from https://www.soundonsound.com/…/classic-tracks-les-paul-mary…
"We had to fold the Murphy bed into the wall in order to put the machinery in there," he recalls. "My buddy Wally Jones built the mixer. This had a channel for Mary to sing on and one for me to play the guitar, and there was no VU meter. With anything that we recorded there was never a VU meter and there were also no equalisers. I was flying absolutely blind. I went by my ear, wearing a pair of Armed Forces headphones that I think were in the range of 5Hz to 50kHz, and I'd just bring the level down a little bit if there was any distortion."
"In my case, I was so used to playing that, even without a meter, if I was going to hit a note I'd know that by hitting it here on the string it wouldn't record as loud as if I hit it there. And it was the same with Mary's vocals. She'd got to the point where no one had to tell her to back up on this note, move forward on that one, move sideways, or watch out for sibilance. We'd been doing it a long time and we were professionals."
"I had only one machine and, by the time we finished, the spliced tapes might be 6dB off and of a different bias. So, I'd press the record button and at that point the tape would go through and I'd be riding the gain to make everything the right level."
