diff --git a/lasp/__init__.py b/lasp/__init__.py
index 54bf4e6..e69de29 100644
--- a/lasp/__init__.py
+++ b/lasp/__init__.py
@@ -1,3 +0,0 @@
-from .wrappers import *
-from .lasp_tools import *
-from .lasp_common import *
\ No newline at end of file
diff --git a/lasp/filter/__init__.py b/lasp/filter/__init__.py
index e69de29..fbd1687 100644
--- a/lasp/filter/__init__.py
+++ b/lasp/filter/__init__.py
@@ -0,0 +1,4 @@
+
+from .freqweighting_fir import A, C
+
+__all__ = ['A', 'Z']
diff --git a/lasp/filter/bandpass_fir.py b/lasp/filter/bandpass_fir.py
index f7d7121..ce30654 100644
--- a/lasp/filter/bandpass_fir.py
+++ b/lasp/filter/bandpass_fir.py
@@ -84,6 +84,14 @@ class FilterBankDesigner:
 
         return frsp(fd, freq, fir)
 
+    def nominal_txt_tox(self, nom_txt):
+        """
+        Returns the x-value corresponding to a certain nominal txt: '1k' -> 0
+        """
+        for x in self.xs:
+            if self.nominal_txt(x) == nom_txt:
+                return x
+        raise ValueError(f'Could not find an x-value corresponding to {nom_txt}.')
 
 class OctaveBankDesigner(FilterBankDesigner):
     """