There is a song on Van Morrison’s 1991 album Hymns to the Silence called Why Must I Always Explain? in which the Northern Irish singer-songwriter appears to rail against the endlessly tiresome process of giving interviews. “And I never turned out to be the person that you wanted me to be,” he sings. “And I tell you who I am, time and time and time again / Tell me why must I always explain?”

The song is in my mind when I meet Morrison on a midweek morning in Cardiff. The singer sits by the window in a fourth-floor hotel room; a pale white knuckle of a man in a blue patterned shirt, his hair a sweep of bracken red. Beyond him, the view over the bay has been obscured by heavy autumn mist.

In an unorthodox move, two members of his management team remain in the room, sitting awkwardly on the bed and making occasional interjections. It is a peculiar setting for a conversation. “Let’s see if I need to make some notes here,” Morrison says, picking up the pad and pencil that lie on the table between us. And so I sit, trapped between the mist and the managers. Before me, my favourite songwriter in the world, a man I have wanted to interview for two decades, holding a notepad. A sour air settles over the room.

We are here to discuss his new album, Three Chords and the Truth. It is the sixth record Morrison, 74, has released in just over three years, and his best since 1997’s The Healing Game. While its five predecessors were largely interpretations of others’ songs – the work of Cole Porter, Sister Rosetta Tharpe, Titus Turner and others mingling with his own compositions – the new album is all his own. It includes March Winds in February – a sublime example of Morrison songwriting – plus a duet with the Righteous Brothers’ Bill Medley and contributions from Jay Berliner, the guitarist who appeared on 1968’s beloved Astral Weeks.

It would apparently be wrong to read too much into Berliner’s return, or to delve too deeply into Morrison’s affection for his playing. “Well, he’s just a genius. You know?” he says. “I mean what else, what other reason?” But where and how does that genius show itself? Where does it hit him? Morrison stares at me. “It’s just what he does,” he says bluntly.

He is a touch more forthcoming about Medley. “I’d been listening to one of his albums, last year sometime,” he recalls. “It was a solo album [Bill Medley 100%] after he left the Righteous Brothers.” Morrison was recording in Las Vegas when he heard Medley was performing there and sought him out. “I went to see his show and talked to him and then when I was doing the track I just got him on,” he says. He has nothing specific to add about the joys of Medley’s voice itself. “I’ve just always liked him as a singer,” he says. “I like singers.”

His own voice is an extraordinary thing – one minute it is hard rain on granite, the next it is possessed by soulful, gut-stirring beauty. Over the course of his career, he has often set it against other voices; in 1966, leading the garage band Them, he closed a residency at the Whiskey A-Go-Go in Los Angeles duetting his own song Gloria with the lead singer of the support act, Jim Morrison of the Doors. In more recent times he has recorded with Cliff Richard, Gregory Porter and John Lee Hooker, and released an album, Duets, in which he revisited some of his own songs in the company of others – Georgie Fame, Mavis Staples and his daughter Shana among them. Soon, he tells me, he will be collaborating with the jazz singer Kurt Elling.

Van Morrison circa 1970. Photograph: Michael Ochs Archives/Michael Ochs Archives/Getty Images

What does he seek in a duet partner? “Well, it’s not just how it fits, it’s how it feels,” he replies. “What is it that you like about it – I can’t explain it.” He says this last sentence quickly, crossly. “See, I don’t need to explain what I do or how I do it, I don’t need to. Other people might do, but I don’t. To me, it’s OK if it’s a mystery.”

Would he, in fact, rather it remained a mystery? “No, I’m just saying it’s OK if it is. I don’t need to probe what I do. You know?” His voice is flinty. “It comes naturally. It is what it is, as they say. There’s not a lot of intellectual pondering about what I’m doing, it’s very kind of instinctive and intuitive, and that’s it.”

This would be quite reasonable were Morrison not such a questing writer, his songs an inquiry into spirituality, language, love. His lyrics have frequently referenced other artists, from Huddie Ledbetter to Edith Piaf via Hank Williams, and poets such as John Donne, William Blake and WB Yeats; the track Summertime in England is in part a discourse on TS Eliot, Wordsworth, Coleridge and how “James Joyce wrote streams of consciousness books”. Does he himself intellectually ponder other artists or writers? Morrison contemplates the idea for a moment. “Uhhhh, maybe,” he says. Might he care to name them? “No.”

