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add DC filter to sound mixer to remove potential PCM DC offset

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This commit is contained in:
kub 2019-12-31 10:55:40 +01:00
parent 9090dc0f22
commit 2a942f0d41
4 changed files with 121 additions and 35 deletions
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79
pico/sound/mix_arm.S
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@ -166,13 +166,6 @@ m16_32_s2_no_unal2:
@ limit and shift up by 16
@ reg=int_sample, lr=1, r3=tmp, kills flags
.macro Limitsh reg
@ movs r4, r3, asr #16
@ cmnne r4, #1
@ beq c32_16_no_overflow
@ tst r4, r4
@ mov r3, #0x8000
@ subpl r3, r3, #1
add r3, lr, \reg, asr #15
bics r3, r3, #1 @ in non-overflow conditions r3 is 0 or 1
moveq \reg, \reg, lsl #16
@ -180,20 +173,30 @@ m16_32_s2_no_unal2:
subpl \reg, \reg, #0x00010000
.endm
@ filter out DC offset
@ in=int_sample (max 20 bit), y=filter memory, r3=tmp
.macro DCfilt in y
rsb r3, \y, \in, asl #12 @ fixpoint 20.12
add \y, \y, r3, asr #13
sub \in, \in, \y, asr #12
sub \in, \in, \in, asr #2 @ reduce audio lvl some
.endm
@ mix 32bit audio (with 16bits really used, upper bits indicate overflow) with normal 16 bit audio with left channel only
@ warning: this function assumes dest is word aligned
.global mix_32_to_16l_stereo @ short *dest, int *src, int count
mix_32_to_16l_stereo:
stmfd sp!, {r4-r8,lr}
mov lr, #1
stmfd sp!, {r4-r8,r10-r11,lr}
mov r2, r2, lsl #1
subs r2, r2, #4
bmi m32_16l_st_end
mov lr, #1
ldr r12, =filter
ldmia r12, {r10-r11}
m32_16l_st_loop:
ldmia r0, {r8,r12}
ldmia r1!, {r4-r7}
@ -203,6 +206,10 @@ m32_16l_st_loop:
add r5, r5, r8, asr #16
add r6, r6, r12,asr #16
add r7, r7, r12,asr #16
DCfilt r4, r10
DCfilt r5, r11
DCfilt r6, r10
DCfilt r7, r11
Limitsh r4
Limitsh r5
Limitsh r6
@ -221,13 +228,17 @@ m32_16l_st_end:
ldmia r1!,{r4,r5}
add r4, r4, r6
add r5, r5, r6
DCfilt r4, r10
DCfilt r5, r11
Limitsh r4
Limitsh r5
orr r4, r5, r4, lsr #16
str r4, [r0], #4
m32_16l_st_no_unal2:
ldmfd sp!, {r4-r8,lr}
ldr r12, =filter
stmia r12, {r10-r11}
ldmfd sp!, {r4-r8,r10-r11,lr}
bx lr
@ -235,9 +246,11 @@ m32_16l_st_no_unal2:
.global mix_32_to_16_mono @ short *dest, int *src, int count
mix_32_to_16_mono:
stmfd sp!, {r4-r8,lr}
stmfd sp!, {r4-r8,r10-r11,lr}
mov lr, #1
ldr r12, =filter
ldr r10, [r12]
@ check if dest is word aligned
tst r0, #2
@ -262,6 +275,10 @@ m32_16_mo_loop:
add r7, r7, r12,asr #16
mov r12,r12,lsl #16
add r6, r6, r12,asr #16
DCfilt r4, r10
DCfilt r5, r10
DCfilt r6, r10
DCfilt r7, r10
Limitsh r4
Limitsh r5
Limitsh r6
@ -281,6 +298,8 @@ m32_16_mo_end:
add r5, r5, r6, asr #16
mov r6, r6, lsl #16
add r4, r4, r6, asr #16
DCfilt r4, r10
DCfilt r5, r10
Limitsh r4
Limitsh r5
orr r4, r5, r4, lsr #16
@ -288,14 +307,18 @@ m32_16_mo_end:
m32_16_mo_no_unal2:
tst r2, #1
ldmeqfd sp!, {r4-r8,pc}
beq m32_16_mo_no_unal
ldrsh r5, [r0]
ldr r4, [r1], #4
add r4, r4, r5
DCfilt r4, r10
Limit r4
strh r4, [r0], #2
ldmfd sp!, {r4-r8,lr}
m32_16_mo_no_unal:
ldr r12, =filter
str r10, [r12]
ldmfd sp!, {r4-r8,r10-r11,lr}
bx lr
@ -315,11 +338,13 @@ mix_32_to_16l_level:
.global mix_32_to_16l_stereo_lvl @ short *dest, int *src, int count
mix_32_to_16l_stereo_lvl:
stmfd sp!, {r4-r9,lr}
stmfd sp!, {r4-r11,lr}
ldr r9, =mix_32_to_16l_level
mov lr, #1
ldr r9, [r9]
ldr r12, =filter
ldm r12, {r10-r11}
mov r2, r2, lsl #1
subs r2, r2, #4
@ -338,6 +363,10 @@ m32_16l_st_l_loop:
mov r5, r5, asr r9
mov r6, r6, asr r9
mov r7, r7, asr r9
DCfilt r4, r10
DCfilt r5, r11
DCfilt r6, r10
DCfilt r7, r11
Limitsh r4
Limitsh r5
Limitsh r6
@ -358,15 +387,33 @@ m32_16l_st_l_end:
add r5, r5, r6
mov r4, r4, asr r9
mov r5, r5, asr r9
DCfilt r4, r10
DCfilt r5, r11
Limitsh r4
Limitsh r5
orr r4, r5, r4, lsr #16
str r4, [r0], #4
m32_16l_st_l_no_unal2:
ldmfd sp!, {r4-r9,lr}
ldr r12, =filter
stmia r12, {r10-r11}
ldmfd sp!, {r4-r11,lr}
bx lr
.global mix_reset @ void
mix_reset:
ldr r0, =filter
mov r1, #0
str r1, [r0]
str r1, [r0, #4]
bx lr
.data
DCfilt r4, r10
DCfilt r5, r11
filter:
.ds 8
#endif /* __GP2X__ */
@ vim:filetype=armasm