When it first came, with mournful insistence, into a world deafened by amplified guitars and a thunderous beat, the pop pundits couldn't believe their ears.
'It will never sell,' they said. 'The kids don't want dreary stuff like that.' But for once they were wrong.
The pop scene at the end of 1966 was aching for something new – and it found it. The new sound was slow and haunting, based on a semi-classical series of minor chords. It was beat-era Baroque and the kids not only wanted it they loved it.
They loved the Procol Harum, too. And yet 'A Whiter Shade of Pale', the song that brought the group out of obscurity into the big league, has proved a very mixed blessing for the Procol Harum.
'It was a great thing for us. It opened all the right doors, not only in Britain but in many other countries as well,' the group's organist, Matthew Fisher, told me.
'Since then we have been kept on our toes proving wrong all the happy knockers who gleefully predicted our demise into obscurity.
'And we've been busy jetting around the world on an incredibly tight schedule. This is why our name isn't often seen in the pop magazines and musical papers.
'We are bursting with plans for the future. Perhaps we shall have some time to spare in the next few months to do something about them.'
Even today after selling over six million copies all over the world, the record is still being bought, and is still one of the most requested discs on radio record programmes.
What made it so different – and popular – was its sound – a cross between Bach and the Beatles ...
And yet now all the hysteria is over, co-writer of 'Pale' Gary Brooker told me: 'Now I think it could have been much better. It didn't really turn out as we wanted it – it could have been really fantastic.
'The sound as it turned out on the record wasn't at all what we had in mind when we went into the studio. Now when we make a record we have more idea of exactly what we want.
Just how did the Procol Harum come to find the elusive sound of success?
Gary Brooker at that time was lead singer of The Paramounts, a group who had enjoyed considerable popularity, but made no impression on the all-important charts.
'The future didn't look very good so I decided to try my hand at song writing: I knew there had to be some survivors when the slump came, and that the big groups would be looking for songs to record.'
A friend, Keith Reid, agreed to join him. Both felt the need to be completely involved in the presentation of their songs.
'We thought it might be to our advantage if Keith was not actively involved with the group, especially when the time came to go into a recording studio.
'He would help find the sound, while I took an active part in the group as pianist and lead singer,' said Gary.
'We decided we needed four other people, and together we toured many back-street cafes and some of the smaller clubs in and around London which at that time were full of young unemployed musicians waiting to be discovered.
They took their name, Procol Harum, from a rare breed of Burmese cat!
It was during the auditioning period that Keith and Gary wrote a song which they felt, given the right treatment, would be a hit.
Keith told me, 'We decided to use this song for the first record as we thought it an ideal debut disc.
'We couldn't afford to have a failure. At that time groups were usually only given one chance by the major record companies.
'We were well aware that the success of any record depends mainly on the recording producer, and we wanted Denny Cordell to find and develop our sound.
'We rehearsed the number and eventually Denny Cordell came along to give us his verdict.'
Cordell told me, 'I was impressed not only by the sound, but their enthusiasm. I thought that with a little more polish it could have commercial possibilities, and several hours later I told them I thought they were ready to make the recording.'
The instruments used were piano, organ, lead guitar, bass guitar and drums, and it was the haunting sound produced on the organ which captured the ears of disc-buyers the world over.'