Unless otherwise specified, all Libre Wave software is released under the GPLv3, and all audio samples are provided under a Creative Commons Plus license.
Why not release the samples under the GPL?
The GPL is designed for software and requires that users have access to the source code. Since samples are audio files without an equivalent to source code, the GPL isn’t suitable for them. Moreover, the GPL mandates that any derivative works must also be released under the same license, meaning that GPL-licensed samples would require users to release their compositions under the GPL, which isn’t ideal.
Instead, I’ve chosen to use the Creative Commons Attribution-NonCommercial-ShareAlike license along with an additional license that grants extra permissions. Feel free to reach out if you have any questions about the licensing terms.
You can find the full license document, which combines the GPL, Creative Commons, and CC+ licenses, here.