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misc: fix issues with perceptual volume calculations

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The constant NVOL_FACTOR used in the calculations needs
to be scaled if the target doesn't represent volumes in
1/10th dB units (ie. most targets). Using a wrong factor
caused the results to be slightly "off", with wide steps
between points on the upper end of the volume curve.

Drop use_linear_dB_scale() because the magic constant
involved has a similar problem (and we don't use this
function anyway).

Also, make sure to account for the guaranteed min/max
points when generating the normalized volume table to
avoid sometimes generating one or two extra volume steps
very close to the min/max volumes.

Change-Id: I5c15809a7306f14bb1befe6d29a5e2b5b0974eaa
This commit is contained in:
Aidan MacDonald 2026-02-01 17:12:37 +00:00
parent ad9471be3b
commit 3f2ca20245
1 changed files with 20 additions and 35 deletions
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51
apps/misc.c
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@ -904,7 +904,7 @@ static void update_norm_tab(void)
norm_tab[0] = min;
norm_tab_size = 1;
for (int i = 0; i < lim; ++i)
for (int i = 1; i < lim - 1; ++i)
{
int vol = from_normalized_volume(i, min, max, lim);
int rem = vol % step;
@ -1944,49 +1944,40 @@ int core_load_bmp(const char * filename, struct bitmap *bm, const int bmformat,
#define NVOL_FRACBITS 16
#define NVOL_UNITY (1L << NVOL_FRACBITS)
#define NVOL_FACTOR (600L << NVOL_FRACBITS)
#define NVOL_MAX_LINEAR_DB_SCALE (240L << NVOL_FRACBITS)
#define nvol_div(x,y) fp_div((x), (y), NVOL_FRACBITS)
#define nvol_mul(x,y) fp_mul((x), (y), NVOL_FRACBITS)
#define nvol_exp10(x) fp_exp10((x), NVOL_FRACBITS)
#define nvol_log10(x) fp_log10((x), NVOL_FRACBITS)
static bool use_linear_dB_scale(long min_vol, long max_vol)
static long get_nvol_factor(void)
{
/*
* Alsamixer uses a linear scale for small ranges.
* Commented out so perceptual volume works as advertised on all targets.
*/
/*
return max_vol - min_vol <= NVOL_MAX_LINEAR_DB_SCALE;
*/
long factor = 600L << NVOL_FRACBITS;
long numdecimals = sound_numdecimals(SOUND_VOLUME);
(void)min_vol;
(void)max_vol;
return false;
if (numdecimals == 0)
factor /= 10;
/* nothing *actually* needs this, but: */
while (numdecimals > 1)
factor *= 10;
return factor;
}
long to_normalized_volume(long vol, long min_vol, long max_vol, long max_norm)
{
long norm, min_norm;
long factor = get_nvol_factor();
vol <<= NVOL_FRACBITS;
min_vol <<= NVOL_FRACBITS;
max_vol <<= NVOL_FRACBITS;
max_norm <<= NVOL_FRACBITS;
if (use_linear_dB_scale(min_vol, max_vol))
{
norm = nvol_div(vol - min_vol, max_vol - min_vol);
}
else
{
min_norm = nvol_exp10(nvol_div(min_vol - max_vol, NVOL_FACTOR));
norm = nvol_exp10(nvol_div(vol - max_vol, NVOL_FACTOR));
min_norm = nvol_exp10(nvol_div(min_vol - max_vol, factor));
norm = nvol_exp10(nvol_div(vol - max_vol, factor));
norm = nvol_div(norm - min_norm, NVOL_UNITY - min_norm);
}
return nvol_mul(norm, max_norm) >> NVOL_FRACBITS;
}
@ -1994,6 +1985,7 @@ long to_normalized_volume(long vol, long min_vol, long max_vol, long max_norm)
long from_normalized_volume(long norm, long min_vol, long max_vol, long max_norm)
{
long vol, min_norm;
long factor = get_nvol_factor();
norm <<= NVOL_FRACBITS;
min_vol <<= NVOL_FRACBITS;
@ -2002,16 +1994,9 @@ long from_normalized_volume(long norm, long min_vol, long max_vol, long max_norm
vol = nvol_div(norm, max_norm);
if (use_linear_dB_scale(min_vol, max_vol))
{
vol = nvol_mul(vol, max_vol - min_vol) + min_vol;
}
else
{
min_norm = nvol_exp10(nvol_div(min_vol - max_vol, NVOL_FACTOR));
min_norm = nvol_exp10(nvol_div(min_vol - max_vol, factor));
vol = nvol_mul(vol, NVOL_UNITY - min_norm) + min_norm;
vol = nvol_mul(nvol_log10(vol), NVOL_FACTOR) + max_vol;
}
vol = nvol_mul(nvol_log10(vol), factor) + max_vol;
return vol >> NVOL_FRACBITS;
}