diff --git a/corems/mass_spectrum/calc/NoiseCalc.py b/corems/mass_spectrum/calc/NoiseCalc.py
index 6c3ad6ef4..129617dc0 100644
--- a/corems/mass_spectrum/calc/NoiseCalc.py
+++ b/corems/mass_spectrum/calc/NoiseCalc.py
@@ -120,20 +120,20 @@ def cut_mz_domain_noise(self):
 
         if max_mz_noise > max_mz_whole_ms:
             max_mz_noise = max_mz_whole_ms
-
-        #print(min_mz_noise, max_mz_noise)
-        low_mz_index = (where(self.mz_exp_profile >= min_mz_noise)[0][0])
-        #print(self.mz_exp_profile[low_mz_index])
-        # low_mz_index = (argmax(self.mz_exp_profile <= min_mz_noise))
-        
-        high_mz_index = (where(self.mz_exp_profile <= max_mz_noise)[-1][-1])
         
+        #the following indexing relies on mz_exp_profile being ordered high mz to low mz
+        low_mz_index = (where(self.mz_exp_profile >= min_mz_noise)[-1][-1])
+        #print(self.mz_exp_profile[low_mz_index])
+        #low_mz_index = (argmax(self.mz_exp_profile <= min_mz_noise))
+
+        high_mz_index = (where(self.mz_exp_profile <= max_mz_noise)[0][0])
+        #print(self.mz_exp_profile[high_mz_index])
         #high_mz_index = (argmax(self.mz_exp_profile <= max_mz_noise))
         
         if high_mz_index > low_mz_index:
             # pyplot.plot(self.mz_exp_profile[low_mz_index:high_mz_index], self.abundance_profile[low_mz_index:high_mz_index])
             # pyplot.show()
-            return self.mz_exp_profile[high_mz_index:low_mz_index], self.abundance_profile[low_mz_index:high_mz_index]
+            return self.mz_exp_profile[low_mz_index:high_mz_index], self.abundance_profile[low_mz_index:high_mz_index]
         else:
             # pyplot.plot(self.mz_exp_profile[high_mz_index:low_mz_index], self.abundance_profile[high_mz_index:low_mz_index])
             # pyplot.show()