WaveSurfer is an open source tool for sound visualization and manipulation. Typical applications are speech/sound analysis and sound annotation/transcription. WaveSurfer may be extended by plug-ins as well as embedded in other applications.
This is a simple DSP simulator for educational purposes: developed as a course supplement of CIT-4617 (Digital Signal Processing) at Islamic University of Technology (IUT). Written in C++.
eXtace is a 3D audiovisualization tool (or eye candy depending on how you look at it). eXtace requires ESD (Esound) for its sound input source. It performs a FFT (fast fourier transform) on audio and displays it via various graphical modes.
jATLAS is a Java implementation of ATLAS [Architecture and Tools for Linguistic Analysis Systems]. For more information, see http://jatlas.sourceforge.net.