(CNN) -- Willie Mitchell, the Memphis producer whose percussive, string-and-horn-tinged R&B sound shaped '70s hits by such artists as Al Green and Ann Peebles, died Tuesday. He was 81.
Mitchell had been having health problems and went into cardiac arrest in December, according to his grandson, Lawrence.
Mitchell "was doing music all the way till he couldn't," his grandson, whom Mitchell helped raise, said. He worked on Rod Stewart's most recent album, "Soulbook," as well as Solomon Burke's forthcoming CD.
Despite being in and out of the hospital, Mitchell would write horn and string arrangements one day and record them the next, Lawrence Mitchell said.
In the 1970s, Mitchell was a principal in Hi Records and owned Royal Studios, where musicians such as drummers Al Jackson and Howard Grimes and guitarist Teenie Hodges plied their trade.
His biggest success came with Green, whom he guided through a number of '70s hits, including "I'm Still in Love With You," "Let's Stay Together," "Love and Happiness" and "Call Me."
In 2003, he and Green re-teamed for "I Can't Stop," their first album together since 1985. Green has often talked about how important Mitchell was to his sound, working him until his voice was just so -- a difference that can be heard on his pre-Mitchell songs, such as "Back Up Train."
Mitchell also helmed Peebles' "I Can't Stand the Rain" and O.V. Wright's "The Ace of Spades." A musician himself, he had several R&B hits in the '60s.
Memphis named the street in front of Royal Studios for Mitchell in 2004.
Funeral arrangements were pending, Lawrence Mitchell said.