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https://github.com/RaySollium99/picodrive.git
synced 2025-09-05 15:27:46 -04:00
add DC filter to sound mixer to remove potential PCM DC offset
This commit is contained in:
kub
parent
9090dc0f22
commit
2a942f0d41
4 changed files with 121 additions and 35 deletions
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@ -6,41 +6,72 @@
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* See COPYING file in the top-level directory.
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*/
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#include "string.h"
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#define MAXOUT (+32767)
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#define MINOUT (-32768)
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/* limitter */
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#define Limit(val, max,min) { \
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if ( val > max ) val = max; \
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else if ( val < min ) val = min; \
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#define Limit16(val) { \
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val -= (val >> 2); \
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if ((short)val != val) val = (val < 0 ? MINOUT : MAXOUT); \
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}
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int mix_32_to_16l_level;
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void mix_32_to_16l_stereo_core(short *dest, int *src, int count, int level)
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{
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int l, r;
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static struct iir2 { // 2-pole IIR
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int x[2]; // sample buffer
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int y[2]; // filter intermediates
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} lfi2, rfi2;
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for (; count > 0; count--)
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{
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l = r = *dest;
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l += *src++ >> level;
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r += *src++ >> level;
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Limit( l, MAXOUT, MINOUT );
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Limit( r, MAXOUT, MINOUT );
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*dest++ = l;
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*dest++ = r;
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}
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// NB ">>" rounds to -infinity, "/" to 0. To compensate the effect possibly use
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// "-(-y>>n)" (round to +infinity) instead of "y>>n" in places.
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// NB uses Q12 fixpoint; samples mustn't have more than 20 bits for this.
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#define QB 12
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// exponential moving average filter for DC filtering
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// y[n] = (x[n]-y[n-1])*(1/8192) (corner approx. 20Hz, gain 1)
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static inline int filter_exp(struct iir2 *fi2, int x)
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{
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int xf = (x<<QB) - fi2->y[0];
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fi2->y[0] += xf >> 13;
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xf -= xf >> 2; // level reduction to avoid clipping from overshoot
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return xf>>QB;
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}
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// unfiltered (for testing)
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static inline int filter_null(struct iir2 *fi2, int x)
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{
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return x;
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}
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#define mix_32_to_16l_stereo_core(dest, src, count, lv, fl) { \
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int l, r; \
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\
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for (; count > 0; count--) \
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{ \
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l = r = *dest; \
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l += *src++ >> lv; \
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r += *src++ >> lv; \
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l = fl(&lfi2, l); \
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r = fl(&rfi2, r); \
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Limit16(l); \
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Limit16(r); \
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*dest++ = l; \
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*dest++ = r; \
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} \
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}
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void mix_32_to_16l_stereo_lvl(short *dest, int *src, int count)
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{
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mix_32_to_16l_stereo_core(dest, src, count, mix_32_to_16l_level);
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mix_32_to_16l_stereo_core(dest, src, count, mix_32_to_16l_level, filter_exp);
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}
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void mix_32_to_16l_stereo(short *dest, int *src, int count)
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{
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mix_32_to_16l_stereo_core(dest, src, count, 0);
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mix_32_to_16l_stereo_core(dest, src, count, 0, filter_exp);
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}
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void mix_32_to_16_mono(short *dest, int *src, int count)
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@ -51,7 +82,8 @@ void mix_32_to_16_mono(short *dest, int *src, int count)
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{
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l = *dest;
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l += *src++;
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Limit( l, MAXOUT, MINOUT );
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l = filter_exp(&lfi2, l);
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Limit16(l);
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*dest++ = l;
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}
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}
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@ -87,3 +119,8 @@ void mix_16h_to_32_s2(int *dest_buf, short *mp3_buf, int count)
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}
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}
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void mix_reset(void)
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{
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memset(&lfi2, 0, sizeof(lfi2));
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memset(&rfi2, 0, sizeof(rfi2));
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}
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@ -8,3 +8,4 @@ void mix_32_to_16_mono(short *dest, int *src, int count);
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extern int mix_32_to_16l_level;
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void mix_32_to_16l_stereo_lvl(short *dest, int *src, int count);
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void mix_reset(void);
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@ -166,13 +166,6 @@ m16_32_s2_no_unal2:
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@ limit and shift up by 16
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@ reg=int_sample, lr=1, r3=tmp, kills flags
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.macro Limitsh reg
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@ movs r4, r3, asr #16
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@ cmnne r4, #1
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@ beq c32_16_no_overflow
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@ tst r4, r4
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@ mov r3, #0x8000
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@ subpl r3, r3, #1
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add r3, lr, \reg, asr #15
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bics r3, r3, #1 @ in non-overflow conditions r3 is 0 or 1
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moveq \reg, \reg, lsl #16
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@ -180,20 +173,30 @@ m16_32_s2_no_unal2:
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subpl \reg, \reg, #0x00010000
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.endm
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@ filter out DC offset
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@ in=int_sample (max 20 bit), y=filter memory, r3=tmp
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.macro DCfilt in y
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rsb r3, \y, \in, asl #12 @ fixpoint 20.12
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add \y, \y, r3, asr #13
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sub \in, \in, \y, asr #12
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sub \in, \in, \in, asr #2 @ reduce audio lvl some
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.endm
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@ mix 32bit audio (with 16bits really used, upper bits indicate overflow) with normal 16 bit audio with left channel only
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@ warning: this function assumes dest is word aligned
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.global mix_32_to_16l_stereo @ short *dest, int *src, int count
