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cubic interpolator: actually sounds way better than linear, i must have screwed up my previous attempt

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Eric Wasylishen 2012-01-04 19:56:39 -07:00
parent d4ae16ee48
commit 2b9e341904
1 changed files with 32 additions and 3 deletions
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35
Quake/snd_mem.c
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@ -115,7 +115,7 @@ void ResamplerConvert(int inrate, int incount, int inwidth, void *indata,
// linearly interpolate between the two closest source samples. // linearly interpolate between the two closest source samples.
// this alone sounds much better than id's method // this alone sounds much better than id's method
for (i = 0, samplefrac = 0; i < outcount; i++, samplefrac += stepscale) /*for (i = 0, samplefrac = 0; i < outcount; i++, samplefrac += stepscale)
{ {
int srcsample1 = CLAMP(0, floor(samplefrac), incount - 1); int srcsample1 = CLAMP(0, floor(samplefrac), incount - 1);
int srcsample2 = CLAMP(0, ceil(samplefrac), incount - 1); int srcsample2 = CLAMP(0, ceil(samplefrac), incount - 1);
@ -127,14 +127,43 @@ void ResamplerConvert(int inrate, int incount, int inwidth, void *indata,
int sample = ((1 - mu) * getsamplefromfile(indata, inwidth, srcsample1)) int sample = ((1 - mu) * getsamplefromfile(indata, inwidth, srcsample1))
+ (mu * getsamplefromfile(indata, inwidth, srcsample2)); + (mu * getsamplefromfile(indata, inwidth, srcsample2));
putsample(outdata, outwidth, i, sample); putsample(outdata, outwidth, i, sample);
}*/
float inpos;
int outpos;
for (outpos = 0, inpos = 0; outpos < outcount; outpos++, inpos += stepscale)
{
int inpos_int = (int)inpos;
float inpos_frac = inpos - inpos_int;
// Cubic interpollation
// Olli Niemitalo, musicdsp.org
int xm1 = getsamplefromfile(indata, inwidth, CLAMP(0, inpos_int - 1, incount - 1));
int x0 = getsamplefromfile(indata, inwidth, CLAMP(0, inpos_int + 0, incount - 1));
int x1 = getsamplefromfile(indata, inwidth, CLAMP(0, inpos_int + 1, incount - 1));
int x2 = getsamplefromfile(indata, inwidth, CLAMP(0, inpos_int + 2, incount - 1));
int a = (3 * (x0-x1) - xm1 + x2) / 2;
int b = 2*x1 + xm1 - (5*x0 + x2) / 2;
int c = (x1 - xm1) / 2;
int sample = (((a * inpos_frac) + b) * inpos_frac + c) * inpos_frac + x0;
// clip
if (sample > 0x7fff)
sample = 0x7fff;
else if (sample < (short)0x8000)
sample = (short)0x8000;
putsample(outdata, outwidth, outpos, sample);
} }
// box filter to filter out garbage high frequencies produced by the upsampling // box filter to filter out garbage high frequencies produced by the upsampling
// for 44100Hz output, a box width of 5 seems to sound the best // for 44100Hz output, a box width of 5 seems to sound the best
const int boxwidth = CLAMP(0, (outrate / 11025) + 1, 4); //const int boxwidth = CLAMP(0, (outrate / 11025) + 1, 4);
BoxFilter(boxwidth, outcount, outwidth, outdata); //BoxFilter(boxwidth, outcount, outwidth, outdata);
} }
else else
{ {