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