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Merge branch 'audio'

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* audio:
  comment code a bit better
  box filter: set the box width only based on the final sample frequency. we don't care what the original frequency was.
  box filter: handle start and end of sample by repeating the first and last sample
  choose box filter width based on ratio of sampling rates
  make the box filter work in-place (O(box-width) memory instead of O(sound-length) memory)
  add a comment
  lowpass filter: read samples centered around the dest sample
  force loading samples as 16-bit
  add a "low-pass filter"
  fix stupid bug and linear interpolation sounds OK but not amazing, as expected
  try linearly interpolating between samples for 11025->44100 upsampling. sounds like crap.

Conflicts:
	Quake/snd_mem.c
This commit is contained in:
Eric Wasylishen 2011-12-30 11:56:44 -07:00
commit d1fc2c314b
1 changed files with 17 additions and 14 deletions
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31
Quake/snd_mem.c
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@ -114,14 +114,12 @@ 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
// 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);
// for 44100Hz output, a box width of 5 (i.e. a box_half_width of 2) seems
// to sound the best
const int box_half_width = CLAMP(0, sc->speed / 22050, 4);
if (box_half_width > 0)
{
@ -129,26 +127,31 @@ static void ResampleSfx (sfx_t *sfx, int inrate, int inwidth, byte *data)
int history[box_half_width];
memset(history, 0, sizeof(history));
int box_sum = 0;
for (i = 0; i < outcount; i++)
for (i = 0; i < (outcount + box_half_width); i++)
{
const int sample_at_i = getsample(sc->data, sc->width, i);
// calculate the new sample we will write
const int sample_at_i = getsample(sc->data, sc->width, CLAMP(0, i, outcount - 1));
box_sum += sample_at_i;
box_sum -= history[0];
const int newsample = box_sum / box_width;
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
// shift the entries in the history buffer left, discarding the entry
// at history[0] and leaving a space at history[box_half_width-1]
int j;
for (j=0; j<(box_half_width-1); j++)
{
history[j] = history[j+1];
}
history[box_half_width-1] = getsample(sc->data, sc->width, write_loc);
putsample(sc->data, sc->width, write_loc, newsample);
// save the sample we are going to overwrite at history[box_half_width-1]
const int write_loc = i - box_half_width;
history[box_half_width-1] = getsample(sc->data, sc->width, CLAMP(0, write_loc, outcount - 1));
// only write the new sample if it lies within the bounds of the output array
if (write_loc >= 0 && write_loc < outcount)
{
putsample(sc->data, sc->width, write_loc, newsample);
}
}
}
}