[FFmpeg-user] Awful audio distortion with line input capture

[DopeLabs]

have you tried https://www.ffmpeg.org/ffmpeg-filters.html#Examples-8

Halve the input audio volume:
 	
volume=volume=0.5
volume=volume=1/2
volume=volume=-6.0206dB

In all the above example the named key for ‘volume’ can be omitted, for example like in:

volume=0.5

Increase input audio power by 6 decibels using fixed-point precision:
 	
volume=volume=6dB:precision=fixed

Fade volume after time 10 with an annihilation period of 5 seconds:
 	
volume='if(lt(t,10),1,max(1-(t-10)/5,0))':eval=frame




and heres this

git clone git://source.ffmpeg.org/ffmpeg.git ffmpeg