In addition to analog or digital outputs, there are a few other specifications for MEMS microphones to consider when making the proper selection. This slide and the following slides will discuss those parameters in greater detail. First comes the decision of whether to select a top port or bottom port microphone. Top port MEMS microphones have a sound hole fabricated in the top of the metal case that houses the internal circuitry, while the bottom port has a hole drilled on the bottom next to the solder pads. With a bottom port, a hole will need to be drilled in the PCB the microphone is mounted to in order to allow sound to enter. In general, the decision to select a top or bottom port MEMS microphone comes down to how the microphone fits in with the overall design.