Shure MX690=-G4 Condenser Microphone (Cardioid) For this wireless system component to work, please make sure your transmitter and receiver match in frequency range (style) Sleek, low profile design. Frequency agile, microprocessor controlled transmitter. Bi-color status indicator. IR link to SLX receiver for automatic frequency synchronization. Programmable mute function. Battery level indicator. Operates on two AA batteries. Logic output for remote LED and mute control. CommShield Technology for improved RF filtering.