Keep your ears open
Worldwide public domain dedication. Easy to use. It allows everything. This is a good license for free and unrestricted sound samples, you are encouraged to contribute content to the FreePats project under CC0 license.
Creative Commons licenses are useful for artistic works. There are several Creative Common licenses, notice that some of them are not free.
The Creative Commons Attribution 4.0 license is a free license which requires attribution. Please read Attribution for more information. Versions older than 3.0 are not suitable because they are not compatible with DFSG.
The GNU General Public License (GPL) is a popular license in free software. It works well for computer programs, but it is not easy to translate to artistic works. At a minimum, we require that GPL licensed sound samples include a special exception similar to the exception proposed by the FSF for typografic fonts:
As a special exception, if you create a composition which uses these sounds, and mix these sounds or unaltered portions of these sounds into the composition, these sounds do not by themselves cause the entire composition as a whole to be covered by the GNU General Public License. This exception does not however invalidate any other reasons why the composition might be covered by the GNU General Public License.
If you modify these sounds, you may extend this exception to your version of the sounds, but you are not obligated to do so. If you do not wish to do so, delete this exception statement from your version.
The exception was edited with the help of Richard Stallman, who was kind enough to answer our questions and proposed a modification to be used specifically for sound samples.
If you want to use the GPL, please include the exception. Otherwise they will have complicated restrictions that would render them practically impossible to use in musical compositions, which is probably not what you want to achieve. Please read Copyleft and ShareAlike for more information.