[alsa-devel] wrong decibel data?

Raymond Yau superquad.vortex2 at gmail.com
Sat Apr 10 02:27:09 CEST 2010

2010/4/10 Nicolo' Chieffo <nicolo.chieffo at gmail.com>

> There's still no way to run the measurement with "pulse" because of
> the previous error:Iteration 1, level is 0 (-inf dB).
>    Volume level measured (0) was too high or too low.
>   Please adjust mixer so that initial level is between 0.8 and 0.97.
>   Test run canceled.
> Are you sure that the test has sense using the pulse device?
> "./dbmeasure plug:front plug_front.csv" works, but seems to never end:
>   Iteration 3297, level is 0.0414072 (-27.6585 dB).
>   Iteration 3298, level is 0.0414074 (-27.6584 dB).
>   Iteration 3299, level is 0.0414064 (-27.6587 dB).
>   Iteration 3300, level is 0.041406 (-27.6587 dB).
>   .....
> "./dbmeasure hw:0 hw.csv" fails with this message: "Cannot set sample
> format: Invalid argument"

The DR range of software ( 16 bits audio data ) need to be same as the range
of hardware volume control if you want  ths slider move at same scale

i.e. if PA only use one hardware volume control of  -48dB to 0 but the DR
range of 16 bits audio is 96dB , PA have to scale up the dB value by two

The best way is of course to sum the DB range of  all  hardware volume
controls in the audio path of the codec  to get a DB range of value close to
-96dB to 0 (i.e. need to use the value of the Volume Knob widget )

However the softvol plugin is in the software side , you have to verify the
step of the solfware volume control "PCM Playback volume" behave as it

The easy way is to play a full amplitude of sine wave to "front" device and
record it using an analog loop cable with 0dB capture gain , try to lower
the PCM volume and observe the amplitude of the recorded sine wave is
decreased at the correct ratio

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