I don’t want my software to take away your freedom so unless otherwise stated all Libre Wave software is released under the GPLv3 license and all audio samples are released under a Creative Commons Plus license. The complete license document combining the GPL, Creative Commons, and CC+ license is available here.
Why not release the samples under the GPL too?
The GPL license is intended for software and one of its requirements is that the user must have access to the software’s source code. Samples are audio files and don’t provide anything that is equivalent to source code, so the GPL is not really appropriate for samples. In addition to this the GPL requires all derivative works to be released under the same license, so providing GPL samples would require users to release their compositions under the GPL too.
I opted to use the standard Creative Commons Attribution-NonCommercial-ShareAlike license plus an additional license that grants extra permissions. Please contact me if you have any queries about the license terms.