Praat

Praat is an application with which phoneticians can analyze, synthesize, and manipulate speech, and can create high-quality images for their articles and doctoral theses.

The source code may be downloaded here.

• Regular expressions: if the pattern is illegal, you'll now get an error message instead of an empty string.
• LongSound: removed a bug introduced in 1999 that could play long stereo sounds much too fast if they had unusual sampling frequencies. This bug has become more noticeable on the Mac since January 2015.
• Guard better against sound files that contain 0 samples.
• Scripting: faster look-up of variables.