[alsa-devel] [BUG] Bad decibel data on C-Media USB sound card

[Allen M.]

Raymond Yau wrote:

>Do the automatic gain has any side effect when it normalise the volume?

I am unsure of how to go about testing that, 'alsamixer' does not appear
to allow me to modify automatic gain.


>Do you mean the sound card does not has 7248 steps?

I am not familiar with how to properly check, however dbverify indicates
'Element volume range is 0..151 (-28.37..-0.06 dB).'

Instructions for dbmeasure on the wiki indicates the need for a Line In,
the sound card only provides Line Out and Mic In. Will it automatically
make use of 'Mic In' if 'Line In' is absent? Or do I even need to use it?


>You need to find out the value of c->res
>As you complain dB range -28.37 to -0.06 are not correct

Quick testing done with dbverify: http://ix.io/eyi


>You need to calibrate the dB range

Volume Steps <=3 are mute while volume step 4 is audible,
based on dbverify testing. This 'seems' to indicate that the
minimum volume is somewhere between -27.81 dB to -27.63 dB?

Additional info logs:
Output of 'amixer -c2 contents': http://ix.io/eyq
Alsa info script output: http://ix.io/eyn