In November 1966, John Lennon walked up to George Martin and strummed the opening chords to a new song. Martin listened closely as Lennon sang what he remembers as "a starry, echoing line" - and the very first airing of Strawberry Fields Forever. Recognising immediately that Lennon had arrived in unchartered territory, Martin asked him how he wanted to record it. The Beatle laughed, reminding him that this was surely the producer's problem, not his.
Such delightful challenges came regularly for George Martin. Having personally signed The Beatles in 1962, he was to produce all the group's recordings right up to Abbey Road in 1970 - a CV which makes him the most successful producer in pop music history. In his other role as Beatles arranger he has been responsible for the most famous recorded sounds in pop - that orchestral element which set The Beatles so far apart from the rest.
While Sir George will politely resist being called the Fifth Beatle, his impact on what they did is certainly quite incalculable. It might be slightly daft to suggest that, without him, The Fab Four would have sounded like Oasis, but it's worth thinking about even so.
"Well, the producer is the person who shapes the sound. If you a have a talent to work with - a singer together with a song - the producer's job is to say, right, you need to put a frame around this, it needs a rhythm section to do this or that and so on. He actually decides what the thing should sound like, and then shapes it in the studio. He may also be an arranger - in which case he may write the necessary parts. There may be a triangle, a Welsh choir, a symphony orchestra or whatever, and he shapes the whole lot. It's like being the director of a firm. He decides what goes and what stays. And it's much easier to tell somebody to do something than to do it yourself - that's why I became a producer."
Martin first met The Beatles in his capacity as record company executive. From the mid-1950s he had been head of Parlophone and had recorded everybody from Humphrey Lyttelton to Shirley Bassey to Jimmy Shand. His particular love was comedy and he worked on albums by Peter Sellers, Spike Milligan and Bernard Cribbins - all of it remarkably relevant to what would develop later with the Beatles.
As the 1960s began, Martin hit an extraordinary run of success with Gerry and the Pacemakers, Billy J. Kramer and Cilla Black. In 1963 he held the number one slot for 37 weeks with his records, as he puts it, "leapfrogging each other." But, despite the successes of others in his care, it was to be John, Paul, George and Pete/Ringo who were to get his full attention.
"You see when I first met them, their music wasn't what appealed to me - it was their characters. It was only really when they started writing really good hit songs in 1963 that I knew we had struck a goldmine. Yes, I knew they would be good and I knew they would be successful, but I never thought that I'd be talking about them 40 years later. You couldn't have foreseen that. I thought I'd have them for a good five years. No more than that."
Martin's achievement was to encourage and realise the musical ideas of Lennon and Mc Cartney. And essential to this was his grounding in classical music - something clearly lacking in John and Paul. He had long recognised the possibilities of bringing classical and pop closer together and, while everyone acknowledged the huge potential in sharing their respective talents, there were times when the rock'n'rollers got a little tired of their producer's musical ambition. The Chuck Berry fan in particular didn't always relish "fancy stuff".
"Yes, John used to get a bit fed up with my talking about classical music. He said to me `Look, I'm a rocker!' When we did Abbey Road he didn't want to have what became `the long side.' He wanted a series of rock'n'roll songs. And, so that's why we compromised on Abbey Road and did what we did - one side of singles and the other side completely different. But John did contribute to that long side and he could see the merit in it. But he rarely listened to symphonic works. Paul would have listened much more."
George Martin has an extremely high regard for pop. And contrary to the way it has been portrayed on occasion, he always was a pop fan. In fact, his understanding of the nature of pop music was, at the time, probably far more acute than that of his mop-top charges.
While Lennon and McCartney looked to Chuck Berry, Little Richard and Smokey Robinson, Martin went even further back to the great bands of the swing era - and, indeed, anywhere where he might locate a melody.
"Pop music has always been part of my life - and jazz come to that. When I was a kid, I used to run a dance band and so I used to listen to all the latest records from America - Woody Herman, Benny Goodman and those kind of people - and I loved them. So, I would buy all the latest pop songs and, of course, what we called pop songs in those days, are now what we call classics. I was kind of weaned on that stuff, but it went hand in hand with classical music.
"And I think there is a crossover point. In fact, I think if Mozart were alive today he would be writing pop songs."
The post-Beatles period might well have been a desolate one, but for Sir George it was a time of deep relief - he was, as he puts it, "no longer responsible." He had his studios in London and Monserrat, he ran his own publishing company, he composed, he produced now and again and he presumably took some pleasure his quite spectacular achievement.
The Beatles rollercoaster can't have been easy for anyone - but the relieved producer and arranger had endured it all with very impressive grace.
Now 73, Sir George Martin remarks that "growing old is a pain in the arse and not to be recommended" - referring in particular to the fact that he cannot hear as well as he did. In fact, he says quite openly that he's not as good as he used to be, and quotes Larry Adler's line about playing Cinderella tennis - "that's where you don't quite get to the ball - and it's the same with music."
His feelings about music, however, are as intense as ever. "It's such a primeval thing - it's right within the human soul. The animal man has been making music for a least 80,000 years and we know that for sure because of discoveries of fragments of little flutes and so on.
"Actually I think man sang before he talked. It's such an essential part of our lives. I don't know what I would have done without music - even if I hadn't made a career out of it. I can't imagine a world without music."
Sir George Martin and his 70-piece orchestra play the National Concert Hall tomorrow, Monday and Tuesday