Expanded Octave and ThirdOctave filter banks to lower frequencies

src/lasp/filter/filterbank_design.py

@@ -172,7 +172,6 @@ class FilterBankDesigner:
         Args:
             x: Band designator
         """
-
         SOS_ORDER = 5
 
         fs = self.fs
@@ -197,6 +196,7 @@ class FilterBankDesigner:
                               (SOS_ORDER-highpass.shape[0], 1))
             return np.vstack((highpass, allpass))  # same shape=(SOS_ORDER, 6)
 
+        # Regular bands
         return butter(SOS_ORDER, [fl_n, fu_n], output='sos', btype='band')
 
     def firFreqResponse(self, x, freq):
@@ -341,7 +341,7 @@ class OctaveBankDesigner(FilterBankDesigner):
     @property
     def xs(self):
         """All possible band designators for an octave band filter."""
-        return list(range(-6, 5))
+        return list(range(-7, 5))
 
     def band_limits(self, x, filter_class=0):
         """Returns the octave band filter limits for filter designator x.
@@ -404,7 +404,8 @@ class OctaveBankDesigner(FilterBankDesigner):
             -3: '125',
             -4: '63',
             -5: '31.5',
-            -6: '16'
+            -6: '16',
+            -7: '8'
         }
         assert len(nominals) == len(self.xs)
         return nominals[x]
@@ -487,9 +488,9 @@ class ThirdOctaveBankDesigner(FilterBankDesigner):
             fs: Sampling frequency in [Hz] - can be None
         """
         super().__init__(fs)
-        self.xs = list(range(-16, 14))
+        self.xs = list(range(-19, 14))
         # Text corresponding to the nominal frequency
-        self._nominal_txt = [
+        self._nominal_txt = ['12.5', '16', '20',
             '25', '31.5', '40', '50', '63', '80', '100', '125', '160', '200',
             '250', '315', '400', '500', '630', '800', '1k', '1.25k', '1.6k',
             '2k', '2.5k', '3.15k', '4k', '5k', '6.3k', '8k', '10k', '12.5k',