diff --git a/agb/src/sound/mixer/mixer.s b/agb/src/sound/mixer/mixer.s
index 69399f33..3b16eeb5 100644
--- a/agb/src/sound/mixer/mixer.s
+++ b/agb/src/sound/mixer/mixer.s
@@ -23,15 +23,21 @@ agb_rs__mixer_add:
 
     mov r5, #0               @ current index we're reading from
 
+    @ kept between iterations:
+    @ r12 - current write offset into the output buffer (r1)
+    @ r8  - the constant 352
+    @ r5  - the current index from the input buffer we're reading from (r0)
+
+    @ all other registers are temporary
 1:
     add r4, r0, r5, asr #8   @ calculate the address of the next read form the sound buffer
-    add r5, r5, r2           @ calculate the position to read the next step from
     ldrsb r10, [r4]          @ load the current value we want to read
+    add r5, r5, r2           @ calculate the position to read the next step from
 
     mov r6, r1               @ r6 = current buffer location
 
-    ldrh r9, [r6, r12]!      @ load the current buffer value (r12 being the offset) but pre-increment r6 by r12
-    mla r7, r10, r3, r9      @ r7 = r10 * r3 + r9 = current sound value * left amount + previous buffer value
+    ldrh r4, [r6, r12]!      @ load the current buffer value (r12 being the offset) but pre-increment r6 by r12
+    mla r7, r10, r3, r4      @ r7 = r10 * r3 + r9 = current sound value * left amount + previous buffer value
     strh r7, [r6], r8        @ *r6 = r7, r6 += r8 where r8 = 352 = offset for the right hand side
 
     ldrh r7, [r6]            @ same for the right hand side, r6 now points to the right hand side location