Radio/Audio System Description and Operation (IOS/IOT/IOU): Microphones

This system utilizes two hands free audio microphones, the primary microphone on the driver side and a secondary/reference microphone for the front passenger side. The primary microphone is connected directly to the Telematics Communication Interface Control Module. It is also connected by an analog pass-through circuit to the radio from the Telematics Communication Interface Control Module. The secondary microphone is connected directly to the radio.

The primary microphone is used for emergency and OnStar^® calls. During normal operating conditions it also provides Bluetooth calls and speech recognition to the radio. The secondary microphone is used as a reference for the primary microphone for Barge-in and Passenger Interference Cancellation during speech recognition and also to enhance the driver side hands free calls. For MY18 and beyond the secondary microphone can also be used for front passenger hands free phone calls. Barge-in allows a user to speak over the system prompts. Passenger Interference Cancellation ignores unwanted inputs from cabin noise that is not related to the prompts given by the user.

The front passenger secondary microphone is never used as a direct source for an OnStar^® call. The second microphone input modifies the primary microphone input to reduce background noise and other interference. An OnStar^® call requires the microphone to be directly connected to the Telematics Communication Interface Control Module. During a normal (non-emergency) OnStar^® call the Telematics Communication Interface Control Module receives an audio signal from the primary microphone and sends the signal to the radio via the Ethernet connection. The radio processes the OnStar^® call audio and sends it back to the Telematics Communication Interface Control Module via the Ethernet connection. During an emergency button call the Telematics Communication Interface Control Module contacts the OnStar^® call center directly and does not send the signal to the radio.