Volume sound control

shogun1234 · 02-11-2018, 05:25 AM

Came across to the lib pyalsaaudio (v0.8.4). When using following code, it prints values [27, 27], but using alsamixer the result shows Master volume level is at 20. What cause such different or how do I interpret the output of pyalsaaudio? Or is there any lib that's more popular if I want to control volume sound?

Thanks

Code:

import alsaaudio

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

treemouse · 02-18-2018, 01:05 AM

According to this, mixer.getvolume() is returning a percent. Presumably this is as a percent of the maximum possible volume, giving it a 0 to 100 scale.

Running alsamixer, it also gives me a percent on a 0 to 100 scale.

So it seems like the two must be using a different maximum volume to base their percents off of.

I suggest experimenting with setting the volume to different levels and seeing what each reports, so you can work out a conversion.

Assuming 0 in alsamixer is also 0 in mixer.getvolume() then your conversion formula would be that every 1% in alsamixer is equal to 1.35% in mixer.getvolume(). To put that in formulas, mixer.getvolume() = 1.35*alsamixer, or alsamixer = mixer.getvolume()/1.35. You can test this by checking to see if 50 in alsamixer is equal to 67 or 68 in mixer.getvolume().

keefaz · 02-18-2018, 06:00 AM

Check volume with amixer instead, alsamixer has its own way to represent volume

Quote:

* 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). For controls with
* a small range (24 dB or less), the mapping is linear in the dB values so
* that each step has the same size visually. Only for controls without dB
* information, a linear mapping of the hardware volume register values is used
* (this is the same algorithm as used in the old alsamixer).

https://github.com/bear24rw/alsa-uti...lume_mapping.c

Code:

amixer sget Master

shogun1234 · 02-20-2018, 10:24 AM

Thanks for the explanation.

keefaz · 02-20-2018, 12:38 PM

Err, I was just quoting a part of source code comments