Which female vocal trio is featured on MFSB's "TSOP"?

The female vocal trio featured on MFSB’s “TSOP (The Sound of Philadelphia)” was The Three Degrees.

Although “TSOP” is primarily an instrumental recording, The Three Degrees sing brief vocal passages, including “People all over the world” and “Let’s get it on, it’s time to get down.” Their appearance is why the record is commonly credited as MFSB featuring The Three Degrees rather than simply MFSB.

MFSB was Philadelphia International Records’ house collective of studio musicians, based around Sigma Sound Studios. Kenneth Gamble and Leon Huff created the track as the theme for Soul Train, and the 1974 single became a landmark of the Philadelphia soul sound’s transition into disco. Its orchestral strings, horns and rhythm section gave the recording a large, polished ensemble character.

A common mistake is to treat The Three Degrees as the main instrumental act. They supplied the featured vocals, while MFSB performed the backing track. The Three Degrees were also successful in their own right, with songs such as “When Will I See You Again,” but they are specifically the trio attached to this MFSB recording.