Page used his "backward echo" technique on this towards the end with Plant's screaming vocals and the guitar. Page first used this production technique, which involved hearing the echo before the main sound instead of after it, on the 1967 Yardbirds single "Ten Little Indians
." In an interview with Guitar Magazine
in 1993 Page recalled how the backwards echo effect came together on this song: "I told the engineer, Glyn Johns, that I wanted to use backwards echo on the end. He said, 'Jimmy, it can't be done.' I said 'Yes, it can. I've already done it.' Then he began arguing, so I said, 'Look, I'm the producer. I'm going to tell you what to do, and just do it.' So he grudgingly did everything I told him to, and when we were finished he started refusing to push the fader up so I could hear the result. Finally, I had to scream, 'Push the bloody fader up!' And lo and behold, the effect worked perfectly."