I have the feeling that Morrison is curling up into a ball before me and closing his eyes so that I might not see him. His answers take on a hulking and impenetrable flatness, with a determined absence of detail. Yet the glory of his music has always lain in its details: in the “clicking-clacking of the high-heeled shoe” in Madame George, the yarragh in “whiskey” and “water” in Linden Arden Stole the Highlights, in his tendency to repetition, his ability to dismantle a single word. He is an intensely sensuous songwriter and singer, his voice finding new crevices, sweetness and joy in language.

I don’t need to explain what I do or how I do it. Other people might do, but I don’t. To me, it’s OK if it’s a mystery Van Morrison

Still, this morning he grows ever more hunkered. He tells me he prefers to listen to jazz or classical music, but, asked why he favours those genres, responds with a shirty: “Cos that’s what I like.” Has he been excited by any of the players on the new jazz scene? “No,” he says. “I don’t know who they are. If you gave me a list I could probably read [some names] off, but I don’t have it at the click of a switch.” He looks at me with a kind of irritable expectancy. “You’d need to give me a list,” he repeats. Moses Boyd, I begin. “Who?” Morrison says. “Never heard of him.” He’s a drummer. “Does he sing?” No. “Well, I only listen to mainly singers.”

As a singer, Morrison tells me, he is “just trying things” and his recent run of blues, jazz and standards records took him into unfamiliar territory. “If it’s not familiar then you have to stretch,” he says. And how does that stretch feel? “Well, you stretch at different points depending on the song, different points in the song, what the chords are, what the arrangements are,” he says. “There’s no set answer to that question. Because if I don’t know it, it could change in take two.”

Certainly it could change live; many of Morrison’s songs have taken on new life and shape over years of performance. We discuss how his biggest hit, 1967’s Brown Eyed Girl, has evolved into a “a calypso jazz arrangement now” and Moondance has become “more like a feature for the band”. The previous evening in Bournemouth, Morrison and his band had tried out a couple of the new songs – the album’s title track and the rock’n’roll number Early Days.

“Cos those are the ones the band learned,” he says, when asked why he chose to unveil those two. “I don’t know, is this a psychiatric examination?” It is not. “It sounds like one,” he says. “The band learned those two songs, so those are the ones they knew. There’s not really any great intellectual Bernard Levin debate, you know. It’s just, it’s just … it’s just music, that’s all it is.”

I do not for one moment believe him. I’m not really sure there is “just music” for anyone, least of all Morrison. He is under no obligation to share any of that with journalists, of course – his music undoubtedly speaks for itself. But I’m sure there is a kinder and more graceful way of declining. “You’re making a big thing about it and it’s not a big deal,” he continues. “It’s what I do. I don’t know what you do, you’re probably a journalist, that’s what you do.” This is not about me, I tell him. “Well, what are ya? Are you a journalist, what are ya?” He looks at me with a kind of disdain. I dutifully reel off the various components of my career. “OK, well, I do music,” he says. “I sing and I write songs and I do gigs. So to me that’s not interesting. You’re trying to make it very, very interesting and something it’s not. Playing gigs is very practical. It’s very repetitive. And it’s no big deal. I’ve been doing it all my life.”

Playing in The Last Waltz with the Band, with guests Dr John, Neil Diamond, Joni Mitchell, Neil Young and Bob Dylan. Photograph: Sportsphoto Ltd/Allstar

For a moment I consider telling him to grow up. But I am chastened by the presence of his managers. Instead I look him in the eye and tell him that I am not trying to psychoanalyse him, that his music has simply meant more to me than any other throughout my life. There is something that moves across his face but I could not name it. “Aehhh,” he breathes.

“Well, shall we end it there?” I say, and stand and shake his hand. As I do I look at the notepad. In the top left hand corner he has drawn an angry rectangle.

Morrison’s work has always in part been about words failing, about inarticulacy and the gulf between the emotion and the tongue. Many of his songs seem to sit at the precise point where language falls apart. The track that closed his 1979 album, Into the Music, was You Know What They’re Writing About – a sublime six-minute rumination on love, creativity, electricity, devotion, desire and the sheer weltering force that carries us forward. It is perhaps my favourite of all his songs. Two minutes in comes one of his most extraordinary lines: “When there’s no more words left to say about love I go …” and then he unleashes a sound that is guttural and rousing and raw, and that we might transcribe something like so: “neeeeeeheeeheeeaaaghhhhheheh.” It is a sound that says more about his music, his life, his psychology than he did in the entire 16 minutes and 28 seconds I spent in his company; a sound he does not have to explain.

Three Chords and the Truth is out now on Exile.