diff --git a/sound/filters/pure_filter.hpp b/sound/filters/pure_filter.hpp
new file mode 100644
index 0000000000..5238d788a7
--- /dev/null
+++ b/sound/filters/pure_filter.hpp
@@ -0,0 +1,67 @@
+#ifndef MANGLE_SOUND_OUTPUT_PUREFILTER_H
+#define MANGLE_SOUND_OUTPUT_PUREFILTER_H
+
+#include "../output.hpp"
+
+namespace Mangle
+{
+  namespace Sound
+  {
+    // For use in writing other filters
+    class SoundFilter : public Sound
+    {
+      SoundPtr client;
+
+    public:
+      SoundFilter(SoundPtr c) : client(c) {}
+      void play() { client->play(); }
+      void stop() { client->stop(); }
+      void pause() { client->pause(); }
+      bool isPlaying() const { return client->isPlaying(); }
+      void setVolume(float f) { client->setVolume(f); }
+      void setPan(float f) { client->setPan(f); }
+      void setPos(float x, float y, float z)
+      { client->setPos(x,y,z); }
+      void setRepeat(bool b) { client->setRepeat(b); }
+      void setStreaming(bool b) { client->setStreaming(b); }
+
+      // The clone() function is not implemented here, as you will
+      // almost certainly want to override it yourself
+    };
+
+    class FactoryFilter : public SoundFactory
+    {
+      SoundFactoryPtr client;
+
+    public:
+      FactoryFilter(SoundFactoryPtr c) : client(c)
+      {
+        needsUpdate = client->needsUpdate;
+        has3D = client->has3D;
+        canLoadFile = client->canLoadFile;
+        canLoadStream = client->canLoadStream;
+        canLoadSource = client->canLoadSource;
+      }
+
+      SoundPtr loadRaw(SampleSourcePtr input)
+      { return client->loadRaw(input); }
+
+      SoundPtr load(Stream::StreamPtr input)
+      { return client->load(input); }
+
+      SoundPtr load(const std::string &file)
+      { return client->load(file); }
+
+      void update()
+      { client->update(); }
+
+      void setListenerPos(float x, float y, float z,
+                          float fx, float fy, float fz,
+                          float ux, float uy, float uz)
+      {
+        client->setListenerPos(x,y,z,fx,fy,fz,ux,uy,uz);
+      }
+    };
+  }
+}
+#endif
diff --git a/sound/output.hpp b/sound/output.hpp
index 2ead277bcc..404dcf4f8d 100644
--- a/sound/output.hpp
+++ b/sound/output.hpp
@@ -2,8 +2,9 @@
 #define MANGLE_SOUND_OUTPUT_H
 
 #include <string>
-#include "source.hpp"
+#include <assert.h>
 
+#include "source.hpp"
 #include "../stream/stream.hpp"
 
 namespace Mangle {
@@ -149,7 +150,7 @@ class SoundFactory
      buffers and similar tasks. Implementations that do not need this
      should set needsUpdate to false.
   */
-  virtual void update() = 0;
+  virtual void update() { assert(0); }
 
   /// Set listener position (coordinates, front and up vectors)
   /**