Shallow trench isolation techniques are disclosed in which a thin nitride layer is formed on a semiconductor substrate, and a trench is formed through the nitride layer and into the semiconductor substrate, which is then filled. Whether the direction of the speech source is identified using audio streams from some of the directional microphones or from all of the directional microphones depends on whether using audio streams from a subgroup of the directional microphones or using audio streams from all of the directional microphones is more likely to correctly identify the direction of the speech source. The deflector is not used to scan a sample with the electron beam.