The patent entitled, 'SYSTEM AND METHOD OF DETECTING A USER'S VOICE ACTIVITY USING AN ACCELEROMETER' notes that "a common complaint with these hands-free modes of operation is that the speech captured by the microphone port or the headset includes environmental noise such as secondary speakers in the background or other background noises. This environmental noise often renders the user's speech unintelligible and thus, degrades the quality of the voice communication."
Being placed in the user's ear canal, the accelerometer may detect speech caused by the vibrations of the user's vocal chords. Using these signals from the accelerometer in combination with the acoustic signals received by microphones in the earbuds and a microphone array in the headset wire, Apple is able to detect the user's speech. A noise suppressor can take this data and suppress the background audio well emphasizing the detected user's speech signals.
The patent was filed March 15, 2013 and published April 3, 2014.
More details at the link below...
Read More [via AppleInsider]