Another Beatles' recording question: What is an "SI"? Dear Steve and all, I hate to be a pest, but this is the forum to learn things, and one thing I have to learn quickly is what a "SI" is in old Beatle studio lore. In order to keep up with my fellow engineers (all male) who chat about the good old days during lunch and on breaks, I need some hard fast info. So, thanks for understanding. SI. What is it, and how does it pertain to old Beatles recordings? Merci.