Comment 4 for bug 1099059

http://cgit.freedesktop.org/pulseaudio/pulseaudio/commit/src/modules/alsa/alsa-sink.c?id=f1e43cd9b82d3d0d1a5b5441510b1e91aa8acc5d

Jan 13 02:16:50 ipokesmot247 pulseaudio[2907]: ( 4.523| 0.003) [alsa-sink] alsa-sink.c: Requested volume: 0: 16% 1: 16%
Jan 13 02:16:50 ipokesmot247 pulseaudio[2907]: ( 4.523| 0.000) [alsa-sink] alsa-sink.c: in dB: 0: -47.25 dB 1: -47.25 dB
Jan 13 02:16:50 ipokesmot247 pulseaudio[2907]: ( 4.524| 0.000) [alsa-sink] alsa-sink.c: Got hardware volume: 0: 16% 1: 16%
Jan 13 02:16:50 ipokesmot247 pulseaudio[2907]: ( 4.524| 0.000) [alsa-sink] alsa-sink.c: in dB: 0: -47.25 dB 1: -47.25 dB
Jan 13 02:16:50 ipokesmot247 pulseaudio[2907]: ( 4.524| 0.000) [alsa-sink] alsa-sink.c: Calculated software volume: 0: 100% 1: 100% (accurate-enough=yes)
Jan 13 02:16:50 ipokesmot247 pulseaudio[2907]: ( 4.524| 0.000) [alsa-sink] alsa-sink.c: in dB: 0: 0.00 dB 1: 0.00 dB
Jan 13 02:16:50 ipokesmot247 pulseaudio[2907]: ( 4.524| 0.000) [alsa-sink] sink.c: Volume not changing

the dB range is -48dB to 0dB for stereo headphone and speaker playback volume with 64 steps

PCM Playbacks volume (stereo) is softvol control with dB range -51dB to 0dB with 256 steps

master playback volume (mono) is the virtual master volume

you have to study the source to find out how pulseaudio calculate 16%

can you post the pulseaudio verbose log ?