The extended composition’s best known version is 75 minutes long and features harmonizing by Tom Waits.

In the early 1970s, the British minimalist composer Gavin Bryars had begun establishing himself as a solo artist. His primary instrument was the double bass and before turning to composition he’d played in a trio called Joseph Holbrook with brilliant guitarist Derek Bailey and renowned percussionist Tony Oxley. 

He’d also formed his own orchestra with some peers. Called the Portsmouth Symfonia, anyone could join it regardless of musical skills or training. Those who could play were required to pick up an instruments unfamiliar to them. Among the early symphony members was Brian Eno, who ended up releasing some of Bryars’ most important early work on Eno’s Obscure Records.

In 1975, Obscure Records issued one of the most beguiling minimalist masterworks of the 1970s: Jesus Blood Never Failed Me Yet. Bryars, who is now 79, described the work’s foundations in the liner notes:

In 1971, when I lived in London, I was working with a friend, Alan Power, on a film about people living rough in the area around Elephant and Castle and Waterloo Station. In the course of being filmed, some people broke into drunken song – sometimes bits of opera, sometimes sentimental ballads – and one, who in fact did not drink, sang a religious song “Jesus’ Blood Never Failed Me Yet.” This was not ultimately used in the film and I was given all the unused sections of tape, including this one.

When I played it at home, I found that his singing was in tune with my piano, and I improvised a simple accompaniment. I noticed, too, that the first section of the song — 13 bars in length – formed an effective loop which repeated in a slightly unpredictable way. I took the tape loop to Leicester, where I was working in the Fine Art Department, and copied the loop onto a continuous reel of tape, thinking about perhaps adding an orchestrated accompaniment to this. The door of the recording room opened on to one of the large painting studios and I left the tape copying, with the door open, while I went to have a cup of coffee. When I came back I found the normally lively room unnaturally subdued. People were moving about much more slowly than usual and a few were sitting alone, quietly weeping.

I was puzzled until I realised that the tape was still playing and that they had been overcome by the old man’s singing. This convinced me of the emotional power of the music and of the possibilities offered by adding a simple, though gradually evolving, orchestral accompaniment that respected the tramp’s nobility and simple faith. Although he died before he could hear what I had done with his singing, the piece remains as an eloquent, but understated testimony to his spirit and optimism.

Since that 1975 release, Bryars has adapted it a few times. Most famously, Bryars revised and extended the piece for Philip Glass’s Point Music in 1993. In doing so, he also added a second singer, Tom Waits, who harmonizes and improvises alongside the original loop.

Jesus’ Blood Never Failed Me Yet is an essential listen: Played loud with focused attention, you can hear Bryars gradually, gracefully move from pure silence to a slow fade-in of the vocal loop and very gradually add orchestration. As the arrangement grows and evolves, the voice at the middle of the swirl remains steadfast – not that he has any choice, as it’s a repeated loop – in his devotion. 

But it’s an equally moving and sublime listen as background ambient music. As you’re piddling around the house or working on a project, the music seems to fade in and out as your attention waxes and wanes. 

The bad news: The composition has never been issued on vinyl. The good news: You can buy a fantastic sounding CD version of it for $3 right now in Discogs.