From 59612aa01775eaaec8c33f2b101948db423cabaa Mon Sep 17 00:00:00 2001
From: Nebuleon Fumika
Date: Sat, 12 Jan 2013 20:30:30 -0500
Subject: ds2sound.h: Set the interrupt interval to 15.36 milliseconds and
 explain why.

---
 source/nds/ds2sound.h | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/source/nds/ds2sound.h b/source/nds/ds2sound.h
index 544a670..d8cfe09 100644
--- a/source/nds/ds2sound.h
+++ b/source/nds/ds2sound.h
@@ -6,7 +6,15 @@
 #define DS2_BUFFER_SIZE_7 1024 /* tested working, slow because of upsampling */
 
 // In microseconds.
-#define INTERRUPT_TIME_4  4000 /* tested working */
+// (512 samples / 22050 samples/sec) = 23000 microseconds.
+// The value needs to be:
+// * not too low, because then every time a new batch of close to 512 samples
+//   is created anew, and that's EXPENSIVE.
+// * not too high, because then missing the end of the buffer creates audible
+//   underflows.
+// * not exactly 16667 (NTSC 60 FPS) or 20000 (PAL 50 FPS), because then
+//   the automatic frame skipper will be extremely messed up.
+#define INTERRUPT_TIME_4 15360 /* 15360 tested working */
 #define INTERRUPT_TIME_5  8000 /* like the SNES! tested working, but slow */
 #define INTERRUPT_TIME_6  4000 /* tested working, slow because of upsampling */
 #define INTERRUPT_TIME_7  4000 /* tested working, slow because of upsampling */
-- 
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