Sample clearance is the process of obtaining permission to reuse part of an existing recording. A sample usually contains two protected works, so clearance normally means two licences: one from the owner of the master recording, typically a label, and one from the owners of the composition, typically publishers.
How strict the law is depends on where it applies. In the US, the Sixth Circuit’s 2005 Bridgeport decision held that copying any part of a sound recording without a licence infringes, while the Ninth Circuit in 2016 accepted that a tiny, unrecognisable sample can be de minimis, leaving the courts split. In the EU, the Court of Justice ruled in Pelham in 2019 that a phonogram producer can object to even a very short sample, unless it is used in a form modified so as to be unrecognisable to the ear.
For lo-fi producers who build tracks from old jazz records, the safer routes are cleared samples, licensed sample packs or replaying the part, which avoids the master licence but may still need permission for the composition. Specific clearances are best handled with a music lawyer or clearance specialist.