The variable resistors adjust three parameters respectively. It is often used in commercial paging sound systems, general public address applications, and live events. It can be used for everything from paging, announcements, or messages to automated emergency alerts or anything that needs a priority source to lower the volume level of a secondary audio source, like the background music, to it's audible for your listeners. Once the Priority signal is no longer present, the other audio source(s) can go back to where they were. Please note: This circuit cannot be directly connected to a microphone. Parameters: Power supply: DC9V-24V Power consumption: 0.12W Frequency response: 20HZ - 20KHZ Input impedance: 50K Output impedance: 600 Gain: 0db Color: Green Material: PCB Package Contents: 1 x Audio Ducking Only the above package content, other products are not included. Note: Light reflection and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.