The Control-USB BT is a basic 3 channel 19" stereo rack mixer with USB/SD/Bluetooth player. Channel 1 is assigned to the microphone input. On Channel 2 you can play back your MP3/WAV music files from USB/SD-card, or connect to another portable audio device via the 3.5mm external stereo-input. Channel 3 lets you control any external line source via a pair of stereo RCA inputs on the rear.