The cause was complications after pneumonia and a series of mini- strokes, Alyn Shipton, Mr. Carr’s biographer, said in an e-mail message. An obituary on the Web site iancarrsnucleus.net — dedicated to the music of Mr. Carr and the band, Nucleus, which he founded nearly 40 years ago — said that Mr. Carr had Alzheimer’s disease.
As a writer and researcher, composer and bandleader, Mr. Carr contributed to jazz history both by making music and by explaining it. He started Nucleus in late 1969, a time when jazz musicians were just beginning to find ways of appropriating the tools of rock ’n’ roll. Nucleus mingled traditional jazz instruments (like trumpet, soprano and tenor sax) with rock band staples (like electric bass and electric guitar) and melded improvisations with a driving, creative bass line and urgent, forward-leaning rhythms. It was a hit at the 1970 Montreux Jazz Festival and the Newport Jazz Festival that year as well.
The band, which had several different rosters, dissolved in the 1980s, though there were several reunions for concert dates and recordings into the 21st century. Its sound was clearly related to that of the rock-infused records Davis was producing as the 1960s turned to the 1970s — “In a Silent Way,” “Bitches Brew” and “A Tribute to Jack Johnson” — and Nucleus pre-dated several better-known bands that became mainstays of jazz-rock fusion, including Weather Report and the Mahavishnu Orchestra.
In its heyday in the 1970s, Nucleus recorded a dozen or so albums, including “Belladonna,” “Alleycat” and “Out of the Long Dark,” the last reflecting Mr. Carr’s battle with depression. (Mr. Shipton appropriated the title for his 2006 biography.)
Mr. Carr wrote for several jazz publications, and his first book, “Music Outside: Contemporary Jazz in Britain,” was published in 1973, but his 1982 book, “Miles Davis: A Critical Biography,” was the high point of his writing life. An evenhanded assessment of Davis’s life and music, it distinguished itself by its careful analysis of Davis’s playing and his innovations. Writing about the book in The New York Times Book Review, Bill Zavatsky lauded the clarity of Mr. Carr’s writing and his ability to explain musical technique to the lay reader. (The book was expanded and revised in the 1990s and republished as “Miles Davis: The Definitive Biography.”)
“He has come as close as any writer can,” Mr. Zavatsky wrote, “to upsetting Davis’s famous dictum that music can’t be talked about and should be left to speak for itself.”
