BigSpeed Voice Chat SDK is a set of two ActiveX controls (Client and Server) that lets you set up a private voice chat network for secure messaging. The transfered data are scrambled using on-the-fly 128-bit AES encryption. The security is provided in two different modes: symmetric encryption with shared secret key and asymmetric encryption with 1024-bit public/private keys. The server is responsible for keeping information on and authentication of online peers. All peers connected to a particular server build a single private community. Fine grained access control is realized by a group of user-oriented permissions. They grant access control privileges to system resources and services in a flexible and secure manner. The voice stream is highly compressed to deliver the best possible sound over a limited-bandwidth connection. In addition, the average bitrate is reduced thanks to the silence compression. In the encoder, a voice activity detector with an adjustable trigger level is used to distinguish between regions with normal speech activity and those with silence or background noise. Significant echo suppression is achieved using a robust double talk detector. Capability to mute recording and mute playback is implemented. The incoming and outgoing audio data are available in raw PCM format for visualization in the application. Two special events notify about signal overloading (possible distorsions) and transmission delays (network congestions). Two different kind of text information can be exchanged between peers: alert and chat messages. File transfer capability is implemented for direct file exchange between peers. BigSpeed Voice Chat SDK utilizes an elegant event-driven paradigm for easy integration into Windows applications.A special attention is paid to provide responsive user interface while avoiding multithreading problems. Sample applications are included in Visual Basic 2005 and Delphi 7.