diff --git a/extra/mmelody.c b/extra/mmelody.c
index 247554e..80fa5fb 100644
--- a/extra/mmelody.c
+++ b/extra/mmelody.c
@@ -3,9 +3,7 @@
     @date   20 April 2007
     @brief  Play simple melodies.
 */
-
-#define MMELODY_TRANSPARENT 1
-
+#include "system.h"
 #include "mmelody.h"
 
 
@@ -43,6 +41,9 @@
    we could separate two indentical quarter notes with a comma, for
    example, A,A.
 
+   Eighth notes and triplets?  *8 switches to interpreting the notes
+   as eighth notes.  *4 switches back to quarter notes.
+
    Rests are easy.  Each space represents one rest of quarter-note
    duration.  Two spaces represent a half-note rest.  Alternatively,
    we could represent this with " /".
@@ -254,6 +255,7 @@ mmelody_play (mmelody_t mmelody, const char *str)
     mmelody->loop_start = 0;
     mmelody->loop_count = 0;
     mmelody->octave = MMELODY_OCTAVE_DEFAULT;
+    /* Default to quarter notes.  */
     mmelody_note_fraction_set (mmelody, 4);
 }
 
diff --git a/extra/mmelody.h b/extra/mmelody.h
index 237b651..bd362d2 100644
--- a/extra/mmelody.h
+++ b/extra/mmelody.h
@@ -43,24 +43,29 @@ typedef mmelody_obj_t *mmelody_t;
 
 typedef void (* mmelody_callback_t) (void *data, uint8_t note, uint8_t volume);
 
-extern mmelody_t
+mmelody_t
 mmelody_init (mmelody_obj_t *dev, 
               uint16_t poll_rate,
               mmelody_callback_t play_callback,
               void *play_callback_data);
 
-extern void 
+/** Start playing a new melody.  */
+void 
 mmelody_play (mmelody_t mmelody, const char *str);
 
-extern void
+
+/** Update melody sequencer.  */
+void
 mmelody_update (mmelody_t mmelody);
 
-/* Set (base) speed in beats per minute (BPM).  */
-extern void 
+
+/** Set (base) speed in beats per minute (BPM).  */
+void 
 mmelody_speed_set (mmelody_t mmelody, mmelody_speed_t speed);
 
-/* Set volume as percentage of maximum.  */
-extern void 
+
+/** Set volume as percentage of maximum.  */
+void 
 mmelody_volume_set (mmelody_t mmelody, mmelody_volume_t volume);
 
 #endif
diff --git a/extra/tweeter.c b/extra/tweeter.c
index fa0f240..239306f 100644
--- a/extra/tweeter.c
+++ b/extra/tweeter.c
@@ -3,9 +3,7 @@
     @date   20 April 2007
     @brief  Generate PWM for a piezo tweeter.
 */
-
-#define TWEETER_TRANSPARENT 1
-
+#include "system.h"
 #include "tweeter.h"
 
 
@@ -65,16 +63,11 @@ tweeter_note_play (tweeter_t tweeter, tweeter_note_t note, uint8_t velocity)
     duty = (period * velocity) >> 8;
 
     tweeter_note_set (tweeter, period, duty);
-
-#if 0
-    printf ("note = %d, octave = %d, period = %d\n",
-            note, index / TWEETER_SCALE_SIZE, period);
-#endif
-
 }
 
 
-int8_t
+/** Decide whether to turn tweeter on.  */
+bool
 tweeter_update (tweeter_t tweeter)
 {
     if (tweeter->note_holdoff)
diff --git a/extra/tweeter.h b/extra/tweeter.h
index 243dc6f..7aa39c5 100644
--- a/extra/tweeter.h
+++ b/extra/tweeter.h
@@ -57,21 +57,24 @@ typedef tweeter_private_t tweeter_obj_t;
 typedef tweeter_obj_t *tweeter_t;
 
 /* The scale table is usually defined with:
-
- static tweeter_scale_t scale_table[] = TWEETER_SCALE_TABLE (LOOP_POLL_RATE);
+   static tweeter_scale_t scale_table[] = TWEETER_SCALE_TABLE (LOOP_POLL_RATE);
 */
 
-extern int8_t 
+
+/** Decide whether to turn tweeter on.  */
+bool
 tweeter_update (tweeter_t tweeter);
 
+
 /* The note and velocity are specified as per the MIDI standard except
    a note value of 0 indicates a rest (note off).  The velocity has a
    maximum value of 127 and gives an indication of the note
    volume.  */
-extern void
+void
 tweeter_note_play (tweeter_t tweeter, tweeter_note_t note, uint8_t velocity);
 
-extern tweeter_t
+
+tweeter_t
 tweeter_init (tweeter_obj_t *dev, 
               uint16_t poll_rate,
               tweeter_scale_t *scale_table);