It affect your measurent if you are using the mic on your usb audio if
the
automatic gain control is switch on
Automatic gain control is now switched off.
Background noise affect the result if you are not using line in and line out with a loopback cable
I am using loopback, noise should not be an issue.
How many steps need to reduce amplitude of the recorded sine wave by half when you play a sine wav through your usb audio and record it back using audacity?
Using recorded sine wav provided by 'speaker-test -t sin' amplitude of recorded sine wave reduced by half at step 77
output of 'amixer -c 2 set Headphone 77': Simple mixer control 'Headphone',0 Capabilities: pvolume pswitch pswitch-joined Playback channels: Front Left - Front Right Limits: Playback 0 - 151 Mono: Front Left: Playback 77 [51%] [-13.94dB] [on] Front Right: Playback 77 [51%] [-13.94dB] [on]
Does this number of steps remain the same when your starting volume are not at 151?
Your value 77 seem quite different from alsamixertest
You many need to change the name of the volume control to headphone playback volume in alsamixertest
Done. alsamixertest output:http://ix.io/ezd
You may need David to analyse the result
Do those measured value match with those in datasheet?
Seem the measured dB range is larger than 27 dB
https://git.kernel.org/cgit/linux/kernel/git/tiwai/sound.git/log/sound/usb?q...