Differential mode noise cancellation with active real-time control for microphone-speaker combinations used in two way audio communications

A method for operating an audio host device, comprising:

• playing a super-audible tone through a speaker contact of a headset connector in the audio host device, while a headset having a microphone is coupled to the connector;
• measuring output of a microphone signal difference amplifier in the audio host device, while the headset is coupled to the connector and the super-audible tone is playing;
• and
• attenuating a signal that is input to the amplifier based on the measurement by an amount that reduces presence of the super-audible tone at the output of the amplifier.

A portable audio host device comprising:

• a headset connector having a speaker contact, a microphone contact, and a reference contact, the reference contact to be shared by a microphone and an speaker;
• a difference amplifier having a first input and a second input, the second input being coupled to the microphone contact;
• a variable voltage attenuator having an input coupled to receive a signal from a sense point for the reference contact, and an output coupled to the first input of the difference amplifier;
• and
• a controller having an output coupled to control the variable attenuator.