You credit those who contributed to the Sound Recording within Recording Details > Recording Credits.

Only contacts which have been assigned the role of Production Contributor will appear in the in-line search results. If you need to add a contributor to your contacts you can do so by clicking Add a New Contributor within the Recording Details screen and that contact upon creation will be assigned the Production Contributor role or you can add the contributors within the Contacts module. Contributors can be selected more than once, which allows you to credit them for each individual role they've played in the creation of the Sound Recording.