“I had a lot of fun with those guys. They were always up to no good, playing pranks and horsing around. Musically, they fit together very well. They were three dynamic and very different personalities. I don’t remember any tensions between them. Whatever problems they had came later in the decade, after I stopped working with them.

Keith Emerson is probably the most technically brilliant pianist in rock ‘n’ roll. I remember doing a song with him called Jeremy Bender [from Tarkus], and he wanted to get a honky tonk sound. There was a Steinway in Advision, and he triple-tracked his part. I slowed the tape down to get that slightly out-of-tune effect, and when I played everything back, it sounded like one guy playing one piano. That’s how spot-on his playing was – every note synced up.

“His organ sounds – my gosh! He’d come to the studio with three or four Leslies and all kinds of Marshall cabinets. He’d take up one entire wall with all of this stuff. It sounded incredible.

“Right around this time, Robert Moog invented the synthesizer. We had one of the first models in the studio. There was a lot of patching involved. At first, I was in charge of programming sounds for Keith. He’d be like, ‘Oh, that sounds good… Oh, I like that.’ Eventually, he perfected it himself and became a real wiz. The first synths weren’t polyphonic; you could only play one note at a time on them. So if you wanted a horn section, you could take up six or eight tracks to get it sounding big. That would be very time-consuming.

“Concepts and structured songs were a little more formed before they got in the studio; they were more together with material than Yes. There was a lot of experimentation with ELP. Songs could change quite a bit sometimes.

“On Tarkus is a song called Are You Ready, Eddy? Normally, before every take, Greg Lake would ask, ‘Are you ready, Eddy?’ And I would say, ‘Yeah, we're rolling.’ What I didn’t know was, they had secretly rehearsed this song, and they went straight into it, just as a joke. Later, they decided to put it on the record.

“There was a very old cockney woman who worked for Advision Studios; she would make sandwiches for us. The band loved to ask her what there was to eat. Her reply was always the same: ‘We've only got 'am or cheese.’ We recorded her and put her on the end of the track.”

Albums engineered are Emerson, Lake & Palmer (1970), Tarkus (1971), Pictures At An Exhibition (1971) and Trilogy (1972).