diff --git a/csdr/chain/analog.py b/csdr/chain/analog.py
index 15b8d1b..c890343 100644
--- a/csdr/chain/analog.py
+++ b/csdr/chain/analog.py
@@ -1,4 +1,4 @@
-from csdr.chain.demodulator import BaseDemodulatorChain
+from csdr.chain.demodulator import BaseDemodulatorChain, FixedIfSampleRateChain, HdAudio
 from pycsdr.modules import AmDemod, DcBlock, FmDemod, Limit, NfmDeemphasis, Agc, WfmDeemphasis, FractionalDecimator, RealPart
 from pycsdr.types import Format, AgcProfile
 
@@ -31,7 +31,7 @@ class NFm(BaseDemodulatorChain):
         super().__init__(workers)
 
 
-class WFm(BaseDemodulatorChain):
+class WFm(BaseDemodulatorChain, FixedIfSampleRateChain, HdAudio):
     def __init__(self, sampleRate: int, tau: float):
         workers = [
             FmDemod(),
diff --git a/csdr/chain/demodulator.py b/csdr/chain/demodulator.py
index 8ca5556..74373c2 100644
--- a/csdr/chain/demodulator.py
+++ b/csdr/chain/demodulator.py
@@ -1,12 +1,27 @@
 from csdr.chain import Chain
+from abc import ABC, abstractmethod
 
 
 class BaseDemodulatorChain(Chain):
     def getFixedIfSampleRate(self):
         return None
 
-    def getFixedAudioRate(self):
-        return None
-
     def supportsSquelch(self):
         return True
+
+
+class FixedAudioRateChain(ABC):
+    @abstractmethod
+    def getFixedAudioRate(self):
+        pass
+
+
+class FixedIfSampleRateChain(ABC):
+    @abstractmethod
+    def getFixedIfSampleRate(self):
+        return self.fixedIfSampleRate
+
+
+# marker interface
+class HdAudio:
+    pass
diff --git a/csdr/chain/digiham.py b/csdr/chain/digiham.py
index fbf2de8..fa52ead 100644
--- a/csdr/chain/digiham.py
+++ b/csdr/chain/digiham.py
@@ -1,11 +1,11 @@
-from csdr.chain.demodulator import BaseDemodulatorChain
+from csdr.chain.demodulator import BaseDemodulatorChain, FixedAudioRateChain, FixedIfSampleRateChain
 from pycsdr.modules import FmDemod, Agc, Writer
 from pycsdr.types import Format
 from digiham.modules import DstarDecoder, DcBlock, FskDemodulator, GfskDemodulator, DigitalVoiceFilter, MbeSynthesizer, NarrowRrcFilter, NxdnDecoder, DmrDecoder, WideRrcFilter, YsfDecoder
 from digiham.ambe import Modes
 
 
-class DigihamChain(BaseDemodulatorChain):
+class DigihamChain(BaseDemodulatorChain, FixedIfSampleRateChain, FixedAudioRateChain):
     def __init__(self, fskDemodulator, decoder, mbeMode, filter=None, codecserver: str = ""):
         self.decoder = decoder
         if codecserver is None:
diff --git a/owrx/dsp.py b/owrx/dsp.py
index 03f0b38..9744ff8 100644
--- a/owrx/dsp.py
+++ b/owrx/dsp.py
@@ -7,10 +7,9 @@ from owrx.source import SdrSourceEventClient, SdrSourceState, SdrClientClass
 from owrx.property import PropertyStack, PropertyLayer, PropertyValidator
 from owrx.property.validators import OrValidator, RegexValidator, BoolValidator
 from owrx.modes import Modes
-from owrx.config.core import CoreConfig
 from csdr.output import Output
 from csdr.chain import Chain
-from csdr.chain.demodulator import BaseDemodulatorChain
+from csdr.chain.demodulator import BaseDemodulatorChain, FixedIfSampleRateChain, FixedAudioRateChain
 from csdr.chain.selector import Selector
 from csdr.chain.clientaudio import ClientAudioChain
 from csdr.chain.analog import NFm, WFm, Am, Ssb
@@ -53,15 +52,13 @@ class ClientDemodulatorChain(Chain):
 
         self.demodulator = demodulator
 
-        ifRate = self.demodulator.getFixedIfSampleRate()
-        if ifRate is not None:
-            self.selector.setOutputRate(ifRate)
+        if isinstance(self.demodulator, FixedIfSampleRateChain):
+            self.selector.setOutputRate(self.demodulator.getFixedIfSampleRate())
         else:
             self.selector.setOutputRate(self.outputRate)
 
-        audioRate = self.demodulator.getFixedAudioRate()
-        if audioRate is not None:
-            self.clientAudioChain.setInputRate(audioRate)
+        if isinstance(self.demodulator, FixedAudioRateChain):
+            self.clientAudioChain.setInputRate(self.demodulator.getFixedAudioRate())
         else:
             self.clientAudioChain.setInputRate(self.outputRate)
 
@@ -102,9 +99,9 @@ class ClientDemodulatorChain(Chain):
             return
 
         self.outputRate = outputRate
-        if self.demodulator.getFixedIfSampleRate() is None:
+        if not isinstance(self.demodulator, FixedIfSampleRateChain):
             self.selector.setOutputRate(outputRate)
-        if self.demodulator.getFixedAudioRate() is None:
+        if not isinstance(self.demodulator, FixedAudioRateChain):
             self.clientAudioChain.setClientRate(outputRate)
 
     def setPowerWriter(self, writer: Writer) -> None: