And while the Fab Four — John, Paul, George and Ringo — and their long-time producer and father-figure George Martin are largely credited with its freewheeling experimentation and astonishingly broad palette of styles and sounds, there was another key figure who was charged with transforming their wild thoughts into sonic reality.

Sound engineer Geoff Emerick was Martin’s right hand man at the famous Abbey Road studios in London and was instrumental in creating the sounds that would define Sgt. Pepper’sas arguably the most important album in the rock music canon.

He knew from the very beginning that he was going to have his work cut out for him.

“John just said that for the next album they were just going to concentrate on sounds and make different sounding songs because they were never, ever going to perform again,” Emerick recalls half a century later.

“And George Martin was open-mouthed because every band performed and John said they were going to create stuff on these records that no one has ever heard before. And then everyone looked at me.”

Emerick was just 20 years old when he worked on The Beatles’ 1967 masterpiece, for which he would later win a Grammy.

RELATED: Oscar-winning director Ron Howard reveals why The Beatles still matter

He’d joined the record label EMI when he was 15, around the same time as the four largely unknown lads from Liverpool had come in to cut the early singles that would set them on the path to being the biggest band in history.

Emerick worked his way through the strict Abbey Road hierarchy quickly and thanks to his inventive approach, work ethic and relationship with Martin was appointed chief engineer for The Beatles previous album, Revolver.

His rapid rise and willingness to push the boundaries of what was considered acceptable at the time — radical microphone placements, stuffing drums with sweaters, pushing equipment to its limits — put plenty of noses of joint within the company, but it was exactly what Martin knew The Beatles would need for their ever more ambitious projects.

“George and I had the same sense of humour so we could observe a situation and look at each other and there would be a wry sort of smile,” Emerick says.

“Later on when we were working together and he was producing and I was engineering, people would say ‘you and George don’t say much do you’. And we didn’t have to — he could read my mind and I could read his mind. It was an odd connection really.”

The first track Emerick worked on for The Beatles was a baptism of fire. Tomorrow Never Knows, the final track from Revolver was the most ambitious song they had attempted to that time and Lennon’s brief was that he “wanted his voice to sound like the Dalai Lama singing on a mountaintop 25 miles away from the studio”.

RELATED: Melbourne went berserk when The Beatles came to town

Nevertheless it gave Emerick a good insight into how the band worked. None of them were especially technically minded or interested in being hands on in the studio, but had a very clear idea of the sounds they wanted.

“They would say things like ‘I know I want to use piano — but I don’t want it to sound like a piano. I want to use this guitar but I don’t want it to sound like a guitar’,” Emerick says. “That was normally the direction — do what you like with it. No one else was recording the way we were then — we were experimenting and trying different ways of recording. Very close mic-ing with condenser mics to keep these colours and tonalities.”

Nevertheless, the band took things to an entirely new level on Sgt. Pepper’s, from the trippy meanderings of Strawberry Fields Forever(which ended up being released as a single and not included on the album), to the circus swirl of Being For the Benefit Of Mr Kiteand of course the epic A Day In the Life, the climax of which Martin later described as “an orchestral orgasm”.

Emerick was instrumental in all of them.

For Strawberry Fieldshe was responsible for seamlessly editing together two takes recorded weeks apart at different speeds and in different keys.

To fulfil John’s instruction on Mr Kiteof wanting to “smell the saw dust on the floor”, he cut recordings of a fairground organ in to small sections of tape, threw them up in the air and reassembled them at random.

But it’s assembling the complex sections of album closer A Day In the Lifehe remembers particularly vividly.

Emerick says the sessions had hit a bit of a lull as the band battled to reach their goal of making each track better than the last, but it turned out to be “the most amazing experience ever”.

The track began with just an acoustic and vocal from John, with 24-bar gaps where Paul’s contribution and the orchestra would later be added.

The band booked 41 classical musicians (Paul’s request for 90 was turned down), who were then presented with just two notes — a start note and finish note — and were instructed to go from one to the other however they chose within the allotted time to create a discordant cacophony.

The classically trained musicians were sceptical, not helped by the fact they had been asked to dress in full evening wear and then were given gag items like fake noses, funny hats and plastic glasses to wear.

“They said ‘we can’t do this’. And George Martin said ‘what do you mean you can’t do it?’. And they said ‘we have to have all the notes written’. And the instruction was to go from the first note to the last note over 24 bars in their own time without listening to the person sitting next to them otherwise they might develop a rhythm,” says Emerick.

“But it took 20 minutes to try to explain that to them. Then Paul spent another 10 minutes trying to explain. Luckily in that orchestra was David Mason, who played the trumpet on Penny Lane and the guy who did the French horn on For No One(Alan Civil) and they were the lead figures of the classical orchestra in London and they said to the rest of the musicians ‘come on lads, we can get this together’. And they started to do it.”

Emerick continued to work with The Beatles on the White Album— but left midway through the recordings.

“They were not very nice people to be with,” he says. “There was a certain anger there. I’d worked on about 11 or 12 of the songs and saw it all gradually falling apart.”

He was coaxed back for their triumphant swan song, Abbey Road, and 50 years on, still thinks we’ll never see the likes of The Beatles again.

“If we do it will be in another 200 years’ time,” he says. “Their music is like Mozart — he was the rebel of his day and his music was pop music. I know now when you see orchestras or other bands — not necessarily silly Beatle cover bands dressed like Beatles with little Beatle wigs on — but good musicians and singers, it’s like a new performance of their music.”