4(1)-IN-1(4)-OUT 3.5mm AUX audio selector designed for customers having several audio sources and outputs, simple to use, plug and play, no power supply required 4 in 1 out: Support up to 4 audio source inputs and select 1 audio source output 1 in 4 out: 1 audio source input,and 4 ports output can be switch to amp or active speakers or headphone (If you need 2 or 3 ports output to play at the same time, you need to press 2 or 3 buttons at the same time and keep them locked.) This is a good idea to solve the problem of unplugging and plugging the wire Build in solid aluminium CNC chassis, looks nice and durable