diff --git a/libs/ardour/ardour/audio_backend.h b/libs/ardour/ardour/audio_backend.h
index 72e40f3665..100832275a 100644
--- a/libs/ardour/ardour/audio_backend.h
+++ b/libs/ardour/ardour/audio_backend.h
@@ -338,6 +338,10 @@ public:
 		return false;
 	}
 
+	typedef std::vector<bool> ChannelMask;
+	ChannelMask const & input_channel_mask() const  { return _input_channel_mask; }
+	ChannelMask const & output_channel_mask() const { return _output_channel_mask; }
+
 	/** Returns a collection of float identifying sample rates that are
 	 * potentially usable with the hardware identified by \p device .
 	 * Any of these values may be supplied in other calls to this backend
@@ -859,6 +863,11 @@ protected:
 	AudioEngine&      engine;
 
 	virtual int _start (bool for_latency_measurement) = 0;
+
+	void setup_channel_masks (size_t in, size_t out);
+
+	ChannelMask _input_channel_mask;
+	ChannelMask _output_channel_mask;
 };
 
 } // namespace ARDOUR
diff --git a/libs/ardour/audio_backend.cc b/libs/ardour/audio_backend.cc
index 30df66c6ff..1f485891d6 100644
--- a/libs/ardour/audio_backend.cc
+++ b/libs/ardour/audio_backend.cc
@@ -111,4 +111,11 @@ AudioBackend::get_standard_device_name (StandardDeviceName device_name)
 	return std::string();
 }
 
+void
+AudioBackend::setup_channel_masks (size_t in, size_t out)
+{
+	_input_channel_mask.assign (in, true);
+	_output_channel_mask.assign (out, true);
+}
+
 } // namespace ARDOUR