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alsa-mixer: round, not truncate, in to_alsa_dB

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to_alsa_dB() returns a result rounded to two decimal places (instead of
using integer truncation) to avoid small errors when converting between
dB and volume.

Consider playback at -22 dB (which is supported by ALSA) but results in
the higher level of -21 dB plus software attenuation.

    pa_sw_volume_from_dB(-22) = 28172
    pa_sw_volume_to_dB(28172) = -21.9997351
    to_alsa_dB(-21.9997351)   = -2199

    ALSA value 106 = -2200
    ALSA value 107 = -2100
    ...

    rounding = +1  /* "accurate or first above" */
    snd_mixer_selem_ask_playback_dB_vol(me, -2199, rounding, &alsa_val)
    alsa_val = -2100

Signed-off-by: Ian Ray <ian.ray@ge.com>
This commit is contained in:
Ian Ray 2017-08-30 11:09:48 +03:00 • committed by Tanu Kaskinen
parent f0dfddead3
commit 739a4b3d23
1 changed files with 1 additions and 1 deletions
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2
src/modules/alsa/alsa-mixer.c
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@ -700,7 +700,7 @@ void pa_alsa_path_set_free(pa_alsa_path_set *ps) {
}
static long to_alsa_dB(pa_volume_t v) {
return (long) (pa_sw_volume_to_dB(v) * 100.0);
return lround(pa_sw_volume_to_dB(v) * 100.0);
}
static pa_volume_t from_alsa_dB(long v) {