Biometric identification

A method of biometric identification of a person comprising, during an enrolment phase:

• determining at least one enrolment transfer function for bone conduction of an audio signal through an enrolling user's head;
• and
• storing the at least one enrolment transfer function, and
• during a verification phase:
• determining at least one verification transfer function for bone conduction of an audio signal through the person's head;
• and
• determining from the at least one verification transfer function and the at least one enrolment transfer function whether the person is the enrolling user;
• wherein, in the enrolment phase and/or in the verification phase, the step of determining at least one enrolment transfer function or at least one verification transfer function for bone conduction of an audio signal through a person's head comprises, while the person is speaking and while the person is wearing an earpiece comprising a first transducer located on an outward facing part of the earpiece and a second transducer located on a part of the earpiece facing into the person's ear canal:
• determining a plurality of times when the speech contains a specific acoustic class;
• generating the first transducer output signal from the first microphone;
• generating the second transducer output signal from the second microphone;
• and
• determining the at least one enrolment transfer function or the at least one verification transfer function for said specific acoustic class based on the relationship between the first transducer output signal and the second transducer output signal at said plurality of times.