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choose box filter width based on ratio of sampling rates

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Eric Wasylishen 2011-12-29 19:33:43 -07:00
parent 382b135cca
commit 2fae63eef2
1 changed files with 33 additions and 25 deletions
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22
Quake/snd_mem.c
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@ -116,10 +116,17 @@ static void ResampleSfx (sfx_t *sfx, int inrate, int inwidth, byte *data)
// box filter
// FIXME: doesn't handle the start or end of the sound properly
const int left = 2;
const int right = 2;
const int box_width = left + right + 1;
int history[left];
// box_half_width is the number of samples on each side of a given sample
// that are averaged together.
// for the most common case, 11025Hz => 44100Hz, i.e. stepscale = 0.25,
// I determined that a box width of 5 (i.e. a box_half_width of 2) produces
// the best sounding results.
const int box_half_width = CLAMP(0, (1 / (stepscale * 2)), 8);
if (box_half_width > 0)
{
const int box_width = (2 * box_half_width) + 1;
int history[box_half_width];
memset(history, 0, sizeof(history));
int box_sum = 0;
for (i = 0; i < outcount; i++)
@ -131,19 +138,20 @@ static void ResampleSfx (sfx_t *sfx, int inrate, int inwidth, byte *data)
const int newsample = box_sum / box_width;
const int write_loc = CLAMP(0, i - right, outcount - 1);
const int write_loc = CLAMP(0, i - box_half_width, outcount - 1);
// before writing the sample at write_loc, copy it to the end of the history buffer
int j;
for (j=0; j<(left-1); j++)
for (j=0; j<(box_half_width-1); j++)
{
history[j] = history[j+1];
}
history[left-1] = getsample(sc->data, sc->width, write_loc);
history[box_half_width-1] = getsample(sc->data, sc->width, write_loc);
putsample(sc->data, sc->width, write_loc, newsample);
}
}
}
else
{
// general case / downsampling