DesignAEC » History » Revision 8
Revision 7 (Adrian Georgescu, 06/28/2009 06:06 PM) → Revision 8/27 (Adrian Georgescu, 06/28/2009 06:10 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) with a better solution to provide a high quality speakerphone user experience.
The developed software will be released under an open source licence and distributed with SIP SIMPLE client library.
== Resources ==
General
* Digital Signal Processing http://www.dsptutor.freeuk.com/
* Graduation thesis about AEC http://innovexpo.itee.uq.edu.au/2003/exhibits/s365914/
* DSP conepts: 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
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
* 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)