A video conference endpoint detects a face and determines a face angle of the detected face relative to a reference direction based on images captured with a camera. The endpoint determines an angle of arrival of sound (i.e., a sound angle) received at a microphone array that transduces the sound relative to the reference direction based on the transduced sound and a sound speed parameter indicative of a speed of sound in air. The endpoint compares the face angle against the sound angle, and adjusts the sound speed parameter so as to reduce the angle difference if the compare indicates an angle difference greater than zero between the face and sound angles.