CC BY 4.0 says about applying DRM (or other "Effective Technological Measures"):
No downstream restrictions. You may not […] apply any Effective Technological Measures to […] the Licensed Material if doing so restricts exercise of the Licensed Rights by any recipient of the Licensed Material.
I wonder when exactly the "exercise of the Licensed Rights" is restricted in case of CC BY.
Let’s say Alice creates a song and uses a sound effect that is licensed under CC BY 4.0. She sells this song, so she has to give attribution for the sound effect. She does not offer the sound effect in a "separate" form (i.e., she offers no download of the sound effect only).
May Alice apply DRM to the song as long as the attribution for the sound effect can be accessed ("DRM-free") by the recipients? Or have the recipients the "Licensed Right" to access ("DRM-free") the song because it contains CC-BY-licensed material?
Does the answer change if Alice modifies the sound effect (i.e., Alice creates "Adapted Material")? In the first case one could argue that recipients could extract the CC-BY-licensed sound effect from the song, but in the second case the original sound effect is no longer part of the song (i.e., recipients are not allowed to use the modified sound effect under CC BY 4.0).