Interpolation and sampling are separate concepts.
And either of them can be infringement; or not. But they get used interchangeably and confusingly. Let’s get clearer on what we mean.
First, interpolation. Merriam-Webster.com says interpolation is “the introduction or insertion of something spurious or foreign.” “Interpolation” in music generally means you take something from elsewhere, often a well known song by you or someone else, and you incorporate it into a new work. Whether it’s a reinterpretation, or a new context that bathes the original in irony, or a straight quote because it’s apropos to your track, interpolations can be a zillion things.
My favorite example is Dr Dre’s 1995 single “Keep Their Heads Ringing,” which opens with a bunch of references to “Funk You Up,” by The Sequence. “Funk You Up” was the second single from Sugar Hill Records (after Rappers Delight) and the first hit ever by a female rap group. It’s an iconic track, and he pays it homage. Give it a few seconds and listen to the verse.
And this is “Funk you up” by The Sequence.
We hear all of these lines interspersed with some of Dre accents.
“Hey, you, sitting over there
You better get up out of your chair
And work your body down
No time to funk around
Because we gonna
Funk You Right On Up…”
And where’d he get the “Ring Ding Dong?” Right here…
This is not a sample. Dre did not “sample Funk You Up.” He did not use the audio from Funk You Up; he just wrote some of Funk You Up’s material into “Keep Their Heads Ringing.” He rerecorded all the parts. It’s the song, “Funk You Up,” that’s employed, not the recording. This is an interpolation.
Same song, starting a few seconds earlier…
What’s that book-book-booyakasha thing at the beginning? It’s this KRS One track, Mad Crew.
Now that’s a sample. Dr Dre took that right off KRS One’s record.
So why did he choose to not sample the Funk You Up record? Several possible reasons, some creative, and others practical. Creatively, the sample, for better or for worse, will always sound pretty much like the sample even if you manipulate it and feather it in to fit your production. More often you let it be what it is and build upon its inherent character. You have far broader flexibility if you rerecord it; you have all the component parts; you can get whatever you want.
On the practical side, you have copyright issues. The recording is likely owned by a record company and there’s no standard statutory price for sampling from it. You have to negotiate with the rights holder. Could get pricey. The song itself, on the other hand; that’s more likely owned by the artist. That license will cost a lot less money generally. Plus, it’s capped. You don’t even have to negotiate directly with the rights holder. You can pay a statutory royalty — about a dime per copy you sell.
By the way, another term, “replayed sample,” just adds to the confusion and this term should go away. Say an artist would’ve liked to have used a sample, but couldn’t get or couldn’t afford permission from the record company that owns the recording, and so the artist “recreates,” or “re-performs” the recognizable piece of sound that is desired. Here the goal is the engineer it so that it sounds just like the record. I know people who recreate samples all the time; it’s what they do, and it’s awesome. I prefer “recreate” because to me it sounds a little more clinically correct and a little less confusing.
So when you hear a piece of something in a song that’s not just similar, but obviously taken wholesale from another well known piece, do you hear the record exactly as you remember it sounding? That’s probably a sample. Or are you hearing the same song, maybe same melody and lyrics, but not like the original record? That’s more likely an “interpolation.”