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 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 Bluetooth-Compatible version: Bluetooth-Compatible 5.1. Bluetooth-Compatible 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-Compatible Transmit. 1) . the mode button to enter the Bluetooth-Compatible transmission mode, and the green light flashes slowly (connecting) It automatically reconnect the Bluetooth-Compatible headset / speaker that was paired successfully last time. 2) . For new Bluetooth-Compatible headset, 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 the mode button to search and pair Bluetooth-Compatible headset. 3). 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 Green light flashes slowly: reconnect (automatically connect the last Bluetooth-Compatible headset / speaker) Green light fast: Bluetooth-Compatible search in progress (search and connect new Bluetooth-Compatible devices) The green light is always on: it has been connected and paired successfully. (wait 10 seconds for sound transmission) Bluetooth-Compatible switching: long the mode key to automatically search and connect Bluetooth-Compatible device Note: different Bluetooth-Compatible headsets / speakers use different schemes and protocols to search for connections ,The time be different. If the search fails, please turn on Bluetooth-Compatible to check. Turn on the Bluetooth-Compatible headset, unplug the USB cable and plug it in again. Color: Black Material: plastic Package Contents: 1 * 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.