Jigasi call in volume is so low

i am using Jigasi for incoming calls.
my problem is: when someone joins meeting with phone (throw Jigasi) his volume is low and other participants can’t hear him easily. is there any way that i can increase Jigasi’s volume (in source code or configs)?
i am using Astrisk (freepbx) too. it can help me to solve this problem?