diff --git a/libs/ardour/ardour/slavable.h b/libs/ardour/ardour/slavable.h
new file mode 100644
index 0000000000..ae53caef38
--- /dev/null
+++ b/libs/ardour/ardour/slavable.h
@@ -0,0 +1,61 @@
+/*
+    Copyright (C) 2016 Paul Davis
+
+    This program is free software; you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation; either version 2 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program; if not, write to the Free Software
+    Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+
+*/
+
+#ifndef __ardour_slavable_h__
+#define __ardour_slavable_h__
+
+#include <set>
+#include <string>
+#include <stdint.h>
+
+#include <boost/shared_ptr.hpp>
+
+class XMLNode;
+
+namespace ARDOUR {
+
+class VCA;
+class Session;
+
+class Slavable
+{
+    public:
+	Slavable ();
+	virtual ~Slavable() {}
+
+	XMLNode& state () const;
+	int assign (Session& s, XMLNode const&);
+
+	void assign (boost::shared_ptr<VCA>);
+	void unassign (boost::shared_ptr<VCA>);
+
+	static std::string xml_node_name;
+
+    protected:
+	virtual int assign_controls (boost::shared_ptr<VCA>) = 0;
+	virtual int unassign_controls (boost::shared_ptr<VCA>) = 0;
+
+    private:
+	mutable Glib::Threads::RWLock master_lock;
+	std::set<uint32_t> _masters;
+};
+
+} // namespace ARDOUR
+
+#endif /* __ardour_slavable_h__ */
diff --git a/libs/ardour/slavable.cc b/libs/ardour/slavable.cc
new file mode 100644
index 0000000000..989c2ec663
--- /dev/null
+++ b/libs/ardour/slavable.cc
@@ -0,0 +1,76 @@
+/*
+    Copyright (C) 2016 Paul Davis
+
+    This program is free software; you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation; either version 2 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program; if not, write to the Free Software
+    Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+
+*/
+
+#include <glibmm/threads.h>
+
+#include "pbd/convert.h"
+#include "pbd/xml++.h"
+
+#include "ardour/slavable.h"
+#include "ardour/vca.h"
+
+#include "i18n.h"
+
+using namespace ARDOUR;
+
+std::string Slavable::xml_node_name = X_("Slavable");
+
+Slavable::Slavable ()
+{
+
+}
+
+XMLNode&
+Slavable::state () const
+{
+	XMLNode* node = new XMLNode (xml_node_name);
+	XMLNode* child;
+
+	Glib::Threads::RWLock::ReaderLock lm (master_lock);
+	for (std::set<uint32_t>::const_iterator i = _masters.begin(); i != _masters.end(); ++i) {
+		child = new XMLNode (X_("Master"));
+		child->add_property (X_("number"), PBD::to_string (*i, std::dec));
+		node->add_child_nocopy (*child);
+	}
+
+	return *node;
+}
+
+int
+Slavable::assign (Session& s, XMLNode const& node)
+{
+	return 0;
+}
+
+void
+Slavable::assign (boost::shared_ptr<VCA> v)
+{
+	if (assign_controls (v) == 0) {
+		Glib::Threads::RWLock::WriterLock lm (master_lock);
+		_masters.insert (v->number());
+	}
+}
+
+void
+Slavable::unassign (boost::shared_ptr<VCA> v)
+{
+	(void) unassign_controls (v);
+	Glib::Threads::RWLock::WriterLock lm (master_lock);
+	_masters.erase (v->number());
+}