Time was not kind to Ray Charles, but for decades he seemed impervious to its machinations. His best years had come in the mid-'50s and the '60s, when he virtually invented soul and then refused to be boxed in by any single genre of music. His voice, his style, his vision -- all were singular, but over the last 35 years of his extraordinary career, the brilliant was too often overwhelmed by the mundane. Charles's albums, and his performances, became rote, peppered with bright moments but sadly routinized.

Aside from 1989's "I'll Be Good to You," a duet with Chaka Khan from an all-star album by lifelong pal Quincy Jones, Charles hadn't visited the Top 20 since 1967. Yet he remained a powerful concert draw, continuing to perform as long as he could. In May 2003 in Los Angeles, Charles gave his 10,000th concert, but a month later, illness forced him to cancel a tour for the first time in 53 years. He died about a year later, on June 10, at the age of 73.

Now the Concord label has released Charles's final studio album, "Genius Loves Company," featuring a dozen duets recorded over a period of a year and completed in March. The Genius's singing partners include old friends and musical peers (B.B. King, Willie Nelson) as well as admirers (Elton John, James Taylor, Bonnie Raitt, Norah Jones). Some encounters sparkle; too many don't. And, sadly, Charles's inexorably waning condition is often apparent: The emotional power of his voice seems muted; he has a hard time hitting high notes or sustaining long phrases. He plays piano on just three tunes.

There are times when Charles's magnificent instrument is reduced to a whisper, anticipating the silence to come. But there are also reminders of his indomitable spirit, including the opening encounter with Norah Jones on "Here We Go Again," which Charles first recorded on the 1967 album "Ray Charles Invites You to Listen." Jones, who grew up listening to Charles's records, proves an empathetic foil, her warm, lazy vocals meshing convivially with his over a spare but funky arrangement featuring smoky Hammond B3 work by Billy Preston, at one time the organist in Charles's band. The album features several other dips into the Ray Charles catalogue, not all of them as rewarding. One of his best known songs, "You Don't Know Me," the Eddy Arnold hit Charles reinvented on 1962's classic "Modern Sounds in Country and Western Music," is appropriately weary but falls strangely flat when shared with Diana Krall, who seems overwhelmed by the company. And "Heaven Help Us All," a gospel-flavored song first popularized by Stevie Wonder, is revisited with Gladys Knight more than 30 years after she and Brother Ray first recorded it on his album "A Message From the People." It simply feels like a too-often-heard sermon.

On the other hand, "Do I Ever Cross Your Mind?," from Charles's 1984 country collection of the same name, gets a wonderfully bluesy makeover with Bonnie Raitt. Transforming the song from plaintive monologue to reflective dialogue deepens it, and the singers' voices mesh wonderfully, with Raitt adding taut slide guitar accents to the conversation.

Even better is "Sinner's Prayer," the Lowell Fulson blues standard that Charles first addressed in 1954. Almost 50 years later, he revisited it with his pals, the venerable bluesman B.B. King and Preston. This was one of the first studio sessions for "Genius Loves Company," from July 2003, and Charles still displays plenty of energy. Willie Nelson, another septuagenarian legend, is aboard for "It Was a Very Good Year," the haunting meditation about yearning for a simpler past. What could have been eloquent testimony is ruined by Victor Vannacore's turgid orchestration, though there is obvious poignancy in hearing a very weak Charles proclaim, "The days are short, I'm in the autumn of my years."

Similar emotions attend "Somewhere Over the Rainbow," on which Johnny Mathis joins a weary Charles. Mathis is another peer -- his first album came out in 1956! -- but his smooth, sophisticated vocals seem untouched by time, and it's he who must carry the last song Ray Charles ever recorded. Disappointments include the slight "Sweet Potato Pie," with its writer, James Taylor; the Carole King-Gerry Goffin chestnut "Hey Girl," featuring Michael McDonald; and "Sorry Seems to Be the Hardest Word," with co-author Elton John. John sounds stentorian, and lugubrious orchestration overwhelms the song.

When Concord signed Charles in 2002, it obviously envisioned the duet concept as a way to regenerate interest in his recording career, as had been done with the likes of Frank Sinatra, George Jones and Carlos Santana.

Despite the label's suggestion, "Genius Loves Company" is not Charles's first all-duets album: 1984's "Friendship" was a No. 1 country album that matched Charles with Johnny Cash, George Jones and Willie Nelson. And 1961's "Ray Charles and Betty Carter" remains a classic encounter. In the end, "Genius Loves Company" is a well-intentioned effort whose best moments recall but sadly cannot match the towering legacy that Ray Charles left behind in numerous reissues and compilations.

Ray Charles performing last year in Nashville. On his final studio album, a weary genius.