An ISWC is a unique identifier for a musical WORK, meaning the underlying composition rather than any particular recording of it.
The mechanism
The work is registered once and receives one code that persists across every recording, cover, remix and live performance of it. Collection societies use the ISWC to gather income from all of those uses and route it to the writers and publishers according to the registered splits.
A worked example
A song covered by four artists has four recordings with four ISRCs, all of which report back to a single ISWC so the original writers are paid for every version.
The work is the thing that persists. The recording is one instance of it.
What it is confused with
- ISRC ISWC is the composition. ISRC is the recording. Writers are paid through the ISWC; performers and masters are paid through the ISRC.
- Split sheet A split sheet is the private agreement about who wrote what. The ISWC is the public registration that agreement should be filed under.
Why it matters
If a work is registered more than once with conflicting splits, income can be frozen while the duplicate registrations are reconciled, and reconciliation is slow.
Sources: US Copyright Office
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Related: Recoupment · Black box royalties · 360 deal