Comment 19 for bug 428619

OK, I found it. The problem - in my case at least - lies in svolume_mmx.c (not svolume_sse.c). Reverting that file back to the previous version gets rid of the problem. These are the changes which caused the appearance of the distorted sound problem on my box:

diff -pruN ../pulseaudio-0.9.16~test7-14-g7ca81/src/pulsecore/svolume_mmx.c src/pulsecore/svolume_mmx.c
--- ../pulseaudio-0.9.16~test7-14-g7ca81/src/pulsecore/svolume_mmx.c 2009-09-20 17:26:04.657239828 +0200
+++ src/pulsecore/svolume_mmx.c 2009-09-18 22:21:44.000000000 +0200
@@ -57,14 +57,12 @@
       " punpcklwd %%mm4, "#s" \n\t" /* .. | 0 | p0 | */ \
       " pcmpgtw "#v", %%mm4 \n\t" /* .. | 0 | s(vl) | */ \
       " pand "#s", %%mm4 \n\t" /* .. | 0 | (p0) | (vl >> 15) & p */ \
- " movq %%mm6, %%mm5 \n\t" /* .. | ffff | 0 | */ \
- " pand "#v", %%mm5 \n\t" /* .. | vh | 0 | */ \
- " por %%mm5, %%mm4 \n\t" /* .. | vh | (p0) | */ \
- " pmulhw "#s", "#v" \n\t" /* .. | 0 | vl*p0 | */ \
- " paddw %%mm4, "#v" \n\t" /* .. | vh | vl*p0 | vh + sign correct */ \
- " pslld $16, "#s" \n\t" /* .. | p0 | 0 | */ \
- " por %%mm7, "#s" \n\t" /* .. | p0 | 1 | */ \
- " pmaddwd "#s", "#v" \n\t" /* .. | p0 * v0 | */ \
+ " movq "#s", %%mm5 \n\t" \
+ " pmulhw "#v", "#s" \n\t" /* .. | 0 | vl*p0 | */ \
+ " paddw %%mm4, "#s" \n\t" /* .. | 0 | vl*p0 | + sign correct */ \
+ " psrld $16, "#v" \n\t" /* .. | 0 | vh | */ \
+ " pmaddwd %%mm5, "#v" \n\t" /* .. | p0 * vh | */ \
+ " paddd "#s", "#v" \n\t" /* .. | p0 * v0 | */ \
       " packssdw "#v", "#v" \n\t" /* .. | p1*v1 | p0*v0 | */

 /* approximately advances %3 = (%3 + a) % b. This function requires that
@@ -105,10 +103,6 @@ pa_volume_s16ne_mmx (int16_t *samples, i
     __asm__ __volatile__ (
         " xor %3, %3 \n\t"
         " sar $1, %2 \n\t" /* length /= sizeof (int16_t) */
- " pcmpeqw %%mm6, %%mm6 \n\t" /* .. | ffff | ffff | */
- " pcmpeqw %%mm7, %%mm7 \n\t" /* .. | ffff | ffff | */
- " pslld $16, %%mm6 \n\t" /* .. | ffff | 0 | */
- " psrld $31, %%mm7 \n\t" /* .. | 0 | 1 | */

         " test $1, %2 \n\t" /* check for odd samples */
         " je 2f \n\t"

The simplest solution is to revert that piece of assembly back to what it was. The attached patch accomplishes this.