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mix_32_to_16l_stereo:
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stmfd sp!, {r4-r8,lr}
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mov lr, #1
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stmfd sp!, {r4-r8,r10-r11,lr}
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mov r2, r2, lsl #1
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subs r2, r2, #4
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bmi m32_16l_st_end
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mov lr, #1
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ldr r12, =filter
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ldmia r12, {r10-r11}
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m32_16l_st_loop:
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ldmia r0, {r8,r12}
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ldmia r1!, {r4-r7}
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@ -203,6 +206,10 @@ m32_16l_st_loop:
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add r5, r5, r8, asr #16
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add r6, r6, r12,asr #16
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add r7, r7, r12,asr #16
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DCfilt r4, r10
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DCfilt r5, r11
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DCfilt r6, r10
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DCfilt r7, r11
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Limitsh r4
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Limitsh r5
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Limitsh r6
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@ -221,13 +228,17 @@ m32_16l_st_end:
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ldmia r1!,{r4,r5}
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add r4, r4, r6
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add r5, r5, r6
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DCfilt r4, r10
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DCfilt r5, r11
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Limitsh r4
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Limitsh r5
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orr r4, r5, r4, lsr #16
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str r4, [r0], #4
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m32_16l_st_no_unal2:
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ldmfd sp!, {r4-r8,lr}
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ldr r12, =filter
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stmia r12, {r10-r11}
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ldmfd sp!, {r4-r8,r10-r11,lr}
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bx lr
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@ -235,9 +246,11 @@ m32_16l_st_no_unal2:
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.global mix_32_to_16_mono @ short *dest, int *src, int count
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mix_32_to_16_mono:
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stmfd sp!, {r4-r8,lr}
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stmfd sp!, {r4-r8,r10-r11,lr}
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mov lr, #1
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ldr r12, =filter
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ldr r10, [r12]
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@ check if dest is word aligned
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tst r0, #2
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@ -262,6 +275,10 @@ m32_16_mo_loop:
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add r7, r7, r12,asr #16
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mov r12,r12,lsl #16
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add r6, r6, r12,asr #16
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DCfilt r4, r10
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DCfilt r5, r10
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DCfilt r6, r10
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DCfilt r7, r10
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Limitsh r4
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Limitsh r5
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Limitsh r6
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@ -281,6 +298,8 @@ m32_16_mo_end:
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add r5, r5, r6, asr #16
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mov r6, r6, lsl #16
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add r4, r4, r6, asr #16
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DCfilt r4, r10
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DCfilt r5, r10
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Limitsh r4
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Limitsh r5
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orr r4, r5, r4, lsr #16
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@ -288,14 +307,18 @@ m32_16_mo_end:
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m32_16_mo_no_unal2:
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tst r2, #1
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ldmeqfd sp!, {r4-r8,pc}
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beq m32_16_mo_no_unal
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ldrsh r5, [r0]
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ldr r4, [r1], #4
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add r4, r4, r5
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DCfilt r4, r10
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Limit r4
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strh r4, [r0], #2
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ldmfd sp!, {r4-r8,lr}
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m32_16_mo_no_unal:
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ldr r12, =filter
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str r10, [r12]
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ldmfd sp!, {r4-r8,r10-r11,lr}
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bx lr
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@ -315,11 +338,13 @@ mix_32_to_16l_level:
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.global mix_32_to_16l_stereo_lvl @ short *dest, int *src, int count
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mix_32_to_16l_stereo_lvl:
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stmfd sp!, {r4-r9,lr}
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stmfd sp!, {r4-r11,lr}
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ldr r9, =mix_32_to_16l_level
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mov lr, #1
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ldr r9, [r9]
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ldr r12, =filter
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ldm r12, {r10-r11}
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mov r2, r2, lsl #1
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subs r2, r2, #4
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@ -338,6 +363,10 @@ m32_16l_st_l_loop:
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mov r5, r5, asr r9
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mov r6, r6, asr r9
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mov r7, r7, asr r9
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DCfilt r4, r10
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DCfilt r5, r11
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DCfilt r6, r10
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DCfilt r7, r11
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Limitsh r4
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Limitsh r5
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Limitsh r6
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@ -358,15 +387,33 @@ m32_16l_st_l_end:
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add r5, r5, r6
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mov r4, r4, asr r9
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mov r5, r5, asr r9
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DCfilt r4, r10
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DCfilt r5, r11
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Limitsh r4
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Limitsh r5
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orr r4, r5, r4, lsr #16
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str r4, [r0], #4
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m32_16l_st_l_no_unal2:
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ldmfd sp!, {r4-r9,lr}
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ldr r12, =filter
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stmia r12, {r10-r11}
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ldmfd sp!, {r4-r11,lr}
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bx lr
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.global mix_reset @ void
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mix_reset:
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ldr r0, =filter
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mov r1, #0
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str r1, [r0]
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str r1, [r0, #4]
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bx lr
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.data
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DCfilt r4, r10
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DCfilt r5, r11
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filter:
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.ds 8
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#endif /* __GP2X__ */
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@ vim:filetype=armasm
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@ -86,6 +86,7 @@ PICO_INTERNAL void PsndReset(void)
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// PsndRerate calls YM2612Init, which also resets
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PsndRerate(0);
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timers_reset();
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mix_reset();
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}
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