DesignAEC » History » Revision 14
Revision 13 (Adrian Georgescu, 08/27/2009 02:56 PM) → Revision 14/27 (Adrian Georgescu, 08/27/2009 02:58 PM)
= Echo cancellation = [[TOC(Design*, depth=1)]] SIP SIMPLE client is a Python software library that allows for easy development of Internet communications end-points based on SIP and related protocols for voice, rich presence, session based instant messaging (IM), file transfers and desktop sharing. Other media types can be easily added by using an extensible high-level API. SIP SIMPLE client uses [http://www.pjsip.org/pjmedia/docs/html/index.htm PJSIP media library] for audio processing (sound card abstraction, audio codec and acoustic echo cancellation). For more information see http://sipsimpleclient.com == Background == The present implementation of the echo canceller from PJSIP media library is not performing to the desired level of quality. Practically, the speaker phone function of SIP SIMPLE client is not reliable and not performing satisfactory unless a headset is used. [[Image(http://www.pjsip.org/images/media-flow.jpg)]] == Project goal == Replace the existing AEC from Pjmedia library (what is displayed as echo.h in the above diagram whihc employes the AEC of the speex project) diagram) with an alternative a better solution to be developed solution that provides provide a high quality speakerphone user experience. The acoustic echo cancelation should perform comparable with any other proven VoIP commercial solution like Skype or iChat making the need of a headset un-necessary. iChat. The developed software will be released under an open source licence and distributed with SIP SIMPLE client library. The deliverable is C written program that can be applied to the pjsip cvs trunk 1.0 with the '''patch''' command. == Resources == General * Digital Signal Processing http://www.dsptutor.freeuk.com/ * Graduation thesis about AEC http://innovexpo.itee.uq.edu.au/2003/exhibits/s365914/ * DSP concepts: http://www.bores.com/courses/intro/basics/index.htm PJSIP media library * PJSIP media library http://pjsip.org, used by this project, AEC is implemented based on the Speex library, the code in pjsip/pjmedia/src/pjmedia/echo_speex.c * Media flow - http://trac.pjsip.org/repos/wiki/media-flow * PJSIP AEC API http://www.pjsip.org/pjmedia/docs/html/group__PJMEDIA__Echo__Cancel.htm Speex AEC * Speex project http://speex.org, the echo canceller implements AEC based on the MDF algorithm, see speex/libspeex/mdf.c. A test client is available in speex/speexclient, this has been used for developing pjmedia equivalent * http://speex.org/docs/api/speex-api-reference/group__SpeexEchoState.html Andree Adrian AEC * Draft AEC http://www.andreadrian.de/echo_cancel/draft-aec-03.txt * http://www.andreadrian.de/intercom/ implements AEC based on NLMS algorithm (not tested yet) * Kphone AEC implemented using above AEC http://www.andreadrian.de/echo_cancel/ (not tested)