diff --git a/src/s_sound.h b/src/s_sound.h
index 859401281..d5323da3a 100644
--- a/src/s_sound.h
+++ b/src/s_sound.h
@@ -20,6 +20,9 @@
 #include "command.h"
 #include "tables.h" // angle_t
 
+// sound timing is calculated by milliseconds
+#define MUSICRATE 1000
+
 // mask used to indicate sound origin is player item pickup
 #define PICKUP_SOUND 0x8000