diff --git a/src/codal_port/microbit_soundeffect.c b/src/codal_port/microbit_soundeffect.c
index cd51f8a..f995293 100644
--- a/src/codal_port/microbit_soundeffect.c
+++ b/src/codal_port/microbit_soundeffect.c
@@ -70,12 +70,12 @@
 #define SOUND_EFFECT_FX_WARBLE                  (3)
 
 // These default fx values are the same as used by MakeCode.
-#define SOUND_EFFECT_FX_VIBRATO_DEFAULT_PARAM   (2)
-#define SOUND_EFFECT_FX_TREMOLO_DEFAULT_PARAM   (3)
-#define SOUND_EFFECT_FX_WARBLE_DEFAULT_PARAM    (2)
-#define SOUND_EFFECT_FX_VIBRATO_DEFAULT_STEPS   (512)
-#define SOUND_EFFECT_FX_TREMOLO_DEFAULT_STEPS   (900)
-#define SOUND_EFFECT_FX_WARBLE_DEFAULT_STEPS    (700)
+#define SOUND_EFFECT_FX_VIBRATO_DEFAULT_PARAM   (2) // SFX_DEFAULT_VIBRATO_PARAM
+#define SOUND_EFFECT_FX_TREMOLO_DEFAULT_PARAM   (3) // SFX_DEFAULT_TREMOLO_PARAM
+#define SOUND_EFFECT_FX_WARBLE_DEFAULT_PARAM    (2) // SFX_DEFAULT_WARBLE_PARAM
+#define SOUND_EFFECT_FX_VIBRATO_DEFAULT_STEPS   (512) // SFX_DEFAULT_VIBRATO_STEPS
+#define SOUND_EFFECT_FX_TREMOLO_DEFAULT_STEPS   (900) // SFX_DEFAULT_TREMOLO_STEPS
+#define SOUND_EFFECT_FX_WARBLE_DEFAULT_STEPS    (700) // SFX_DEFAULT_WARBLE_STEPS
 
 #define SOUND_EFFECT_DEFAULT_FREQ_START         (500)
 #define SOUND_EFFECT_DEFAULT_FREQ_END           (2500)