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Provide a more natural volume percentage with ALSA.

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The rationale of the code is explained in the header:
http://git.alsa-project.org/?p=alsa-utils.git;a=blob;f=alsamixer/volume_mapping.c;h=1c0d7c45e6686239464e1b0bbc8983ea57f3914f;hb=HEAD
> The mapping is designed so that the position in the interval is
> proportional to the volume as a human ear would perceive it (i.e., the
> position is the cubic root of the linear sample multiplication
> factor).

and the commit message:
http://git.alsa-project.org/?p=alsa-utils.git;a=commit;h=34bb514b5fd1d6f91ba9a7b3a70b0ea0c6014250
> use a mapping where the bar height is proportional to the audible
> volume, i.e., where the amplitude is the cube of the bar height.

and further explanation can be found in the pull request:
https://github.com/i3/i3status/pull/268#pullrequestreview-147429763
This commit is contained in:
arcnmx 2018-02-21 13:25:08 -05:00 committed by Orestis
parent 494efd49a2
commit ddadc8e4d7
1 changed files with 28 additions and 7 deletions
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35
src/print_volume.c
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@ -11,6 +11,7 @@
#ifdef LINUX
#include <alsa/asoundlib.h>
#include <alloca.h>
#include <math.h>
#endif
#if defined(__FreeBSD__) || defined(__DragonFly__)
@ -111,11 +112,13 @@ void print_volume(yajl_gen json_gen, char *buffer, const char *fmt, const char *
#endif
#ifdef LINUX
const long MAX_LINEAR_DB_SCALE = 24;
int err;
snd_mixer_t *m;
snd_mixer_selem_id_t *sid;
snd_mixer_elem_t *elem;
long min, max, val;
bool force_linear = false;
int avg;
if ((err = snd_mixer_open(&m, 0)) < 0) {
@ -161,16 +164,34 @@ void print_volume(yajl_gen json_gen, char *buffer, const char *fmt, const char *
}
/* Get the volume range to convert the volume later */
snd_mixer_selem_get_playback_volume_range(elem, &min, &max);
snd_mixer_handle_events(m);
snd_mixer_selem_get_playback_volume(elem, 0, &val);
if (max != 100) {
float avgf = ((float)val / max) * 100;
err = snd_mixer_selem_get_playback_dB_range(elem, &min, &max) ||
snd_mixer_selem_get_playback_dB(elem, 0, &val);
if (err != 0 || min >= max) {
err = snd_mixer_selem_get_playback_volume_range(elem, &min, &max) ||
snd_mixer_selem_get_playback_volume(elem, 0, &val);
force_linear = true;
}
if (err != 0) {
fprintf(stderr, "i3status: ALSA: Cannot get playback volume.\n");
goto out;
}
/* Use linear mapping for raw register values or small ranges of 24 dB */
if (force_linear || max - min <= MAX_LINEAR_DB_SCALE * 100) {
float avgf = ((float)(val - min) / (max - min)) * 100;
avg = (int)avgf;
avg = (avgf - avg < 0.5 ? avg : (avg + 1));
} else
avg = (int)val;
} else {
/* mapped volume to be more natural for the human ear */
double normalized = exp10((val - max) / 6000.0);
if (min != SND_CTL_TLV_DB_GAIN_MUTE) {
double min_norm = exp10((min - max) / 6000.0);
normalized = (normalized - min_norm) / (1 - min_norm);
}
avg = lround(normalized * 100);
}
/* Check for mute */
if (snd_mixer_selem_has_playback_switch(elem)) {