What is audio "common" wire?

[timmerk]

Does anyone know what the "audio common" wire is (see attached)? I understand the left and right channels, and ground appears to be just connected to the bare metal shield in the audio cable, so I don't think common = ground. Maybe it's a center channel? I'm basically trying to hook up the audio aux input in the center console of a 2018 Sierra to an aftermarket headunit. When I connect just left, right, and ground, I hear both channels, but it seems quieter and less has less bass than if I plugged directly into the aux port of the headunit.

2018 Connector.pdf 2018 Radio.pdf

[Ak_grown]

have you tried to connect just one side? check if the volume is better. did you connect to chassis ground? or the audio common ground? 

[JH1973]

The audio common is the inverted signal on a balanced input.Unlike unbalanced inputs where there is basically a shield and a signal, a balanced input has a hot signal and also an inverted signal that is completely out of phase with the hot signal. The inverted signal is also known as the audio common.

[timmerk]

22 hours ago, Ak_grown said:

have you tried to connect just one side? check if the volume is better. did you connect to chassis ground? or the audio common ground? 

Thanks, I will try tomorrow and let you know.

[timmerk]

11 hours ago, JH1973 said:

The audio common is the inverted signal on a balanced input.Unlike unbalanced inputs where there is basically a shield and a signal, a balanced input has a hot signal and also an inverted signal that is completely out of phase with the hot signal. The inverted signal is also known as the audio common.

Thank you! Do you know how I would hook this up to a standard TRS 3.5mm jack?