Python control sound volume

[jtodd.fr]

I was playing with pyalsaaudio (v0.8.4) using python (v2.7.12 with GCC 5.4.0 20160609) on Ubuntu 16.04.3 LTS. My goal is to read the current sound volume level and then adjust the value by e.g. increment by 10% or 10. When testing the sample code



import alsaaudio


mixer = alsaaudio.Mixer()
vol = mixer.getvolume()
print(vol)


It prints [27, 27], but checking with alsamixer it shows master sound is 20 where View is F3:[Playback] and Item is Master [dB gain: -33.50].

How should I interpret such different? I completely don't understand Linux sound system, so I appreciate any suggestions.

Thanks.

[norobro]

From the alsamixer man page:
VOLUME MAPPING
In alsamixer, the volume is mapped to a value that is more natural for a human ear.
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.

So, if I understand the above, the devs modified the display scale for alsamixer.

On my machine:
In [1]: import alsaaudio

In [2]: mixer = alsaaudio.Mixer()

In [3]: mixer.getvolume()
Out[3]: [48L]

In [4]: mixer.getrange()
Out[4]: [0, 42]
$ amixer -c 0 sget Master
Simple mixer control 'Master',0
Capabilities: pvolume pvolume-joined pswitch pswitch-joined
Playback channels: Mono
Limits: Playback 0 - 42
Mono: Playback 20 [48%] [-33.00dB] [on]
And alsamixer shows master sound at 21 with dB gain: -33.00

What concerns do you have?