Freesound Forums

Do I attribute the sound to a freesound username or is the artists actual details somewhere I haven't seen yet?

You can always send a Private message to the user to ask how to credit them but this mostly depends on the license type for the sound.
If you haven't already you should read the legality terms for Freesound.org by following the link below or reading the excerpt I have copied for you from said link.

Excerpt from this helpful link.

https://freesound.org/help/faq/#how-do-i-creditattribute

How do I credit/attribute?
Crediting people is easy, just say something like this:

This [video/theatre piece/...] uses these sounds from freesound:
sound1 by user1 ( http://freesound.org/people/user1/ )
sound2, sound3 by user2 ( http://freesound.org/people/user2/ )
etc..
If you want to know which files you have downloaded since you joined freesound, you can see this in the attribution list attribution list.

If you have a particularly long list of files or very little space to attribute sounds you can always do:

This [video/theatre piece/...] uses many sounds from freesound,
for the full list see here: http://www.mysite.com/work-credits.html
If you want to see a practical example from the movie Children of Men.

License restrictions when publishing new sounds that include/modify/remix other sounds
In the event of using sounds in Freesound to create new sounds, the following table helps you understanding how you can mix them, what can the resulting license/s be, and what the attribution obligations are. Lets say that a user B adds a new sound of her own that includes/modifies/remixes a sound from another user A, then:

License of sound of A B wants to distribute the new sound under Can B do this?
cc0 cc0 Yes
cc0 by Yes (*)
cc0 by-nc Yes (*)
by cc0 No
by by Yes (**)
by by-nc Yes (**)
by-nc cc0 No
by-nc by No
by-nc by-nc Yes (**)
(*) If a third user C uses the sound from B, she must attribute to B.

(**) B must attribute the sound to A. If a third user C uses the sound from B, she must attribute both A and B.