The sample wav audio clips provided are under Creative Commons License (Creative Commons Attribution 4.0 International Public License). The source is http://download.tensorflow.org/data/speech_commands_v0.02.tar.gz, in particular the files used are listed here for traceability:
yes_no_go_stop.wav
speech_commands_v0.02 ├── go │ └── 0c2ca723_nohash_2.wav ├── no │ └── 0a2b400e_nohash_0.wav ├── stop │ └── 0a196374_nohash_0.wav └── yes └── 0b40aa8e_nohash_0.wav
Creative Commons Attribution 4.0 International Public License.