snd_ducking_off audio command can be found some high-profile autoexec files. How does setting
1 change audio?
Ducking audio is when the volume of other tracks/present audio is lowered on the introduction of a new audio track to make it stand out. This can be done for a variety of reasons in games, such as to have voice chat/communications be able to be heard regardless of other things going on or to make things like gunfire/explosions stand out more without having to go crazy with volume (and allowing your "normal" hearing to blend back in).
It is likely that if snd_ducking_off is set to 1 that this effect will not be applied and the background audio in situations where the audio would normally be ducked will remain at full volume.