If These Walls Could Sing documents Abbey Road Studios, its impact on The Beatles and all the legendary music that followed that was born inside those four walls.

Paul McCartney‘s daughter Mary McCartney, who serves as the director on the film, recently took time to sit for a conversation with uInterview founder Erik Meers to discuss how the the studio played a part on The Beatles’ transformation.

>WATCH: PART 2 of MARY McCARTNEY’s uINTERVIEW!

“That’s the thing! It was so interesting because in a way, [producer] George Martin‘s like, ‘They weren’t very good,’ but they were a live band who had just been sort of out gigging and they weren’t used to recording,” McCartney said. “George Martin was looking for a lead act, like Cliff Richards, in the beginning, like which one’s Cliff and which ones are the shadows. He hadn’t sort of realized that the four of them came together as a package. What was really interesting that I wanted to highlight is that when they came there, people would come and they would do like an audition, so I think they’d just play and I think they were really nervous. Then George Martin sort of had to as a producer take that apart and put his arm around them and show them the recording process. It was also then that recording sessions were done in three-hour slots. You arrived at the studios, you were well-rehearsed, you played the songs, they would mix the song, then you’d have a break and then do another one. They recorded their first album in one day over those three-hour sessions. As they grew as artists and in confidence, they had unlimited space and unlimited hours and they changed how recording worked within the Abbey Road space.”

She also revealed a bit about how Elton John came to be involved in the project.

“I wanted to show session musicians and was like who was a session musician there? They were like Elton John and Jimmy Page. I said, ‘That’ll do me!'” McCartney laughed. “We found out that he’d played on ‘He Ain’t Heavy’ and we’ve managed to isolate the recording so you can actually hear his piano on it which for me is quite a special moment. You really can tell it’s really his style.”

The documentary is now streaming on Disney+.