diff --git a/zsnes/src/gui/gui.asm b/zsnes/src/gui/gui.asm
index 8a0a3f28..ccea774e 100644
--- a/zsnes/src/gui/gui.asm
+++ b/zsnes/src/gui/gui.asm
@@ -537,6 +537,8 @@ NEWSYM KeyRewind, dd 0
 NEWSYM ChatNick, times 16 db 0
 NEWSYM KeySlowDown, dd 0
 
+NEWSYM UseCubicSpline, db 1
+
 GUIsave equ $-GUIRAdd
 
 NEWSYM CombinDataGlob, times 3300 db 0 ; 20-name, 42-combo, 2-key#, 1-P#, 1-ff
@@ -556,7 +558,7 @@ ModemOKStat  db 0       ; OK is detected on modem status
 GUIwinposxo dd 0,5   ,60  ,30  ,55  ,50  ,65  ,5   ,30  ,20   ,10   ,80  ,65  ,20  ,70  ,50  ,3   ,50
 GUIwinposyo dd 0,20  ,70  ,30  ,20  ,22  ,36  ,20  ,30  ,20   ,30   ,70  ,60  ,30  ,65  ,50  ,22  ,60
 GUIwinsizex dd 0,244 ,126 ,189 ,167 ,170 ,148 ,244 ,8*16,13*16,176  ,7*16,9*16,8*16,9*16,140 ,250 ,160
-GUIwinsizey dd 0,190 ,3*16,166 ,190 ,186 ,158 ,191 ,40  ,189  ,152  ,68  ,42  ,40  ,42  ,70  ,190 ,60
+GUIwinsizey dd 0,190 ,3*16,166 ,190 ,186 ,168 ,191 ,40  ,189  ,152  ,68  ,42  ,40  ,42  ,70  ,190 ,60
 GUIwinptr   db 0
 
 GUItextcolor db 0,0,0,0,0
diff --git a/zsnes/src/gui/guimouse.inc b/zsnes/src/gui/guimouse.inc
index 9baaedd5..786ae55a 100644
--- a/zsnes/src/gui/guimouse.inc
+++ b/zsnes/src/gui/guimouse.inc
@@ -2105,6 +2105,7 @@ DisplayGUISoundClick:
     GUIClickCButton 11,131,byte[InterSound]
     GUIClickCButton 11,141,byte[LowPassFilter]
     GUIClickCButton 11,151,byte[SoundBufEn]
+    GUIClickCButton 11,161,byte[UseCubicSpline]
     cmp eax,15
     jl near .nosrate
     cmp edx,61
diff --git a/zsnes/src/gui/guiwindp.inc b/zsnes/src/gui/guiwindp.inc
index 9eecfdec..dcc5fd6d 100644
--- a/zsnes/src/gui/guiwindp.inc
+++ b/zsnes/src/gui/guiwindp.inc
@@ -2007,6 +2007,7 @@ DisplayGUISound:
     GUIOuttextwin2 6,26,136,GUISoundTextJ
     GUIOuttextwin2 6,26,146,GUISoundTextK
     GUIOuttextwin2 6,26,156,GUISoundTextL
+    GUIOuttextwin2 6,26,166,GUISoundTextM
     add byte[GUItextcolor],15
     GUIOuttextwin2 6,25,25,GUISoundText1
     GUIOuttextwin2 6,25,34,GUISoundText3
@@ -2023,6 +2024,7 @@ DisplayGUISound:
     GUIOuttextwin2 6,25,135,GUISoundTextJ
     GUIOuttextwin2 6,25,145,GUISoundTextK
     GUIOuttextwin2 6,25,155,GUISoundTextL
+    GUIOuttextwin2 6,25,165,GUISoundTextM
     mov al,[GUIWincol]
     mov byte[GUItextcolor],al
     GUIOuttextwin2 6,6,16,GUISoundText6
@@ -2096,6 +2098,12 @@ DisplayGUISound:
     mov dword[GUITemp],GUIIconDataCheckBoxC
 .nocheckbox7
     GUIDisplayIconWin 6,11,151,[GUITemp]
+    mov dword[GUITemp],GUIIconDataCheckBoxUC
+    cmp byte[UseCubicSpline],0
+    je .nocheckbox8
+    mov dword[GUITemp],GUIIconDataCheckBoxC
+.nocheckbox8
+    GUIDisplayIconWin 6,11,161,[GUITemp]
     DrawGUIWinBox 6,15,61,69,69,167
     mov dword[GUITemp],GUISoundText7
     xor eax,eax
@@ -2186,6 +2194,7 @@ GUISoundTextI db 'SURROUND SOUND',0
 GUISoundTextJ db 'SOUND INTERPOLATION',0
 GUISoundTextK db 'LOW PASS FILTER',0
 GUISoundTextL db 'SOUND BUFFERING',0
+GUISoundTextM db 'CUBIC SPLINE INTERP',0
 
 DisplayGUICheatConv:
     mov eax,[ccheatnpos]