restore audio chopper decoding

csdr/chain/demodulator.py

@@ -1,3 +1,4 @@
+from pycsdr.modules import Reader
 from csdr.chain import Chain
 from abc import ABC, abstractmethod
 
@@ -10,6 +11,10 @@ class BaseDemodulatorChain(Chain):
         return True
 
 
+class SecondaryDemodulator(Chain):
+    pass
+
+
 class FixedAudioRateChain(ABC):
     @abstractmethod
     def getFixedAudioRate(self):