This parameter specifies the gain in decibel to applied on the signal received from an analog interface.
A positive value increases the volume of the signal.
A negative value decreases the volume of the signal.
Set this parameter to 0.0 to keep the signal untouched
Valid values for a FXS interface are: -3.5, 0.0 and 3.5 dB.
Valid values for a FXO interface are: -15.0 to 12.0 dB.