Legal.
The DSP pack uses code of
FFMPEG licensed under the
LGPLv2.1 and its source can be downloaded
here.
The DSP pack uses code of
Libflac/Tremor licensed under the
Xiph BSD license.
The DSP pack uses code of
Wavpack licensed under the BSD license.
The DSP pack uses code of
Libsndfile licensed under the
LGPLv2.1.
Copies of all licenses are included in the DSP pack and readable via the "Licenses" option menu item.