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

[Raymond Yau]

>
> >Does this number of steps remain the same when your starting volume are
not at 151?
> >Your value 77 seem quite different from  alsamixertest
>
> recording a sine wave with an amplitude of 1 in Audacity at step 151
shows that the recorded
> value is amplitude 0.885. Does this indicates some loss? The loopback
cable I am using
> is 2 meters in length, is the resistance of the cable is too high?

Did you use mono or stereo in playback and capture?

Did your capture volume /boost set to 0dB?

Do your sound card support the sampling rate ?

It depends on frequency of sine wave, sampling rate, playback gain/atten
capture gain/atten

http://wiki.linuxaudio.org/apps/all/jaaa

Do the frequency response of your card look like a straight line at 0dB
similar to those cards loopback test ?

http://audio.rightmark.org/test_results.shtml

Refer to the datasheet and your alsamixertest result , the card seem not
has fixed gain for each step

> >You many need to change the name of the volume control to headphone
> >playback volume in alsamixertest
> > Done. alsamixertest output:http://ix.io/ezd

Are you using version 48.11?

Seem alsamixertest is not suitable for testing volume control with less
than 1dB per step or variable dB per step