diff --git a/Timeline/Audio_Sequence.C b/Timeline/Audio_Sequence.C
index cf28fe8..69e56bb 100644
--- a/Timeline/Audio_Sequence.C
+++ b/Timeline/Audio_Sequence.C
@@ -131,7 +131,7 @@ Audio_Sequence::play ( sample_t *buf, nframes_t frame, nframes_t nframes, int ch
 
     /* quick and dirty--let the regions figure out coverage for themselves */
     for ( list <Sequence_Widget *>::const_iterator i = _widgets.begin();
-          i != _widgets.end(); i++ )
+          i != _widgets.end(); ++i )
     {
         const Region *r = (Region*)(*i);
 
diff --git a/Timeline/Control_Point.H b/Timeline/Control_Point.H
index 3ef484d..da0e267 100644
--- a/Timeline/Control_Point.H
+++ b/Timeline/Control_Point.H
@@ -110,6 +110,9 @@ public:
 
     float control ( void ) const { return _y; }
     void control ( float v ) { _y = v; }
+    /* only for playback thread */
+    nframes_t when ( void ) const { return _range.offset; }
+
 
     int
     handle ( int m )
diff --git a/Timeline/Control_Sequence.C b/Timeline/Control_Sequence.C
index 6061a54..12befc3 100644
--- a/Timeline/Control_Sequence.C
+++ b/Timeline/Control_Sequence.C
@@ -20,11 +20,14 @@
 #include "Control_Sequence.H"
 #include "Track.H"
 
+
+#include "Transport.H" // for transport->frame
+
 bool Control_Sequence::draw_with_gradient = true;
 bool Control_Sequence::draw_with_polygon = true;
 bool Control_Sequence::draw_with_grid = true;
 
-Control_Sequence::Control_Sequence ( Track *track ) : Sequence( 0, 0, 0, 0 )
+Control_Sequence::Control_Sequence ( Track *track ) : Sequence( 0, 0, 0, 0 ), output( "foo", Port::Output )
 {
     init();
 
@@ -267,3 +270,72 @@ Control_Sequence::handle ( int m )
             return 0;
     }
 }
+
+
+/**********/
+/* Engine */
+/**********/
+
+
+static inline float
+linear_interpolate ( float y1, float y2, float mu )
+{
+    return y1 * (1 - mu) + y2 * mu;
+}
+
+static inline float
+sigmoid_interpolate ( float y1, float y2, float mu )
+{
+    return linear_interpolate( y1, y2, ( 1 - cos( mu * M_PI ) ) / 2 );
+}
+
+/* static inline float */
+/* exponential_interpolate ( float y1, float y2, float mu ) */
+/* { */
+
+
+/* } */
+
+/* THREAD: ?? */
+/** fill buf with /nframes/ of interpolated control curve values
+ * starting at /frame/  */
+nframes_t
+Control_Sequence::play ( sample_t *buf, nframes_t frame, nframes_t nframes )
+{
+    Control_Point *p2, *p1 = (Control_Point*)&_widgets.front();
+
+    nframes_t n = nframes;
+
+    for ( list <Sequence_Widget *>::const_iterator i = _widgets.begin();
+          i != _widgets.end(); ++i, p1 = p2 )
+    {
+        p2 = (Control_Point*)(*i);
+
+        if ( p2->when() < frame )
+            continue;
+
+        nframes_t d = p2->when() - p1->when();
+
+        for ( nframes_t i = frame - p1->when(); i < d; ++i )
+        {
+            *(buf++) = 1.0f - ( 2 * sigmoid_interpolate( p1->control(), p2->control(), i / (float)d ) );
+
+            if ( ! n-- )
+                return nframes;
+
+            frame++;
+        }
+    }
+
+    return frame;
+}
+
+
+/* THREAD: RT */
+nframes_t
+Control_Sequence::process ( nframes_t nframes )
+{
+    void *buf = output.buffer( nframes );
+
+    return play( (sample_t*)buf, transport->frame, nframes );
+}
diff --git a/Timeline/Control_Sequence.H b/Timeline/Control_Sequence.H
index a0033a7..e38f441 100644
--- a/Timeline/Control_Sequence.H
+++ b/Timeline/Control_Sequence.H
@@ -21,6 +21,7 @@
 
 #include "Sequence.H"
 #include "Control_Point.H"
+#include "Port.H"
 
 class Control_Sequence : public Sequence
 {
@@ -29,13 +30,15 @@ class Control_Sequence : public Sequence
 
     void init ( void );
 
+    Port output;
+
 protected:
 
 
     virtual void get ( Log_Entry &e ) const;
     void set ( Log_Entry &e );
 
-    Control_Sequence (  ) : Sequence( 0, 0, 0, 1 )
+    Control_Sequence (  ) : Sequence( 0, 0, 0, 1 ), output( "foo", Port::Output )
         {
             init();
         }
@@ -60,4 +63,9 @@ public:
     void draw ( void );
     int handle ( int m );
 
+
+    /* Engine */
+    nframes_t play ( sample_t *buf, nframes_t frame, nframes_t nframes );
+    nframes_t process ( nframes_t nframes );
+
 };
diff --git a/Timeline/Track.C b/Timeline/Track.C
index 9f09185..fdf3e38 100644
--- a/Timeline/Track.C
+++ b/Timeline/Track.C
@@ -615,6 +615,9 @@ Track::configure_inputs ( int n )
 nframes_t
 Track::process ( nframes_t nframes )
 {
+    for ( int i = control->children(); i--; )
+        ((Control_Sequence*)control->child( i ))->process( nframes );
+
     if ( playback_ds )
     {
         record_ds->process( nframes );