Shure A15AS Switchable Attenuator (15, 20, 25 dB), Passes Phantom Power In-Line Attenuator reduces the level of any balanced microphone or line-level signal by 15, 20, or 25 dB Specially suited to reducing the level of a high-output microphone to prevent it from overloading the microphone input of a mixer or recorder in applications with high sound pressure levels. A15AS may be used to reduce the level of a line-level mixer output to prevent overloading the aux-level input of a recorder.