WIKIPEDIA:

“ MFSB (Mother Father Sister Brother) was a pool of more than thirty studio musicians based at Philadelphia’s famed Sigma Sound Studios. They worked closely with the production team of Gamble and Huff and producer/arranger Thom Bell, and backed up such groups as Harold Melvin & the Blue Notes, the O’Jays, the Stylistics, the Spinners, Wilson Pickett, and Billy Paul.
In 1972, MFSB began recording as a named act for the Philadelphia International label. "TSOP (The Sound of Philadelphia)" also known as the Soul Train theme was their first and most successful single. Released in March 1974, it peaked at #1 on the Billboard pop and R&B charts. "TSOP" was influential in establishing the disco sound. The track sold over one million copies, and was awarded a gold disc by the R.I.A.A. in April 1974.

Overview
Assembled by record producers Kenneth Gamble and Leon Huff, MFSB was the house band for their Philadelphia International Records label and originated the signature smooth "Philly sound" sound that dominated the early 1970s for the artists who recorded at the Sigma Sound Studios, including the O'Jays, the Spinners, the Bluenotes, The Delfonics, Blue Magic, The Intruders, Three Degrees, Jerry Butler, and Teddy Pendergrass. Later [......] ”

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