This is a question posed to any developer who has hired some kind of session musician to record for their library - eg. a drummer for a drum library, guitarist for a guitar library, you get the idea. Assume this individual has no other part in the creation of the library outside of bringing their instrument and playing everything you tell them to - there is someone else who rents the studio, sets up the recording, edits the samples, makes the sampler patches, and markets the product.
Obviously, the individual would be compensated either a flat fee for the project or be paid an hourly rate. However, would they be offered royalties out of product sales as well? If so, how much? For the purposes of this hypothetical, assume the musician is the sole performer for the library (eg. you are releasing a guitar-only library, and all samples were played by this one person.)
Additionally, on a slightly related note, would you typically pay any royalties to an engineer at the studio you are recording the library? eg. They select and place the mics, correct any phase problems, manage the recording process, set up and take everything down, and so forth.
Thanks in advance!