An audio host device has a headset electrical interface in which a reference contact is shared by a microphone and a speaker. A variable or programmable gain amplifier, PGA, has a signal input coupled to a sense point for the reference contact. A first difference amplifier has its inputs coupled to a microphone contact and the PGA through a first gain stage; a second difference amplifier has its inputs coupled to the microphone contact and to the output of the PGA, through a second gain stage having a different gain than the first gain stage; a third difference amplifier has its inputs coupled to the microphone contact and the output of the PGA through a third gain stage having a gain in between that of the first and second gain stages. A controller monitors outputs of the first and second difference amplifiers and changes a gain setting of the PGA. Other embodiments are also described and claimed.