Features: brand new and high quality MIC: It is a 3.5MM microphone interface. When you use it, connect the self-made microphone of our shop to the destination and collect it. BPF: It is a frequency switching knob. There are five gears for frequency switching, and the frequency must be adjusted according to personal needs. REC VOL: Volume adjustment knob during recording. ON-OFF: adjust knob for monitoring volume and power switch. Next to the indicator light, DC-5V when starting and charging: it is the charging interface. When the indicator light flashes 4 times continuously, it indicates 4 grids, 3 times indicates 3 grids, and so on, it is always on when fully charged. DC5V: The charging port can be charged with the mobile phone charging head. Please do not use it during charging. REC out: It is a 3.5MM mobile phone recording interface. GAON SW: It is a gain switching switch. It is about 200 times when it is popped up and 600 times when it is pressed down. Specifications: Type:Audio Signal Mixer Board Colour: Black Material: Metal Package Includes: 1 x Mixer Board note: Please allow 0-1cm error due to manual measurement. pls make sure you do not mind before you order. Due to the difference between different monitors, the picture may not reflect the actual color of the item. Thank you!