You may
Train your own voice; train a voice when the speaker has knowingly given you permission; create legitimate music, performance, accessibility, research, parody, or creative work that respects the speaker and applicable law.
You may not
Train a voice taken without permission; impersonate someone deceptively; create fraud, scams, non-consensual sexual content, harassment, threats, or election manipulation; evade another service's safety controls; violate privacy, publicity, copyright, contractual, or other legal rights; probe, overload, resell access to, or interfere with this beta.
Image models
NiceVois no longer offers image-model training. Anyone who trained an image model with NiceVois while that experiment was open remains responsible for the dataset, the trained file, and every image generated with it.
Covers and the songs you upload
A cover involves two separate permissions, not one: the voice, and the song. The voice rules above apply unchanged. For the song, you may upload a recording you made or own, or one you have permission to use. You may not upload a commercial recording you have no right to use, and you may not publish or sell a cover without the rights to both the underlying recording and the composition. NiceVois does not supply songs, does not fetch them from links on your behalf, and does not clear any licence for you.
Keeping a cover and publishing one
These are different acts with different rules. Making a cover for your own listening is not the same as releasing it, and a cover that is fine on your own machine can still infringe once it is uploaded, monetised, or presented as an artist's own work. The permission you need is the permission for what you actually intend to do with it.
When in doubt
Do not upload the audio. Permission to hear, possess, or publish a recording does not automatically mean permission to create a reusable voice model from it, or to build a new recording on top of it.
Reporting
Report suspected misuse to the service operator. Access and files may be suspended while a report is reviewed.