ReSpeaker 6-Mic Circular Array microphone gain, what gain is set up in AC108 ADC?

Hey, I would like to ask what is the gain of mic signal set in ADC? I know the operating voltage of microphones and i know that the gain in ALSA is set to 0. Soo what is the gain beween mic and raspberry? Is it dependable on such kind of algorithm or is it set up on precise value?

Regards Wiktor