Standard MINI USB Interface: Connect with PC to make digital audio transfer possible and make battery charge possible 3.5mm two-channel Headphone Output: Suitable for various headphones with 16 ohm-300 ohm 3.5mm SPDIF input connector: Connect with high-definition player and receive PCM signal 3.5mm Line In interface: Connect with audio output LO&PO of audio players 18 Pin multifunctional interface: To make audio and data transfer possible in conjunction with L7 and E9