Description from manual:
The AM4 is designed to solve problems that are common in churches, lecture halls and other facilities. It is designed to benefit new and existing sound systems, providing "hands off" control with or without an operator. It does this by connecting to any available mic or line input.
As additional mics are turned on, the gains of the other active mics must be reduced to prevent feedback. The AM4 does this automatically by continuously sensing the signal from each mic and quickly distributing the available gain among the channels in use. Additionally, the AM4 eliminates the distortion that often occurs when a person using a wireless lapel mic moves close to an active podium mic. The AM4 also has two convenient front panel Mute switches with indicator to avoid the difficulty of locating the tiny mute switch on wireless transmitters. Send and Return jacks on the back allow for easy connection of an external graphic equalizer, if needed, to further reduce feedback.
The AM4 is designed for easy installation. Its small size allows it to be installed either with the rest of the sound system or in a podium where the user has easy access to the mute controls. The convenient mounting tabs allow the AM4 to be securely screwed or bolted to a shelf.