Social Robot Lumen is a humanoid robot created to act like human and be human friend. In this study, Lumen scenario is limited on Lumen as an exhibition guide in Electrical Engineering Days 2015, a seminar and exhibition of electrical engineering undergraduate and graduate student of Bandung Institute of Technology. To be an exhibition guide, Lumen is equipped by Nao robot, a server, and processing applications. Audio communication system is one of the processing applications. The purpose of the system is to create verbal communication that allow Lumen to receive human voice and respond naturally to it. To be able to communicate like a human, audio communication system is built with speech recognition module to transform speech data into text, speech synthesizer module to transform text data into speech, and gender identification module to distinguish adult female and male voice. Speech recognition module is implemented using Google Speech Recognition API, speech synthesizer module is implemented using Acapela engine, and gender identification module implemented by utilizing speech signal feature that is extracted using Fast Fourier Transform algorithm. Hardware used for implementation are Nao robot, computer, and wireless modem. ----- Lumen Robot Sosial Robot merupakan robot humanoid yang diciptakan agar dapat bersikap seperti manusia dan menjadi teman bagi manusia. Sistem komunikasi audio merupakan salah satu aplikasi pengolah yang bertujuan agar Lumen dapat menerima suara manusia dan meresponnya dengan natural, yaitu seperti cara manusia merespon manusia lainnya. Untuk dapat berkomunikasi seperti manusia, sistem komunikasi audio dilengkapi dengan tiga buah modul: speech recognition untuk mengubah data suara menjadi teks, speech synthesizer untuk mengubah data teks menjadi suara, dan gender identification untuk membedakan suara wanita dan pria.