A. Sound control: The red ON, the knob adjusts the volume of the computer, -key mute, the song up/down song switch. B. 3.5mm audio output: Blue ON, wired earphone is inserted into AUX OUT hole, computer voice is output from earphone. C. Bluetooth-Compatible Transmit: When the green ON, long press the MODE button to enter. Bluetooth-Compatible search, and the green light flashes quickly to automatically match around. Bluetooth-Compatible headset, Bluetooth-Compatible speaker and other devices, the green light is steady on after successful pairing. Parameters Bluetooth version:Bluetooth 5.1 Bluetooth protocol:A2dp/avctp/avdtp/avrcp/hfp/spp//att /gatt/rfcomm//l2cap Music format: MP3, WMA, APE, FLAC, AAC, MP4, M4A, WAV, AIF, AIFC Signal to noise ratio: 90dB Compatible system: for Win XP 7 8 10, for os, plug and play, no driver required Bluetooth Transmit 1) . press the mode button to enter the Bluetooth-Compatible transmission mode, and the green light flashes slowly (connecting) It will automatically reconnect the Bluetooth-Compatible headset / speaker that was paired successfully last time. 2) . For new Bluetooth-Compatible headset, press the mode button for 3s, the green light flashes quickly. To enter the Bluetooth-Compatible search mode, automatically search and connect a new Bluetooth-Compatible headset/speaker. If not the correct Bluetooth-Compatible headset, continue to press the mode button to search and pair Bluetooth-Compatible headset. 3).Press and hold the mode key to access the Bluetooth-Compatible headset from (A) to (B), (B) to (C), (C) to (D). If you need to reconnect the Bluetooth-Compatible headset (A), you need to unplug and plug in the USB cable Different batches may have different appearances, but will not affect the use Colour:Black Material:plastic Package Contents: 1 x USB Volume Controller 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.