Fans are generally categorized by the way air enters and leaves the fan, which comes in two common forms: the axial fan where air is drawn in from one side and expelled from the other on the same plane or the centrifugal fan design where air is drawn in and expelled in a different direction. This style of fan, most commonly found as a blower, effectively compresses the air, allowing for the delivery of airflow at 90° to the intake under different pressures. The application requirements will determine which design is more suitable as axial fans deliver greater airflow in systems with low static pressure, while centrifugal fans offer lower airflow, but can deliver it against higher static pressure. Audible and electrical noise are also important considerations when selecting a fan. In general, the greater the airflow required, the greater the audible noise which means that careful design to optimize airflow and reduce system impedance will reduce the required CFM and minimize noise. Axial fans will also tend to be quieter than their centrifugal fan counterparts. In addition to noise, electromagnetic interference (EMI) generated by the DC motor in a fan should also be considered. This unwanted system effect is usually limited to conducted EMI in the power leads and can be effectively suppressed with ferrite beads, shielding, or filtering.