Backwards Compatible 3D Audio Conference Server Using HRTF Synthesis and SIP

This paper describes an integration of a 3D sound convolution engine into a telephone conference server software. Our system virtually places participants of a telephone conference to different positions around the listeners by using Head Related Transfer Functions (HRTFs), which helps to identify active speakers in an audio conference. Intelligibility of communication is also increased by making use of the cocktail party effect which helps to concentrate on one specific participant, even if there are more simultaneously active speakers. To support regular telephone systems, we focus in particular on compatibility to existing Voice over IP (VoIP) infrastructure by using standardized protocols like the Session Initiation Protocol (SIP) and the Real-Time Transport Protocol (RTP). Both traditional telephone devices and software clients are put into one heterogeneous conference. While the conference server transmits the down-mixed, mono single-channel conference signal to regular phones, the software clients can receive a stereo-signal enabling full 3D audio.