Two of the great pioneering geniuses of jazz are united on this epochal record, created from sessions cut in April 1961 when Duke Ellington sat in as pianist with Louis Armstrong’s All-Stars, a touring band which Louis took with him all over the world.

I was discussing a lifelong love of jazz with Pedro, a Chilean friend, a comrade who had been a militant during the Popular Unity years and later a socialist prisoner in Pinochet’s prisons who had managed to find refuge in Britain with the support of Sheffield trade unionists in the mid ’70s.

Yes, he said, he had heard of Armstrong and his All-Stars in his home city of Valparaiso as a boy, and the vibrancy of his sound had never left him.

That’s what Louis did to his listeners, inspired them for life, all over the world.

On these “summit” sessions the common factor for both musical giants is the New Orleans clarinet virtuoso Leon “Barney” Bigard, a staunch member of early post-war versions of the often-changing All-Stars, while also a veteran of Ellington’s greatest orchestral line-ups between 1927 and 1942.

Bigard’s curlicuing, rococo clarinet licks were an essential part of many classic Ellington recordings. From Mood Indigo to Creole Love Call and Harlem Air Shaft, his waving reedsong was one of the Duke’s great sound posts.

All the tracks are classic Ellington tunes, start from a vibrant rendition of Duke’s Place with the quasi-stride Ellington piano, Bigard’s birdsong clarinet and the rumbling notes of the wonder trombonist from Savannah, Georgia, Trummy Young.

Louis’s regular rhythm men, bassist Mort Herbert and drummer Danny Barcelona, keep the beat succulent and on I’m Just a Lucky So-and-So the lyrics are absolutely born for the soulful and eternally optimistic Armstrong treatment.

Ellington is completely at ease, having at last found an equal jazz brother.

He zooms into Cottontail: Bigard catches his old maestro up with his serpentine phrases and Louis digs into his notes in no fear at all of being left behind.

Trummy growls a chorus and Louis joyfully scats his way towards the end. Bigard, who blew on the original 1930 recorded version of Mood Indigo, now hears Armstrong etch out its chorus before he enters, low and beautiful, prefacing the improvised Louis vocal while Duke noodles on his keys.

It is the height of jazz insouciance, and these incomparable elders love it.

It seems strange to hear Black and Tan Fantasy, its muted and wailing 1927 trumpet solo a Bubber Miley creation, played with Armstrong’s mighty and crystalline notes, but it works powerfully and the Duke’s piano seems well in the mood too as a muted Trummy comes growling in and Bigard’s clarinet seeks the skies.

It’s followed by Louis’s amble through Drop Me Off In Harlem, the home of black genius as well as “red beans and rice,” its savour pouring out of the horns of Bigard and Young.

Ellington’s familiar prelude to The Mooche introduces Bigard transcendent solo and Young’s gruff slides above Herbert’s jumping bass.

Louis comes striding in, his notes like bugle calls of peace and Ellington chivvies up his keys in a summative ending.

In a Mellow Tone follows with the Duke in fine fettle and Trummy in mellifluous form: all a prelude to the undeniable Ellington dictat voiced by Louis, It Don’t Mean a Thing if it Ain’t Got That Swing, and all six of them prove it, with the Armstrong horn as lucid as ice.

Solitude could have been written for Louis, so sharp and impassioned is its tone, and there is a defiance too in the two giants’ version of the 1941 song from Duke’s musical revue Jump for Joy, its title to become an anti-depression rallying cry: I Got It Bad and That Ain’t Good.

Louis plays its theme plain and truculent like the slogan for betterment that it was, then sings and scats its love-worn lyrics like a man somewhere near the end of his tether as Duke thumps his own tune all along the keyboard.

As Louis exclaims his satisfaction at the very end of the track over Ellington’s shoulder, you can sense his happiness that this summit meeting ever happened.

But it did and we can listen and wonder just like Pedro did, marvelling at Armstrong in Valparaiso, Chile, some five decades ago.

Louis Armstrong and Duke Ellington

The Great Summit

(Essential Jazz Classics, EJC 55536)