py
@@ -41,8 +41,8 @@ def voss(nrows, ncols=16):
 
 # tone synthesis
 def note(freq, len, amp=1, rate=RATE):
-    t = np.linspace(0, len, len * rate)
-    if freq is 0:
+    t = np.linspace(0, len, int(len * rate))
+    if freq == 0:
         data = np.zeros(int(len * rate))
     else:
         data = np.sin(2*np.pi*freq*t)*amp
@@ -79,6 +79,6 @@ ax_corr.set_title('Cross-correlated with Reference')
 ax_orig.margins(0, 0.1)
 
 fig.set_tight_layout(True)
-fig.show()
+plt.show()
 
 write('test.wav', 44100, sig_noise)
diff --git a/scripts/selcald/match_frequency.py b/scripts/selcald/match_frequency.py
index 95d17f8..1120a6a 100644
--- a/scripts/selcald/match_frequency.py
+++ b/scripts/selcald/match_frequency.py
@@ -12,8 +12,8 @@ RATE = 44100
 # tone synthesis
 def tone(freq, cycles, amp=1, rate=RATE):
     len = cycles * (1.0/rate)
-    t = np.linspace(0, len, len * rate)
-    if freq is 0:
+    t = np.linspace(0, len, int(len * rate))
+    if freq == 0:
         data = np.zeros(int(len * rate))
     else:
         data = np.sin(2 * np.pi * freq * t) * amp
@@ -37,11 +37,11 @@ for carrier in [312, 473, 716, 1084, 1479]:
     ax.semilogy(freqs, response, label='tone = {}'.format(carrier))
     ax.set_title('Matched filter response')
 
-    # ax.axvline(626.67, ls=':')  # Guardband markers
-    # ax.axvline(695.01, ls=':')
+    ax.axvline(626.67, ls=':')  # Guardband markers
+    ax.axvline(695.01, ls=':')
 
     ax.legend(loc='best')
     ax.margins(0, 0.1)
 
 fig.set_tight_layout(True)
-fig.show()
+plt.show()
diff --git a/scripts/selcald/receiver.py b/scripts/selcald/receiver.py
index 29fdf51..aef5eb1 100644
--- a/scripts/selcald/receiver.py
+++ b/scripts/selcald/receiver.py
@@ -69,8 +69,8 @@ def butter_bandpass_filter(data, lowcut, highcut, fs, order=5):
 # tone synthesis
 def note(freq, cycles, amp=32767.0, rate=44100):
     len = cycles * (1.0/rate)
-    t = np.linspace(0, len, len * rate)
-    if freq is 0:
+    t = np.linspace(0, len, int(len * rate))
+    if freq == 0:
         data = np.zeros(int(len * rate))
     else:
         data = np.sin(2 * np.pi * freq * t) * amp