A stereo mix is the finished two-channel balance and is the correct input for Bounce Sessions (staging) automatic mastering. Stems are grouped parts such as drums, vocals, and instruments. They allow deeper intervention, require more decisions, and belong in a personal mastering or mix-revision conversation.
What filename should you use?
Use artist, title, and an unambiguous version such as “Artist - Song - Mix 04.wav”, with plain hyphens. Avoid calling a file “final” until it has passed the quality check. The audio itself matters; the clear label protects the handoff.
Before upload
Confirm that this is the same mix everyone approved. Format settings cannot repair a version mistake.