Phantom power is a steady DC current, usually sent by mixers and preamps down the mic cable to power condenser microphones, active DI boxes, and other mics requiring power for their head amplifier. True phantom power is +48 V DC. This chapter shows how a microphone responds to sound coming from directly in front of it, on-axis. In a multi-mic recording situation, or any live sound situation, there is also spill-unintended sound from adjacent sound sources reaching the mic off-axis from the sides or behind. Self-noise is only quoted for condenser microphones, where it is a measure of the noise created by the head-amp in the mic itself. This noise is usually greater than the noise introduced by high quality preamp, and can be audible when the gain is turned up high when recording quiet sound sources. If a mic is overloaded by being put in front of a sound source that is too loud, it will distort.