When connecting FiiO BTR7 to Android mobile phone which supports Aptx adaptive Bluetooth codec, the default Bluetooth codec will be Aptx adaptive.(This is depended by the mobile phone.) If you would like to use other Bluetooth codec (Like LDAC), please follow this steps for help: 1. Enter FiiO Control app-BTR7-Status 2. Click'Select Bluetooth code' 3. Cancel the selection of 'Aptx adaptive' ,then click'ok'。 4. The BTR7 will restart and reconnect to the mobile phone via LDAC or other Bluetooth codec. Note: The iOS device only supports SBC and AAC Bluetooth codec. And the default Bluetooth codec will be AAC.