diff --git a/libs/ardour/ardour/chan_mapping.h b/libs/ardour/ardour/chan_mapping.h
index 6fbf8bc96e..4b0b930b02 100644
--- a/libs/ardour/ardour/chan_mapping.h
+++ b/libs/ardour/ardour/chan_mapping.h
@@ -42,14 +42,14 @@ public:
 	ChanMapping(ARDOUR::ChanCount identity);
 	ChanMapping(const ChanMapping&);
 
-	uint32_t get(DataType t, uint32_t from, bool* valid);
+	uint32_t get(DataType t, uint32_t from, bool* valid) const;
 
 	/** get buffer mapping for given data type and pin
 	 * @param type data type
 	 * @param from pin
 	 * @returns mapped buffer number (or ChanMapping::Invalid)
 	 */
-	uint32_t get(DataType t, uint32_t from) { return get (t, from, NULL); }
+	uint32_t get(DataType t, uint32_t from) const { return get (t, from, NULL); }
 	/** set buffer mapping for given data type
 	 * @param type data type
 	 * @param from pin
@@ -59,6 +59,30 @@ public:
 	void     offset_from(DataType t, int32_t delta);
 	void     offset_to(DataType t, int32_t delta);
 
+	/** remove mapping
+	 * @param type data type
+	 * @param from source to remove from mapping
+	 */
+	void     unset(DataType t, uint32_t from);
+
+	/** Test mapping matrix for identity
+	 * @param offset per data-type offset to take into account
+	 * @returns true if the mapping is a channel identity map
+	 */
+	bool     is_identity (ARDOUR::ChanCount offset = ARDOUR::ChanCount()) const;
+
+	/** Test if this mapping is monotonic (useful to see if inplace processing is feasible)
+	 * @returns true if the map is a strict monotonic set
+	 */
+	bool     is_monotonic () const;
+
+
+	/** Test if this mapping is a subset
+	 * @param superset to test against
+	 * @returns true if all mapping are also present in the superset
+	 */
+	bool     is_subset (const ChanMapping& superset) const;
+
 	typedef std::map<uint32_t, uint32_t>    TypeMapping;
 	typedef std::map<DataType, TypeMapping> Mappings;
 
diff --git a/libs/ardour/chan_mapping.cc b/libs/ardour/chan_mapping.cc
index 83ded4141c..bc6c4051fc 100644
--- a/libs/ardour/chan_mapping.cc
+++ b/libs/ardour/chan_mapping.cc
@@ -46,14 +46,14 @@ ChanMapping::ChanMapping (const ChanMapping& other )
 }
 
 uint32_t
-ChanMapping::get(DataType t, uint32_t from, bool* valid)
+ChanMapping::get(DataType t, uint32_t from, bool* valid) const
 {
-	Mappings::iterator tm = _mappings.find(t);
+	Mappings::const_iterator tm = _mappings.find(t);
 	if (tm == _mappings.end()) {
 		if (valid) { *valid = false; }
 		return -1;
 	}
-	TypeMapping::iterator m = tm->second.find(from);
+	TypeMapping::const_iterator m = tm->second.find(from);
 	if (m == tm->second.end()) {
 		if (valid) { *valid = false; }
 		return -1;
@@ -73,6 +73,17 @@ ChanMapping::set(DataType t, uint32_t from, uint32_t to)
 	tm->second.insert(std::make_pair(from, to));
 }
 
+void
+ChanMapping::unset(DataType t, uint32_t from)
+{
+	assert(t != DataType::NIL);
+	Mappings::iterator tm = _mappings.find(t);
+	if (tm == _mappings.end()) {
+		return;
+	}
+	tm->second.erase(from);
+}
+
 /** Offset the 'from' field of every mapping for type @a t by @a delta */
 void
 ChanMapping::offset_from(DataType t, int32_t delta)
@@ -99,6 +110,52 @@ ChanMapping::offset_to(DataType t, int32_t delta)
 	}
 }
 
+bool
+ChanMapping::is_subset (const ChanMapping& superset) const
+{
+	for (ARDOUR::ChanMapping::Mappings::const_iterator tm = mappings().begin(); tm != mappings().end(); ++tm) {
+		for (ARDOUR::ChanMapping::TypeMapping::const_iterator i = tm->second.begin(); i != tm->second.end(); ++i) {
+			bool valid;
+			if (i->second != superset.get (tm->first, i->first, &valid)) {
+				return false;
+			}
+			if (!valid) {
+				return false;
+			}
+		}
+	}
+	return true;
+}
+
+bool
+ChanMapping::is_monotonic () const
+{
+	for (ARDOUR::ChanMapping::Mappings::const_iterator tm = mappings().begin(); tm != mappings().end(); ++tm) {
+		uint32_t prev = UINT32_MAX;
+		for (ARDOUR::ChanMapping::TypeMapping::const_iterator i = tm->second.begin(); i != tm->second.end(); ++i) {
+			// set keys are strictly weak ordered
+			if (i->first < i->second || i->second == prev) {
+				return false;
+			}
+			prev = i->second;
+		}
+	}
+	return true;
+}
+
+bool
+ChanMapping::is_identity (ChanCount offset) const
+{
+	for (ARDOUR::ChanMapping::Mappings::const_iterator tm = mappings().begin(); tm != mappings().end(); ++tm) {
+		for (ARDOUR::ChanMapping::TypeMapping::const_iterator i = tm->second.begin(); i != tm->second.end(); ++i) {
+			if (i->first + offset.get (tm->first) != i->second) {
+				return false;
+			}
+		}
+	}
+	return true;
+}
+
 } // namespace ARDOUR
 
 std::ostream& operator<<(std::ostream& o, const ARDOUR::ChanMapping& cm)
diff --git a/libs/ardour/luabindings.cc b/libs/ardour/luabindings.cc
index 9639f37a74..dfcdfaec61 100644
--- a/libs/ardour/luabindings.cc
+++ b/libs/ardour/luabindings.cc
@@ -181,7 +181,7 @@ LuaBindings::common (lua_State* L)
 
 		.beginClass <ChanMapping> ("ChanMapping")
 		.addVoidConstructor ()
-		.addFunction ("get", static_cast<uint32_t(ChanMapping::*)(DataType, uint32_t)>(&ChanMapping::get))
+		.addFunction ("get", static_cast<uint32_t(ChanMapping::*)(DataType, uint32_t) const>(&ChanMapping::get))
 		.addFunction ("set", &ChanMapping::set)
 		.addConst ("Invalid", 4294967295) // UINT32_MAX
 		.endClass ()